The Risk Contract of War: Offense and Defense in the Adapted Mind

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The Risk Contract of War:

Anthony Christopher Lopez

Ph.D., Brown University, 2012

Dissertation

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Political Science at Brown University

PROVIDENCE, RHODE ISLAND

MAY 2012

This dissertation by Anthony C. Lopez is accepted in its present form by the department of Political Science as satisfying the dissertation requirement for the degree of Doctor of Philosophy

Date______Rose McDermott, Advisor

Recommended to the Graduate Council

Date______Mark Blyth, Reader

Date______Leda Cosmides, Reader

Approved by the Graduate Council

Date______Peter M. Weber, Dean of the Graduate School

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CURRICULUM VITAE

Anthony Christopher Lopez was born on August 2, 1980 in Los Angeles,

California. He received a B.A. from Pitzer College in 2002, and an M.A. in Global

Finance, Trade, and Economic Integration from the Korbel School of International

Studies at the University of Denver in 2005. During this time, Anthony was a research assistant with the Center for Strategic and International Studies in Washington, D.C.

(2001), as well as with the Foundation for Strategic and International Studies in Tbilisi,

Republic of Georgia (2004). Anthony began his Ph.D. in Political Science at the

University of California, Santa Barbara in 2005, and moved with his advisor, Rose

McDermott, to Brown University in 2009, to complete his graduate training.

While completing his Ph.D. at UCSB and Brown, Anthony has been a research affiliate with the Center for Evolutionary Psychology at UCSB. His publications during this time include “States in Mind: Evolution, Coalitional Psychology, and International

Politics,” which was published in International Security (co-authored with Rose

McDermott and Michael Petersen), and “Adaptationism, Heritability, and the Emergence of Evolutionary Political Science,” which was published in Political Psychology (co- authored with Rose McDermott). Anthony also has a book chapter, “Psychology and

Constructivism: Uneasy Bedfellows?” which is co-authored with Rose McDermott and appears in the volume Ideational Allies, published by University of Michigan Press.

PREFACE AND ACKNOWLEDGMENTS

This project was conceived in 2006 as a consequence of two propitious events.

The first was an inspiring discussion in the fall of 2005 with Rose McDermott, which not only reinforced my belief in the importance of evolutionary theory for understanding political behavior, but also led me to the realization that research in this area was increasingly common and viable. The second event was meeting Leda Cosmides in the spring of 2006 as a student in her course, “Evolution and Cognition.” It is no understatement that Rose and Leda together are the twin forces responsible for much of how I think about political behavior and human nature generally.

Rose and Leda quickly introduced me to the vibrant intellectual community at the

Center for Evolutionary Psychology (CEP) at the University of California, Santa Barbara, and my thinking about evolutionary psychology and the evolution of warfare has been shaped largely through many interesting and engaging conversations with these scholars.

Indeed, the framework I develop and refer to as the “risk contract of war” is built directly upon theoretical insights established by John Tooby and Leda Cosmides at the CEP.

Thus, my greatest intellectual debt in this project is undoubtedly to scholars at the CEP, especially Rose, Leda, and John, and also to Steve Gaulin, Andy Delton, Max Krasnow,

Dave Pietraszewski, Daniel Sznycer, and Aaron Sell.

This academic journey has led to interactions with many individuals who have also impacted my views on evolution and political behavior. Of this I should like to

v particularly note Michael Bang Petersen, with whom I have collaborated and continue to collaborate on many engaging and exciting projects. In addition, I have had the good fortune to learn directly from many of the seminal thinkers in this emerging field of inquiry. Among these are (in alphabetical order): John Alford, Oliver Curry, Mark Flinn,

Azar Gat, Pete Hatemi, John Hibbing, Dom Johnson, John Orbell, Stephen Rosen, Darren

Schreiber, Brad Thayer, Michael Wilson, and Richard Wrangham. Undoubtedly, I am especially grateful to Mark Blyth, whose advice and mentorship has enhanced my understanding of psychology, behavior, and institutions. This dissertation is greatly improved in rigor as a consequence of his critical eye.

I would be remiss if I did not also take this opportunity to give a special thank you to Suzanne Brough in the Political Science Department at Brown University. I can say without exaggeration that it is because of Suzanne’s invaluable help and advice that I have been able to successfully complete what has been required of me at Brown!

Of course, I must thank those who have been with me and supported me from the beginning. In this regard I am forever indebted to my mother, Melissa Hernandez, my grandfather, Pete Hernandez, and my grandmother, Dolores Hernandez, for giving me life and encouraging me every step of the way.

My research has focused on the evolution of coalitional behavior in the political context, and in this regard, I have given great attention to the study of alliances. It is a happy twist of fate that I find myself engaged in the greatest alliance of all, with my wife,

Nicole Cerra. I am forever fortunate for her partnership, which has been a steady source of love, support, and adventure throughout.

TABLE OF CONTENTS

I. Introduction: The Evolution of War

II. Chapter 1: The Risk Contract of War

III. Chapter 2: Study 1 & Study 2

IV. Chapter 3: General Discussion

V. Chapter 4: Evolutionary Politics

VI. Appendix A: Survey 1

VII. Appendix B: Survey 2

VIII. Appendix C: Additional Data

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LIST OF GRAPHS AND TABLES

Graph 1: Domain-Specificity of Willingness to Participate

Graph 2: Sex Differences in Expected Benefits – Defense

Graph 3: Sex Differences in Expected Benefits – Offense

Graph 4: Expected Probability of Success (Offense)

Graph 5: Expected Probability of Success (Defense)

Graph 5: Willingness to Participate (Males)

Graph 6: Willingness to Participate (Females)

Table 1 & 2: Sex Differences in Willingness to Participate

Table 3: Male Punitive Sentiment Toward Non-Participating Males

Table 4: Male Punitive Sentiment Toward Non-Participating Females

Table 5: Female Punitive Sentiment Toward Non-Participating Males

Table 6: Female Punitive Sentiment Toward Non-Participating Females

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INTRODUCTION: THE EVOLUTION OF WAR

Offensive and defensive warfare represent two major, recurrent, and distinct forms of coalitional violence; however, the direct effects of these two types of warfare on decision-making and motivation have been largely ignored by political scientists specifically, as well as by social and natural scientists generally. Where it has been examined, it has been considered indirectly and in passing (Durham 1976; Gat 2006;

Schultheiss and Wirth 2009), or it has been considered in non-human animals such as rats

(Albert, Jonik, and Walsh 1992). Scholars of international relations often discuss the

“offense-defense balance,” which represents an area of inquiry characterized by the attempt to understand how the nature of offensive and defensive military capabilities influences the likelihood and quality of warfare (Biddle 2001; Brown et al. 2004). Yet, none have examined how the quality of warfare affects political psychology.

I argue that humans possess distinct psychological adaptations, built by natural selection, specialized for regulating behavior and motivation in offensive and defensive coalitional aggression, or warfare (Tooby and Cosmides 1988; Lopez 2010). Indeed, warfare has been a recurrent fixture of ancestral landscapes (Keeley 1996; Wrangham and Peterson 1996; LeBlanc and Register 2003), such that it is plausible to expect natural selection to have designed psychological adaptations in humans for the adaptive regulation of behavior in warfare (Johnson, Wrangham, and Rosen 2002; Gat 2006; Choi and Bowles 2007; McDonald, Navarrete, and Van Vugt 2012). However, not all warfare

1 is the same; thus, I hypothesize that offensive and defensive warfare have constituted distinct selection pressures, such that we can expect selection to have favored distinct psychological adaptations for behavior and motivation in each domain. I apply an adaptationist framework (Williams 1966; Mayr 1983; Cosmides and Tooby 1987; Confer et al. 2010) in combination with theory and evidence from social psychology and anthropology in order to examine the specific ways in which these psychological adaptations condition motivation and decision-making upon cues in the environment that indicate offensive or defensive warfare.

One axis of differentiation between offensive and defensive forms of coalitional aggression, or warfare, is the reward of success. Archaeological and anthropological research on warfare suggests that the gains from offensive raids tend to be subject to privatization among the raiders, while the gains from defense against out-group incursions are mostly intangible public goods, such as survival and threat removal

(Keeley 1996; LeBlanc and Register 2003). Given the evolutionarily recurrent structural asymmetry characterizing the fitness benefits from victory in each form of warfare, it is reasonable to expect that natural selection has shaped psychological adaptations that regulate participation in aggression to be sensitive to these contextual cues.

In general, given that humans possess psychological adaptations that regulate behavior in specific domains, the central analytic question is therefore: under what conditions would natural selection have favored behavior X in ancestral environments, and how is this strategic conditionality instantiated in the behavior-regulatory logic of evolved psychological adaptations? For example, scholars who study cooperation have learned that psychological adaptations exist to regulate cooperative behavior in situations

2 of social exchange, and that these adaptations render cooperation conditional on a range of cues, such as phenotypic cues in the face and voice, as well as cues embedded in observed behavior (Trivers 1971; Yamagishi et al. 2003; Cosmides and Tooby 2005;

Lieberman, Tooby, and Cosmides 2007; Haselhuhn and Wong 2011). Similarly, scholars who study warfare have begun to outline the conditions under which natural selection would have favored aggression in individuals and groups as a reproductively successful strategy in both chimpanzees and humans. For example, given a backdrop of inter-group conflict, warfare in chimpanzees tends to erupt when a 3:1 size ratio exists between two coalitions and the probability of success is high from the perspective of the larger coalition (Manson and Wrangham 1991; Wrangham 1999a). In humans, it was hypothesized and confirmed that people possess psychological adaptations designed to render aggression conditional upon cues in the face, voice, and body of others (as well as other relevant cues in the environment) indicating relative formidability (Parker 1974;

Sell et al. 2009; Sell et al. 2010; Short et al. 2012; Puts, Apicella, and Cárdenas 2012).

The lesson is that selection pressures posed by ancestral social environments were complex, such that psychological adaptations designed to regulate behavior in response to such challenges should reflect this adaptive conditionality in the logic by which they regulate behavior. Thus, what I refer to below as the “risk contract of war” represents the psychological conditions that must hold in order for coalitional aggression to be successfully initiated, and I argue that this conditionality is distinct depending on whether the domain of warfare is offensive or defensive.

Before proceeding further, it is necessary to define terms. Once the terminological groundwork has been established, I will proceed to a literature review of

3 scholarship on the evolution of warfare, which will conclude the introductory chapter.

Following the introduction, Chapter 1 introduces evolutionary psychology and outlines the theoretical framework used to generate hypotheses regarding psychological adaptations for offensive and defensive coalitional aggression. Chapter 2 presents evidence from two rounds of experiment-based surveys, and Chapter 3 is a general discussion of findings in light of theory regarding the evolution of war. The concluding chapter explores implications for the application of evolutionary theory to political science in general.

Terminology

Warfare: I follow a definition of warfare employed by primatologist Richard

Wrangham and Luke Glowacki (2012) and economist Sam Bowles (2009). War refers to

“relationships in which coalitions of members of a group seek to inflict bodily harm on one or more members of another group.” Importantly, this definition does not depend upon the instruments used in conflict nor its complexity and scale. Throughout history, the practice of warfare has changed in quantitative and qualitative ways as a consequence of innovations in political-economic organization as well as innovations in military capabilities, such as fortifications, gunpowder, and nuclear weapons. Yet, when I speak of warfare, I refer to the underlying social relations that have inspired and exploited such innovations. Definitions of warfare are at the heart of many disagreements regarding its persistence throughout human history, and I directly engage these debates below.

Adaptationism: By the middle of the 20th century, innovations in genetics combined with modern understanding of Darwinian evolutionary theory inspired what

4 remains known as the “modern synthesis” in evolutionary biology. Many of the leading thinkers of this synthesis attempted to establish a theoretical framework by which to discover and examine the structure of adaptations designed by natural selection. These

“adaptationists,” much like classic Darwinists, were focused on the functional fit between adaptations and the ancestral selection pressures that favored their emergence, as I explain further in chapter 1 (Williams 1966; Mayr 1983). Adaptationists are variously referred to as “Neo-Darwinists,” “Evolutionary Psychologists,” or “Sociobiologists,” although sociobiology is generally considered a precursor to evolutionary psychology, the latter which is especially focused on the information-processing structure of adaptations in the brain (Barkow, Cosmides, and Tooby 1992).

Adaptation: A biological adaptation is not a discrete unit fixed in time and space, but rather a set of units, the overall design of which is under the constant push and pull of various evolutionary forces, such as entropy and natural selection. An adaptation can be as simple as a single gene, maintained by natural selection because of its positive on- average fitness benefits, or it can be increasingly complex, such as the human heart or eye, and coded for by a vast suite of underlying genes. The body, or phenotype, is composed of adaptations from head to feet, and in this dissertation I am concerned with adaptations in the brain, or psychological adaptations. I refer to psychological adaptations also as psychological “mechanisms,” and as “information-processing systems.” As I discuss in chapter 1, the main function of the brain is to regulate behavior in response to the environment, and adaptations must exist that regulate behavior, motivation, and cognition based on evolutionarily recurrent and adaptively relevant cues.

In this sense, the general operation of psychological adaptations is to receive input from

5 the environment, and transform that information into adaptively useful output. Thus, it is often convenient to refer to these mechanisms as “information-processing systems” since their basic work is the processing and transformation of information.

Characteristics of Adaptations: In a broad sense, adaptations may be obligate or facultative. An adaptation is obligate if its output is relatively independent of environmental perturbation; conversely, an adaptation is facultative if it is functionally dependent upon information in the environment for its contingent output (Maynard Smith

1993). In a real sense, however, no adaptation is perfectly obligate, since environmental triggers are required at every stage of phenotypic development, or ontogeny. Given the role of psychological adaptations in regulating behavior in response to the environment, and given that adaptations are specialized solutions to adaptive problems in the environment, complex problems such as cooperation often require conditional solutions.

In these cases, it is likely that adaptations that regulate behavior according to conditional strategies (e.g. “cooperate first, then do what your opponent did last time”) will be on- average more successful than obligate strategies (e.g. “always cooperate”). Although adaptations have many more characteristics than this one distinction, this is perhaps the most useful characteristic for social scientists to consider when engaging adaptationist claims regarding social behavior.

Evolution: The universe is under the constant eroding pressure of entropy, and the only physical process that acts against this trend is natural selection. Evolution is merely a process of change over time, and in a way, therefore, evolution is a description the deep-time consequences of the tug-of-war between entropy and natural selection. Natural selection is not an active force, but a passive one. As a sift, and in general, natural

6 selection is the process whereby replicators that are better at making copies of themselves become more abundant in a population over time. For example, if a genetic mutation (i.e. heritable design feature) has the effect of increasing the reproduction of an individual organism relative to other organisms that lack this mutation, then all things equal, that gene will increase in frequency in future generations. Over time, the accumulation of additional mutations associated with this original design feature may result in a complex adaptation (Dawkins 1986; Carroll 2006). Despite the fact that this process is passive and lacks foresight, evolutionary biologists employ the convenient shorthand that, for example, natural selection is likely to “favor” a certain type of adaptation given known or suspected adaptive problems faced by an organism. Quite simply, it is easier to say that natural selection has “favored” an adaptation than to repeatedly have to say, “ancestral conditions prevailed such that individuals that possessed design feature X were on- average more likely to pass on the genetic component of this feature in future generations relative to alternative features, such that design feature X became species-typical in the population.” I follow the convention of evolutionary biologists of employing the shorthand of adaptations being “favored” by selection in certain circumstances, while acknowledging that this shorthand is not meant to ascribe anthropomorphic features to a physical process that is irrevocably passive and blind.

The Evolution of Warfare

The evolution of warfare has received significant attention across the social sciences, yet the topic contains many conceptual ambiguities, most obviously regarding what one means by “evolution” and what one means by “warfare.” Consequently, and

7 not unlike many other areas of research, scientists have battled just as much over definitions as over substantive claims. For example, how one conceptualizes “warfare” will determine one’s conclusions about when and how warfare originated. If one defines warfare as the sustained mechanized engagement of organized political units, then one must be forced to conclude that warfare emerged relatively recently with the establishment of early proto-states. If, however, one defines warfare somewhat more loosely as sustained coordinated violence between political organizations, we may identify the origins of warfare as having occurred earlier, perhaps with the emergence of agriculture. Even more broadly, if one defines warfare as coordinated violence between coalitional factions, warfare may be as old – and even older – than our species.

The definitions we employ allow researchers to ask different questions. Using a narrow definition of warfare is to identify its origins with the proto-state, and the

“evolutionary” question, in this case, is the following: what were the social forces that led to the emergence of warfare, and how do changes in those social forces affect changes in warfare over time? This is primarily a historical question of change and continuity, in which we consider how changes in a system (e.g. political and economic organization) affect one dynamic or set of dynamics (e.g. warfare) within that system. However, using a broader definition of warfare allows us to realize that the general pattern of coordinated violence between coalitional factions is an ancient practice in the hominid line, pre-dating even the earliest forms of political organization. This perspective opens up the possibility of a new evolutionary question: how has the persistence of coalitional aggression shaped the way our species reasons about and engages in warfare? This is primarily a biological question in which we consider how sustained selection pressures over evolutionary time

8 have shaped adaptations in the brain that are responsible for regulating behavior in social domains.

As mentioned above, I define warfare loosely as coordinated violence between coalitional factions, and my general argument contains the following components. First, warfare and its consequences for survival and reproduction have constituted an evolutionarily recurrent adaptive challenge for our species. Second, natural selection has designed specialized psychological systems – adaptations – specifically for the purpose of generating adaptively useful inferences and behavior in the context of warfare. Third, not all warfare is the same; offensive and defensive warfare represent two distinct types of warfare that have constituted distinct adaptive challenges, in response to which natural selection has shaped “separate psychologies” for these domains. Fourth, because the reproductive challenges that males and females have faced over evolutionary time are in certain instances – especially aggression and violence – divergent, I show that the motivational systems that govern reasoning and behavior in warfare operate differently in males and females. In sum, humans have evolved to reason about and engage in warfare in specific ways, and one of the ways natural selection has left its mark upon human war psychology is through the design of separate motivational systems for offensive and defensive warfare.

Adaptationism in evolutionary biology is an approach for understanding the design of adaptations built by natural selection (Williams 1966; Mayr 1983; Godfrey-

Smith and Wilkins 2008). The application of adaptationist principles toward the understanding of human behavior has gained prevalence since at least the 1960s and 70s, and has assumed many forms. Early ethologists and later sociobiologists, sought to

9 extrapolate from evolutionary patterns and pressures to generate hypotheses about behavior, especially in the realm of aggression (Lorenz 1966; E. O. Wilson 2000). Later, evolutionary psychologists emphasized the role of psychological adaptations as the products of natural selection, and provided a framework for the study of their design

(Barkow, Cosmides, and Tooby 1992). Thus, I utilize evolutionary psychology as a framework for outlining and testing the hypothesis that natural selection has designed psychological adaptations specialized to operate in offensive and defensive warfare.

Evolutionary psychology is an explicit attempt to bridge our understanding of natural selection and its products (adaptations) with the study of human behavior. Consequently, evolutionary psychology is not a theory, nor is it a field of study within any particular discipline, such as psychology. Instead, evolutionary psychology represents an approach for understanding behavior that allows researchers to gain insight from the understanding that the human brain is a complex set of adaptations built by natural selection.

The application of evolutionary psychology toward an understanding of political behavior is relatively new to political science (Sidanius and Kurzban 2003; Petersen

2009; Lopez, McDermott, and Petersen 2011). However, the question of the evolution of warfare is anything but new in the social sciences. Therefore, I begin here in the introduction with a review of the literature on the evolution of war, which is necessary since my arguments regarding the existence of psychological adaptations take as given an evolutionary past characterized by recurrent warfare. Since this question has been investigated most by anthropologists and political scientists, the literature review focuses on this research; however, I also review recent work especially by psychologists and

10 economists who have begun to directly examine the psychological dynamics of human warfare from an evolutionary perspective.

Literature Review: On the origins and evolution of warfare

Conceptual Organization. There is an abundance of literature on the question of the evolution of war, and therefore I must first offer a means by which to organize this literature before engaging with it directly. The evolution of warfare has been investigated in many ways and for many purposes. One major distinction regards usage of the word

“evolution.” Scholars tend to utilize the label “evolution” in either a biological or a metaphorical sense. My argument here is restricted to the biological sense, and the relevant question is the existence of biological systems that shape political behavior.

Nevertheless, there is an emerging trend, isolated mostly to the sub-field of international relations, to consider the “evolution” of many political dynamics by considering the ways in which they emerge in various forms, are “selected” and favored in certain social environments, and “co-evolve” with other political dynamics (Thompson 2001; Barnett

2009). In this research, evolution is used as a metaphor that facilitates the explanation and understanding of change and continuity in political dynamics, such as, but not limited to, warfare. In this literature review, I do not consider work that utilizes evolution in a strictly metaphorical sense because the main explanatory mechanism in this research is evolutionary only in form and not in substance. Although these scholars employ the familiar labels of evolutionary science such as variation, selection, and co-evolutionary dynamics, the substantive application of these terms would be almost unrecognizable to evolutionary scientists. Furthermore, scholars within the metaphor tradition have denied

11 that the label “evolutionary” should be used in only one way, thus asserting the legitimacy of employing existing terminology in novel ways, even if incommensurate with original and intended usages. Thus, if this review were to consider all research merely by virtue of the fact that its authors label it “evolutionary” in some way, this review would not only be overwhelmingly dense, but also relatively incoherent and, more importantly, tangential to the central question of this dissertation. Therefore, the first criterion for inclusion in this literature review is that the research employs evolution in a biological sense.

I am interested in the evolution of warfare from a biological perspective, and the questions I consider are fundamentally psychological in nature, regarding motivation and reasoning in the context of coalitional aggression. Thus, the second criterion for inclusion in this review is that the research must consider the psychological dimensions of coalitional behavior in the context of warfare. Much of the research that has examined the psychological foundations of behavior in warfare has occurred in the backdrop of a larger debate in evolutionary biology – the debate over the level at which natural selection operates. Scholars who acknowledge that adaptations exist for warfare are often divided on whether these are the products of natural selection operating at the level of the individual (Tooby, Cosmides, and Price 2006), the group (Sober and Wilson 1999), or whether relevant behavior is the product of cultural group selection (Richerson and

Boyd 2006). Thus, it is also necessary consider the alternative evolutionary pathways by which adaptations for warfare may have emerged.

Lastly, although the evolution of war is a relatively new topic of consideration for scholars of international relations, the study of the mechanisms of war is not. For

12 example, researchers have examined the “offense-defense balance” as a variable that affects the likelihood and quality of warfare in the international system. Since my own argument essentially reverses this analysis by investigating how the quality of warfare

(offense vs. defense) affects the psychology of political behavior, it is necessary to examine existing research that explores differences in these two forms of warfare.

This literature review is divided into three sections: First, I review research on the evolution of warfare from an evolutionary biological perspective, which will focus on examining the origins, prevalence, and intensity of warfare in human history. Second, I consider research on the psychological dynamics of warfare, particularly by scholars who have used evolutionary theory to guide hypothesis formation. In this section I also consider the contrasting evolutionary pathways represented by genetic/individual-level selection, group selection, and cultural group selection. Research in the first area has been conducted primarily by primatologists, archaeologists, anthropologists, and political scientists. Research in the second area has primarily been conducted by psychologists and economists. Third, I examine research on the offense-defense balance in international relations, which has been conducted exclusively by political scientists.

The Evolution of Warfare. In this sub-section, I will review the literature that has sought to explain questions such as: How far back into human evolution can we trace warfare or war-like behavior? What can we say about whether warfare is a part of

“human nature”? What implications do the answers to these questions have for understanding warfare today?

To begin, researchers who study the evolution of war typically argue that 1) warfare is as old or older than our species; or 2) that warfare can in fact only be traced to

13 the emergence of agriculture or shortly thereafter. Those who argue that warfare is older than our own species are, unsurprisingly, mostly primatologists. The most well known in this regard has been Richard Wrangham, who provides evidence that it may be the case that we can trace the origins of human violence to our nearest cousins – chimpanzees.

Wrangham and Peterson (1996) argue that there are many important similarities between human and chimpanzee violence, and because chimpanzees have persisted in an environment of conservative selection pressures (i.e. selection pressures have not changed much since the chimpanzee-hominid split about 5 million years ago), we can, for the most part, use the example of chimpanzee violence as a window into our own evolutionary past. Wrangham and Petersen explain coalitional aggression primarily with reference to ecological pressures such as the economic costs and benefits (in terms of fitness) of group size and stability, as well as the operation of sexual selection, which is used to explain why violence tends to be carried out disproportionately by males.

With respect to the quality of groups, Wrangham and Peterson show that the dispersal of resources in time and space will affect the economics of group size and stability. As resources become more plentiful, conflict tends to increase. This is particularly true when those resources are of high metabolic value and can be monopolized, which makes aggression, though risky, worth the potential costs given a relatively high benefit. However, where such resources are dispersed in space in time, a given group will have to travel farther in order to satisfy the nutritional needs of the group members, rendering the efficient size of groups much smaller and less stable.

Thus, chimpanzees are characterized by “fission-fusion” groupings, in which groups fluctuate in size as a consequence of divisions and mergers within and between groups. It

14 is likely that chimpanzees and humans exhibited similar trends with respect to coalition size and stability during their evolution, especially given ecologically similar niches. For example, both chimpanzees and humans have evolved to depend on nutritionally rich foods such as roots and meat, the availability of which varies by season and chance.

Wrangham and Petersen use the theory of sexual selection to explain the higher incidence of aggression among males. They show that due to high obligate female parental investment relative to males in both chimpanzees and humans (which also happens to be generally true of most mammals), females constitute a limiting resource over which males tend to compete. Aggression is thus favored by selection for use in this competition. Importantly, however, Wrangham and Peterson show that for bonobos, because of the feasibility of female alliances and the difficulty for males of perceiving female ovulation periods, male aggression is moderated. By occupying a niche similar to that of gorillas, bonobos have evolved to rely on resources that “buffer the effects of seasonal fruit shortages and allow bonobos to travel with their fellows more easily than chimpanzees can afford to” (p. 223). Thus, bonobo group size can be large and stable, and consequently, large group-size imbalances are less frequent, raising the costs of coalitional aggression and increasing the feasibility of female consortships.

This point is significant because it forces scholars to recognize that there are limits to the use of another primate species as a model from which to draw inferences regarding the behavior of humans. For example, one must first establish that the selection pressures faced by one species have been similar to those faced by humans.

Wrangham and Petersen show that this has to a large extent been the case with chimpanzees, and further, they provide the counter example of bonobos, which, given the

15 presence of a different set of adaptive challenges, have evolved to meet those challenges in ways that are distinct from their chimpanzee and human relatives. Indeed, bonobos are perhaps the most famously peaceful primates, and many who appeal to the human potential for peace often use bonobos as illustration (Sapolsky 2006; Fry 2007).

Nevertheless, because of the similarities between the selection pressures faced by chimpanzees and humans, it can be fruitful to begin by examining the psychological adaptations natural selection has favored in chimpanzees to engage in aggression at the coalitional level.1

Wrangham and his colleagues have focused in particular on the relationship between group-size imbalances and the outbreak of chimpanzee coalitional aggression

(Wrangham 1999a; Wrangham 1999b; Johnson, Wrangham, and Rosen 2002). The most common form of coalitional aggression among chimpanzees and many human societies is lethal raiding. How can we explain the existence and distribution of lethal raiding and other forms of coalitional violence among chimpanzees, and what does this tell us about human forms of coalitional violence? Although early ethologists (Lorenz 1966; Tiger

2004) argued that chimpanzees and humans possessed a “killer instinct,” in which a general and inherent tendency toward aggression generated periodic outbursts of violence between individuals and groups, later research revealed this model to be theoretically and empirically flawed. Decades of subsequent research on chimpanzees (Harcourt and Waal

1 Despite these similarities, one should not neglect that real differences exist as well. As a simple illustration, humans can achieve much greater group sizes than chimpanzees. Robin Dunbar, for example, has proposed a relationship between neocortex size and the size of social groups in primates (Dunbar 1993; Aiello and Dunbar 1993). Humans, with the largest neocortex, also live in the largest social groups. As I discuss below (especially in chapter 1), coalitional complexity suggests the presence of equally complex psychological adaptations for managing relations in these environments, so Dunbar’s findings are to be expected. This does not render the comparison between humans and chimpanzees invalid; rather, it helps to remind us that chimpanzee models of coalitional aggression can only provide a partial picture of the evolutionary story of human coalitional aggression. I engage this consideration below.

16 1992) has led researchers to recognize that the distribution of coalitional violence in chimpanzees seems to follow an evolutionary logic that is adaptively contingent upon ecological and social conditions (Manson and Wrangham 1991; Wrangham 1999a).2 In other words, the claim that chimpanzees – and by implication, humans – are naturally predisposed to aggression in a context-neutral or domain-general obligate sense, has been replaced by the claim that the distribution of violence is better understood as the product of adaptations designed to operate in a context-dependent or domain-specific facultative sense. The relevant analytic question is therefore to identify the conditions under which natural selection would have favored the use of violence by coalitions against other individuals or coalitions of the same species.

In this regard, Wrangham (1999a) has offered the “imbalance of power” hypothesis to explain the incidence of lethal raids by chimpanzee coalitions. According to this hypothesis, given the background conditions of fission-fusion groupings (in which groups are relatively unstable and short-lived) and the existence of hostilities between groups, lethal raiding should occur when a substantial asymmetry exists between antagonistic coalitions. In combination with the element of surprise, numerical superiority virtually guarantees both low-risk and high probably of success for the aggressors. Thus, chimpanzees typically engage an enemy individual or coalition when the ratio of aggressor-to-victim reaches 3:1, not unlike doctrines of numerical superiority followed by modern military institutions. Lethal raiding in these contexts is favored by natural selection for two main reasons. First, the access to resources that would be a consequence of lethal raiding enhances the reproductive fitness of the raiders and their

2 Otterbein (2004, 27) wrongly categorizes Richard Wrangham as part of the group of scholars that advocate the “killer ape” hypothesis; however, Wrangham (1999a) explicitly rejects this position.

17 group by providing expanded and/or superior resources (Mitani, Watts, and Amsler

2010); second, the decrease in relative size – and hence resource holding potential – experienced by losing coalitions would have placed them at a strategic disadvantage relative to other coalitions, leading to downstream fitness losses (Parker 1974).

Although the incidence of chimpanzee violence is fairly well-explained by the imbalance of power hypothesis, human coalitional violence, while characterized by frequent raiding, is also characterized by other forms of coalitional violence in which coalitional asymmetry does not always exist and campaigns are sustained rather than fleeting. In these contexts the imbalance of power hypothesis is less useful for explaining the outbreak and dynamics of sustained coalitional violence, especially where asymmetry between coalitions does not exist. Although it appears that the imbalance of power hypothesis would nicely explain certain forms of human coalitional aggression such as various forms of “stealth raids” (Chagnon 1988; Mathew and Boyd 2011), alternative theoretical models are needed to explain sustained battles between comparably sized coalitions.

It is because of this limitation that we must leave chimpanzee studies and focus on human evolutionary history proper. Although primatologists have offered substantial evidence that certain forms of human coalitional aggression can be traced to our chimpanzee ancestors, we must also look to the selection pressures that prevailed after our split with chimpanzees. There is much debate regarding the existence, regularity, and intensity of warfare over human evolutionary history, and the answers to these questions are often used as justification for claims about how deeply rooted warfare is in our very nature. Unsurprisingly, the further back in our evolutionary history warfare seems to

18 originate, the more scholars seem to interpret this as evidence of the immutability of warfare in human nature. In other words, the further back we find evidence of warfare, the more we view our future as doomed to repeat this past. Although primatologists, as mentioned above, have increasingly recognized that adaptations in chimpanzees for coalitional aggression are context-dependent and therefore behaviorally plastic, many scholars of human coalitional aggression remain wedded to the view that we are either inherently violent, or that warfare is entirely a cultural invention that can be summarily dismissed (Mead 1940).

Whereas early social scientists tended to view the “primitive” state of human societies as peaceful and nonviolent (Sumner 1970), subsequent observations by primatologists (Goodall 1986; Harcourt and Waal 1992; Wrangham and Peterson 1996), as well as new evidence by cultural anthropologists (Ember 1978; Chagnon 1983), led scholars to recognize that warfare did indeed have a place in our evolutionary past. The question then became: How prevalent was it, did it constitute a selection pressure great enough to select for adaptations in humans for fighting, and what is the nature of those adaptations, if they exist? There are two dominant points of view on these questions.

The first perspective argues that human coalitional violence was both frequent and intense in our species’ history (Keeley 1996; LeBlanc and Register 2003; Pinker

2011). This perspective emerges as a direct counter-argument to early and seminal writings on primitive warfare, which argued not only that primitive warfare (and by extension, the forms of warfare practiced by our earliest ancestors) was scarce, but also that it could not usefully be compared to modern institutionalized warfare in any way

(Turney-High 1949; Wright 1983). These early scholars argued that primitive warfare

19 was nowhere as lethal as modern warfare, and displayed little discipline and poor organization, such that the motivations and goals of modern warfare required fundamentally distinct explanations. For example, Turney-High famously argued that there was a real and significant “military horizon,” above which “real” warfare took place, and below which only ritualized and undisciplined acts of aggression occurred.

Keeley’s War Before Civilization offers a well-known rebuttal these claims, drawing extensively on archaeological evidence of early settlement fortifications as well as on fossil evidence of major battles that occurred prior to the emergence of state-level organizations. Utilizing cross-cultural research by anthropologists, Keeley demonstrates that hunter-gatherer violence has been just as frequent and deadly as state-level violence, and that modern military strategy and hunter-gatherer battle tactics are more similar than previously claimed, especially in the realm of knowledge and use of terrain, application of the principles of cover and concealment, and the exploitation of stealth and surprise.

None of this is to claim that there is no difference between warfare above and below the military horizon; rather, it is to claim that 1) primitive warfare was at least as frequent and intense as modern warfare, and 2) many of the forms of primitive warfare resemble modern warfare even in the context of modern logistics and command and control systems. Therefore the main contribution of this research is the recognition that human coalitional violence seems to be characterized by a superstructure that has persisted throughout human history, even while political and economic innovations have altered the scale and style of warfare. Notably, proponents of this first perspective do not argue that war is inevitable; indeed, some utilize the context-specificity of adaptations for

20 warfare to explain why coalitional violence seems to actually be on the decline in human societies (Pinker 2011), or to show how it can be contained (Potts and Hayden 2008).

The second perspective argues that human coalitional violence, although it likely existed prehistorically in some rudimentary forms, was not frequent or intense enough to have selected for adaptations in humans for warfare. Perhaps the best example of this line of argument comes from the primatologist Douglas Fry (2007). In Beyond War: the

Human Potential for Peace, Fry contends that warfare was in fact not evolutionarily recurrent in human ancestral environments, and thus, natural selection could not have designed psychological adaptations for warfare. All of the biological adaptations we possess (psychological or otherwise) were designed in response to ancestral adaptive problems. Quite simply, in addition to the presence of genetic variation upon which natural selection may act, everything depends on the environment in which the adaptation is selected. In other words, a terrestrial vertebrate that never encounters water will probably never evolve fins. Fry argues that since evidence of systematic warfare in ancestral societies is scarce to non-existent, it does not follow that humans possess adaptations for fighting in this context. Fry also argues that if there was psychological design in humans specialized for warfare, then warfare should be cross-culturally universal. Since Fry points to evidence of the existence of peaceful societies, he argues that we can infer that adaptations for warfare do not exist, and we can also infer that there was no selection for them ancestrally.

Scholars of this perspective often point to the archaeological record and remind us that unambiguous direct evidence of warfare does not exist much further back in time than the emergence of agriculture about 10,000 B.C. (Nettleship, Givens, and Nettleship

21 1975). According to Kelly, for example, this “strongly implies” that warfare did not exist prior to the dawn of agriculture, and indeed that a “global condition of warlessness” must have prevailed for millions of years prior (Kelly 2000, 2). However, to draw such an inference in this case would be the scientific equivalent of wandering into a forest at midnight with a lantern and concluding that the forest must only extend about a hundred feet in any direction since your light illuminates no forest beyond this revealed zone.

Furthermore, even if warfare did exist in prehistoric times, the existence of weaponry that would survive to be discovered was a relatively recent development (ca. 40,000 years ago), and the fortifications and burnt villages that are often good evidence of coalitional violence emerged only with the transition to sedentary lifestyle, itself also a relatively recent development that seems to have paralleled the emergence of agriculture (Keeley

1996). As LeBlanc and Register point out, however, “The world was hardly peaceful until someone in China or Mesopotamia hammered out the first bronze sword,” and to focus so narrowly on evidence of the instruments of war “confuses the methods of war with the results of war” (2003, 57). Thus, those scholars of the first perspective who view coalitional violence as extending deep into human prehistory often acknowledge archaeological limitations, but extrapolate based on knowledge of modern hunter- gatherer societies (which lack agriculture) and comparisons with primate societies.

Those scholars of the second perspective who disagree are inclined the take the more conservative approach in which the absence of evidence is the evidence of absence.

Conclusions based solely on the archaeological record are necessarily incomplete.

To return to my analogy above, the absence of visible forest beyond the illumination of one’s lantern does not indicate either the presence or absence of forest. There are gaps in

22 the primate fossil record; yet, few serious scholars would conclude that those gaps are indicative of time periods in which primates simply did not exist. Similarly, trends among modern hunter-gatherer groups, pre-historic primitive societies, and chimpanzee coalitions suggest that primate aggression and warfare is part of a trend dating back to before the chimpanzee hominid split. Therefore conclusions regarding primate warfare require a combination of faith and an appeal to parsimony. For example, what is more likely – that warfare among chimpanzees and humans represents an evolutionary pattern dating back to the chimpanzee-hominid split, or that coalitional aggression appeared in chimpanzees long after the split with hominids and just happened to emerge among humans in a similar form once they became more adept at fashioning weapons detectable by modern archaeological methods?

In addition to disagreement over the implications of prehistoric archaeological evidence for warfare, there is disagreement over what is meant by warfare to begin with.

Thus, divergence between the positions represented by Keeley and Fry can be reconciled by the fact that they do not share the same definition and conceptualization of warfare.

Keeley defines warfare much as I do here, as characterized by coordinated violence between opposing coalitions. This definition encompasses, for example, both pitched battles and lethal raids, and enables one to understand warfare as an ancient practice.

Fry, on the other hand, defines warfare so as to omit revenge killings, coalitional raids targeted at specific individuals, as well as coalitional violence between kin groups, since he instead prefers a definition that corresponds to the “common usage of the word” (Fry

2007, 16). Conforming with prevailing definitional conventions is to be applauded; however, conventional definitions of warfare are useful when studying conventional (i.e.

23 modern) warfare, but not so much when examining the evolution of warfare as a human practice. For example, Fry does not consider coalitional violence between kin groups as a form of warfare; however, human groups were ancestrally organized around kin structures, and any violence that occurred between them would automatically be omitted by such a restrictive definition as Fry’s. Operationalizing warfare according to modern conventions in order to study its evolution ancestrally is a nonstarter. The real question should be: What forms of warfare have existed ancestrally, how did these dynamics translate into evolutionarily recurrent selection pressures, and what adaptations might these selection pressures have produced that influence and shape modern warfare today?

A final point raised by the contrast between the first two perspectives concerns the universality of warfare. Again, the expansive definition of Keeley allows him to identify warfare as much more ubiquitous than Fry, but one thing is for certain: anthropologists will always be able to identify at least some cultures that, for a given period of time, appear nonviolent. The relevant question must be: What does the evidence of near-universality allow us to conclude about the existence of psychological adaptations for warfare? Human nature optimists argue that the existence of peaceful societies is evidence that warfare is a cultural invention, while pessimists seem to suggest that what matters is that warfare is the norm among the overwhelming majority of cultures.

The truth, however, is that most adaptations for social behavior are expected to be deeply facultative, meaning that the behavior they generate follows an ancestrally adaptive context-dependent logic (Cosmides and Tooby 1994; Alcock 2005). Given the expected facultative structure of psychological adaptations for social behavior, cultural

24 variation in a given behavior is never evidence for the lack of an adaptation or set of adaptations regulating that behavior; instead, that variation is likely the product of such adaptations. Therefore, the best way to test for adaptations for any given behavior is to generate hypotheses about how these adaptations would calibrate behavioral and motivational output in ancestral environments. In this sense, we should not look for evidence that a particular output (e.g. behavior, such as aggression) of an adaptive system is universal; rather, we need to look for evidence that the psychological mechanism that generates this context-dependent output is universal. Thus, evidence that coalitional violence (a class of outputs) is not perfectly universal does not allow us to conclude that there is not a universal set of psychological adaptations designed to regulate behavior and motivation in warfare.

The above two perspectives have charted two opposing positions characterized by claims about the frequency and intensity of primitive warfare, as well as implications for human nature. Before we engage the psychology of war, we must evaluate what we have learned from this discussion on the evolution of war. First, how one defines warfare will permit different views of its tenure in human history. What seems clear is that the most common form of coalitional violence that has characterized our early evolutionary history is lethal raiding punctuated by cycles of attack/counter-attack spirals of violence

(Boehm 1984; Chagnon 1988). On the one hand, it is likely that the persistence of coalitional violence is as old as the chimpanzee-hominid split and has led to psychological adaptations for certain evolutionarily old forms of coalitional violence. On the other hand, it is unlikely that humans possess adaptations for large-scale sustained battles typical of early proto-states, but rather that these forms of warfare were the result

25 of socio-political innovations that built upon existing forms of coalitional violence (Levy and Thompson 2011).

The Psychology of War. The defining feature of research in this section is that here we confront more directly the role of psychological mechanisms as the link between evolution and behavior. This group of scholars draws upon evidence from primatology, paleoarchaeology, modern hunter-gatherer studies, and experimental cross-cultural evidence to argue that coalitional violence has constituted a significant selection pressure over our species’ evolutionary history (Tooby and Cosmides 1988; Van der Dennen

1995; Thayer 2004; Gat 2006; Lopez, McDermott, and Petersen 2011; McDonald,

Navarrete, and Van Vugt 2012). Just as the “killer ape” hypotheses was replaced by recognition that warfare in chimpanzees was context-specific, so also these scholars argue that the resultant adaptations in humans for coalitional violence are facultative, and that by understanding the context-specificity of these adaptations, we can learn about the conditions that fuel war and foster peace.

For example, Azar Gat has argued that humans are neither inherently peaceful nor aggressive. Instead, Gat argues that humans come equipped by natural selection with a

“motivational complex” that is responsible for generating the diversity of pro-social and aggressive behavior demonstrated by human societies (Gat 2000). This motivational system is the product of natural selection operating over the course of our species’ evolution as our ancestors navigated adaptive challenges related to the competition for resources and mates (Durham 1976).

Gat (2000) illustrates this dynamic with a discussion of the zoological relationship between aggression and the quality of resources over which organisms may compete.

26 When resources are nutritionally dense and subject to monopolization, organisms can afford to attempt to control them by force, and the fitness benefits for doing so are substantial (Dyson-Hudson and Smith 1978). However, when resources are not nutrionally dense and are also difficult to monopolize, the cost-benefit calculus governing the acquisition of resources militates against aggressive conflict. Thus, it has been observed that herbivores rarely fight over food, while carnivores often do, which is in part a consequence of natural selection shaping the motivational systems of these species to be adaptively responsive to the ecological profile of the resources on which they depend. Gat shows that natural selection has likely shaped the motivational complex of humans in similar ways, and he provides evidence that warfare among hunter-gatherers tends to be more frequent where contested resources are nutritionally dense and subject to monopolization.

One interesting consequence of the evolutionary “calculus” governing the use of coalitional violence in humans is the proclivity for spirals of violence, in which one violent act is revenged by another, which itself sparks further outrage and leads to incessant conflict between communities. Gat (2006) offers an intriguing explanation for these dynamics with reference to ancestral selection pressures, as well as implications for how this dynamic manifests itself in modern warfare. Spirals of violence can be characterized as situations in which mutual deterrence fails. The question is therefore to explain the forces that militate against deterrence. Gat argues that the human capacity for tool-making, when applied toward weapons for use in combat, meant that an individual equipped with a weapon needed to rely less on muscle mass than an unequipped individual. As weapons became more sophisticated and common, and the human

27 physique became increasingly slender, humans became “quintessential first-strike creatures” (Gat 2006, 129).

The surprise attack became a staple of human coalitional violence as “the growth in human offensive capability was linked with a steady decrease in their natural defenses”

(Gat 2006, 128). As Gat observes, with most species it is nearly impossible for an animal to approach a rival without being noticed, and even when this can be accomplished, it is even more difficult to finish off this rival with a single blow. In humans, however, the situation is reversed. The combination of weaponry with the relatively vulnerable physique of humans meant that if an individual can be caught unaware (and unarmed), they would be at a massive disadvantage. The result is that “true first-strike capability gives an enormous advantage to the side that strikes first, and thus theoretically, almost forces one to pre-empt” (Gat 2006, 132). These dynamics are of course readily understood by even the most casual observer of warfare and can be summed up by the adage: “the best defense is a good offense.”

As we have seen earlier, however, Wrangham’s imbalance of power hypothesis also explains the prevalence of lethal/surprise raiding between coalitions, and in chimpanzees this type of raiding prevails in the absence the co-evolutionary dynamic between weaponry and physique described by Gat. One notable difference, however, between the coalitional violence of chimpanzees and humans is that in chimpanzees this coalitional violence does not translate into cycles of retaliatory strikes. Thus, although the behavioral ecology of chimpanzee coalitions favors the asymmetric surprise attack, lethal raids by chimpanzees do not seem to be characterized by the kind of “security dilemmas” in which humans are often caught. Thus it may be that the behavioral ecology

28 of chimpanzee and human ancestral environments was one that strongly favored lethal raiding as the dominant form of coalitional aggression, yet, the co-evolutionary dynamic between weaponry and physique that occurred in humans enhanced the security dilemma in which humans became, as Gat notes, “quintessential first-strike creatures.”

Like Azar Gat, several political scientists have sought to apply evolutionary theory toward an understanding of coalitional competition and violence (Somit and

Peterson 1997; Thayer 2000; Thayer 2004; Rosen 2005). However, these authors have been mischaracterized as having made claims that aggression is universal, inevitable, and even natural (Bell and MacDonald 2001; Bell 2006; Goodwin 2010). For example,

Thayer (2000; 2001) has argued that the egoism upon which realist perspectives in international relations depend can be offered a biological and scientific grounding by recognizing that these impulses were designed by natural selection in response to the dynamics of dominance contests between individuals and coalitions. Yet, Thayer himself recognizes that “evolutionary theory explains why individual animals are egoistic… or why they may be altruistic” (2001, 197). Thus, as we proceed to examine the psychological dimensions of warfare in the context of our evolutionary history, it is important to remember that: 1) putative adaptations, unless otherwise specified, are expected to be facultative; and 2) humans possess a complex motivational architecture that enables and generates a range of pro-social and aggressive behavior, including coalitional violence.

Perhaps the best illustration of these dynamics is the intimate relationship between inter-group violence and within-group cooperation (Burton-Chellew, Ross-

Gillespie, and West 2010). There is an emerging literature that examines the ways in

29 which coalitional violence between groups enhances cooperation and pro-social behavior within groups. This literature shows that within-group pro-social dynamics such as guilt over nonparticipation (Puurtinen and Mappes 2009), punishment of defectors (Gneezy and Fessler 2011), heroism (Choi and Bowles 2007; Bowles 2009; Orbell and Morikawa

2011), and leadership (Smith et al. 2007; Vugt and Ahuja 2011) are likely the products of intense selection pressures surrounding coalitional violence and competition. In other words, natural selection seems to have designed a suite of adaptations in humans specialized to regulate a behavioral and motivational repertoire for use in conflict with out-groups.

The hallmark component of these dynamics is the tendency toward outgroup derogation and ingroup preference that has been well outlined by researchers of social identity theory (SIT). Briefly, SIT argues that one’s personal identity is a function of one’s coalitional identity, and therefore, one pathway toward self-enhancement is the enhancement of one’s coalitional identity (often at the expense of an outgroup). Tajfel and Turner (1986) performed the seminal research in SIT by showing that even arbitrarily imposed associations among individuals are sufficient to prompt them to derogate outgroups, and this framework has been applied in international relations to explain patterns of conflict and cooperation (Mercer 1995; Curley 2009). Subsequent research has demonstrated that individuals experience significantly less empathy toward outgroup members (Cikara, Bruneau, and Saxe 2011), and that brain regions associated with pleasure, such as the ventral striatum, are activated both when one observes ingroup success as well as when one observes outgroup failure (Cikara, Botvinick, and Fiske

2011). Additionally, there is a tradeoff between the extent to which individuals attribute

30 a singular mind to outgroups versus individuating between particular people in an outgroup (Waytz and Young 2011).

These dynamics resonate well with the observation that coalitional violence is often characterized by dehumanization of outgroups, and in which the target of aggression is not a particular individual but rather any given outgroup member.

According to one account of the evolution of warfare, this is a distinctive trademark of coalitional violence – the impersonal nature of warfare in which the goal is not to attack an individual qua individual, but rather, to attack an individual qua outgroup member

(Kelly 2000). The result is the social substitutability of outgroup members as targets of violence in the context of coalitional competition.

The flip side of outgroup derogation is ingroup preference. For example, scholars have shown that the evolutionary recurrence of conflict between coalitions has led, through processes of genetic or cultural group selection, to the emergence of pro-social norms and psychological biases that regulate intra-group cooperation (Choi and Bowles

2007; Bowles 2009; Mathew and Boyd 2011; Gneezy and Fessler 2011).

One of the characteristic features of the psychological dynamics that are activated in the context of coalitional competition is that they operate quickly, efficiently, and often seem to bypass processes of rational deliberation. As noted above, it is sufficient merely to place individuals in groups in order to trigger ingroup preference and outgroup derogation. For example, Wagner et al. (2002) have shown that changing the context of competition between two individuals from “intra-group” to “between-group” is sufficient to raise testosterone and cortisol levels in the competitors. Gneezy and Fessler (2011) have shown that the presence of violent inter-group conflict is sufficient to motivate

31 individuals to incur greater costs so that non-cooperative group members may be punished. Importantly, however, Yamagishi and Mifune (2009) have demonstrated that in-group bias does not require inter-group aggression as a prerequisite, nor does in-group bias necessarily promote out-group derogation; instead, in-group bias can emerge in minimal groups carried by expectations of generalized group reciprocity.

A recent study by Ginges and Atran (2011) demonstrates that individuals do not decide to support warfare in an instrumentally rational manner, but in a deontological manner. In other words, people do not support violence because the expected outcomes maximize utility, but rather, because it feels like “the right thing to do,” even in the face of clear evidence that warfare as a policy will fail to achieve its goals. The novelty of this contribution is that it is the first to directly test whether people engage in rational decision-making regarding warfare. Although there is an abundance of research in international relations that offers rationalist explanations for war, these are mathematical models that describe how agents should behave given a set of defined preferences in the context of assumed environmental constraints (Fearon 1995; Powell 2006). Indeed, this is true by design since rationalist models are normative in nature (Kahler 1998; Mercer

2005), and unfortunately these models are often not backed up with empirical demonstrations of people actually behaving this way (Green and Shapiro 1996).

Importantly, this evidence does not suggest that people are not thinking or calculating; instead, it suggests that the structure of mental processing operates according to logics that do not privilege the maximization subjective expected utility. As Ginges and Atran argue, these processes conditionally (e.g. in war but not diplomacy) follow a

“rule-bound logic of moral appropriateness,” independent of expected material reward.

32 In short, thinking and calculating are not supervened; rather, they may serve goals that do not privilege the maximization of expected utility. Many of the authors above have argued that psychological decision-making adaptations were designed to generate behavior that would have enhanced reproductive fitness on average in ancestral environments, regardless of whether that behavior correlated with individual utility.

Ginges and Atran argue that the goals privileged by deontological reasoning in warfare were shaped by norms that became deeply entrenched through the evolutionary processes of cultural group selection. Although researchers above would generally agree that rationalist models fail to correctly answer the “what-is-being-maximized” question, scholars disagree on the evolutionary pathway by which decision-making systems – whether instantiated as psychological adaptations or cultural norms – come to exist. At this point, we are forced to confront the level of selection problem in evolutionary biology, which explains various evolutionary pathways by which patterns of social behavior can be explained.

The Level of Selection Problem. The level of selection problem in evolutionary theory is compounded with (and often confused with) the unit of selection problem, and therefore I consider both in turn. Once these processes are understood, I turn to the application of these evolutionary processes toward the study of warfare.

The unit of selection. To begin, we must recall some points about evolutionary theory. First, for natural selection to occur, replicating entities (“replicators”) must exist, and there must be design-variation among replicators that affects their ability to replicate.

Second, in the abstract, natural selection is the algorithmic process by which replicators become more or less frequent in future generations as a consequence of their reproductive

33 success (i.e. how well they “replicate”). Given these elements, what entities in nature are the “units” among which selection “chooses”? There have been many candidates proposed as the unit of selection, such as genes, individuals, groups, and even species as a whole. However, consider that every population of organisms is a unique combination of individuals that will never again occur in history; the same is true of sub-groups within such populations. Even the individuals that compose groups, as well as the genomes within individuals, are unique. Due to sexual reproduction, which rips apart the genomes of each individual during each reproductive event to create a new individual, every genome in every individual has never existed and will never exist again.

Natural selection cannot “select” among species or groups quite simply because these entities have poor copying fidelity (i.e. they are not true “replicators”), and the same is true of individuals and the genomes that they possess; viz. if Anthony has many offspring, it is not the case that Anthony becomes more common in the population. If there is a population of entities, each of which is unique and will never reoccur, then not a single one of them can ever become more or less common in future generations.

Classical Darwinists operated under the assumption that individuals are the unit of selection; indeed, some individuals survive to reproduce, others are less successful.

Those more successful individuals will pass on their traits to future generations. This is of course true, but since the incorporation of Mendelian genetics with Darwinian evolutionary theory, it is now conventionally understood that genes, not individuals, are the unit of selection.

To see why this is the case, consider the properties of genes. Richard Dawkins has made the most persuasive case for why genes are the only true replicators and

34 represent the unit of selection (Dawkins 1976; Dawkins 1983). Unlike groups, individuals, or genomes, it is the case that genes are good candidates for replicators because they possess three key features: longevity, fecundity, and high copying-fidelity.

Genes, represented in DNA, are relatively stable self-replicating entities that are relatively good at reproducing exact replicas of themselves most of the time. It is this

“most of the time” that opens the door to genetic variation, since occasionally a copying error is made, and a new variant is generated. If the new variant is better at replicating itself, it becomes more frequent relative to its alternative version or “allele.”

In the beginning of life, theoretically, there were no complex organisms, only replicators. However, over time, as evolution progressed, replicators became more sophisticated, and organisms evolved as “vehicles” in which genetic material was carried

(Dawkins 1976). Thus, we can think of organisms, and the adaptations that compose them, as the evolutionary products of selection among genes. Genes that built vehicles that were more effective at delivering copies of themselves into future generations increased in frequency relative to other genes whose vehicles were relatively less successful. Thus, adaptations do not exist for the good of the individual or the good of the group, but for the good of the gene. As Dawkins has colorfully put it, “a bird is a gene’s way of making another gene” (Dawkins 1983, 98).

It is generally accepted that genes are the unit of selection (Williams 1966;

Maynard Smith 1993; Ridley 2004). Although some evolutionary theorists continue to find it useful to operate under the assumption that selection operates “as if” to select among individuals (Mayr 2001), this conventional shorthand is nevertheless technically false. Natural selection operates to increase or decrease the frequency of genes in a gene

35 pool as a consequence of their phenotypic effects, which are expressed through the adaptations in the bodies of individuals. This will become clearer as we consider the level of selection problem.

The level of selection. Genes are the units of selection, and as we observed above, genes do not exist independently on a plane of inter-genic commune; rather, they exist within organisms. These organisms can be thought of as the “vehicles” in which genes are carried, and these vehicles affect the likelihood that a given gene will filter into future generations. Thus, the unit of selection problem deals with identifying the units in nature that are the objects of selection, and the level of selection problem deals with the question of which “vehicles” (individuals, groups of individuals, etc.) affect the likelihood of genes to increase or decrease in frequency, as well as how.

Individual-level selection. A given genetic variant may be expressed as a phenotypic trait, for example, that causes a bird to fly faster, see farther, or be more colorful and attractive to mates. These are examples of phenotypic effects – they are coded for by genes, they are the properties of individuals, and they cause an individual to have more or less offspring, thus affecting the frequencies of the genes that generate them. In this sense, individual organisms operate as the “vehicle” for the replicators

(genes), and the success of the vehicle determines whether the genes it carries are transmitted into future generations. In other words, phenotypic effects expressed in the individual act as a “target” for selection. Thus, selection operating at the level of the individual means that individuals are the most important vehicles that determine the ability of their genes to filter into future generations. For the most part, therefore, the various genes in individuals “cooperate” to “benefit” the individual; a gene may code for

36 better eyesight, which benefits the individual in its encounters with others.3 Thus it is convenient to think of adaptations as “for the good of the individual” even if we recognize that ultimately, this benefit manifests as changes in the frequencies of genes as the unit of selection. This is the essence of “individual-level” selection: genes increase or decrease in frequency as a consequence of the success of their “vehicle” to reproduce.4

Natural selection is the process whereby genes increase or decrease in frequency depending on the interaction between what genes produce (i.e. their phenotypic effects) and the environment in which they exist.

Group-level selection. If the interactions between “vehicles” and the environment help to determine whether the genes vehicles carry become more or less numerous, are there other vehicles in addition to individual organisms that may have similar effects on gene frequencies? As seen above, selection can operate at the level of the individual because the fates of the genes within individuals are largely shared. However, others have argued that groups can act as vehicles when the fate of the individuals within these groups (and by extension the genes in those individuals) is also shared (Wynne-Edwards

1967). Above we saw that selection acting at the level of the individual operates to favor adaptations “for the benefit of the individual.” Similarly, group selectionists point out

3 For interesting counter-examples, see Burt and Trivers (2006) and Cosmides and Tooby (1981). 4 Of course, a gene present in one person may also be present in another, for example, by virtue of common descent, such as between siblings. Thus, a gene that caused an individual to incur a small cost in order to confer a great benefit to a brother, would on the one hand reduce the reproductive success of its own vehicle, but increase its own fitness as a gene. Thus, evolutionary theorists have demonstrated that one pathway for the evolution of altruism is that it can be favored between genetically related individuals when a gene for altruism confers benefits to other individuals that are likely to carry the same genes. This illustrates the fact that although individual-level selection can be a useful shorthand for understanding the design of many adaptations, it may be incomplete and misleading, since a gene may favor behaviors that impose a cost on its “vehicle” in order to benefit copies of itself in other vehicles. The net result of such behaviors are said to enhance the “inclusive” fitness of the gene (Hamilton 1964a; Hamilton 1964b).

37 that selection acting at the level of the group operates to favor adaptations “for the benefit of the group.”

For example, group selectionists have argued that altruism (i.e. behaviorally, an act that increases the fitness of another individual at the expense of one’s self) only makes sense as the output of adaptations designed for the benefit of the group. Given an evolutionary history full of competition between groups, in which groups composed of altruistic individuals outcompeted groups composed of selfish individuals, it would come to be the case that groups composed of selfish individuals would be defeated/eliminated, and the population would eventually consist entirely of groups of altruists. Absent the pressure of inter-group conflict, group selectionists argue, it is not clear how or why within-group altruism (e.g. individual-level selection) could be favored by genic or individual level selection.5

Group selection was dealt a serious blow by George Williams in his seminal

Adaptation and Natural Selection, in which he made two points that seemed to put the final nail in the coffin of this once widely accepted hypothesis (Williams 1966). First, adaptations that appear designed “for the benefit of the group” can usually be more parsimoniously (and accurately) explained by selection operating at the level of the gene or individual. Second – and this was the critical blow – selection at higher levels tends to be undermined by selection at lower levels. Williams showed that in order for group selection to operate, it would be necessary for the rate of group extinction to 1) exceed the rate at which selfish individuals would “invade” groups otherwise composed of altruists, and 2) exceed the rate of between-group migration. A positive extinction-to-

5 See fn. 5 for one explanation of how selection at lower levels can produce adaptations for altruistic or cooperative behavior. For just a few other examples, see Trivers (1971), Delton et al. (2011), and Price (2012)

38 invasion ratio is necessary if selection between groups is not to be contravened by selection within groups, while a positive extinction-to-migration ratio is necessary if groups are to be stable enough to act as vehicles of selection in the first place.6 These conditions were later formalized by Maynard Smith (1976), and it was believed that the conditions that were necessary in order for group selection to take place rendered it a negligible evolutionary force.

Despite the seemingly air-tight case against group selection as a significant evolutionary force, proponents have recently reinvigorated group selection by explaining that the previous conditions limiting the prevalence of group selection were too stringent

(e.g. group “extinction” is not actually necessary at all), and that even if group selection does not fully contravene individual and genic level selection, it may act in conjunction with these levels (Wilson and Sober 1994; Sober and Wilson 1999). In other words, it may prove useful to consider multilevel selection, in which adaptations are explained as the functional “compromise” of the push and pull between higher and lower levels of selection, rather than selection operating at exclusively one level. Awkwardly, despite the fact that this approach is taken seriously by many, its plausibility seems to be matched only by its mathematical intractability as a model. Nevertheless, debate continues regarding the identification of the conditions under which group selection may hold, and the identification of whether such conditions prevailed in ancestral environments (Nowak

6 A caveat is in order: Selection operating at the level of groups does not imply that groups in this case are the unit of selection. Although in a proximate sense, group selection assumes that groups are stable enough to be “selected” relative to other groups, ultimately the units that are replicated are not groups but rather the genes of the individuals that compose the successful groups. In other words, even an extremely high extinction:migration rate does not change the fact that each group represents a unique set of individuals that have never existed and will never again exist. Group selection suggests that the fate of the group in the context of inter-group competition becomes an important selective force that acts to shape adaptations for the benefit of the group even where these adaptations may be “locally disadvantageous” to the individuals that bear them (Eldakar and Wilson 2011).

39 2006; Hagen and Hammerstein 2006; Lehmann et al. 2007; Nowak, Tarnita, and Wilson

2010; Price 2012).

Cultural group selection. Some scholars reject that genic and individual-level selection alone can favor adaptations for altruism and cooperation (Henrich et al. 2006;

Henrich et al. 2010), and given the difficulties of group selection, others have argued that within-group altruism and cooperation can emerge through cultural group selection

(Henrich 2004; Mathew and Boyd 2011). Cultural group selection operates much the way group selection does, except instead of genetically-encoded phenotypic traits as the unit of selection, cultural norms are the unit of selection. Strictly speaking, this is not a process of biological evolution, but of cultural evolution; however, proponents argue that once this process of cultural evolution is set in place, it establishes an environment in which natural selection favors biological adaptations designed to operate in these culturally selected environments (Richerson and Boyd 2006). This represents a form of gene-culture co-evolution, though this co-evolutionary dynamic is not necessary in order for cultural group selection to operate.

Proponents of cultural group selection begin much the same way genetic group selectionists7 begin – by recognizing the central importance of inter-group competition.

The presence of systematic inter-group conflict over evolutionary time meant that groups that adopted norms of within-group altruism were more successful in competition against groups that did not adopt these norms. As a consequence, successful groups bearing altruism-promoting norms multiplied. These norms, or moral rules, became entrenched and spread precisely because they commit individuals to collective action that benefits

7 To differentiate group selectionists from cultural group selectionists, it is conventional to label the former “genetic” group selectionists to emphasize that the unit of selection remains genetically-coded traits.

40 the group in its efforts against other groups, even though such actions would be prohibitively costly for the individual, such as risking one’s life in war.

Although work discussed above often employs cultural group selection to explain the existence of pro-social biases and norms, alternative theoretical models argue that these motivational dynamics are the product of adaptations designed by natural selection working at the level of the individual, which also allow for cooperation in large groups and even with strangers (Hagen and Hammerstein 2006; Delton et al. 2011). This illustrates an often overlooked point regarding debates over the level of selection and its relevance for the evolution of war, which is that both models yield similar predictions

(i.e. cooperation in the context of large groups and with unrelated strangers, but see also

Lehmann et al. 2007). At a minimum, and until further research is conducted, we must acknowledge the theoretical plausibility of more than one pathway by which pro-social behavior and attitudes for use in coalitional competition could evolve. Indeed, it may be likely that models that take advantage of multi-level selection may offer a more complete explanation than those that focus on either individual or group level selection to the exclusion of other levels. I do not argue in this dissertation that my predictions and findings must be explained as a product of genic/individual-level selection; however, where relevant, I will occasionally explain how they can be explained by selection operating at this level, and leave future research to resolve the level of analysis question more directly.

The Offense-Defense Balance. Thus far I have examined literature that investigates war as the product of evolutionary processes, and I have engaged scholarship that directly examines the psychology of war in light of such evolutionary processes. At

41 that point it became necessary to engage the level of selection problem, since understanding this problem is at the heart of debates regarding the evolutionary mechanism by which selection pressures shape psychological adaptations for warfare.

Now, however, it is necessary to switch gears a bit. To anticipate, in the next chapter I will outline a theoretical framework for explaining the existence and structure of psychological adaptations for warfare, and I will also explain that it is likely that humans possess “separate psychologies” for offensive and defensive aggression. As I mentioned above, there is no scholarship in international relations or elsewhere that examines the possibility that these two forms of warfare have systematically different effects on behavior and motivation. However, there is a literature that engages a similar question:

How does the distinct nature of military capabilities for offensive and defensive warfare affect the likelihood of war and its character? It is to this literature that I now turn.

Formal acknowledgment of a theoretically useful distinction between offensive and defensive armaments developed shortly after WWI.8 At the time, and indeed since, it was believed that if there were a way to eliminate offensive weapons specifically, this would aid the cause of peace tremendously (Bennett 2011). The challenge, of course, was to identify those weapons and capabilities that were clearly offensive in nature.

Perhaps the first academic treatment of the topic was from Quincy Wright (1983), who presaged much of what would become known as the offense-defense balance. Wright argued that when offense is easier (i.e. the offense is “superior”), the result is a general increase in the probability of war marked by efforts such as empire building, decrease in the number of states, and the outbreak of shorter, cheaper wars. However, as defense

8 An exception that I will again discuss in passing in the next chapter is in the writings of Clausewitz and Sun Tzu, although a distinction between offense and defense was more incidental in these works than a central component of them.

42 became superior, Wright argued that we should see the opposite: empires fall apart, proliferation in the number of states, and the outbreak of war should be less frequent while warfare should be less decisive and more protracted.

Perhaps the most significant contributions to theory regarding the offense-defense balance were by George Quester (2002) and Robert Jervis (1978). Quester’s book,

Offense and Defense in the International System, was the first direct theoretical and historical investigation into the question of the effect on various forms of military capabilities on the likelihood and quality of warfare. Quester was also one of the earliest scholars to consider how nuclear weapons affected the offense-defense balance, arguing that nuclear weapons, as counter-value weapons, favor the defense and promote peace.

Although Quester’s was the first direct development of offense-defense theory, Jervis was the first to place the offense-defense balance under the analytic framework of the

“security dilemma,” which gave it deeper theoretical traction for political scientists.

Because his framework remains central to subsequent and current theorizing on the offense-defense balance, I explore it in detail.

Jervis (1978) begins with what for international relations scholars are the fundamentals: anarchy—the absence of formal government at the international level to compel behavior and enforce agreements. In this environment, states find it challenging to cooperate for three reasons: 1) state reputation and behavior is unstable, so credible commitments are difficult to establish; 2) some forms of cooperation (e.g. trade) can establish dependency, and hence vulnerability; 3) efforts by states to defend themselves may paradoxically make other states less secure. The third element is known as the

“security dilemma,” in which efforts by one state to defend itself from attack (e.g.

43 building a bigger, stronger navy) lead others to do the same out of insecurity, thus generating many forms of arms races. The result of these arms races, at best, is that the overall level of security, in material terms, remains the same, though at worst, insecurity and mistrust is heightened as a by-product of such arms races. However, Jervis argues that when defensive warfare is superior, the negative consequences of the security dilemma are mitigated, and when the offense has the advantage, they are instead enhanced. The central question, therefore, is two-fold: How do we distinguish between the two forms of warfare, and given that a distinction can be recognized, how do we know when one has the advantage over the other?

Put simply, offense has the advantage when “it is easier to destroy the other’s army and take its territory than it is to defend one’s own.” In contrast, defense is superior when “it is easier to protect and to hold than it is to move forward, destroy, and take”

(187). The two main factors that determine the “balance” of superiority between offense and defense are technology and geography. For example, stable borders along natural geographical boundaries such as oceans or mountains naturally increase the cost of invasion and favor the defense. Technology also affects the balance quite directly through its affect on the character of armaments. The development of nuclear weapons, for example, has strongly favored the defense, according to Jervis, by making the costs of warfare and invasion almost entirely unbearable to rational decision-makers.

When offense is superior, incentives for pre-emption are great and states live in fear of surprise attack. In addition, as we have seen previously, wars tend to be frequent and short, states are biased toward threat perception, and there are great premiums on striking first and winning. Conversely, when defense has the advantage, the reverse tends

44 to hold. Although the cause of peace could be enhanced by, for example, superiority of defense, the difficulty faced by statesmen to effectively distinguish between offensive and defensive characters of any given armament remains a significant problem. For example, falsely evaluating the international system as “offense-dominant” (when it was in fact defense-dominant) was perhaps one reason leaders hastened into WWI, believing that battles would be resolved quickly and decisively (Van Evera 1984).

Jack Levy (1984) reviews the burgeoning literature on the offense-defense balance and argues that three problems exist with the framework. First, scholars falsely assume that the offense-defense balance can be correctly perceived. This suggests that the framework should be interpreted in terms of policymakers’ perceptions rather than the true material state of the balance, since it is these perceptions, rather than objective realities, that drive patterns of warfare in international politics. The objective state of the balance will, nevertheless, affect the consequences of war, even if the outbreak of war is better understood in terms of subjective perceptions. This objective balance should be defined in terms of the ratio of troops necessary to overcome a given defensive position.

Second, the framework lends itself to tautological conceptions. For example, as Levy says, “it is meaningless to hypothesize that offensive superiority increases the incentive to strike first if the offensive/defensive balance is defined by the incentive to strike first”

(222). Third, Levy laments the lack of empirical testing of the auxiliary hypotheses, which he believes is at least partly due to the above discrepancies.

Perhaps the most recent and comprehensive treatment of offense-defense balance theory is Steven Van Evera’s (1998) framework, in which he details the specific causes and effects of the balance. In this framework, the balance is determined by military

45 technology and doctrine, geography, national social structure, and diplomatic arrangements. Where Levy was specific and narrow in conceptualization of the balance,

Van Evera seeks to disaggregate the web of causal inputs that together determine the nature of the balance between offense and defense. In terms of the effects of the balance, Van Evera is largely consistent with the set of observations of preceding scholars. For example, offense superiority tends to generate opportunistic expansionism in which there are significant premiums to the first-mover. Van Evera’s contribution in this regard is in specific identification and disambiguation between the causes of the balance, and its effects.

It is probably already apparent that although the general framework of offense- defense balance remains consistent across scholars (e.g. character of armaments  policy), these scholars nevertheless vary in terms of their specific definition of the balance, and on how expansively they operationalize the balance itself, its determinants, and its effects. One tendency is to define the balance in terms of the cost of invasion relative to defense in terms of troop deployments. For example, Glaser and Kaufman

(1998) define the balance as the ratio of the cost of taking territory to the cost of defenders to repel them, and they argue that we can measure the balance in the same way that states regularly perform net assessment regarding the capabilities of other states.

Glaser and Kaufman prefer to omit perceptual factors from operationalization of the balance, and instead argue that military doctrines and force deployment reflect and do not determine the offense-defense balance.

Much of the scholarship above takes for granted that the offense-defense balance is a feature of the international system and is thus a “structural” character that all states

46 face equally. However, Biddle (2001) argues that the offense-defense balance is one that is specific to each pair of states and is not a structural component that generalizes to the system as a whole. In addition, although Biddle argues that the offense-defense balance is indeed a question of the character of military capabilities, it is equally important to consider force employment, or the way in which these capabilities are used, which will affect the prevailing character of the offense-defense balance. Thus, the offense-defense balance is determined by the character and employment of military force, and its effects are observable in combat outcomes between specific dyads of countries.

Just as Biddle argued that the effects of the offense-defense balance are observable in the combat outcomes of specific conflicts, Karen Ruth Adams (2004) argues that most previous research has examined the effects of the balance on arms races and military doctrine instead of examining the incidence and outcomes of actual battles.

She derives a set of hypotheses regarding battle outcomes that should be expected under offense- and defense-superiority and examines the historical incidence of such events to evaluate the robustness of offense-defense balance theory. For example, in offense, attacks should more often culminate in conquest and wars should involve many attacks; however in defense, attacks will less often culminate in conquest and we should observe few attacks when war is declared. By examining attacks and conquests, we are provided with a source of greater variation upon which to test hypotheses than if we were to limit analysis to warfare or arms races. Ruth Adams finds empirical support for these hypotheses, which also suggest that the effects of offense-defense theory are better operationalized in terms of battle outcomes or operations instead of more generally on the incidence of warfare.

47 In sum, the offense-defense literature has examined how the character of armaments affects the likelihood and character of warfare. There is debate regarding whether actors can correctly perceive the balance, which opens the door to a range of misperceptions that may operate to generate outcomes at variance with what would be expected given the objective nature of the balance. There is also disagreement over narrow versus broad conceptualizations of the balance itself, as well as disagreement regarding whether the effects of the balance are best observed at the level of wars or battles. However, the theoretical and empirical contributions by Biddle and Ruth Adams suggest that effects are best observed at the level of battle outcomes. Lastly, it is likely the case that the offense-defense balance is dyad-specific and not a property of the international system as whole.

This research is largely agnostic on the role of psychology, except for various discussions in passing regarding how misperceptions may generate counterintuitive and otherwise irrational outcomes. Furthermore, although scholars recognize the distinction between offense and defense as a general form of warfare independent of armaments

(briefly, taking versus holding territory and resources), the main variable of interest is the character of armaments in determining the likelihood of the initiation of warfare. Given a constellation of armaments, beliefs, geography, and institutional features, states are either more or less likely to initiate warfare. The question I investigate here is how the choice between initiating and responding to aggression leads to distinct motivational dynamics.

For example, do people reason about warfare differently when the question is whether to initiate aggression (offensive warfare) versus whether to respond to aggression (defensive warfare)? This will be the main topic of investigation in the proceeding chapters.

48 Thus, in the next chapter I outline evolutionary psychology as an approach for understanding the dynamic relationship between evolution, psychology, and behavior. I utilize evolutionary psychology, as well as insights from social psychology and the anthropology of war, to develop a framework with which to investigate the psychological mechanisms designed by natural selection for the regulation of coalitional violence, or warfare. This framework, labeled “the risk contract of war” constitutes the theoretical model from which hypotheses will be generated and subsequently tested.

Adams, Karen Ruth. 2004. “Attack and Conquer? International Anarchy and the Offense- Defense-Deterrence Balance.” International Security 28 (3): 45–83. doi:10.1162/016228803773100075. Aiello, Leslie C., and R. I. M. Dunbar. 1993. “Neocortex Size, Group Size, and the Evolution of Language.” Current Anthropology 34 (2) (April 1): 184–193. Albert, D J, R H Jonik, and M L Walsh. 1992. “Hormone-dependent Aggression in Male and Female Rats: Experiential, Hormonal, and Neural Foundations.” Neuroscience and Biobehavioral Reviews 16 (2): 177–192. Alcock, John. 1975. Animal Behavior: An Evolutionary Approach. Sunderland, Mass.: Sinauer Associates. ———. 2005. Animal Behavior: An Evolutionary Approach, Eighth Edition. 8th ed. Sinauer Associates. Alexander, Richard D. 1979. Darwinism and Human Affairs. Seattle: University of Washington Press. ———. 1987. The Biology of Moral Systems. Hawthorne, N.Y.: A. de Gruyter. Alford, J R, C. L. Funk, and J R Hibbing. 2005. “Are Political Orientations Genetically Transmitted?” American Political Science Review 99 (2): 153–167. Alford, John R., and John R. Hibbing. 2004. “The Origin of Politics: An Evolutionary Theory of Political Behavior.” Perspectives on Politics 2 (4): 707–723. Archer, J. 2006. “Testosterone and Human Aggression: An Evaluation of the Challenge Hypothesis.” Neuroscience & Biobehavioral Reviews 30 (3): 319–345. Archer, John. 1988. The Behavioural Biology of Aggression. Cambridge: Cambridge University Press. http://www.loc.gov/catdir/enhancements/fy0906/87021792- d.html.

49 ———. 2006. “Testosterone and Human Aggression: An Evaluation of the Challenge Hypothesis.” Neuroscience & Biobehavioral Reviews 30 (3): 319–345. doi:10.1016/J.Neubiorev.2004.12.007. Axelrod, Robert, and William D. Hamilton. 1981. “The Evolution of Cooperation.” Science 211 (4489): 1390–1396. Axelrod, Robert M. 1984. The Evolution of Cooperation. New York: Basic Books. http://www.loc.gov/catdir/enhancements/fy0831/83045255-d.html. Barkow, Jerome H., Leda Cosmides, and John Tooby. 1992. The Adapted Mind: Evolutionary Psychology and the Generation of Culture. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0636/91025307- d.html. Barnett, Michael. 2009. “Evolution Without Progress? Humanitarianism in a World of Hurt.” International Organization 63 (04): 621–663. Bell, D. 2006. “Beware of False Prophets: Biology, Human Nature and the Future of International Relations Theory - BELL - 2006 - International Affairs - Wiley Online Library.” International Affairs. http://onlinelibrary.wiley.com/doi/10.1111/j.1468-2346.2006.00547.x/full. Bell, DSA, and PK MacDonald. 2001. “Start the Evolution Without Us.” International Security 26 (1): 187–194. Bennett, John W. Wheeler. 2011. The Pipe Dream Of Peace The Story Of The Collapse Of Disarmament. Nabu Press. Betzig, Laura L. 1986. Despotism and Differential Reproduction : a Darwinian View of History. New York: Aldine Pub. Biddle, Stephen. 2001. “Rebuilding the Foundations of Offense-Defense Theory.” Journal of Politics 63 (3) (August 1): 741–774. doi:10.1111/0022-3816.00086. Boehm, Christopher. 1984. Blood Revenge : the Anthropology of Feuding in Montenegro and Other Tribal Societies. Lawrence, Kan.: University Press of Kansas. ———. 1999. Hierarchy in the Forest: The Evolution of Egalitarian Behavior. Cambridge, Mass.: Harvard University Press. Bowles, S. 2009. “Did Warfare Among Ancestral Hunter-gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932): 1293. Bowles, Samuel. 2009. “Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932) (June 5): 1293–1298. doi:10.1126/science.1168112. Boyd, R., and P. J. Richerson. 1992. “Punishment Allows the Evolution of Cooperation (or Anything Else) in Sizable Groups.” Ethology and Sociobiology 13 (3): 171– 195. Boyd, Robert, and Peter J. Richerson. 1988. “The Evolution of Reciprocity in Sizable Groups.” Journal of Theoretical Biology 132 (3) (June 7): 337–356. doi:10.1016/S0022-5193(88)80219-4. Brown, Michael E., Owen R. Coté Jr, Sean M. Lynn-Jones, and Steven E. Miller, eds. 2004. Offense, Defense, and War. 1st ed. The MIT Press. Burt, Austin, and Robert Trivers. 2006. Genes in Conflict: The Biology of Selfish Genetic Elements. Belknap Press of Harvard University Press.

50 Burton-Chellew, Maxwell N., Adin Ross-Gillespie, and Stuart A West. 2010. “Cooperation in Humans: Competition Between Groups and Proximate Emotions.” Evolution and Human Behavior 31 (2): 104–108. Buss, D. M., and D. P. Schmitt. 1993. “Sexual Strategies Theory - an Evolutionary Perspective on Human Mating.” Psychological Review 100 (2): 204–232. Buss, D. M., and T. Shackelford. 1997. “Human Aggression in Evolutionary Psychological Perspective.” Clinical Psychology Review 17: 605–619. Buss, David M. 2004. Evolutionary Psychology: The New Science of the Mind. Boston: Allyn and Bacon. Campbell, Bernard, ed. 1972. Sexual Selection and the Descent of Man: 1871-1971. Aldine Transaction. Carroll, Sean B. 2006. The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. New York, N.Y.: W.W. Norton & Co. Chagnon, Napoleon A. 1983. Yanomamö : the Fierce People. New York: Holt, Rinehart and Winston. ———. 1988. “Life Histories, Blood Revenge, and Warfare in a Tribal Population.” Science 239 (4843): 985–992. Charney, Evan. 2008. “Genes and Ideologies.” Perspectives on Politics 6 (02). doi:10.1017/S1537592708080626. http://www.journals.cambridge.org/abstract_S1537592708080626. Choi, J K, and S Bowles. 2007. “The Coevolution of Parochial Altruism and War.” Science 318 (5850): 636–640. doi:10.1126/science.1144237. Cikara, Mina, Emile G. Bruneau, and Rebecca R. Saxe. 2011. “Us and Them.” Current Directions in Psychological Science 20 (3) (June 1): 149 –153. doi:10.1177/0963721411408713. Cohen, Ronald. 1978. Origins of the State: The Anthropology of Political Evolution. Ed. Elman Rogers Service. Inst for the Study of Human Is. Confer, Jaime C., Judith A. Easton, Diana S. Fleischman, Cari D. Goetz, David M. G. Lewis, Carin Perilloux, and David M Buss. 2010. “Evolutionary Psychology: Controversies, Questions, Prospects, and Limitations.” American Psychologist 65 (2): 110–126. Cosmides, Leda, H. Clark Barrett, and John Tooby. 2010. “Adaptive Specializations, Social Exchange, and the Evolution of Human Intelligence.” Proceedings of the National Academy of Sciences (May 5). doi:10.1073/pnas.0914623107. http://www.pnas.org/content/early/2010/05/04/0914623107.abstract. Cosmides, Leda, and John Tooby. 1981. “Cytoplasmic Inheritance and Intragenomic Conflict.” Journal of Theoretical Biology 89 (1) (March 7): 83–129. doi:10.1016/0022-5193(81)90181-8. ———. 1987. “From Evolution to Behavior: Evolutionary Psychology as the Missing Link.” In The Latest on the Best: Essays on Evolution and Optimality, 276–306. Cambridge, Mass.: MIT Press. ———. 1994a. “Origins of Domain Specificity: The Evolution of Functional Organization.” In Mapping the Mind: Domain Specificity in Cognition and Culture, 85–116. New York: Cambridge University Press. ———. 1994b. “Better Than Rational - Evolutionary Psychology and the Invisible Hand.” American Economic Review 84 (2): 327–332.

51 ———. 2005. “Neurocognitive Adaptations Designed for Social Exchange.” In The Handbook of Evolutionary Psychology, 584–627. Hoboken, NJ: Wiley. Crawford, Neta C. 2009. “Human Nature and World Politics: Rethinking `Man’.” International Relations 23 (2) (June 1): 271–288. doi:10.1177/0047117809104639. Curley, Tyler M. 2009. “Social Identity Theory and EU Expansion.” International Studies Quarterly 53 (3) (September 1): 649–668. doi:10.1111/j.1468- 2478.2009.00550.x. Daly, Martin, and Margo Wilson. 1983. Sex, Evolution, and Behavior. Boston: Willard Grant Press. ———. 1988. Homicide. New York: A. de Gruyter. Dawkins, Richard. 1976. The Selfish Gene. Oxford: Oxford University Press. ———. 1980. “Good Strategy or Evolutionarily Stable Strategy?” In Sociobiology: Beyond Nature/Nurture?, 331–367. Boulder: Westview Press. ———. 1983. The Extended Phenotype : the Long Reach of the Gene. Oxford ; New York: Oxford University Press. ———. 1986. The Blind Watchmaker. New York: Norton. Delton, Andrew W., Max M. Krasnow, Leda Cosmides, and John Tooby. 2011. “Evolution of Direct Reciprocity Under Uncertainty Can Explain Human Generosity in One-shot Encounters.” Proceedings of the National Academy of Sciences 108 (July 25): 13335–13340. doi:10.1073/pnas.1102131108. Van der Dennen, J.M.G. 1995. The Origin of War: The Evolution of a Male-coalitional Reproductive Strategy. Groningen: Origin Press. Dennett, Daniel. 1995. Darwin’s Dangerous Idea : Evolution and the Meanings of Life. New York: Simon & Schuster. Dunbar, Robin I. M. 1993. “Coevolution of Neocortical Size, Group Size, and Language in Humans.” Behavioral and Brain Sciences 16 (4): 681–735. Durham, W. H. 1976. “Resource Competition and Human Aggression .1. Review of Primitive War.” Quarterly Review of Biology 51 (3): 385–415. Dyson-Hudson, Rada, and Eric Alden Smith. 1978. “Human Territoriality: An Ecological Reassessment.” American Anthropologist 80 (1): 21–41. Eaves, L., P. Hatemi, N. Gillespie, and N. Martin. 2008. “Looking for Politically Relevant Genes.” Behavior Genetics 38 (6): 623–623 101. Eldakar, Omar Tonsi, and David Sloan Wilson. 2011. “Eight Criticisms Not to Make About Group Selection.” Evolution 65 (6) (June 1): 1523–1526. Ember, C. R. 1978. “Myths About Hunter-Gatherers.” Ethnology 17 (4): 439–448. Ermer, E., L Cosmides, and J Tooby. 2008. “Relative Status Regulates Risky Decision Making About Resources in Men: Evidence for the Co-evolution of Motivation and Cognition.” Evolution and Human Behavior 29 (2): 106–118. doi:10.1016/J.Evolhumbehav.2007.11.002. Van Evera, S. 1998. “Offense, Defense, and the Causes of War.” International Security 22 (4): 5–43. Van Evera, Stephen. 1984. “The Cult of the Offensive and the Origins of the First World War.” International Security 9 (1): 58–107. Fearon, J. D. 1995. “Rationalist Explanations for War.” International Organization 49 (3): 379–414.

52 Feldstein, Martin. 1999. “A Self-Help Guide for Emerging Markets.” Foreign Affairs, March 1. http://www.foreignaffairs.com/articles/54801/martin-feldstein/a-self- help-guide-for-emerging-markets. Flinn, M. V., D. C. Geary, and C. V. Ward. 2005. “Ecological Dominance, Social Competition, and Coalitionary Arms Races: Why Humans Evolved Extraordinary Intelligence.” Evolution and Human Behavior 26 (1): 10–46. doi:10.1016/J.Evolhumbehav.2004.08.005. Forgas, Joseph P., Martie Haselton, and William von Hippel. 2007. Evolution and the Social Mind : Evolutionary Psychology and Social Cognition. New York, NY: Psychology Press. Fowler, J H, and D Schreiber. 2008. “Biology, Politics, and the Emerging Science of Human Nature.” Science 322 (5903): 912–914. doi:10.1126/science.1158188. Fowler, James H, and Christopher T Dawes. 2008. “Two Genes Predict Voter Turnout.” The Journal of Politics 70 (03). doi:10.1017/S0022381608080638. http://www.journals.cambridge.org/abstract_S0022381608080638. Fry, Douglas P. 2007. Beyond War: The Human Potential for Peace. 1St ed. Oxford University Press, USA. Gallistel, Charles R. 1990. The Organization of Learning. Cambridge, Mass.: MIT Press. Gat, Azar. 2000a. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-gatherer Fighting, Part II. Proximate, Subordinate, and Derivative Causes.” Anthropological Quarterly 73 (2): 74–88. ———. 2000b. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-Gatherer Fighting. Part I. Primary Somatic and Reproductive Causes.” Anthropological Quarterly 73 (1): 20–34. ———. 2006. War in Human Civlization. Oxford: Oxford University Press. http://www.loc.gov/catdir/toc/ecip0614/2006017223.html. Gazzaniga, Michael S. 2000. Cognitive Neuroscience : a Reader. Malden, Mass.: Blackwell. Gazzaniga, Michael S., Diana Steen, and Bruce T. Volpe. 1979. Functional Neuroscience. New York: Harper & Row. Gigerenzer, Gerd. 2000. Adaptive Thinking : Rationality in the Real World. New York: Oxford University Press. Gigerenzer, Gerd, and Reinhard Selten. 2001. Bounded Rationality : the Adaptive Toolbox. Cambridge, Mass.: MIT Press. Ginges, J, and S Atran. 2011. “War as a Moral Imperative (not Just Practical Politics by Other Means).” Proceedings of the Royal Society B: Biological Sciences 278 (1720): 2930–2938. doi:10.1098/rspb.2010.2384. Glaser, Charles L., and Chaim Kaufmann. 1998. “What Is the Offense-defense Balance and Can We Measure It?” International Security 22 (4): 44–82. Gneezy, Ayelet, and Daniel M. T. Fessler. 2011. “Conflict, Sticks and Carrots: War Increases Prosocial Punishments and Rewards.” Proceedings of the Royal Society B: Biological Sciences (June 8). doi:10.1098/rspb.2011.0805. http://rspb.royalsocietypublishing.org/content/early/2011/06/03/rspb.2011.0805.a bstract. Godfrey-Smith, Peter, and Jon F. Wilkins. 2008. “Adaptationism.” In A Companion to the Philosophy of Biology, Chapter 11. Oxford: Blackwell.

53 Goodall, Jane. 1986. The Chimpanzees of Gombe : Patterns of Behavior. Cambridge, Mass.: Belknap Press of Harvard University Press. Goodwin, Adam. 2010. “Evolution and Anarchism in International Relations: The Challenge of Kropotkin’s Biological Ontology.” Millennium - Journal of International Studies 39 (2): 417–437. doi:10.1177/0305829810384676. Green, Donald, and Ian Shapiro. 1996. Pathologies of Rational Choice Theory: A Critique of Applications in Political Science. Yale University Press. Hagen, Edward H, and Peter Hammerstein. 2006. “Game Theory and Human Evolution: a Critique of Some Recent Interpretations of Experimental Games.” Theoretical Population Biology 69 (3) (May): 339–348. doi:10.1016/j.tpb.2005.09.005. Hamilton, W. D. 1964a. “Genetical Evolution of Social Behaviour I.” Journal of Theoretical Biology 7 (1): 1–16. ———. 1964b. “Genetical Evolution of Social Behaviour 2.” Journal of Theoretical Biology 7 (1): 17–52. Harcourt, A. H., and F. B. M. de Waal. 1992. Coalitions and Alliances in Humans and Other Animals. Oxford [England] ; New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0639/91004285-d.html. Haselhuhn, Michael P, and Elaine M Wong. 2011. “Bad to the Bone: Facial Structure Predicts Unethical Behaviour.” Proceedings of the Royal Society B: Biological Sciences (July 6). doi:10.1098/rspb.2011.1193. http://rspb.royalsocietypublishing.org/content/early/2011/06/29/rspb.2011.1193. Hatemi, P K, J R Alford, J R Hibbing, N G Martin, and L J Eaves. 2009. “Is There a ‘Party’ in Your Genes?” Political Research Quarterly 62 (3): 584–600. doi:10.1177/1065912908327606. Heckhausen, Jutta, and Heinz Heckhausen. 2010. Motivation and Action. Cambridge University Press. Henrich, Joseph. 2004. “Cultural Group Selection, Coevolutionary Processes and Large- scale Cooperation.” Journal of Economic Behavior & Organization 53 (1) (January): 3–35. doi:10.1016/S0167-2681(03)00094-5. Henrich, Joseph, Jean Ensminger, Richard McElreath, Abigail Barr, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2010. “Markets, Religion, Community Size, and the Evolution of Fairness and Punishment.” Science 327 (5972) (March 19): 1480–1484. doi:10.1126/science.1182238. Henrich, Joseph, Richard McElreath, Abigail Barr, Jean Ensminger, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2006. “Costly Punishment Across Human Societies.” Science 312 (5781) (June 23): 1767–1770. doi:10.1126/science.1127333. Hooper, Paul L., Hillard S. Kaplan, and James L. Boone. 2010. “A Theory of Leadership in Human Cooperative Groups.” Journal of Theoretical Biology 265 (4) (August 21): 633–646. doi:10.1016/j.jtbi.2010.05.034. Hudson, Valerie M., and Andrea Den Boer. 2002. “A Surplus of Men, A Deficit of Peace: Security and Sex Ratios in Asia’s Largest States.” International Security 26 (4): 5–38. doi:10.1162/016228802753696753. Huntington, Samuel P. 1993. The Third Wave: Democratization in the Late 20th Century. University of Oklahoma Press.

54 Jervis, R. 1978a. “Cooperation Under the Security Dilemma.” World Politics: A Quarterly Journal of International …. http://www.jstor.org/stable/2009958. ———. 1978b. “Cooperation Under Security Dilemma.” World Politics 30 (2): 167–214. ———. 2003. “Understanding the Bush Doctrine.” Political Science Quarterly. http://www.ingentaconnect.com/content/taps/psq/2003/00000118/00000003/art00 001. Johnson, Dominic D. P., and James H. Fowler. 2011. “The Evolution of Overconfidence.” Nature 477 (7364): 317–320. doi:10.1038/nature10384. Johnson, Dominic D. P., Rose McDermott, Emily S. Barrett, Jonathan Cowden, Richard W. Wrangham, Matthew H. McIntyre, and Stephen Peter Rosen. 2006. “Overconfidence in Wargames: Experimental Evidence on Expectations, Aggression, Gender and Testosterone.” Proceedings of the Royal Society of London Series B-Biological Sciences: 2513–2520. doi:10.1098/Rspb.2006.3606. Johnson, Dominic D. P., Richard W. Wrangham, and Steven P. Rosen. 2002. “Is Military Incompetence Adaptive? An Empirical Test with Risk-taking Behaviour in Modem Warfare.” Evolution and Human Behavior 23 (4): 245–264. Johnson, Dominic D.P., and Dominic Tierney. 2011. “The Rubicon Theory of War: How the Path to Conflict Reaches the Point of No Return.” International Security 36 (1): 7–40. doi:i: 10.1162/ISEC_a_00043

55 Kurzban, Robert, John Tooby, and L Cosmides. 2001a. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences 98 (26): 15387–15392. Kurzban, Robert, John Tooby, and Leda Cosmides. 2001b. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences of the United States of America 98 (26): 15387–15392. LeBlanc, Steven A., and Katherine E. Register. 2003. Constant Battles: The Myth of the Peaceful, Noble Savage. New York: St. Martin’s. http://www.loc.gov/catdir/bios/hol052/2002036880.html. Lehmann, Laurent, Laurent Keller, Stuart West, and Denis Roze. 2007. “Group Selection and Kin Selection: Two Concepts but One Process.” Proceedings of the National Academy of Sciences 104 (16) (April 17): 6736 –6739. doi:10.1073/pnas.0700662104. Lerner, J S, and D Keltner. 2001. “Fear, Anger, and Risk.” Journal of Personality and Social Psychology 81 (1) (July): 146–159. Levy, Jack S. 1984. “The Offensive/defensive Balance of Military Technology: A Theoretical and Historical Analysis.” International Studies Quarterly 28 (2): 219– 238. Levy, Jack S., and William R. Thompson. 2011. The Arc of War: Origins, Escalation, and Transformation. University Of Chicago Press. Lieberman, D., J Tooby, and L Cosmides. 2007. “The Architecture of Human Kin Detection.” Nature 445 (7129): 727–731. doi:10.1038/Nature05510. Lieberman, Matthew D., Darren Schreiber, and Kevin N. Ochsner. 2003. “Is Political Cognition Like Riding a Bicycle? How Cognitive Neuroscience Can Inform Research on Political Thinking.” Political Psychology 24 (4) (December): 681– 704. doi:10.1046/j.1467-9221.2003.00347.x. Lopez, Anthony C. 2010. Evolution, Coalitional Psychology, and War. H-Diplo ISSF Roundtable on “Biology and Security.” Lopez, Anthony C., and Rose McDermott. “Adaptation, Heritability, and the Emergence of Evolutionary Political Science.” Political Psychology. Lopez, Anthony C., Rose McDermott, and Michael Bang Petersen. 2011. “States in Mind: Evolution, Coalitional Psychology, and International Politics.” International Security 36 (2): 48–83. Lorenz, Konrad. 1966. On Aggression. London,: Methuen. Manson, Joseph H., and Richard W. Wrangham. 1991. “Intergroup Aggression in Chimpanzees and Humans.” Current Anthropology 32 (4): 369–390. Martin, N G, L J Eaves, A C Heath, R. Jardine, L M Feingold, and H J Eysenck. 1986. “Transmission of Social Attitudes.” Proceedings of the National Academy of Sciences 83 (12) (June 1): 4364–4368. Masters, Roger D. 1989. The Nature of Politics. New Haven: Yale University Press. Mathew, Sarah, and Robert Boyd. 2011. “Punishment Sustains Large-scale Cooperation in Prestate Warfare.” Proceedings of the National Academy of Sciences. http://www.pnas.org/content/108/28/11375.short. Maynard Smith, J. 1976. “Group Selection.” Quarterly Review of Biology 51: 277–283.

56 Maynard Smith, John. 1982. Evolution and the Theory of Games. Cambridge ; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam022/81021595.html. ———. 1993. The Theory of Evolution. Cambridge [England] ; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam025/93020358.html. ———. 1998. Evolutionary Genetics. Oxford; New York: Oxford University Press. ———. 1999. Shaping Life : Genes, Embryos, and Evolution. New Haven: Yale University Press. Mayr, Ernst. 1983. “How to Carry Out the Adaptationist Program?” The American Naturalist 121 (3): 324–334. ———. 2001. What Evolution Is. New York: Basic Books. McDermott, R, D Tingley, J Cowden, G Frazzetto, and D D P Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. doi:10.1073/pnas.0808376106. McDermott, Rose. 2004. “The Feeling of Rationality: The Meaning of Neuroscientific Advances for Political Science.” Perspectives on Politics 2 (4): 691–706. McDermott, Rose, James H Fowler, and Oleg Smirnov. 2008. “On the Evolutionary Origin of Prospect Theory Preferences.” The Journal of Politics 70 (02). doi:10.1017/S0022381608080341. http://www.journals.cambridge.org/abstract_S0022381608080341. McDermott, Rose, Dustin Tingley, Jonathan Cowden, Giovanni Frazetto, and Dominic D. P. Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. McDonald, Melissa M., Carlos David Navarrete, and Mark Van Vugt. 2012. “Evolution and the Psychology of Intergroup Conflict: The Male Warrior Hypothesis.” Philosophical Transactions of the Royal Society B: Biological Sciences 367 (1589) (March 5): 670 –679. doi:10.1098/rstb.2011.0301. Mead, M. 1940. “Warfare Is Only an Invention—not a Biological Necessity.” Asia 40 (8): 402–405. Mehta, Pranjal H, Amanda C Jones, and Robert A Josephs. 2008. “The Social Endocrinology of Dominance: Basal Testosterone Predicts Cortisol Changes and Behavior Following Victory and Defeat.” Journal of Personality and Social Psychology 94 (6): 1078–1093. doi:10.1037/0022-3514.94.6.1078. Mercer, Jonathan. 1995. “Anarchy and Identity.” International Organization 49 (2): 229– 252. ———. 2005. “Rationality and Psychology in International Relations.” International Organization 59 (Winter): 77–106. Mesquida, C. G., and N. I. Wiener. 1999. “Male Age Composition and Severity of Conflicts.” Politics and the Life Sciences 18 (2): 181–189. Milner, Helen. 1992. “International Theories of Cooperation Among Nations: Strengths and Weaknesses.” World Politics 44 (3): 466–496. Mitani, John C., David P. Watts, and Sylvia Amsler J. 2010. “Lethal Intergroup Aggression Leads to Territorial Expansion in Wild Chimpanzees.” Current Biology 20 (12) (June 22): R507–R508.

57 Mitchell, Gregory, Philip E Tetlock, Daniel G Newman, and Jennifer S Lerner. 2003. “Experiments Behind the Veil: Structural Influences on Judgments of Social Justice.” Political Psychology 24 (3) (September 1): 519–547. doi:10.1111/0162- 895X.00339. Morgan, T. J. H, L. E Rendell, M. Ehn, W. Hoppitt, and K. N Laland. 2011. “The Evolutionary Basis of Human Social Learning.” Proceedings of the Royal Society B: Biological Sciences (July 27). doi:10.1098/rspb.2011.1172. http://rspb.royalsocietypublishing.org/content/early/2011/07/21/rspb.2011.1172.a bstract. Morgenthau, Hans Joachim, and Kenneth W. Thompson. 1993. Politics Among Nations: The Struggle for Power and Peace. McGraw-Hill. Nettleship, Martin A., R. Dale Givens, and Anderson Nettleship. 1975. War, Its Causes and Correlates. The Hague Chicago: Mouton ; distributed by Aldine. Nowak, Martin A, Corina E Tarnita, and Edward O Wilson. 2010. “The Evolution of Eusociality.” Nature 466 (7310): 1057–1062. doi:10.1038/nature09205. Nowak, Martin A. 2006. “Five Rules for the Evolution of Cooperation.” Science 314 (5805) (December 8): 1560 –1563. doi:10.1126/science.1133755. Olson, Mancur. 1965. The Logic of Collective Action; Public Goods and the Theory of Groups. Cambridge, Mass.,: Harvard University Press. Orbell, John, and Tomonori Morikawa. 2011. “An Evolutionary Account of Suicide Attacks: The Kamikaze Case.” Political Psychology 32 (2): 297–322. doi:10.1111/j.1467-9221.2010.00808.x. Otterbein, Keith F. 2004. How War Began. 1st ed. TAMU Press. Oxley, D R, K B Smith, J R Alford, M V Hibbing, J L Miller, M Scalora, P K Hatemi, and J R Hibbing. 2008. “Political Attitudes Vary with Physiological Traits.” Science 321 (5896): 1667–1670. doi:10.1126/science.1157627. Panchanathan, Karthik, and Robert Boyd. 2004. “Indirect Reciprocity Can Stabilize Cooperation Without the Second-order Free Rider Problem.” Nature 432 (7016) (November 25): 499–502. doi:10.1038/nature02978. Parker, Geoff. 1974. “Assessment Strategy and the Evolution of Fighting Behaviour.” Journal of Theoretical Biology 47 (1) (September): 223–243. Petersen, Michael Bang. 2009. “Public Opinion and Evolved Heuristics: The Role of Category-Based Inference.” Journal of Cognition and Culture 9 (3): 367–389. doi:10.1163/156770909X12518536414376. ———. 2012. “Social Welfare as Small-Scale Help: Evolutionary Psychology and the Deservingness Heuristic.” American Journal of Political Science 56 (1) (January 1): 1–16. doi:10.1111/j.1540-5907.2011.00545.x. Pinker, Steven. 2011. The Better Angels of Our Nature: Why Violence Has Declined. Viking Adult. Potts, Malcolm, and Thomas Hayden. 2008. Sex and War: How Biology Explains Warfare and Terrorism and Offers a Path to a Safer World. BenBella Books. Powell, Robert. 2006. “War as a Commitment Problem.” International Organization 60 (1): 169–203. Price, Michael. 2012. “Group Selection Theories Are Now More Sophisticated, but Are They More Predictive? A Review of Samuel Bowles and Herbert Gintis, A

58 Cooperative Species: Human Reciprocity and Its Evolution.” Evolutionary Psychology 10 (1): 45–49. Price, Michael E, Leda Cosmides, and John Tooby. 2002. “Punitive Sentiment as an Anti-Free Rider Psychological Device.” Evolution and Human Behavior 23 (3): 203–231. Puts, David A, Coren L Apicella, and Rodrigo A Cárdenas. 2012. “Masculine Voices Signal Men’s Threat Potential in Forager and Industrial Societies.” Proceedings of the Royal Society B: Biological Sciences 279 (1728) (February 7): 601–609. doi:10.1098/rspb.2011.0829. Puurtinen, Mikael, and Tapio Mappes. 2009. “Between-group Competition and Human Cooperation.” Proceedings of the Royal Society B: Biological Sciences 276 (1655) (January 22): 355 –360. doi:10.1098/rspb.2008.1060. Quester, George H. 2002. Offense and Defense in the International System. 3rd ed. Transaction Publishers. Rand, David G., Samuel Arbesman, and Nicholas A. Christakis. 2011. “Dynamic Social Networks Promote Cooperation in Experiments with Humans.” Proceedings of the National Academy of Sciences 108 (48) (November 29): 19193 –19198. doi:10.1073/pnas.1108243108. Richerson, Peter J., and Robert Boyd. 2006. Not by Genes Alone: How Culture Transformed Human Evolution. University Of Chicago Press. Ridley, Mark. 2004. Evolution. Malden, MA: Blackwell Pub. Ridley, Matt. 1994. The Red Queen: Sex and the Evolution of Human Nature. New York: Maxwell Macmillan International. ———. 1997. The Origins of Virtue : Human Instincts and the Evolution of Cooperation. New York: Viking. Rosen, Stephen Peter. 2005. War and Human Nature. Princeton, N.J.: Princeton University Press. http://www.loc.gov/catdir/enhancements/fy0654/2003065590- d.html. Sapolsky, Robert M. 2006. “A Natural History of Peace.” Foreign Affairs. Schultheiss, O, and M Wirth. 2009. “Biopsychological Aspects of Motivation”: 1–91. Sell, Aaron, Gregory A. Bryant, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Reuden, Andre Krauss, and Michael Gurven. 2010. “Adaptations in Humans for Assessing Physical Strength from the Voice.” Proceedings of the Royal Society B: Biological Sciences: 3509–3518. Sell, Aaron, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Rueden, and Michael Gurven. 2009. “Human Adaptations for the Visual Assessment of Strength and Fighting Ability from the Body and Face.” Proceedings of the Royal Society of London Series B-Biological Sciences 276 (1656): 575–584. doi:10.1098/rspb.2008.1177. Sell, Aaron, John Tooby, and Leda Cosmides. 2009. “Formidability and the Logic of Human Anger.” Proceedings of the National Academy of Sciences 106 (35): 15073–15078. Sellers, JG, MR Mehl, and RA Josephs. 2007. “Hormones and Personality: Testosterone as a Marker of Individual Differences.” Journal of Research in Personality 41 (1): 126–138.

59 Sharansky, Natan, and Ron Dermer. 2004. The Case for Democracy: The Power of Freedom to Overcome Tyranny and Terror. 1ST ed. PublicAffairs. Short, Lindsey A., Catherine J. Mondloch, Cheryl M. McCormick, Justin M. Carré, Ruqian Ma, Genyue Fu, and Kang Lee. 2012. “Detection of Propensity for Aggression Based on Facial Structure Irrespective of Face Race.” Evolution and Human Behavior 33 (2) (March): 121–129. doi:10.1016/j.evolhumbehav.2011.07.002. Sidanius, Jim, and Robert Kurzban. 2003. “Evolutionary Approaches to Political Psychology.” In Oxford Handbook of Political Psychology. New York: Oxford University Press. Silverberg, James, and J. Patrick Gray. 1992. Aggression and Peacefulness in Humans and Other Primates. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0604/91020318-d.html. Simmons, Beth A, Frank Dobbin, and Geoffrey Garrett. 2006. “Introduction: The International Diffusion of Liberalism.” International Organization 60 (4): 781– 810. Smith, Kevin B, Christopher W Larimer, Levente Littvay, and John R Hibbing. 2007. “Evolutionary Theory and Political Leadership: Why Certain People Do Not Trust Decision Makers.” The Journal of Politics 69 (2): 285–299. doi:10.1111/j.1468- 2508.2007.00532.x. Smith, Kevin B, Douglas R Oxley, Matthew V Hibbing, John R. Alford, and John R. Hibbing. 2011a. “Linking Genetics and Political Attitudes: Reconceptualizing Political Ideology.” Political Psychology 32 (3): 369–397. doi:10.1111/j.1467- 9221.2010.00821.x. Smith, Kevin B., Douglas Oxley, Matthew V. Hibbing, John R. Alford, and John R. Hibbing. 2011b. “Disgust Sensitivity and the Neurophysiology of Left-Right Political Orientations.” PLoS ONE 6 (10) (October 19): e25552. doi:10.1371/journal.pone.0025552. Sober, Elliott, and David Sloan Wilson. 1999. Unto Others: The Evolution and Psychology of Unselfish Behavior. Harvard University Press. Somit, A., and S. A. Peterson. 1998. “Review Article: Biopolitics After Three Decades - A Balance Sheet.” British Journal of Political Science 28: 559–571. Somit, Albert, and Steven A. Peterson. 1997. Darwinism, Dominance, and Democracy : the Biological Bases of Authoritarianism. Westport, Conn.: Praeger. Sperber, Dan. 1996. Explaining Culture: a Naturalistic Approach. Oxford: Blackwell. Stanton, SJ, and OC Schultheiss. 2007. “Basal and Dynamic Relationships Between Implicit Power Motivation and Estradiol in Women.” Hormones and Behavior 52 (5): 571–580. Sumner, William Graham. 1970. War and Other Essays. Ams Pr Inc. Symons, Donald. 1979. The Evolution of Human Sexuality. New York: Oxford University Press. ———. 1992. “On the Use and Misuse of Darwinism in the Study of Human Behavior.” In The Adapted Mind: Evolutionary Psychology and the Generation of Culture, 137–160. New York: Oxford University Press. Tajfel, Henry, and John C. Turner. 1986. “The Social Identity Theory of Intergroup Behavior.” In Psychology of Intergroup Relations. Chicago: Nelson Hall.

60 Takezawa, Masanori, and Michael E Price. 2010. “Revisiting ‘The Evolution of Reciprocity in Sizable Groups’: Continuous Reciprocity in the Repeated N-person Prisoner’s Dilemma.” Journal of Theoretical Biology 264 (2) (May 21): 188–196. doi:10.1016/j.jtbi.2010.01.028. Thayer, BA. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security. http://www.mitpressjournals.org/doi/pdf/10.1162/016228800560471. Thayer, Bradley A. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security 25 (2): 124–151. ———. 2001. “Correspondence: Start the Evolution Without Us.” International Security 26 (1): 194–198. ———. 2004. Darwin and International Relations: On the Evolutionary Origins of War and Ethnic Conflict. Lexington: University Press of Kentucky. Thayer, Bradley A, and Valerie M Hudson. 2010. “Sex and the Shaheed: Insights from the Life Sciences on Islamic Suicide Terrorism.” International Security 34 (4): 37–62. Thompson, William R. 2001. Evolutionary Interpretations of World Politics. New York: Routledge. http://www.loc.gov/catdir/toc/fy022/00066485.html. Tiger, Lionel. 2004. Men in Groups. Revised. Transaction Publishers. Tooby, John, and Leda Cosmides. 1988. “The Evolution of War and Its Cognitive Foundations.” Institute for Evolutionary Studies Technical …. http://www.psych.ucsb.edu/research/cep/papers/EvolutionofWar.pdf. ———. 1990. “On the Universality of Human Nature and the Uniqueness of the Individual: The Role of Genetics and Adaptation.” Journal of Personality 58 (1): 17–67. Tooby, John, Leda Cosmides, and Michael E Price. 2006. “Cognitive Adaptations for N- person Exchange: The Evolutionary Roots of Organizational Behavior.” Managerial and Decision Economics 27 (2-3): 103–129. Trivers, Robert. 1971. “The Evolution of Reciprocal Altruism.” The Quarterly Review of Biology 46 (1): 35–57. ———. 1972. “Parental Investment and Sexual Selection.” In Sexual Selection and the Descent of Man. Chicago: Aldine Publishing. ———. 2000. “The Elements of a Scientific Theory of Self-Deception.” Annals of the New York Academy of Sciences 907 (April): 114–131. ———. 2011. The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life. 1st ed. Basic Books. Turney-High, Harry Holbert. 1949. Primitive War: Its Practice and Concepts. Columbia,: Univ. of South Carolina Press. Van Vugt, Mark. 2009. “Sex Differences in Intergroup Competition, Aggression, and Warfare: The Male Warrior Hypothesis.” Annals of the New York Academy of Sciences 1167 (June): 124–134. doi:10.1111/j.1749-6632.2009.04539.x. Vugt, Mark Van, and Anjana Ahuja. 2011. Naturally Selected: The Evolutionary Science of Leadership. HarperCollins. van Vugt, Mark, and Rob Kurzban. 2007. “Cogntive and Social Adaptations for Leadership and Followership: Evolutionary Game Theory and Group Dynamics.”

61 In Evolution and the Social Mind: Evolutionary Psychology and Social Cognition, 229–243. New York: Psychology Press. Wagner, John D., Mark V. Flinn, and Barry G. England. 2002. “Hormonal Response to Competition Among Male Coalitions.” Evolution and Human Behavior 23 (6): 437–442. Waytz, Adam, and Liane Young. 2011. “The Group-Member Mind Trade-Off.” Psychological Science 22 (12) (December 8): 1–9. doi:10.1177/0956797611423546. Wendt, A. E. 1987. “The Agent-Structure Problem in International-Relations Theory.” International Organization 41 (3): 335–370. Williams, George C. 1966. Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought. Princeton, N.J.: Princeton University Press. Wilson, D.S., and E. Sober. 1994. “Reintroducing Group Selection to the Human Behavioral Sciences.” Behavioral and Brain Sciences 17 (4): 585–607. Wilson, Edward O. 1980. Sociobiology. Cambridge, Mass.: Belknap Press of Harvard University Press. ———. 2000. Sociobiology : the New Synthesis. Cambridge, Mass.: Belknap Press of Harvard University Press. Wilson, M, and M Daly. 2002. “An Evolutionary Psychological Perspective on the Modulation of Competitive Confrontation and Risk Taking.” Hormones. http://134.83.117.117/3518/PDF/PoundetalEvolutionaryPsychPerspective.pdf. Wrangham, Richard. 1999a. “Evolution of Coalitionary Killing.” Yearbook of Physical Anthropology 42: 1–30. ———. 1999b. “Is Military Incompetence Adaptive?” Evolution and Human Behavior 20 (1): 3–17. Wrangham, Richard, and Dale Peterson. 1996. Demonic Males: Apes and the Origins of Human Violence. Boston: Houghton Mifflin. Wrangham, Richard W, and Luke Glowacki. 2012. “Intergroup Aggression in Chimpanzees and War in Nomadic Hunter-Gatherers : Evaluating the Chimpanzee Model.” Human Nature (March 3). doi:10.1007/s12110-012-9132-1. http://www.ncbi.nlm.nih.gov/pubmed/22388773. Wright, Quincy. 1983. A Study of War, 2nd Edition. 2nd ed. University Of Chicago Press. Wright, Robert. 2000. NonZero : the Logic of Human Destiny. New York: Pantheon Books. http://www.loc.gov/catdir/bios/random059/99040859.html. Wynne-Edwards, V. C. 1967. Animal Dispersion in Relation to Social Behaviour. Hafner Publishing Company. Yamagishi, Toshio, and Nobuhiro Mifune. 2009. “Social Exchange and Solidarity: In- group Love or Out-group Hate?” Evolution and Human Behavior 30 (4) (July): 229–237. doi:10.1016/j.evolhumbehav.2009.02.004. Yamagishi, Toshio, Shigehito Tanida, Rie Mashima, Eri Shimoma, and Satoshi Kanazawa. 2003. “You Can Judge A Book by Its Cover: Evidence That Cheaters May Look Different From Cooperators.” Evolution and Human Behavior 24 (4): 290–301.

CHAPTER ONE: THE RISK CONTRACT OF WAR

This dissertation argues that psychological adaptations in the human brain exist that are designed for defensive and offensive coalitional violence. In order to substantiate adaptationist claims, it is necessary to seek multiple types of evidence. For example, since adaptations are designed in response to ancestral selection pressures, we must identify the relevant selection pressures that have favored the design of a putative adaptation. Also, given identification of the relevant selection pressures, we must generate and test hypotheses about how an evolved mechanism would be designed to have generated adaptive outputs in the context of those selection pressures. In other words, two important forms of evidence are knowledge of ancestral environments, as well as experimental evidence in humans that reflects the operation of adaptations designed for these environments.

The previous chapter reviewed arguments and evidence regarding the evolution of warfare. We have seen that, although the evidence for hominid coalitional violence is not absolute, there is substantial evidence that suggests it may have persisted throughout our species evolutionary history and even far back into the evolutionary history of chimpanzees, our nearest relatives. We have also seen that there is substantial experimental evidence of humans behaving in ways that suggest that we are equipped with a “coalitional psychology” designed by natural selection in response to ancestral

63 selection pressures related to cooperating and competing in groups (e.g. Kurzban, Tooby, and Cosmides 2001; Forgas, Haselton, and Hippel 2007).

I take the existence and significance of evolutionarily recurrent coalitional violence in humans as a given, and I apply an adaptationist framework for examining the design of these mechanisms given the persistence of these selection pressures. In this regard, I follow the work of primatologists, biological anthropologists, and political scientists who have sought to investigate adaptationist claims regarding human coalitional behavior (Johnson, Wrangham, and Rosen 2002; Sidanius and Kurzban 2003;

Thayer 2004; Rosen 2005; Gat 2006; Johnson et al. 2006; Tooby, Cosmides, and Price

2006; McDermott, Fowler, and Smirnov 2008; Petersen 2009; McDermott et al. 2009).

In this chapter, therefore, I must begin by briefly outlining evolutionary psychology as a framework with which to understand the design of psychological adaptations. Next, I outline the “risk contract of war,” which represents the prerequisite psychological conditions that must hold in order for coalitional aggression to be initiated. I then outline the hypotheses to be tested.

Evolutionary Psychology

The evolutionary function of a brain and central nervous system in organisms is to generate conditionally appropriate behavior in a complex environment (Alcock 1975;

Gazzaniga 2000). However, the brain is not one general problem-solving device mass manufactured by natural selection for organisms capable of dynamic behavior. Every organism confronts a unique environment, and the structures in the brain designed by natural selection in each organism represent unique solutions to challenges in these

64 environments (Symons 1992). As we have seen in the previous chapter, for example, bonobos and chimpanzees have confronted different social and ecological challenges, and this difference is reflected in the unique suite of psychological adaptations that each species possess for social behavior.

Neuroscientists who study the brain have recognized two major features of its structure. First, the brain consists of myriad structures and systemic interconnections that operate in unique ways across many environments. Second, the human brain and its component systems display a remarkable degree of plasticity, such that many behaviors that seem deeply engrained can actually be altered in certain circumstances (Gazzaniga,

Steen, and Volpe 1979; Sapolsky 2006). These two features, in combination with an understanding of how natural selection builds adaptations, lead us again to the main theoretical premises of this dissertation: 1) Humans contain psychological adaptations designed in response to ancestral selection pressures; 2) These adaptations are myriad and domain-specific, and; 3) These adaptations are facultative, meaning that they are designed to generate behavior that would have been adaptively conditional in ancestral environments (Cosmides and Tooby 1994a; Buss 2004). Evolutionary psychology argues that adaptations in the brain are the necessary link between evolution and behavior. The theoretical foundation of evolutionary psychology is natural selection; thus, we must examine how natural selection operates before we can understand the implications for the content and design of human psychology in the light of known or suspected selection pressures.

To understand natural selection, one must begin with the understanding that the defining feature of life from a biological perspective is reproduction (Ridley 2004).

65 Charles Darwin recognized that all organisms display phenotypic variation. Some of this variation can be accounted for by genetic differences between individuals; in other words, as a consequence of the necessary imperfection of genetic reproduction, offspring may vary in any aspect of their design. To the extent that this variation improves the ability of the organism to reproduce, that variation is likely to be more common in subsequent generations. Natural selection is therefore the process whereby heritable design features that enhance reproductive success become more frequent in a population relative to other heritable design features (Williams 1966).

This process explains the major pathway by which genetic frequencies change in an environment. Indeed, at the genetic level, natural selection is merely the process by which a gene or set of genes spread in a population relative to other genes (Maynard

Smith 1998). The resultant evolutionary change is one of adaptation. Quantitatively, natural selection may “tweak” existing adaptations in response to novel environments.

For example, the emergence of agriculture in certain societies has led to adaptations for digesting lactose as adults, which are absent in other societies that did not experience similar environments. All humans possess a structurally similar digestive tract; yet, quantitative variation around these adaptations, maintained by natural selection as a response to distinct environments, has altered the digestive capacity of certain societies to reflect the challenges of living in these environments.

Over evolutionary time, quantitative changes can accumulate in the presence of sustained selection pressures to produce complex adaptations, most often involving the expression of a suite of genes. Of course the most popular example of a complex adaptation that emerges from a series of small changes is the eye. Evolutionary theorists

66 have shown that complex adaptations such as the eye are fully explainable as the consequence of the accumulation of a series of small directional changes (Dawkins 1986;

Carroll 2006). The point is that even very small changes can accumulate into complex adaptations, and even very small selection pressures, when sustained over evolutionary time, can generate complex adaptations. The sensitivity of natural selection is important to keep in mind, especially when considering a point often raised by those who argue that violence is not, or has not been, frequent enough to have selected for adaptations for the regulation of aggression. Clearly, this is to misunderstand how natural selection operates, as well as the time-scales over which adaptations can be built. It is important, therefore, not to confuse claims regarding the intensity of selection pressures with claims regarding the existence of selection pressures.9

The central tenet of evolutionary psychology is that psychological adaptations are built by natural selection in response to adaptive problems in ancestral environments

(Cosmides and Tooby 1987; Confer et al. 2010). Adaptive problems (i.e. selection pressures) are threats and opportunities that organisms confront in their environment, the solution to which would enhance reproductive success. Although one-time problems can lead to genetic “adaptation” given the existence of genetic variation upon which selection can act, complex adaptations are generally the result of evolutionarily recurrent selection

9 Clearly, the evolution of the vertebrate eye has taken place over a time-scale that is overwhelmingly longer than the evolution of coalitional aggression in primates. Nevertheless, the empirical question remains centered on the balance between the intensity of the selection pressure and the time-scale over which the selection pressure exists. Given the fact that warfare, as we have seen in the previous chapter and will revisit below, has constituted an especially significant selection pressure, it is likely that even if coalitional aggression was relatively infrequent and emerged sometime between the hominid-chimpanzee split and the emergence of anatomically modern humans, it remains likely that adaptations could have been favored in response to such intense selection pressures. There are two ways to test this conjecture: through collection of empirical evidence regarding ancestral environments, and through testing of hypotheses regarding the way information-processing in the brain ought to be structured if indeed it is designed in part to solve this specific adaptive problem.

67 pressures operating over thousands of generations (Mayr 1983). In addition, because natural selection operates to drive reproductively successful traits to fixation in a population, another characteristic of adaptations is that they tend to be species-typical, or universal (Daly and Wilson 1983). However, there are two caveats to consider regarding the species-typicality of adaptations.

First, a genetically heritable trait can spread to fixation in a population and become universal merely by virtue of random processes, such as genetic drift. Therefore, genetic universality alone is not sufficient to identify the existence of an adaptation.

Second, there are several processes by which an adaptation may not become universal in a population, but rather, natural selection may fix it at some proportion of the population or within a subset of the population. For example, frequency-dependent selection is a process by which the fitness of one heritable trait (and its subsequent spread in a population) depends on the frequency of another trait in the population (Dawkins 1980).

The most common example of this is the hawk-dove game, in which the fitness of hawks

(and their resultant frequency within the population) depends on the frequency of doves in the population (Maynard Smith 1982).10 Another example of non-universal adaptations is the case in which distinct local ecologies favor adaptations in one sub-set of the population, but not in the population as a whole. The above example of lactose intolerance illustrates this principle.

Despite these caveats, natural selection tends to drive adaptations to universality in a population, and these adaptations tend to be built in response to evolutionarily recurrent selection pressures. Once an adaptive problem has been identified, or once

10 In this example from evolutionary game theory, “hawks” and “doves” represent distinct genetically encoded strategies that spread or decline in frequency as a function of the payoff they achieve in their interactions with each other.

68 there is substantial evidence to suggest that an adaptive problem may have favored the existence of an adaptation in a particular domain, researchers may begin to ask questions about how that adaptation is expected to operate. In other words, we must generate hypotheses regarding the information-processing structure of the adaptation: how is the adaptation designed to take information from its environment and translate that information into output that would have achieved adaptive targets in the ancestral environment in which it was favored?

Clearly, knowledge of ancestral environments can guide hypothesis formation in this regard. For example, Kurzban et al. (2001) showed that it is unlikely that natural selection has designed adaptations in humans for the instinctual coding of race in strangers. The reason for this is quite simply because ancestral social environments did not consist of inter-racial encounters. Travel on foot would have precluded interaction with strangers from another race ancestrally, and therefore, given the necessary relationship between adaptations and ancestral environments described above, natural selection could have not have designed adaptations specifically for encoding race.

Kurzban and colleagues showed that the encoding of race is instead a by-product of adaptations in the brain designed for coalitional encoding, which, in modern environments characterized by racial segregation, encode race as a coalitional marker.

However, in these experiments, when subjects were placed in environments in which race was irrelevant to coalitional identification, the researchers were able to demonstrate the first example of subjects actually failing to categorize others by their race.

In addition to knowledge of ancestral environments, researchers can perform task analyses, which inquire into the logical information-processing structure that the

69 adaptation is expected to have given that natural selection has tailored it to a specific task.

For example, scholars have recognized that in order for humans to adaptively regulate cooperation with others, mechanisms must exist that: 1) distinguish relatives from non- relatives (Lieberman, Tooby, and Cosmides 2007); 2) scan for evidence of defection from others (Cosmides, Barrett, and Tooby 2010), and; 3) discriminate in favor of cooperators through systematic exclusion of defectors (Rand, Arbesman, and Christakis 2011). These features had been predicted in advance based on actual and inferred evidence of ancestral environments, as well as evolutionary game theory and task analyses of how such adaptations should be designed given these selection pressures (Trivers 1971; Axelrod and Hamilton 1981). In the realm of aggression, the examination of ancestral selection pressures in humans and other animals has suggested that adaptations must exist that regulate the use of violence in competitive encounters with conspecifics (Archer 1988).

Researchers have hypothesized that adaptations likely exist for the evaluation of relative strength and resource-holding potential (Parker 1974). Subsequently, evolutionary psychologists have provided the first experimental evidence of psychological adaptations designed specifically for the regulation of aggression in humans. These mechanisms are designed to attend to evolutionarily relevant cues in the body, face, and voice in their assessment of relative formidability, which in turn regulates not only aggression, but also feelings of entitlement as well as views on the justifiability of coalitional aggression (Sell et al. 2009; Sell et al. 2010).

These examples demonstrate another value of evolutionary psychology as an approach for understanding behavior. Many of the hypotheses generated from this perspective would be difficult or impossible to predict from alternative frameworks that

70 do not consider the relevance of ancestral environments for understanding modern psychology (e.g. racial categorization). Additionally, because psychological adaptations were designed in response to an ancestral environment that has since been altered in many substantive ways, the motivational and behavioral output of these systems can appear irrational or maladaptive in modern contexts. Although processes of “bounded rationality” are often an attempt reconcile the persistence of irrationality within a rational choice framework, it may be the case that irrational behavior is the product of mechanisms that operate on assumptions that are no longer valid in modern environments

(Cosmides and Tooby 1994b; Gigerenzer 2000; Gigerenzer and Selten 2001).

Evolutionary psychology is an approach for understanding behavior that examines the information-processing structure of adaptations in the brain built by natural selection in ancestral environments. Knowledge of ancestral environments and selection pressures can be combined with task analyses in order to generate hypotheses regarding the information-processing structure of putative adaptations. In the next section, I outline an example of these efforts in the domain of coalitional violence, and I present specific hypotheses to be tested.

The Risk Contract of War

Evolutionary psychologists have argued that coalitional violence has been evolutionary recurrent and represents a set of adaptive problems in response to which natural selection has favored a suite of adaptations for the regulation of behavior in these domains (Buss and Shackelford 1997). Before we explore the logical structure of these information-processing mechanisms, it is important to point out that coalitional violence

71 cannot be explained merely as the aggregation of individual-level dynamics.

Empirically, we observe that there are a great number of species that engage in dyadic aggression with conspecifics; however, relatively few engage in coalitional aggression

(Silverberg and Gray 1992). With the exception of the eusocial insects, which possess unique systems of genetic relatedness, the existence of coalitional behavior suggests the presence of specialized cognitive systems that can solve a number of adaptive problems unique to coalitional behavior, such as the free rider and second-order free rider problems

(Price, Cosmides, and Tooby 2002; Panchanathan and Boyd 2004), managing reciprocity among multiple individuals simultaneously (Boyd and Richerson 1988; Takezawa and

Price 2010), and especially in warfare, achieving a motivational consensus regarding the target of violence and contribution levels, a problem often solved most efficiently through leadership mechanisms (Van Vugt and Kurzban 2007; Hooper, Kaplan, and

Boone 2010; Van Vugt and Ahuja 2011).

Based on primatological and anthropological evidence, it is likely that the most common form of coalitional violence in human ancestral environments approximated that of the lethal raid (Wrangham 1999a; Chagnon 1988; Gat 2000; Otterbein 2004;

Wrangham and Glowacki 2012). Raids demonstrate a number of cross-cultural similarities (Keeley 1996; LeBlanc and Register 2003). For example, they tend to occur under cover of darkness, in order to take maximal advantage of the element of surprise; the focus of attacks tends to be on isolated members of the target group that are vulnerable, and against which the aggressors possess numerical superiority; they tend not to be sustained – that is, once the targeted individuals are attacked, the raiders often

72 retreat from whence they came; the element of surprise and numerical superiority combine to assure that raids are often characterized by high success-to-risk ratio.

Despite the prevalence of raids, it is likely that larger sustained battles also occurred from time to time. For example, Mathew and Boyd (2011) present evidence from the Turkana in East Africa, which demonstrate at least two prominent forms of coalitional violence. First, as I have already described, the Turkana engage in lethal raids, or what Mathew and Boyd refer to as “stealth raids.” Second, they also engage in

“force raids,” which consist of larger numbers of men who intend to engage in combat with an enemy group. In these force raids, participants were significantly more likely to die than in stealth raids, regardless of whether the coalitional violence was initiated in defense or offense. Although direct evidence of ancestral environments is incomplete, it is possible to assume that, given competition between groups, violence between coalitions most often took the form of raiding, for the evolutionary reasons mentioned in the previous chapter (Wrangham 1999; Gat 2006). Lethal raiding, given the characteristics described above, tends to be undertaken when it has the characteristic of a low-risk and high-yield endeavor. This is similar to the logic followed by chimpanzees, which has led some evolutionary theorists to argue that adaptations in humans for coalitional aggression may in part be an behavioral legacy handed down from our evolutionary cousins.

However, just as coalitional aggression cannot be explained merely as the aggregation of individual-level strategies for aggression, I argue that coalitional violence characterized by sustained symmetric engagement between antagonistic coalitions cannot be explained merely as a consequence of a psychology designed for raiding, although

73 some of the logic undoubtedly overlaps. Wrangham (1999a) has argued that although the imbalance-of-power hypothesis explains the logic and motivation for stealth raiding in chimpanzees, this model cannot sufficiently explain the outbreak and distribution of coalitional violence in humans.

My goal here is not to describe separate evolutionary theories for stealth and force raids. Instead, it should more generally be possible to outline the conditions under which engagement in coalitional violence is profitable in terms of reproductive fitness. Once these general conditions are outlined, we can examine how these prerequisite conditions vary depending on the specific type of coalitional aggression. Tooby and Cosmides

(1988) have outlined the “risk contract of war,” which represents the psychological conditions necessary in order for coalitional violence to be initiated. Natural selection can favor a motivation to engage in coalitional violence when the probability of success is great,

The two types of coalitional aggression I will be examining here are offensive and defensive coalitional aggression. Offensive aggression is characterized by the unprovoked initiation of violence against an adversary in order to acquire resources, while defensive aggression is characterized by resistance against offensive encroachments by another (Durham 1976; Jervis 1978). The dichotomy operates most effectively at the outbreak of violence; after violence erupts, especially where violence is sustained, offense can transition into defense and vice versa. Additionally, as will be discussed further below, group members (especially elites) are likely to manipulate the perceptions of others regarding the character of aggression, rendering objective analysis of the constituent features of violence difficult at best. Therefore, my analysis is

74 restricted to the conditions that must be met in order for the initiation of coalitional violence to be a reproductively worthwhile endeavor for a social species subject to natural selection. If there are adaptations in humans designed for coalitional aggression, they must be sensitive to the fulfillment of these conditions and regulate motivational and behavioral outcomes in war contingent upon them.

Tooby and Cosmides (1988) provide an adaptive task analysis of the expected component features of a coalitional psychology designed for coalitional violence, and I have elaborated on its elements elsewhere (Lopez 2010). The adaptive regulation of coalitional violence by adaptations in the brain must effectively match environmental cues with specific motivational and behavioral output, the result of which would have enhanced reproductive success on average in ancestral environments. For example, we have seen that adaptations designed for the regulation of individual level aggression moderate the expression of violence contingent upon adaptively relevant features corresponding to relative formidability (Parker 1974; Sell, Tooby, and Cosmides 2009).

Similarly, adaptations designed for the regulation of coalitional level aggression moderate the expression of violence at this level contingent upon adaptively relevant features in this domain. Our task, therefore, it to outline what these adaptively relevant features are, as well as how psychological adaptations regulate motivational and behavioral output contingent upon these features.

The initiation of coalitional violence is possible when the risk contract of war among participants has been satisfied. The risk contract represents the set of conditions that must be satisfied among the participants in order for coalitional violence to be reproductively worthwhile. Coalitional aggression between groups assumes successful

75 coordination and cooperation within coalitions, and the risk contract of war regulates the within-coalition dynamics that enable between-coalition violence. There are two broad components of the risk contract: the regulation of an individual’s own level of participation, and the enforcement of the risk contract on others. In other words, at the broadest level, the initiation of coalitional violence consists of the personal decision to participate, as well as the effort by participants to build and maintain coalitional dynamics among each other relating to the successful execution of coalitional violence, including efforts aimed at labor recruitment, punishment of free-riders, and reward toward participants. I will consider these two components in turn.

Regulation of Direct Participation: To Cooperate or Not?

Coalitional aggression is an example of collective action, and as with all collective behaviors, the individual must decide whether or not to participate. The choice to participate in coalitional violence naturally comes with mortal risk. Consequently, mechanisms designed by natural selection to regulate individual participation in coalitional aggression will likely be highly attuned to one’s perceived individual risk.

But what makes coalitional violence risky? As one example, all else equal, a highly formidable individual is likely to find the average aggressive encounter less risky than an individual of low formidability. Therefore, evolved mechanisms must also attend to self- assessments of formidability, given the fact that formidability has a twin effect: It increases the likelihood of success by magnifying the strength of one’s own coalition, and it decreases the on-average physical risk that one is likely to encounter. In addition, since ancestral coalitional aggression fundamentally depended on strength in numbers –

76 whether it occurred asymmetrically or not – mechanisms must attend to relative numbers as a key component affecting one’s decision to participate. All else equal, the larger the coalition, the more likely you are to participate.

Together, these factors inform the key component regulating participation in coalitional aggression: The probability of success. Adaptations designed for coalitional aggression should take as input the above-mentioned variables and compute a probability of success, which should positively vary with willingness to participate in warfare. In other words, these adaptations should be designed to actively track variables in the environment that would have ancestrally correlated with success and failure in coalitional violence, and should use these variables to regulate motivational and behavioral outcomes.

When the probability of success is great, individuals should be more likely to participate in coalitional aggression – but why would an individual choose to participate in any form of coalitional aggression that entailed even the slightest possibility of death?

From an evolutionary perspective (and indeed from a rationalist perspective), it seems odd that selection could favor a strategy that might lead to the death of the organism and the end of its reproductive career. The resolution to this problem, however, comes through recognition that natural selection favors strategies (i.e. genetically encoded psychological design features that motivate participation in aggression under certain conditions) that are reproductively beneficial on average, over thousands of generations.

Thus, it is possible for selection to favor a behavior-regulatory system that occasionally leads to death as long as the average reproductive payoff of the behavior is positive over successive generations. This will happen as long as there are (net) reproductive benefits

77 from initiating conflict, and as long as these are distributed among the participating coalition members in proportion to the costs each incurred (an anti-free rider measure).

One or more individuals may die, but the benefits that would have gone to them are redistributed to those who survived. When this happens, the average benefit per person remains the same: 10 units of benefit distributed among 10 individuals produces the same average—1 unit per person—as when one survivor gets all 10 units and the other nine die and, therefore, get nothing. Natural selection acts on average outcomes. As Tooby and

Cosmides (1988) point out, this feature of the risk contract of war implies that, when the conditions are right, decision rules that favor initiating warfare can be selected for even when the level of casualties is very high. I discuss this dynamic in greater detail below regarding sex differences.

Although this helps to understand the mechanism by which selection could favor participation in asymmetric forms of coalitional violence, it raises a new question: why do humans engage in symmetric coalitional violence, but chimpanzees do not? It has been observed by anthropologists and archaeologists that instances of symmetric coalitional violence involve engagements by groups that are larger than those that assemble for lethal raiding (LeBlanc and Register 2003; Mathew and Boyd 2011).

Chimpanzees, however, do not typically engage in lethal raiding parties of greater than 4 or 5 males. Also consider that as group size increases, cognitive mechanisms for regulating coalitional behavior face the adaptive problem of tracking and updating information regarding the participation of others. As Tooby et al. (2006) point out, the cognitive sophistication required by n-party coordination and cooperation is itself a significant hurdle that limits the zoological prevalence of coalitional behavior on the

78 scale that we observe with humans. This would seem to suggest two possible explanations for the existence of symmetric coalitional aggression in humans.

First, it is possible that humans possess special adaptations distinct from chimpanzees for coalitional aggression, and that the chimpanzee model is insufficient on its own for explaining the full variety of human warfare. Second, special adaptations for symmetric conflict may not exist, and the prevalence of this form of warfare may be a consequence of various cultural innovations (Wrangham and Glowacki 2012). The resolution of this question is not necessary here since the symmetry of conflict is not directly considered in my studies. However, if specialized psychological mechanisms exist that regulate behavior in both lethal raids as well as pitched battles, it suggests certain testable predictions about how motivational dynamics might vary in these two contexts. For example, given that lethal raids are less risky than the latter, considerations such as the within-group distribution of risk will likely loom larger in pitched battles than in lethal raids.

One final consideration regarding the prevalence of pitched battles in human coalitional violence as it relates to one’s decision to participate in warfare is the question of self-deception. Robert Trivers (2000; 2011) has conducted the pioneering theoretical work on self-deception in organisms, and this phenomenon is hypothesized to serve the function of enhancing the effectiveness of bluffs. In other words, in many instances throughout nature, natural selection has designed organisms to deceive themselves, the better to deceive others. One prominent form of self-deception involves positive illusions, or overconfidence. I previously noted that the prevalence of aggressive encounters between individuals and groups tends to select for psychological mechanisms

79 designed for capabilities assessment (Parker 1974; Sell et al. 2010). However, the case of overconfidence seems to be one in which organisms are designed to ignore these assessments and instead allow themselves to be motivated by the illusion of positive expectations (Johnson et al. 2006; Johnson and Fowler 2011). Wrangham (1999b) has argued that this may be adaptive when the motivational output generated by positive illusions results in the delivery of a credible bluff sufficient to deter enemy initiatives.

Again, the question is not whether this is a foolproof strategy; indeed, history is replete with examples of outnumbered coalitions leaping into battle when they clearly should not. However, the question is whether this has been effective on average in ancestral environments. Johnson, Wrangham, and Rosen (2002) provide evidence that indeed overconfidence does seem to serve the specific function of bluff enhancement in symmetric contests, and does not operate to generate such illusions in the context of lethal raids, further suggesting the existence of specialized design for symmetric coalitional conflict.

The first component of the risk contract of war is the regulation of direct participation in coalitional violence. We have seen that adaptations designed for this purpose should actively scan variables in the environment and self such as personal formidability, relative numbers, the distribution of risk, and the probability of success.

Additionally, overconfidence may serve the function of bluff enhancement in certain instances of relatively symmetric pitched battles, and the logic of natural selection suggests that when the reproductive benefits from coalitional aggression are zero-sum, adaptations for coalitional violence in these contexts can evolve. The second component of the risk contract relates to the effort to build and maintain aggressive coalitions.

Enforcement of Risk Contract on Others: Making “My” Problem “Our” Problem

Beyond the adaptive problems faced by the individual when deciding whether to participate, the individual and group faces the challenge of whether and how to recruit labor and punish free riders. The central problem here is manipulation; adaptations for enforcement of the risk contract on others must be able to generate output that recalibrates adaptations in the minds of prospective recruits such that the risk contract is maintained and coalitional action initiated.

War is fundamentally a cooperative endeavor (Harcourt and Waal 1992; Matt

Ridley 1997; Price, Cosmides, and Tooby 2002). As discussed in the introduction, the mere presence of inter-group conflict is sufficient to trigger a host of pro-social behavior.

This phenomenon is witnessed at the level of individuals even where inter-group identities are arbitrarily created, and it is also evident at the international level. For example, one of the most well-known and persuasive explanations for the success of the

Bretton Woods financial system during the Cold War was the shared threat posed by the

Soviet Union to the West. In short, the threat of conflict provided the glue necessary to make possible a host of institutional developments, both between the U.S. and Europe, and also within Europe itself.

Given the fact that coalitional aggression between groups seems to precipitate within-group cooperation, many of the elements necessary for the successful prosecution of coalitional aggression (both offensive and defensive) will be similar to, yet distinct from, those required for collective action in general. For example, numerous studies have shown that punishment is a necessary ingredient for sustained cooperation in many public

81 goods environments (Boyd and Richerson 1992; Fehr and Gachter 2000). In war, both offensive and defensive aggression represent types of collective action. Thus, the success coalitional aggression will depend, in part, on the ability to punish free riders.

As I have mentioned above, success in war should also have depended on the ability to recruit allies. In the hunter-gatherer world of our ancestors, one of the best predictors of successful coalitional aggression would have been relative numbers. Below the threshold of mechanized militarized conflict, in combination with the element of surprise and an accommodation for skill, numerical superiority would have almost certainly guaranteed victory (Wrangham 1999). Successful coalitional aggression requires not only adaptations for eliminating free riding, but also adaptations designed specifically to recruit sufficient labor.11

In general, the elimination of free riders and the recruitment of labor can be accomplished through two mechanisms: positive inducements and negative repercussions. In other words, natural selection may fashion “carrots” or “sticks” for use in the effort to resist free riding and build participation. The types of “carrots” selection may have favored for use in these domains consist of motivational features such as gratitude, friendship, perceptions of status and honor, and other forms of reward (Gneezy and Fessler 2011). Natural selection may have also favored “sticks” such as moral opprobrium, social exclusion, physical punishment, and reduced perceptions of status and honor.

Michael Price and colleagues (2002) have demonstrated that “reward sentiments” were unlikely to have been designed by natural selection for the purpose of eliminating

11 Of course, it is important to recognize that there are problems in both directions. While too few participants will compromise the probability of success, too many complicates the free rider problem and multiplies the cognitive demands of coordination.

82 free riders. This is because the fitness costs delivered by free riders is a consequence of their having received a benefit from collective action without paying the cost of participation (e.g. staying on the “sidelines” of battle while your comrades incur the brunt of enemy aggression). In short, the utilization of reward as a mechanism for enticing free riders toward participation would not have been evolutionarily stable. Absent the imposition of negative costs on free riders, an evolved free riding strategy such as “stay on the sidelines but enjoy the spoils of war” would continue to enjoy the spoils of war in addition to the rewards offered by others as enticement away from this strategy. As a consequence, a free rider strategy would only continue to prosper and undermine the prevalence and stability of collective action. Given a free rider strategy that instead responds to incentives, participants (who are already incurring the cost of contributing) would have to offer free riders a reward for changing their behavior (causing them to contribute) that is higher than the net benefit they already get by not contributing; this puts contributors at an even greater fitness disadvantage than they experience as a result of the free riding. Thus, Price et al. hypothesize and find evidence to support the hypothesis that punitive sentiments operate efficiently and specifically for the purpose of eliminating free riders in collective action. In these cases, punishment functions to reverse the fitness differential that exists between free riders and full participants, and thus punitive sentiments should be most intensely felt by participants, since the fitness differential is greatest between free riders and participants.

Price and colleagues provide evidence that reward sentiments may have evolved for the function of recruiting labor, and they show that the motivation to reward participants is positively associated with one’s expected gain from collective action,

83 independent of one’s willingness to participate. This is because regardless of whether you participate in collective action (e.g. perhaps you are sick or otherwise unable), if you expect to benefit, and the benefit offered to recruits does not exceed your expected benefit from the collective action, selection should favor a motivation to reward recruits so long as this recruitment is likely to lead to coalitional success.

Clearly the issue here is the balance of resolve between initiators and recruits, as well as the costs that the recruits are willing to bear to build and sustain coalitional action. Framed in this way, the fulfillment of the risk contract becomes a question of:

Who will initiate, and how will participants enforce the risk contract on others? As discussed above, it is apparent that free riding and labor recruitment are two significant adaptive problems facing the initiation of coalitional violence, and that these problems are best solved through a combination of positive and negative inducements motivationally instantiated through forms of punitive and reward sentiment. Given the challenges of enforcement entailed by the risk contract, the question of Who? can be answered in several ways. All things equal, adaptations designed for enforcement of the risk contract on others should motivate individuals to engage in the punishment of free riders and the recruitment of labor when they: 1) have more at stake; 2) are highly formidable, and; 3) enjoy high status. Taken together, the analysis suggests that natural selection should up-regulate willingness to enforce the risk contract on others in those individuals who have more to gain from coalitional aggression, and who are most capable of delivering rewards and costs to maintain coalitional strength.

Ancestrally, formidable and high-status individuals were most likely in positions of leadership and enhanced influence within social groups (Boehm 1999; Chagnon 1988).

84 There is also formal evidence that suggests that in certain situations group members should prefer to cooperate under the supervision of a leader rather than absent leadership, even when the leader receives additional resources for this role (Hooper, Kaplan, and

Boone 2010). This should always be considered alongside the fact that leadership sets up counter selection pressures to chose leadership wisely and to resist exploitation (Van

Vugt and Kurzban 2007; Smith et al. 2007). These and other dynamics suggest that leaders or highly influential individuals had more to gain from successful coalitional aggression. Furthermore, since this influence and status likely correlated with formidability in ancestral environments, the imposition of costs and the conferral of benefits was also more “cost-effective” for such individuals.

Offense and Defense in the Adapted Mind

The human brain is hypothesized to contain adaptations designed to regulate one’s own participation in coalitional aggression, as well as efforts toward building and maintaining coalitional effectiveness. When the calibration of these adaptations in the minds of group members motivates their participation and successfully enforces the participation of others, the risk contract of war has been satisfied and coalitional aggression can be initiated. This balancing of these factors can take many forms; for example, in the case of defensive warfare, it may be the case that motivation among group members will be enough to compel participation in counter-aggression without the need for costly within-group efforts at enforcement. However, in the case of offensive warfare, it may be the case that members (i.e. potential recruits) need to be convinced of

85 the merits of any particular adventure, and therefore enforcement of the risk contract on others may play a more central role.

The distinction between offensive and defensive aggression is an old consideration in the study of warfare. While Sun Tzu considered offense the more effective form of warfare, Clausewitz argued that defense was the easier strategic position. Of course Sun Tzu and Clausewitz wrote in the background of vastly different military contexts. Modern scholars approach the question in a more sophisticated way by considering the interaction between offensive and defensive capabalities and incentives to go to war, as discussed in the previous chapter (Jervis 1978; Biddle 2001; Brown et al.

2004). In addition to scholarship by political scientists, the distinction between offensive and defensive forms of aggression has also been considered by students of animal behavior (Durham 1976; Heckhausen and Heckhausen 2010 Ch. 10).

If psychological adaptations exist that are designed to contingently respond to the unique challenges posed by defensive and offensive coalitional aggression, then we must begin by considering the evolutionarily recurrent and reproductively significant differences that may have existed between these two domains. Ancestrally, one very basic difference between offensive and defensive coalitional behavior would have been that the benefits of successful offensive aggression include non-public goods to a relatively greater degree than those derived from successful defensive aggression.12 For example, a successful defense that repels an intruder and denies it access to territory and resources confers the benefits of this success (e.g. security, preservation of resources, threat removal, status, etc.) to the entire group. However, offensive aggression that is

12 A public good is any resource that is both non-excludable (I cannot prevent others from using it) and non-rival (my use of it does not diminish the ability of others to benefit from it).

86 successful in taking resources from another is more likely to include a non-negligible amount of privatized resources, including perishable food and mating opportunities, which asymmetrically accrue to the participants rather than the group as a whole.13 In short, the major distinction between offense and defense that frames the following discussion is that successful defensive coalitional aggression mirrors the structure of a public good, and successful offensive coalitional aggression confers benefits that are relatively more privatized among those who choose to participate in violence. Thus, these two types of aggression can be distinguished in terms of the ancestral cost-benefit structure of each as separate adaptive problem.

The above discussion of the risk contract of war emphasized the costs and risks of participation as key variables that psychological adaptations assess in the regulation of a decision to participate. The flip side of this equation is the question of the gains from coalitional aggression. Given that the benefit of defensive coalitional aggression is a public good, each individual is assured of gain in the event of success. Furthermore, given the strength of perceptions of shared fate between individuals and the group, the group’s gain becomes the individual’s gain. This would have been particularly true in ancestral environments characterized by hunter-gatherer bands in which membership was relatively stable and organized around kin-structure.

In defense, an out-group initiates aggression, and the challenge is to respond quickly and effectively. The pre-existing bonds characterized by kin-based hunter- gatherer bands facilitate a quick defensive response to external aggression. Additionally, we have seen that inter-group dynamics such as shadenfreude and reduced empathy for

13 It may be, however, that in terms of the structure of benefits conferred, offensive coalitional aggression may represent more of a club good (excludable, but nonrival), while defensive coalitional aggression is more clearly a public good. Future research along these lines is forthcoming.

87 outgroupers in competitive environments is likely to fuel the motivational component of defensive action. Thus, there is a preexisting bias toward group support that operates to motivate participation in defensive coalitional aggression. In contrast, the initiation of offensive aggression shifts the burden of satisfying the risk contract of war onto those who would initiate aggression. Unlike the case of defense, in which benefits are distributed relatively symmetrically and publicly, in offensive aggression benefits accrue asymmetrically and privately to participants, and the relevant consideration in this domain will be that of personal gain, rather than group gain. Thus, the calibration of behavior-regulatory mechanisms in the brain for participation in coalitional aggression seek cues from the environment indicating domain of aggression, and regulate the motivation to participate according to distinct considerations: In offense, the relevant consideration is personal gain, while in defense, the relevant consideration is group gain

(H1 and H2, respectively).14

The difference in type of gains represented by offensive and defensive coalitional aggression also affects punitive and reward sentiments toward non-participants.

Previously, I noted that punitive sentiment toward non-participants should be stronger the more willing one is to participate, since the greater your level of participation, the more severe is the differential between yourself and a free rider. However, since the participants more easily privatize the benefits of offensive aggression, punitive sentiment by participants toward non-participants should be triggered by willingness to participate in defense, but not in offense (H6).

14 Hypotheses are listed at the end of the chapter.

88 I have noted that the domain of offensive aggression shifts the motivational burden to initiators, and that their ability to enforce the risk contract on others depends on their ability and willingness to absorb the costs of this enforcement on others. Also as noted earlier, Price et al. (2002) provide evidence that reward sentiment toward participants is triggered specifically by one’s expected gain from coalitional aggression, independent of one’s actual level of participation. This will remain true in defense; however, since participants more easily privatize benefits in offensive aggression, reward sentiment toward participants in offense will be triggered by one’s willingness to participate (H7). In other words, in offense, nonparticipants who reward participants but who (necessarily) receive no benefit would be at a fitness disadvantage. Only participants would have an interest in rewarding other participants, to the extent it solves the labor recruitment problem. Thus, we have reason to expect that the domain of coalitional aggression (offense vs. defense) will contingently and adaptively regulate: 1)

The willingness of individuals to participate, and; 2) Their ability and motivation to enforce participation by others through positive (reward) and negative (punishment) inducements. In other words, the fulfillment of the risk contract of war is adaptively contingent upon the domain of coalitional aggression.

Sexual Dimorphism in Warfare

Before presenting an organized list of hypotheses, I consider one last feature of adaptations for coalitional aggression – sex differences. As explained above, natural selection operates to build adaptations in response to evolutionarily recurrent selection pressures. However, it may be the case that selection pressures faced by one sex are

89 different than those faced by the other sex. This phenomenon is explained by sexual selection (Campbell 1972; Daly and Wilson 1983; Buss and Schmitt 1993). Charles

Darwin was the first to explain sexual selection as the operation of natural selection to produce adaptations that aid specifically and directly in the competition for mates.

Robert Trivers developed parental investment theory, which explains the occurrence and intensity of sexual selection in organisms (Trivers 1972; Symons 1979).

Trivers argued that the operation of sexual selection is shaped by the relative levels of parental investment, which is defined as any investment by the parent in its offspring that increases the offspring’s fitness, the cost of which is the parent’s ability to invest in other offspring. The sex that invests more will constitute a limiting resource on the fitness of the opposite sex, relegating the sex that invests less to compete, often aggressively, over access to reproductive resources. The greater the investment differential between the two sexes, the higher the variability in reproductive success experienced by the sex that invests less, and the greater the intra-sexual competition for access to reproductive opportunities among the low investors. The intensity of intra-sexual competition by low investors over access to high investors results in adaptations, often for aggression, favored by sexual selection in low investors in response to these pressures.

In humans, due to the small obligate initial investment by males (i.e. sperm production), the most significant limiting factor on the reproductive success of males is the number and availability of females. Females, however, due to a relatively large initial investment (e.g. egg production, nine month gestation period), have more to lose from reproductive failure and are consequently the “choosier” sex, amplifying the inter-sexual competition among males for access to females. In primates, as well as with most

90 mammals in general, it is the case that females are characterized by greater levels of parental investment, which has led to adaptations in males for engaging in the intra- sexual (male v. male) competition for mates. Sexual selection and parental investment theory have proven remarkably successful at predicting and explaining the zoological diversity of sexual dimorphism (i.e. phenotypic differences between sexes). These theories have been used to explain a range of sexual dimorphisms in humans (Daly and

Wilson 1988; Buss and Schmitt 1993; Mesquida and Wiener 1999; Wilson and Daly

2002; Hudson and Boer 2002; Johnson et al. 2006; Archer 2006; Ermer, Cosmides, and

Tooby 2008). This theoretical framework, in combination with supporting evidence from closely related primate studies (Wrangham and Peterson 1996; Manson and Wrangham

1991), leads us to expect that, all else equal, males should be more willing to participate in coalitional aggression than females.

On the one hand, sexual selection and parental investment theory explain why males, given lower levels of parental investment, have been equipped by natural selection with the phenotypic weapons of aggressive intra-sexual (male v. male) competition

(Trivers 1972; Symons 1979). On the other hand, it is a direct consequence of this investment asymmetry that coalitional aggression has been reproductively advantageous for men more than for women (Tooby and Cosmides 1988; McDonald, Navarrete, and

Van Vugt 2012). To see why, consider the fitness consequences of warfare in light of parental investment.

Given that the risk contract of war, representing the conditions favoring the initiation of coalitional aggression, is fulfilled, victory guarantees that average male fitness is enhanced even if only a single male survives the encounter. This is possible

91 when the allocation of available reproductive resources in a coalition is zero-sum (e.g. survivors receive what the fallen have “lost”), meaning that the average reproductive success of victorious males in coalitional aggression is undiminished by even significant within-coalition mortality. This is a direct consequence of low parental investment by males relative to females; it takes little time and energy for any given male – given access

– to impregnate multiple women in a short period. In contrast, for women, once conception has occurred, there is no additional fitness benefit to additional copulations in the near future. Again, the upper bounds of female reproductive success is primarily limited by the size of female obligate investment, while the upper bounds of male reproductive success is primarily limited by access.

Participation in coalitional aggression by females is therefore less reproductively advantageous as a consequence of this investment asymmetry – whereas male mortality does not diminish average male reproductive success among men in the victorious coalition, female mortality in coalitional aggression would diminish average reproductive success in direct proportion to female mortality rate. For example, consider the case in which females engage in coalitional aggression. If it were the case that such a battle left all but one female survivor, the reallocation of males to this female would have no appreciable effect on her reproductive success. It would make little difference, reproductively, whether she had sexual access to 1 or 100 males, and therefore the

“reallocation” of males to surviving females is of no consequence – the upper bound on female reproductive success is limited by size of investment. As Tooby and Cosmides

(1988) explain, for males, “This zero-sum nature of within coalition reproductive reallocation cushions successful [male] coalitions from most of the negative fitness

92 consequences that would seem to necessarily follow from the decision to initiate warfare.”

In sum, when the risk contract of war is fulfilled, males stand to reap great reproductive benefits from coalitional aggression even when combat claims the lives of many males; females, however, stand to lose in direct proportion to lives lost in combat.

Since males have less to lose and more to gain from coalitional aggression, while females have more to lose and less to gain, it is the case that psychological adaptations should have been favored by natural selection that possessed distinct behavior-regulatory rules for males and females regarding willingness to participate in, and expected benefit from, coalitional aggression. At the outset, therefore, we should expect that, regardless of whether the domain is offensive or defensive, males should be more willing to participate in coalitional aggression than females (H3).

In terms of expected benefit, however, given that successful defense confers more in the way of public goods than successful offense, all group members experience the main benefits of successful defensive aggression, regardless of sex. Despite the fact that investment asymmetries render female coalitional aggression a high-cost, low benefit endeavor, this does not mean that aggression avoidance should be psychologically instantiated as an unconditional strategy in females. Despite the fact that the fitness benefits to females of engaging in coalitional violence are low relative to males, the threat of invasion by a male coalition is a particularly costly prospect for females (Van der Dennen 1995; Van Vugt 2009; McDonald, Navarrete, and Van Vugt 2012), such that we are therefore unlikely to observe sex differences in expected benefit in defense (H4).

In contrast, we are likely to observe greater relative levels of expected benefit by males

93 than by females in offense (H5). This is a direct reflection of the fact that women have more to lose and less to gain, either directly or indirectly, from offensive coalitional aggression since the benefits of such action remain privatized among participants, even accepting the fact that the material benefits of such coalitional action may be shared among close family or allies.

Summary and Final Considerations

The risk contract of war represents the psychological conditions that must hold among coalition members in order to successfully initiate coalitional aggression against a target coalition. In general, selection can favor a tendency to engage in coalitional violence when the probability of success is high, a veil of ignorance exists regarding the distribution of risk and expected death, and the structure of the allocation of reproductive resources is zero-sum. Consequently, adaptations ought to exist that monitor the environment to determine whether these conditions are fulfilled and act to regulate behavior accordingly. Individuals can affect the initiation of coalitional violence in two ways: the regulation of their own behavior, and through their influence on others. Thus, consideration of the risk contract of war leads to analyses regarding two sets of adaptations: 1) adaptations for the regulation of an individual’s own level of participation

(should I participate?), and; 2) adaptations for the enforcement of the risk contract on others (how do I get others to join?). These adaptations regulate behavior and motivation in warfare contingent on the presence and quality of adaptively relevant cues in the coalitional environment. The cue structure that I investigate is represented by the distinction between offensive and defensive coalitional aggression. In short, adaptations

94 will regulate behavior and motivation in warfare contingent upon whether the mind receives cues that the domain of warfare is offensive or defensive.

On the one hand I have argued that psychological adaptations exist that regulate behavior, cognition, and motivation in many domains of social behavior, and I have suggested that the operation of these adaptations operate outside of conscious awareness.

On the other hand, I have discussed the risk “contract” of war, and discussed how

“decisions” to participate are determined by cues such as the type of benefit expected.

Superficially, this seems to generate an awkward tension between two contrasting understandings of how behavior is generated. Colloquially, we think of behavior as either under our control, in which we make decisions consciously and somewhat rationally, or we think of behavior as generated by inflexible “instincts”15 such as hunger or lust, which may compel certain actions relatively independent of explicit cost-benefit deliberation. However, the distinction between “conscious calculation” and “the operation of psychological adaptations” is largely illusory. To see why, let us reconsider the nature of psychological adaptations in the context of warfare.

Regarding the risk contract of war, as with any set of psychological adaptations designed for social behavior, putative adaptations must exist that pair adaptively relevant behavior and motivation (output) with appropriate environmental cues (input). In war, the cues that have mattered most in ancestral environments were, inter alia, physical formidability and coalition size. To take a simple example, therefore, imagine that it was the case, on average, that bigger and stronger coalitions won more often than they lost

(indeed, all evidence suggests this was true), and that winning generated reproductive

15 As I have discussed in the introduction, this conceptualization of behavioral “instincts” is antiquated and false.

95 benefits for the victors. Also assume that this dynamic was a statistically reliable feature of the ancestral coalitional environment. Given the above, it should be the case that individuals that possessed heritable psychological design features that increased motivation to participate in warfare as these perceived cues (i.e. coalition size, formidability) increased in value would have left more copies of this design feature (i.e. the pairing of a motivation to participate with environmental cues such as coalition size) in future generations. It is precisely because the strategy solves the adaptive problem that the genes that code for it spread relative to other genes.

If it is the case that psychological adaptations are designed specifically to track these cues in order to successfully solve this adaptive problem (i.e. regulating participation in warfare), then in effect these psychological adaptations represent physically-instantiated “privileged hypotheses” about the world in which they developed.

The hypothesis that is privileged by this particular adaptation would be: “the bigger coalition wins,” and it is privileged because if the assumptions are met (e.g. I have a bigger coalition than you), then motivational output (I want to participate!) can overwhelm other information that it “rationally” should not (e.g. the other coalition has more guns). The psychological gamble is that on average this has been a reproductively successful strategy, and the gamble represents a privileged hypothesis in the brain that regulates behavior and motivation.

Consequently, psychological adaptations do not operate at the “expense” of conscious calculation and choice; rather, these adaptations structure calculation and choice by privileging certain forms of evidence over others. For example, an angry unarmed mob may rationally “know” that the much smaller group of police they are about

96 to attack is armed with weapons, however the adaptively relevant cue of numerical superiority may overwhelm the conclusion that should otherwise rationally follow: the police have guns and will defeat us, so we should back down.16 Clearly it is not the case that the mob members have not made a decision or calculation; instead, their very real calculation and choice was biased in favor of privileged hypotheses in the brain that are designed to consider adaptively relevant cues given the prospect of coalitional violence.

Importantly, this is not to say that a privileged hypothesis is always the right one.

It would also be false to conclude that privileged hypotheses are always the ones that are

“chosen” in any given circumstance. A privileged hypothesis is just that – a hypothesis regarding the causal relationship between social variables that on average is an evolutionarily good bet. Indeed, we should expect that the privilege that this hypothesis is accorded in the mind would diminish in the face of “supernormal” cues indicating that this hypothesis is indeed false in any particular instance. Thus, it seems to have taken the prospect of complete annihilation with the advent of nuclear weapons to inspire doubt regarding the prospects of conventional warfare, even between coalitions (e.g. states) of vastly unequal size. Ironically, modern warfare is in many ways returning to the logic of the lethal raid, as asymmetric warfare increases in prominence and conventional battle seems increasingly rare.

In short, humans are endowed with psychological adaptations that conditionally regulate behavior in response to a range of environmental cues, and the information- processing structure of these adaptations represent specialized solutions to ancestrally recurrent adaptive problems. We do make decisions, and our decisions are guided by

16 Indeed, the operation of these same evolved heuristics in the police may motivate them to irrationally abandon their positions instead of relying on their armed superiority.

97 privileged hypotheses that have been designed by natural selection to render decision- making contingent upon cues that would have correlated with increased fitness in ancestral environments. The risk contract of war represents the psychological conditions that must hold for a coalition to successfully initiate coalitional aggression. The initiation of warfare poses significant fitness consequences; therefore it is especially likely in this instance that natural selection should have shaped psychological adaptations to differentially attend to the cues that would have correlated with success and defeat in ancestral warfare. I proceed now to test hypotheses generated from this framework.

Hypotheses

H1: In offense, willingness to participate will be triggered by expectations of personal benefit, even controlling for expectations of group benefit;

H2: In defense, willingness to participate will be triggered by expectations of group benefit, even controlling for expectations of personal benefit;

H3: Males will be more willing than females to participate in both offensive and defensive coalitional aggression;

H4: There will be no sex difference in expected benefit from defensive coalitional aggression;

H5: Males will expect greater benefit than females from offensive coalitional aggression;

98 H6: In defense, but not in offense, punitive sentiment toward non-participants will be triggered by one’s willingness to participate;

H7: In defense, reward sentiment toward participants will be triggered by one’s expected benefit from coalitional aggression, but in offense, reward sentiment toward participants will be triggered by one’s willingness to participate.

99 University Press. http://www.loc.gov/catdir/enhancements/fy0636/91025307- d.html. Barnett, Michael. 2009. “Evolution Without Progress? Humanitarianism in a World of Hurt.” International Organization 63 (04): 621–663. Bell, D. 2006. “Beware of False Prophets: Biology, Human Nature and the Future of International Relations Theory - BELL - 2006 - International Affairs - Wiley Online Library.” International Affairs. http://onlinelibrary.wiley.com/doi/10.1111/j.1468-2346.2006.00547.x/full. Bell, DSA, and PK MacDonald. 2001. “Start the Evolution Without Us.” International Security 26 (1): 187–194. Bennett, John W. Wheeler. 2011. The Pipe Dream Of Peace The Story Of The Collapse Of Disarmament. Nabu Press. Betzig, Laura L. 1986. Despotism and Differential Reproduction : a Darwinian View of History. New York: Aldine Pub. Biddle, Stephen. 2001. “Rebuilding the Foundations of Offense-Defense Theory.” Journal of Politics 63 (3) (August 1): 741–774. doi:10.1111/0022-3816.00086. Boehm, Christopher. 1984. Blood Revenge : the Anthropology of Feuding in Montenegro and Other Tribal Societies. Lawrence, Kan.: University Press of Kansas. ———. 1999. Hierarchy in the Forest: The Evolution of Egalitarian Behavior. Cambridge, Mass.: Harvard University Press. Bowles, S. 2009. “Did Warfare Among Ancestral Hunter-gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932): 1293. Bowles, Samuel. 2009. “Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932) (June 5): 1293–1298. doi:10.1126/science.1168112. Boyd, R., and P. J. Richerson. 1992. “Punishment Allows the Evolution of Cooperation (or Anything Else) in Sizable Groups.” Ethology and Sociobiology 13 (3): 171– 195. Boyd, Robert, and Peter J. Richerson. 1988. “The Evolution of Reciprocity in Sizable Groups.” Journal of Theoretical Biology 132 (3) (June 7): 337–356. doi:10.1016/S0022-5193(88)80219-4. Brown, Michael E., Owen R. Coté Jr, Sean M. Lynn-Jones, and Steven E. Miller, eds. 2004. Offense, Defense, and War. 1st ed. The MIT Press. Burt, Austin, and Robert Trivers. 2006. Genes in Conflict: The Biology of Selfish Genetic Elements. Belknap Press of Harvard University Press. Burton-Chellew, Maxwell N., Adin Ross-Gillespie, and Stuart A West. 2010. “Cooperation in Humans: Competition Between Groups and Proximate Emotions.” Evolution and Human Behavior 31 (2): 104–108. Buss, D. M., and D. P. Schmitt. 1993. “Sexual Strategies Theory - an Evolutionary Perspective on Human Mating.” Psychological Review 100 (2): 204–232. Buss, D. M., and T. Shackelford. 1997. “Human Aggression in Evolutionary Psychological Perspective.” Clinical Psychology Review 17: 605–619. Buss, David M. 2004. Evolutionary Psychology: The New Science of the Mind. Boston: Allyn and Bacon. Campbell, Bernard, ed. 1972. Sexual Selection and the Descent of Man: 1871-1971. Aldine Transaction.

100 Carroll, Sean B. 2006. The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. New York, N.Y.: W.W. Norton & Co. Chagnon, Napoleon A. 1983. Yanomamö : the Fierce People. New York: Holt, Rinehart and Winston. ———. 1988. “Life Histories, Blood Revenge, and Warfare in a Tribal Population.” Science 239 (4843): 985–992. Charney, Evan. 2008. “Genes and Ideologies.” Perspectives on Politics 6 (02). doi:10.1017/S1537592708080626. http://www.journals.cambridge.org/abstract_S1537592708080626. Choi, J K, and S Bowles. 2007. “The Coevolution of Parochial Altruism and War.” Science 318 (5850): 636–640. doi:10.1126/science.1144237. Cikara, Mina, Emile G. Bruneau, and Rebecca R. Saxe. 2011. “Us and Them.” Current Directions in Psychological Science 20 (3) (June 1): 149 –153. doi:10.1177/0963721411408713. Cohen, Ronald. 1978. Origins of the State: The Anthropology of Political Evolution. Ed. Elman Rogers Service. Inst for the Study of Human Is. Confer, Jaime C., Judith A. Easton, Diana S. Fleischman, Cari D. Goetz, David M. G. Lewis, Carin Perilloux, and David M Buss. 2010. “Evolutionary Psychology: Controversies, Questions, Prospects, and Limitations.” American Psychologist 65 (2): 110–126. Cosmides, Leda, H. Clark Barrett, and John Tooby. 2010. “Adaptive Specializations, Social Exchange, and the Evolution of Human Intelligence.” Proceedings of the National Academy of Sciences (May 5). doi:10.1073/pnas.0914623107. http://www.pnas.org/content/early/2010/05/04/0914623107.abstract. Cosmides, Leda, and John Tooby. 1981. “Cytoplasmic Inheritance and Intragenomic Conflict.” Journal of Theoretical Biology 89 (1) (March 7): 83–129. doi:10.1016/0022-5193(81)90181-8. ———. 1987. “From Evolution to Behavior: Evolutionary Psychology as the Missing Link.” In The Latest on the Best: Essays on Evolution and Optimality, 276–306. Cambridge, Mass.: MIT Press. ———. 1994a. “Origins of Domain Specificity: The Evolution of Functional Organization.” In Mapping the Mind: Domain Specificity in Cognition and Culture, 85–116. New York: Cambridge University Press. ———. 1994b. “Better Than Rational - Evolutionary Psychology and the Invisible Hand.” American Economic Review 84 (2): 327–332. ———. 2005. “Neurocognitive Adaptations Designed for Social Exchange.” In The Handbook of Evolutionary Psychology, 584–627. Hoboken, NJ: Wiley. Crawford, Neta C. 2009. “Human Nature and World Politics: Rethinking `Man’.” International Relations 23 (2) (June 1): 271–288. doi:10.1177/0047117809104639. Curley, Tyler M. 2009. “Social Identity Theory and EU Expansion.” International Studies Quarterly 53 (3) (September 1): 649–668. doi:10.1111/j.1468- 2478.2009.00550.x. Daly, Martin, and Margo Wilson. 1983. Sex, Evolution, and Behavior. Boston: Willard Grant Press. ———. 1988. Homicide. New York: A. de Gruyter.

101 Dawkins, Richard. 1976. The Selfish Gene. Oxford: Oxford University Press. ———. 1980. “Good Strategy or Evolutionarily Stable Strategy?” In Sociobiology: Beyond Nature/Nurture?, 331–367. Boulder: Westview Press. ———. 1983. The Extended Phenotype : the Long Reach of the Gene. Oxford ; New York: Oxford University Press. ———. 1986. The Blind Watchmaker. New York: Norton. Delton, Andrew W., Max M. Krasnow, Leda Cosmides, and John Tooby. 2011. “Evolution of Direct Reciprocity Under Uncertainty Can Explain Human Generosity in One-shot Encounters.” Proceedings of the National Academy of Sciences 108 (July 25): 13335–13340. doi:10.1073/pnas.1102131108. Van der Dennen, J.M.G. 1995. The Origin of War: The Evolution of a Male-coalitional Reproductive Strategy. Groningen: Origin Press. Dennett, Daniel. 1995. Darwin’s Dangerous Idea : Evolution and the Meanings of Life. New York: Simon & Schuster. Dunbar, Robin I. M. 1993. “Coevolution of Neocortical Size, Group Size, and Language in Humans.” Behavioral and Brain Sciences 16 (4): 681–735. Durham, W. H. 1976. “Resource Competition and Human Aggression .1. Review of Primitive War.” Quarterly Review of Biology 51 (3): 385–415. Dyson-Hudson, Rada, and Eric Alden Smith. 1978. “Human Territoriality: An Ecological Reassessment.” American Anthropologist 80 (1): 21–41. Eaves, L., P. Hatemi, N. Gillespie, and N. Martin. 2008. “Looking for Politically Relevant Genes.” Behavior Genetics 38 (6): 623–623 101. Eldakar, Omar Tonsi, and David Sloan Wilson. 2011. “Eight Criticisms Not to Make About Group Selection.” Evolution 65 (6) (June 1): 1523–1526. Ember, C. R. 1978. “Myths About Hunter-Gatherers.” Ethnology 17 (4): 439–448. Ermer, E., L Cosmides, and J Tooby. 2008. “Relative Status Regulates Risky Decision Making About Resources in Men: Evidence for the Co-evolution of Motivation and Cognition.” Evolution and Human Behavior 29 (2): 106–118. doi:10.1016/J.Evolhumbehav.2007.11.002. Van Evera, S. 1998. “Offense, Defense, and the Causes of War.” International Security 22 (4): 5–43. Van Evera, Stephen. 1984. “The Cult of the Offensive and the Origins of the First World War.” International Security 9 (1): 58–107. Fearon, J. D. 1995. “Rationalist Explanations for War.” International Organization 49 (3): 379–414. Feldstein, Martin. 1999. “A Self-Help Guide for Emerging Markets.” Foreign Affairs, March 1. http://www.foreignaffairs.com/articles/54801/martin-feldstein/a-self- help-guide-for-emerging-markets. Flinn, M. V., D. C. Geary, and C. V. Ward. 2005. “Ecological Dominance, Social Competition, and Coalitionary Arms Races: Why Humans Evolved Extraordinary Intelligence.” Evolution and Human Behavior 26 (1): 10–46. doi:10.1016/J.Evolhumbehav.2004.08.005. Forgas, Joseph P., Martie Haselton, and William von Hippel. 2007. Evolution and the Social Mind : Evolutionary Psychology and Social Cognition. New York, NY: Psychology Press.

102 Fowler, J H, and D Schreiber. 2008. “Biology, Politics, and the Emerging Science of Human Nature.” Science 322 (5903): 912–914. doi:10.1126/science.1158188. Fowler, James H, and Christopher T Dawes. 2008. “Two Genes Predict Voter Turnout.” The Journal of Politics 70 (03). doi:10.1017/S0022381608080638. http://www.journals.cambridge.org/abstract_S0022381608080638. Fry, Douglas P. 2007. Beyond War: The Human Potential for Peace. 1St ed. Oxford University Press, USA. Gallistel, Charles R. 1990. The Organization of Learning. Cambridge, Mass.: MIT Press. Gat, Azar. 2000a. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-gatherer Fighting, Part II. Proximate, Subordinate, and Derivative Causes.” Anthropological Quarterly 73 (2): 74–88. ———. 2000b. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-Gatherer Fighting. Part I. Primary Somatic and Reproductive Causes.” Anthropological Quarterly 73 (1): 20–34. ———. 2006. War in Human Civlization. Oxford: Oxford University Press. http://www.loc.gov/catdir/toc/ecip0614/2006017223.html. Gazzaniga, Michael S. 2000. Cognitive Neuroscience : a Reader. Malden, Mass.: Blackwell. Gazzaniga, Michael S., Diana Steen, and Bruce T. Volpe. 1979. Functional Neuroscience. New York: Harper & Row. Gigerenzer, Gerd. 2000. Adaptive Thinking : Rationality in the Real World. New York: Oxford University Press. Gigerenzer, Gerd, and Reinhard Selten. 2001. Bounded Rationality : the Adaptive Toolbox. Cambridge, Mass.: MIT Press. Ginges, J, and S Atran. 2011. “War as a Moral Imperative (not Just Practical Politics by Other Means).” Proceedings of the Royal Society B: Biological Sciences 278 (1720): 2930–2938. doi:10.1098/rspb.2010.2384. Glaser, Charles L., and Chaim Kaufmann. 1998. “What Is the Offense-defense Balance and Can We Measure It?” International Security 22 (4): 44–82. Gneezy, Ayelet, and Daniel M. T. Fessler. 2011. “Conflict, Sticks and Carrots: War Increases Prosocial Punishments and Rewards.” Proceedings of the Royal Society B: Biological Sciences (June 8). doi:10.1098/rspb.2011.0805. http://rspb.royalsocietypublishing.org/content/early/2011/06/03/rspb.2011.0805.a bstract. Godfrey-Smith, Peter, and Jon F. Wilkins. 2008. “Adaptationism.” In A Companion to the Philosophy of Biology, Chapter 11. Oxford: Blackwell. Goodall, Jane. 1986. The Chimpanzees of Gombe : Patterns of Behavior. Cambridge, Mass.: Belknap Press of Harvard University Press. Goodwin, Adam. 2010. “Evolution and Anarchism in International Relations: The Challenge of Kropotkin’s Biological Ontology.” Millennium - Journal of International Studies 39 (2): 417–437. doi:10.1177/0305829810384676. Green, Donald, and Ian Shapiro. 1996. Pathologies of Rational Choice Theory: A Critique of Applications in Political Science. Yale University Press. Hagen, Edward H, and Peter Hammerstein. 2006. “Game Theory and Human Evolution: a Critique of Some Recent Interpretations of Experimental Games.” Theoretical Population Biology 69 (3) (May): 339–348. doi:10.1016/j.tpb.2005.09.005.

103 Hamilton, W. D. 1964a. “Genetical Evolution of Social Behaviour I.” Journal of Theoretical Biology 7 (1): 1–16. ———. 1964b. “Genetical Evolution of Social Behaviour 2.” Journal of Theoretical Biology 7 (1): 17–52. Harcourt, A. H., and F. B. M. de Waal. 1992. Coalitions and Alliances in Humans and Other Animals. Oxford [England] ; New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0639/91004285-d.html. Haselhuhn, Michael P, and Elaine M Wong. 2011. “Bad to the Bone: Facial Structure Predicts Unethical Behaviour.” Proceedings of the Royal Society B: Biological Sciences (July 6). doi:10.1098/rspb.2011.1193. http://rspb.royalsocietypublishing.org/content/early/2011/06/29/rspb.2011.1193. Hatemi, P K, J R Alford, J R Hibbing, N G Martin, and L J Eaves. 2009. “Is There a ‘Party’ in Your Genes?” Political Research Quarterly 62 (3): 584–600. doi:10.1177/1065912908327606. Heckhausen, Jutta, and Heinz Heckhausen. 2010. Motivation and Action. Cambridge University Press. Henrich, Joseph. 2004. “Cultural Group Selection, Coevolutionary Processes and Large- scale Cooperation.” Journal of Economic Behavior & Organization 53 (1) (January): 3–35. doi:10.1016/S0167-2681(03)00094-5. Henrich, Joseph, Jean Ensminger, Richard McElreath, Abigail Barr, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2010. “Markets, Religion, Community Size, and the Evolution of Fairness and Punishment.” Science 327 (5972) (March 19): 1480–1484. doi:10.1126/science.1182238. Henrich, Joseph, Richard McElreath, Abigail Barr, Jean Ensminger, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2006. “Costly Punishment Across Human Societies.” Science 312 (5781) (June 23): 1767–1770. doi:10.1126/science.1127333. Hooper, Paul L., Hillard S. Kaplan, and James L. Boone. 2010. “A Theory of Leadership in Human Cooperative Groups.” Journal of Theoretical Biology 265 (4) (August 21): 633–646. doi:10.1016/j.jtbi.2010.05.034. Hudson, Valerie M., and Andrea Den Boer. 2002. “A Surplus of Men, A Deficit of Peace: Security and Sex Ratios in Asia’s Largest States.” International Security 26 (4): 5–38. doi:10.1162/016228802753696753. Huntington, Samuel P. 1993. The Third Wave: Democratization in the Late 20th Century. University of Oklahoma Press. Jervis, R. 1978a. “Cooperation Under the Security Dilemma.” World Politics: A Quarterly Journal of International …. http://www.jstor.org/stable/2009958. ———. 1978b. “Cooperation Under Security Dilemma.” World Politics 30 (2): 167–214. ———. 2003. “Understanding the Bush Doctrine.” Political Science Quarterly. http://www.ingentaconnect.com/content/taps/psq/2003/00000118/00000003/art00 001. Johnson, Dominic D. P., and James H. Fowler. 2011. “The Evolution of Overconfidence.” Nature 477 (7364): 317–320. doi:10.1038/nature10384. Johnson, Dominic D. P., Rose McDermott, Emily S. Barrett, Jonathan Cowden, Richard W. Wrangham, Matthew H. McIntyre, and Stephen Peter Rosen. 2006. “Overconfidence in Wargames: Experimental Evidence on Expectations,

104 Aggression, Gender and Testosterone.” Proceedings of the Royal Society of London Series B-Biological Sciences: 2513–2520. doi:10.1098/Rspb.2006.3606. Johnson, Dominic D. P., Richard W. Wrangham, and Steven P. Rosen. 2002. “Is Military Incompetence Adaptive? An Empirical Test with Risk-taking Behaviour in Modem Warfare.” Evolution and Human Behavior 23 (4): 245–264. Johnson, Dominic D.P., and Dominic Tierney. 2011. “The Rubicon Theory of War: How the Path to Conflict Reaches the Point of No Return.” International Security 36 (1): 7–40. doi:i: 10.1162/ISEC_a_00043

. Kahler, Miles. 1998. “Rationality in International Relations.” International Organization 52 (04): 919–941. doi:10.1162/002081898550680. Kameda, T., M. Takezawa, R. S. Tindale, and C. M. Smith. 2002. “Social Sharing and Risk Reduction - Exploring a Computational Algorithm for the Psychology of Windfall Gains.” Evolution and Human Behavior 23 (1): 11–33. Kanai, Ryota, Tom Feilden, Colin Firth, and Geraint Rees. 2011. “Political Orientations Are Correlated with Brain Structure in Young Adults.” Current Biology 21 (8) (April 26): 677–680. doi:10.1016/j.cub.2011.03.017. Kaplan, H., and K. Hill. 1985. “Food Sharing Among Ache Foragers - Tests of Explanatory Hypotheses.” Current Anthropology 26 (2): 223–246. Keeley, Lawrence H. 1996. War Before Civilization: The Myth of the Peaceful Savage. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0638/94008998-d.html. Kelly, Raymond C. 2000. Warless Societies and the Origin of War. University of Michigan Press. Kratochwil, Friedrich, and John Gerard Ruggie. 1986. “International Organization: A State of the Art on an Art of the State.” International Organization 40 (04): 753– 775. doi:10.1017/S0020818300027363. Kurzban, Robert, and Daniel Houser. 2005. “Experiments Investigating Cooperative Types in Humans: A Complement to Evolutionary Theory and Simulations.” Proceedings of the National Academy of Sciences of the United States of America 102 (5): 1803–1807. Kurzban, Robert, and Steven Neuberg. 2005. “Managing Ingroup and Outgroup Relations.” In The Handbook of Evolutionary Psychology, 653–675. Hoboken: John Wiley & Sons. Kurzban, Robert, John Tooby, and L Cosmides. 2001a. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences 98 (26): 15387–15392. Kurzban, Robert, John Tooby, and Leda Cosmides. 2001b. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences of the United States of America 98 (26): 15387–15392. LeBlanc, Steven A., and Katherine E. Register. 2003. Constant Battles: The Myth of the Peaceful, Noble Savage. New York: St. Martin’s. http://www.loc.gov/catdir/bios/hol052/2002036880.html. Lehmann, Laurent, Laurent Keller, Stuart West, and Denis Roze. 2007. “Group Selection and Kin Selection: Two Concepts but One Process.” Proceedings of the National Academy of Sciences 104 (16) (April 17): 6736 –6739. doi:10.1073/pnas.0700662104.

105 Lerner, J S, and D Keltner. 2001. “Fear, Anger, and Risk.” Journal of Personality and Social Psychology 81 (1) (July): 146–159. Levy, Jack S. 1984. “The Offensive/defensive Balance of Military Technology: A Theoretical and Historical Analysis.” International Studies Quarterly 28 (2): 219– 238. Levy, Jack S., and William R. Thompson. 2011. The Arc of War: Origins, Escalation, and Transformation. University Of Chicago Press. Lieberman, D., J Tooby, and L Cosmides. 2007. “The Architecture of Human Kin Detection.” Nature 445 (7129): 727–731. doi:10.1038/Nature05510. Lieberman, Matthew D., Darren Schreiber, and Kevin N. Ochsner. 2003. “Is Political Cognition Like Riding a Bicycle? How Cognitive Neuroscience Can Inform Research on Political Thinking.” Political Psychology 24 (4) (December): 681– 704. doi:10.1046/j.1467-9221.2003.00347.x. Lopez, Anthony C. 2010. Evolution, Coalitional Psychology, and War. H-Diplo ISSF Roundtable on “Biology and Security.” Lopez, Anthony C., and Rose McDermott. “Adaptation, Heritability, and the Emergence of Evolutionary Political Science.” Political Psychology. Lopez, Anthony C., Rose McDermott, and Michael Bang Petersen. 2011. “States in Mind: Evolution, Coalitional Psychology, and International Politics.” International Security 36 (2): 48–83. Lorenz, Konrad. 1966. On Aggression. London,: Methuen. Manson, Joseph H., and Richard W. Wrangham. 1991. “Intergroup Aggression in Chimpanzees and Humans.” Current Anthropology 32 (4): 369–390. Martin, N G, L J Eaves, A C Heath, R. Jardine, L M Feingold, and H J Eysenck. 1986. “Transmission of Social Attitudes.” Proceedings of the National Academy of Sciences 83 (12) (June 1): 4364–4368. Masters, Roger D. 1989. The Nature of Politics. New Haven: Yale University Press. Mathew, Sarah, and Robert Boyd. 2011. “Punishment Sustains Large-scale Cooperation in Prestate Warfare.” Proceedings of the National Academy of Sciences. http://www.pnas.org/content/108/28/11375.short. Maynard Smith, J. 1976. “Group Selection.” Quarterly Review of Biology 51: 277–283. Maynard Smith, John. 1982. Evolution and the Theory of Games. Cambridge ; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam022/81021595.html. ———. 1993. The Theory of Evolution. Cambridge [England] ; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam025/93020358.html. ———. 1998. Evolutionary Genetics. Oxford; New York: Oxford University Press. ———. 1999. Shaping Life : Genes, Embryos, and Evolution. New Haven: Yale University Press. Mayr, Ernst. 1983. “How to Carry Out the Adaptationist Program?” The American Naturalist 121 (3): 324–334. ———. 2001. What Evolution Is. New York: Basic Books. McDermott, R, D Tingley, J Cowden, G Frazzetto, and D D P Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. doi:10.1073/pnas.0808376106.

106 McDermott, Rose. 2004. “The Feeling of Rationality: The Meaning of Neuroscientific Advances for Political Science.” Perspectives on Politics 2 (4): 691–706. McDermott, Rose, James H Fowler, and Oleg Smirnov. 2008. “On the Evolutionary Origin of Prospect Theory Preferences.” The Journal of Politics 70 (02). doi:10.1017/S0022381608080341. http://www.journals.cambridge.org/abstract_S0022381608080341. McDermott, Rose, Dustin Tingley, Jonathan Cowden, Giovanni Frazetto, and Dominic D. P. Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. McDonald, Melissa M., Carlos David Navarrete, and Mark Van Vugt. 2012. “Evolution and the Psychology of Intergroup Conflict: The Male Warrior Hypothesis.” Philosophical Transactions of the Royal Society B: Biological Sciences 367 (1589) (March 5): 670 –679. doi:10.1098/rstb.2011.0301. Mead, M. 1940. “Warfare Is Only an Invention—not a Biological Necessity.” Asia 40 (8): 402–405. Mehta, Pranjal H, Amanda C Jones, and Robert A Josephs. 2008. “The Social Endocrinology of Dominance: Basal Testosterone Predicts Cortisol Changes and Behavior Following Victory and Defeat.” Journal of Personality and Social Psychology 94 (6): 1078–1093. doi:10.1037/0022-3514.94.6.1078. Mercer, Jonathan. 1995. “Anarchy and Identity.” International Organization 49 (2): 229– 252. ———. 2005. “Rationality and Psychology in International Relations.” International Organization 59 (Winter): 77–106. Mesquida, C. G., and N. I. Wiener. 1999. “Male Age Composition and Severity of Conflicts.” Politics and the Life Sciences 18 (2): 181–189. Milner, Helen. 1992. “International Theories of Cooperation Among Nations: Strengths and Weaknesses.” World Politics 44 (3): 466–496. Mitani, John C., David P. Watts, and Sylvia Amsler J. 2010. “Lethal Intergroup Aggression Leads to Territorial Expansion in Wild Chimpanzees.” Current Biology 20 (12) (June 22): R507–R508. Mitchell, Gregory, Philip E Tetlock, Daniel G Newman, and Jennifer S Lerner. 2003. “Experiments Behind the Veil: Structural Influences on Judgments of Social Justice.” Political Psychology 24 (3) (September 1): 519–547. doi:10.1111/0162- 895X.00339. Morgan, T. J. H, L. E Rendell, M. Ehn, W. Hoppitt, and K. N Laland. 2011. “The Evolutionary Basis of Human Social Learning.” Proceedings of the Royal Society B: Biological Sciences (July 27). doi:10.1098/rspb.2011.1172. http://rspb.royalsocietypublishing.org/content/early/2011/07/21/rspb.2011.1172.a bstract. Morgenthau, Hans Joachim, and Kenneth W. Thompson. 1993. Politics Among Nations: The Struggle for Power and Peace. McGraw-Hill. Nettleship, Martin A., R. Dale Givens, and Anderson Nettleship. 1975. War, Its Causes and Correlates. The Hague Chicago: Mouton ; distributed by Aldine. Nowak, Martin A, Corina E Tarnita, and Edward O Wilson. 2010. “The Evolution of Eusociality.” Nature 466 (7310): 1057–1062. doi:10.1038/nature09205.

107 Nowak, Martin A. 2006. “Five Rules for the Evolution of Cooperation.” Science 314 (5805) (December 8): 1560 –1563. doi:10.1126/science.1133755. Olson, Mancur. 1965. The Logic of Collective Action; Public Goods and the Theory of Groups. Cambridge, Mass.,: Harvard University Press. Orbell, John, and Tomonori Morikawa. 2011. “An Evolutionary Account of Suicide Attacks: The Kamikaze Case.” Political Psychology 32 (2): 297–322. doi:10.1111/j.1467-9221.2010.00808.x. Otterbein, Keith F. 2004. How War Began. 1st ed. TAMU Press. Oxley, D R, K B Smith, J R Alford, M V Hibbing, J L Miller, M Scalora, P K Hatemi, and J R Hibbing. 2008. “Political Attitudes Vary with Physiological Traits.” Science 321 (5896): 1667–1670. doi:10.1126/science.1157627. Panchanathan, Karthik, and Robert Boyd. 2004. “Indirect Reciprocity Can Stabilize Cooperation Without the Second-order Free Rider Problem.” Nature 432 (7016) (November 25): 499–502. doi:10.1038/nature02978. Parker, Geoff. 1974. “Assessment Strategy and the Evolution of Fighting Behaviour.” Journal of Theoretical Biology 47 (1) (September): 223–243. Petersen, Michael Bang. 2009. “Public Opinion and Evolved Heuristics: The Role of Category-Based Inference.” Journal of Cognition and Culture 9 (3): 367–389. doi:10.1163/156770909X12518536414376. ———. 2012. “Social Welfare as Small-Scale Help: Evolutionary Psychology and the Deservingness Heuristic.” American Journal of Political Science 56 (1) (January 1): 1–16. doi:10.1111/j.1540-5907.2011.00545.x. Pinker, Steven. 2011. The Better Angels of Our Nature: Why Violence Has Declined. Viking Adult. Potts, Malcolm, and Thomas Hayden. 2008. Sex and War: How Biology Explains Warfare and Terrorism and Offers a Path to a Safer World. BenBella Books. Powell, Robert. 2006. “War as a Commitment Problem.” International Organization 60 (1): 169–203. Price, Michael. 2012. “Group Selection Theories Are Now More Sophisticated, but Are They More Predictive? A Review of Samuel Bowles and Herbert Gintis, A Cooperative Species: Human Reciprocity and Its Evolution.” Evolutionary Psychology 10 (1): 45–49. Price, Michael E, Leda Cosmides, and John Tooby. 2002. “Punitive Sentiment as an Anti-Free Rider Psychological Device.” Evolution and Human Behavior 23 (3): 203–231. Puts, David A, Coren L Apicella, and Rodrigo A Cárdenas. 2012. “Masculine Voices Signal Men’s Threat Potential in Forager and Industrial Societies.” Proceedings of the Royal Society B: Biological Sciences 279 (1728) (February 7): 601–609. doi:10.1098/rspb.2011.0829. Puurtinen, Mikael, and Tapio Mappes. 2009. “Between-group Competition and Human Cooperation.” Proceedings of the Royal Society B: Biological Sciences 276 (1655) (January 22): 355 –360. doi:10.1098/rspb.2008.1060. Quester, George H. 2002. Offense and Defense in the International System. 3rd ed. Transaction Publishers. Rand, David G., Samuel Arbesman, and Nicholas A. Christakis. 2011. “Dynamic Social Networks Promote Cooperation in Experiments with Humans.” Proceedings of

108 the National Academy of Sciences 108 (48) (November 29): 19193 –19198. doi:10.1073/pnas.1108243108. Richerson, Peter J., and Robert Boyd. 2006. Not by Genes Alone: How Culture Transformed Human Evolution. University Of Chicago Press. Ridley, Mark. 2004. Evolution. Malden, MA: Blackwell Pub. Ridley, Matt. 1994. The Red Queen: Sex and the Evolution of Human Nature. New York: Maxwell Macmillan International. ———. 1997. The Origins of Virtue : Human Instincts and the Evolution of Cooperation. New York: Viking. Rosen, Stephen Peter. 2005. War and Human Nature. Princeton, N.J.: Princeton University Press. http://www.loc.gov/catdir/enhancements/fy0654/2003065590- d.html. Sapolsky, Robert M. 2006. “A Natural History of Peace.” Foreign Affairs. Schultheiss, O, and M Wirth. 2009. “Biopsychological Aspects of Motivation”: 1–91. Sell, Aaron, Gregory A. Bryant, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Reuden, Andre Krauss, and Michael Gurven. 2010. “Adaptations in Humans for Assessing Physical Strength from the Voice.” Proceedings of the Royal Society B: Biological Sciences: 3509–3518. Sell, Aaron, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Rueden, and Michael Gurven. 2009. “Human Adaptations for the Visual Assessment of Strength and Fighting Ability from the Body and Face.” Proceedings of the Royal Society of London Series B-Biological Sciences 276 (1656): 575–584. doi:10.1098/rspb.2008.1177. Sell, Aaron, John Tooby, and Leda Cosmides. 2009. “Formidability and the Logic of Human Anger.” Proceedings of the National Academy of Sciences 106 (35): 15073–15078. Sellers, JG, MR Mehl, and RA Josephs. 2007. “Hormones and Personality: Testosterone as a Marker of Individual Differences.” Journal of Research in Personality 41 (1): 126–138. Sharansky, Natan, and Ron Dermer. 2004. The Case for Democracy: The Power of Freedom to Overcome Tyranny and Terror. 1ST ed. PublicAffairs. Short, Lindsey A., Catherine J. Mondloch, Cheryl M. McCormick, Justin M. Carré, Ruqian Ma, Genyue Fu, and Kang Lee. 2012. “Detection of Propensity for Aggression Based on Facial Structure Irrespective of Face Race.” Evolution and Human Behavior 33 (2) (March): 121–129. doi:10.1016/j.evolhumbehav.2011.07.002. Sidanius, Jim, and Robert Kurzban. 2003. “Evolutionary Approaches to Political Psychology.” In Oxford Handbook of Political Psychology. New York: Oxford University Press. Silverberg, James, and J. Patrick Gray. 1992. Aggression and Peacefulness in Humans and Other Primates. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0604/91020318-d.html. Simmons, Beth A, Frank Dobbin, and Geoffrey Garrett. 2006. “Introduction: The International Diffusion of Liberalism.” International Organization 60 (4): 781– 810.

109 Smith, Kevin B, Christopher W Larimer, Levente Littvay, and John R Hibbing. 2007. “Evolutionary Theory and Political Leadership: Why Certain People Do Not Trust Decision Makers.” The Journal of Politics 69 (2): 285–299. doi:10.1111/j.1468- 2508.2007.00532.x. Smith, Kevin B, Douglas R Oxley, Matthew V Hibbing, John R. Alford, and John R. Hibbing. 2011a. “Linking Genetics and Political Attitudes: Reconceptualizing Political Ideology.” Political Psychology 32 (3): 369–397. doi:10.1111/j.1467- 9221.2010.00821.x. Smith, Kevin B., Douglas Oxley, Matthew V. Hibbing, John R. Alford, and John R. Hibbing. 2011b. “Disgust Sensitivity and the Neurophysiology of Left-Right Political Orientations.” PLoS ONE 6 (10) (October 19): e25552. doi:10.1371/journal.pone.0025552. Sober, Elliott, and David Sloan Wilson. 1999. Unto Others: The Evolution and Psychology of Unselfish Behavior. Harvard University Press. Somit, A., and S. A. Peterson. 1998. “Review Article: Biopolitics After Three Decades - A Balance Sheet.” British Journal of Political Science 28: 559–571. Somit, Albert, and Steven A. Peterson. 1997. Darwinism, Dominance, and Democracy : the Biological Bases of Authoritarianism. Westport, Conn.: Praeger. Sperber, Dan. 1996. Explaining Culture: a Naturalistic Approach. Oxford: Blackwell. Stanton, SJ, and OC Schultheiss. 2007. “Basal and Dynamic Relationships Between Implicit Power Motivation and Estradiol in Women.” Hormones and Behavior 52 (5): 571–580. Sumner, William Graham. 1970. War and Other Essays. Ams Pr Inc. Symons, Donald. 1979. The Evolution of Human Sexuality. New York: Oxford University Press. ———. 1992. “On the Use and Misuse of Darwinism in the Study of Human Behavior.” In The Adapted Mind: Evolutionary Psychology and the Generation of Culture, 137–160. New York: Oxford University Press. Tajfel, Henry, and John C. Turner. 1986. “The Social Identity Theory of Intergroup Behavior.” In Psychology of Intergroup Relations. Chicago: Nelson Hall. Takezawa, Masanori, and Michael E Price. 2010. “Revisiting ‘The Evolution of Reciprocity in Sizable Groups’: Continuous Reciprocity in the Repeated N-person Prisoner’s Dilemma.” Journal of Theoretical Biology 264 (2) (May 21): 188–196. doi:10.1016/j.jtbi.2010.01.028. Thayer, BA. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security. http://www.mitpressjournals.org/doi/pdf/10.1162/016228800560471. Thayer, Bradley A. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security 25 (2): 124–151. ———. 2001. “Correspondence: Start the Evolution Without Us.” International Security 26 (1): 194–198. ———. 2004. Darwin and International Relations: On the Evolutionary Origins of War and Ethnic Conflict. Lexington: University Press of Kentucky. Thayer, Bradley A, and Valerie M Hudson. 2010. “Sex and the Shaheed: Insights from the Life Sciences on Islamic Suicide Terrorism.” International Security 34 (4): 37–62.

110 Thompson, William R. 2001. Evolutionary Interpretations of World Politics. New York: Routledge. http://www.loc.gov/catdir/toc/fy022/00066485.html. Tiger, Lionel. 2004. Men in Groups. Revised. Transaction Publishers. Tooby, John, and Leda Cosmides. 1988. “The Evolution of War and Its Cognitive Foundations.” Institute for Evolutionary Studies Technical …. http://www.psych.ucsb.edu/research/cep/papers/EvolutionofWar.pdf. ———. 1990. “On the Universality of Human Nature and the Uniqueness of the Individual: The Role of Genetics and Adaptation.” Journal of Personality 58 (1): 17–67. Tooby, John, Leda Cosmides, and Michael E Price. 2006. “Cognitive Adaptations for N- person Exchange: The Evolutionary Roots of Organizational Behavior.” Managerial and Decision Economics 27 (2-3): 103–129. Trivers, Robert. 1971. “The Evolution of Reciprocal Altruism.” The Quarterly Review of Biology 46 (1): 35–57. ———. 1972. “Parental Investment and Sexual Selection.” In Sexual Selection and the Descent of Man. Chicago: Aldine Publishing. ———. 2000. “The Elements of a Scientific Theory of Self-Deception.” Annals of the New York Academy of Sciences 907 (April): 114–131. ———. 2011. The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life. 1st ed. Basic Books. Turney-High, Harry Holbert. 1949. Primitive War: Its Practice and Concepts. Columbia,: Univ. of South Carolina Press. Van Vugt, Mark. 2009. “Sex Differences in Intergroup Competition, Aggression, and Warfare: The Male Warrior Hypothesis.” Annals of the New York Academy of Sciences 1167 (June): 124–134. doi:10.1111/j.1749-6632.2009.04539.x. Vugt, Mark Van, and Anjana Ahuja. 2011. Naturally Selected: The Evolutionary Science of Leadership. HarperCollins. van Vugt, Mark, and Rob Kurzban. 2007. “Cogntive and Social Adaptations for Leadership and Followership: Evolutionary Game Theory and Group Dynamics.” In Evolution and the Social Mind: Evolutionary Psychology and Social Cognition, 229–243. New York: Psychology Press. Wagner, John D., Mark V. Flinn, and Barry G. England. 2002. “Hormonal Response to Competition Among Male Coalitions.” Evolution and Human Behavior 23 (6): 437–442. Waytz, Adam, and Liane Young. 2011. “The Group-Member Mind Trade-Off.” Psychological Science 22 (12) (December 8): 1–9. doi:10.1177/0956797611423546. Wendt, A. E. 1987. “The Agent-Structure Problem in International-Relations Theory.” International Organization 41 (3): 335–370. Williams, George C. 1966. Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought. Princeton, N.J.: Princeton University Press. Wilson, D.S., and E. Sober. 1994. “Reintroducing Group Selection to the Human Behavioral Sciences.” Behavioral and Brain Sciences 17 (4): 585–607. Wilson, Edward O. 1980. Sociobiology. Cambridge, Mass.: Belknap Press of Harvard University Press.

111 ———. 2000. Sociobiology : the New Synthesis. Cambridge, Mass.: Belknap Press of Harvard University Press. Wilson, M, and M Daly. 2002. “An Evolutionary Psychological Perspective on the Modulation of Competitive Confrontation and Risk Taking.” Hormones. http://134.83.117.117/3518/PDF/PoundetalEvolutionaryPsychPerspective.pdf. Wrangham, Richard. 1999a. “Evolution of Coalitionary Killing.” Yearbook of Physical Anthropology 42: 1–30. ———. 1999b. “Is Military Incompetence Adaptive?” Evolution and Human Behavior 20 (1): 3–17. Wrangham, Richard, and Dale Peterson. 1996. Demonic Males: Apes and the Origins of Human Violence. Boston: Houghton Mifflin. Wrangham, Richard W, and Luke Glowacki. 2012. “Intergroup Aggression in Chimpanzees and War in Nomadic Hunter-Gatherers : Evaluating the Chimpanzee Model.” Human Nature (March 3). doi:10.1007/s12110-012-9132-1. http://www.ncbi.nlm.nih.gov/pubmed/22388773. Wright, Quincy. 1983. A Study of War, 2nd Edition. 2nd ed. University Of Chicago Press. Wright, Robert. 2000. NonZero : the Logic of Human Destiny. New York: Pantheon Books. http://www.loc.gov/catdir/bios/random059/99040859.html. Wynne-Edwards, V. C. 1967. Animal Dispersion in Relation to Social Behaviour. Hafner Publishing Company. Yamagishi, Toshio, and Nobuhiro Mifune. 2009. “Social Exchange and Solidarity: In- group Love or Out-group Hate?” Evolution and Human Behavior 30 (4) (July): 229–237. doi:10.1016/j.evolhumbehav.2009.02.004. Yamagishi, Toshio, Shigehito Tanida, Rie Mashima, Eri Shimoma, and Satoshi Kanazawa. 2003. “You Can Judge A Book by Its Cover: Evidence That Cheaters May Look Different From Cooperators.” Evolution and Human Behavior 24 (4): 290–301.

112

CHAPTER TWO: TWO STUDIES

The Argument, Revisited

The introduction reviewed and evaluated the evidence for warfare in evolutionary history. I argued that although archaeological evidence alone is currently indeterminate, there is sufficient evidence from this and other fields of research to expect that coalitional violence has been an evolutionarily recurrent selection pressure faced by our species. In chapter 1, I introduced evolutionary psychology, which is an approach for understanding the design of the brain in the light of knowledge of ancestral selection pressures. The link between deep evolutionary time and modern behavior is the psychological adaptation; thus, if coalitional violence has constituted an adaptive problem for our species, then indeed evidence of this fact must lie within our modern skulls. Therefore, the main consideration of adaptationists, and my concern here, is the functional fit between ancestral selection pressures and resultant adaptations for social behavior.

Drawing upon direct and indirect evidence of ancestral environments, and combined with task analyses that investigate the features that adaptations must logically contain if they are built by natural selection for specific selection pressures, evolutionary psychologists have outlined the “risk contract of war,” which details the psychological conditions that must be satisfied in order for the initiation of coalitional violence to occur.

The risk contract is comprised of two distinct sets of adaptive problems, which have

113 likely resulted in adaptations that must: 1) regulate one’s own level of participation in coalitional aggression, and; 2) motivate enforcement of the risk contract on others through, for example, the tools of labor recruitment such as punishment and reward.

When, in a given conflict, these two components of the risk contract are satisfied – resulting in sufficient participation and enforcement – the initiation of coalitional violence can occur.

Coalitional violence represents a subset of collective action, and the risk contract outlines the psychological conditions that must hold in order for coalitional violence to be feasible. However, to the extent that different types of coalitional violence have constituted distinct selection pressures, the fulfillment of the risk contract may pose distinct challenges. I have argued that offensive and defensive coalitional aggression represent separate adaptive problems, such that adaptations that govern the risk contract operate differently in these two domains. For example, adaptations for participation in coalitional aggression in general must assess, inter alia, the value of the expected benefit to be achieved from group action.17 However, offensive and defensive warfare have tended to confer benefits that differ in structure: whereas the benefits of successful defense against intruders confer gains to the entire group and are thus public, successful offensive coalitional aggression is characterized more often by the acquisition of resources that can be privatized among the participants.

In addition, to the extent that the adaptive problems that warfare represents have posed distinct fitness costs and benefits on each sex, it is also likely that sex differences

17 This is a useful point at which to remind readers that the assessment of an environmental cue by a psychological adaptation is not necessarily a computation that happens consciously. Thus, although adaptations for warfare must consider the value of prospective gain, this is not the same as saying that individuals consciously weigh the fitness consequences of a range of goals to be achieved in warfare. Indeed, it is likely the opposite. As just one example, see Ginges and Atran (2011).

114 exist in the operation of these systems. Findings along these lines suggest that the overall behavior-regulatory pattern observed in this dissertation cannot be accounted for by aspects of the “institutional environment” alone, or more generally by rational deliberation, since there is no obvious reason how such approaches would arrive at the specific sex differences predicted and found below.

The hypotheses to be tested are the following:

H1: In defense, willingness to participate will be triggered by expectations of group benefit, even controlling for expectations of personal benefit;

H2: In offense, willingness to participate will be triggered by expectations of personal benefit, even controlling for expectations of group benefit;

H3: Males will be more willing than females to participate in both offensive and defensive coalitional aggression;

H4: Males will expect greater benefit than females from offensive coalitional aggression;

H5: There will be no sex difference in expected benefit from defensive coalitional aggression;

H6: In defense, but not in offense, punitive sentiment toward non-participants will be triggered by one’s willingness to participate;

115 Study 1

I tested these hypotheses by running an experiment-based survey in the spring of

2007. The subject population consisted of 195 undergraduate students (83 female) at the

University of California, Santa Barbara, mostly political science majors between the ages of 18 and 39. The survey presented both an offensive and defensive scenario. Each subject read both scenarios, and the order in which the scenarios were presented was counterbalanced across subjects to minimize order effects.

This experiment-based survey is adapted from and expands upon an earlier survey conducted by Price et al. (2000); however, in our study the scenarios are fully reworked and new questions are added.18 The survey design in Price et al. (2000), while not focused on examining separate psychologies of offense and defense, nevertheless tested for this and found no supportive evidence. I believe this is at least partly because their offensive scenario depicted retaliatory action against a foreign country, which could easily have triggered defensive rather than offensive psychology. Indeed, as I explore in the discussion section below, it is often difficult to distinguish between offensive and defensive aggression, and there are good reasons why people should self-deceive in order to misrepresent offensive action as defensive to allies and recruits, both potential and actual. However, the phenomenological difficulty of distinguishing between offense and defense is not evidence enough on its own to argue that there is no effective distinction between the two types of aggression psychologically. This subjective ambiguity is instead, I believe, at least in part the product of the complex relationship between the two

18 Special thanks to Leda Cosmides and John Tooby

116 psychologies, rather than evidence of the absence of a distinction. I include the survey design in the appendix.

In Price et al. (2000), subjects read the following offensive and defensive vignettes:

Offense: Imagine that a few years from now, several oil-rich Middle Eastern countries get together and decide that to increase profits, they will dramatically raise the price of their oil. This price increase devastates US industry and causes high inflation in the USA. US gas prices triple, and several US oil companies go bankrupt. After talks with these Middle Eastern countries fail, the USA declares war on them. But war was unexpected, so the USA has allowed its army to get relatively small, and it must start drafting US citizens in order to have a chance of victory. How would you feel about this war?

Defense: Imagine that a few years from now, the Russian people elect a new, warlike dictator who claims that Alaska should rightfully belong to Russia. Under this dictator, Russia invades and conquers Alaska. There is good evidence that Russia also intends to conquer more US territory, in addition to Alaska. In response to this invasion, the USA declares war on Russia. But because this war was unexpected, the USA has allowed its army to get relatively small, and it must start drafting US citizens in order to have a chance of winning this war. How would you feel about this war?

Two major changes were made to these vignettes. First, both scenarios are rewritten in a nomadic context 1000 years ago. This is done in order to “de-couple,” as best as possible, modern views toward war in the context of nation-states and our beliefs regarding those states from the operation of the psychological adaptations themselves.

For example, the above vignettes invoked the prospect of war with Russia and with

Middle Eastern countries, all of which represent culturally significant out-groups with unique history of interaction that is likely to (understandably) affect the calibration of psychological adaptations in confounding ways (e.g. inspiring especially high motivation to engage in violence against a Russian invasion, as well as increased susceptibility to

117 outrage in the offensive scenario given the intersection of oil and politics in the Middle

East).

Second, the offense scenario specifically was conceptually reorganized in order to make sure that it was clear that the question is whether to initiate unprovoked aggression.

In the offense scenario utilized by Price et al. (2001), it is possible that subjects interpreted the scenario as one of retaliation for price-hikes, especially since this action has clear and direct consequences on in-group welfare (e.g. devastation of US industry).

In that instance, it is likely that a defense psychology would have been activated, instead of an offense psychology. In sum, I utilized vignettes that engaged subjects in hypothetical scenarios, and the offense scenario specifically was reworked in order to ensure that the decision was over whether to initiate unprovoked aggression against an out-group. It is worth noting that the use of hypothetical scenarios for exactly this purpose in experimental designs is increasingly common (Mitchell et al. 2003). The new scenarios are:

Defense: Imagine that you and your friends and kinsmen are members of a nomadic horse-riding people, the Pathans, in the year 1050. You and your group are tough and strong, but your life is meager. You cook over dung-fires, drink fermented mare’s milk, sleep in yurts under skins, and freeze every winter. Your ancestral territory is on the dry steppe, but you also border on the prosperous Chinese province of Sinkiang. You have heard that the governor of the province is ambitious, and intends to extend his control into your territory. If you lose your grasslands, you and your family will have nothing. The governor has assembled a war party, which has launched a series of nighttime raids on your people. Some of your women have been kidnapped and some of your men were killed. You hear rumors that another raid is going to happen tonight. You and your friends and fellow tribesmen begin to discuss whether you should form a war party to repel the raiders.

118 Offense: Imagine that you and your friends and kinsmen are members of a nomadic horse-riding people, the Pathans, in the year 1050. You and your group are tough and strong, but your life is meager. You cook over dung-fires, drink fermented mare’s milk, sleep in yurts under skins, and freeze every winter. Your ancestral territory is on the dry steppe, but you also border on the prosperous Chinese province of Sinkiang. You sometimes enter these cities to trade, but the Chinese men and women laugh at your poor clothes, your dirt, and your lack of refinement. You do notice that the men are short, weak, and cowardly, despite the fact that they give themselves airs. The women are also beautiful, and dressed in the best silks. You and your friends have heard that the Mongols to the North had attacked and taken over several cities, and are now wealthy, powerful, and have substantial harems. The Chinese troops had run like rabbits. You and your friends and fellow tribesmen begin to discuss whether you should form a war party to seize one of the neighboring cities.

Immediately following each scenario, subjects were asked a series of questions relating to their willingness to participate, the extent to which they personally expected to benefit, anticipated benefit to the group, expectations that others would join, desire to punish free riders, and desire to reward participants. Answers to each question were self- reported on a 7-point Likert scale, from strongly disagree (1) to strongly agree (7). An identical battery of questions followed each scenario, with minor modifications where contextually appropriate.

119 Results and Discussion

H1 and H2: Willingness to participate (“I would be willing to participate in this war effort”) is predicted by expected benefit to the group (“If my group succeeded…it would benefit us as a group”) in defense (H1), but by expected personal benefit (If my group succeeded…it would benefit me personally”) in offense (H2).

H1 and H2 are expected if defense confers more of a public good, while the benefits of offense tend to be subject to privatization. As reported in Graph 1 below, in defense, willingness to participate was indeed predicted by the perceived benefit to the group (b = .34, p < .001), even when controlling for perceived benefit to self. In contrast, benefit to self predicted no unique variance in one’s willingness to participate.

In offense, however, willingness to participate was predicted by expected benefit to self (b = .43, p < .001), even when controlling for expected benefit to the group.

Expected benefit to group did not independently predict willingness to participate, as the results in Graph 1 demonstrate.

The circumstances that trigger one’s willingness to participate in coalitional aggression are different for offensive and defensive scenarios. Whereas expected group benefit independently predicts willingness to participate in the defensive scenario, it does not for the offensive one. Similarly, expected benefit to self independently predicts willingness to participate for the offensive scenario, but not for the defensive one. This difference was found despite the fact that precisely the same subjects provided responses to both scenarios. These findings confirm the domain-specific operation of these processing systems, which is visually illustrated in Graph 1 below.

120

Graph 1: Domain-specificity of Willingness to Participate

Note: Values along y-axis represent non-standardized OLS multiple regression coefficients. Dependent variable is willingness to participate, independent variables are perceived benefit to self, and perceived benefit to the group of successful coalitional aggression. *** = p < .001; n.s. = not significant at .05 level.

H3: Males are more willing than females to participate in both offensive and defensive aggression.

I conducted a two-sample t-test for difference in means, assuming unequal variances, between male and female averages on each of the four measures of willingness to participate: “I would be willing to participate in this war effort”; “If I chose to participate in this war effort, I would want to contribute a lot to help it succeed”; “I would be willing to sacrifice a lot to help this war effort succeed”; “If I chose to participate, I would be willing to risk my life” (Offense: α = .87; Defense: α = .90). As predicted,

Tables 1 and 2 demonstrate greater relative levels of willingness to participate, contribute, sacrifice a lot, and risk one’s life by males in both offense and defense.

121

Table 1: Sex Differences in Willingness to Participate - DEFENSE Defense Male Female Effect Size (r)* Average Average (p-value) Participate 6.19 5.63 r = .23 (sd = 1.13) (sd = 1.46) (p < .01) Contribute 6.33 6.00 r = .15 (sd = 1.09) (sd = 1.12) (p < .05) Sacrifice 6.08 5.45 r = .24 (sd = 1.31) (sd = 1.38) (p = .0014) Risk Life 5.78 4.94 r = .27 (sd = 1.47) (sd = 1.80) (p < .001) Note: Two-sample, two-tailed t-test for differences in means, assuming unequal variances. N = 112 male, 83 female. *Effect size calculated as r = √[t2 / (t2+df)].

Table 2: Sex Differences in Willingness to Participate - OFFENSE Offense Male Female Effect Size Average Average (p-value) Participate 4.43 3.63 r = .23 (sd = 1.84) (sd = 1.66) (p = .002) Contribute 5.23 4.30 r = .27 (sd = 1.73) (sd = 1.80) (p < .001) Sacrifice 4.24 3.46 r = .21 (sd = 1.86) (sd = 1.86) (p = .004) Risk Life 3.94 2.78 r = .30 (sd = 1.98) (sd = 1.83) (p < .001) Note: Two-sample, two-tailed t-test for differences in means, assuming unequal variances. N = 112 male, 83 female.

H4 and H5: Males perceive greater expected benefit than females in offensive, but not in defensive, coalitional aggression.

Three measures of perceived benefit were used: “If my group succeeded in repelling the invaders/seizing a city, I would feel very happy”; “If my group succeeded in repelling the invaders/seizing a city, it would benefit me personally”; and “If my group succeeded in repelling the invaders/seizing a city, it would benefit us as a group”

(Offense: α = .89; Defense: α = .77). Graphs 2 and 3 below present the results for hypotheses 4 and 5. As predicted, there were no sex differences in expected benefit in

122 defense; however in the offensive scenario, men reported that success in the offensive scenario would make them happier, benefit them more personally, and benefit their group more than women did.

Graph 2: Sex Differences in Expected Benefits - DEFENSE

Note for Graphs 2 and 3: Two-sample, two-tailed t-test for differences in means, assuming equal variances. N = 112 male, 83 female. Y-axis represents mean scores on 1-7 Likert Scale. * = p < .05; ** = p < .01. Reported p-values next to male averages correspond to the statistical significance of the differences of means between male and female averages for each variable.

123

Graph 3: Sex Differences in Expected Benefits - OFFENSE

H6: Willingness to participate will track punitive sentiment (“If one of my fellow tribesmen did not participate, I’d think they should be punished”) in defense but not in offense.

If benefits are privatized in offense, then there is no adverse fitness differential between nonparticipants and participants that punitive sentiment would seek to reverse. I found that, when controlling for perceived benefit to self, willingness to participate predicted punitive sentiment in both defensive (b = .51, p < .001) and offensive (b = .40, p < .001) scenarios, rather than only in defense, as predicted. In short, the relationship found by Price et al. (2002) was replicated: punitive sentiment was independently predicted by willingness to participate.

124 H7: Expected benefit to self should predict sentiments for rewarding participants in defense, but willingness to participate should predict reward sentiment (“If one of my fellow tribesmen did participate, I’d think they should be rewarded”) in offense.

In offense, nonparticipants who reward participants but who (necessarily) receive no benefit would be at a fitness disadvantage. Only participants would have an interest in rewarding other participants, to the extent it solves the labor recruitment problem.

The results support the hypothesis in defense: expected benefit to self predicted reward sentiment in defense (b = .36, p < .001), even when controlling for willingness to participate. However, there was a weak effect of willingness to participate on motivations to reward participants in the defensive scenario (b = .22, p < .05)

In offense, both benefit to self (b = .31, p < .001) and willingness to participate (b

= .50, p < .001) independently predicted reward sentiment. One possible explanation for this finding derives from the earlier discussion of the distinction between defense and offense as public v. private goods. To the extent that the benefits from successful offense are mostly private goods, but include a non-negligible amount of public goods (e.g. status, deterrence, etc.), it follows that benefit to self should predict reward sentiment in offense as in defense. For example, if there are at least some public benefits that accrue as a consequence of offensive coalitional aggression, then it follows that there may some individuals who 1) expect the benefits of action will make them better off, either directly or through benefits that inhere to the group, and; 2) for some reason may wish to participate but are not able to (e.g. sickness, injury, etc). In these instances, as in defense, the (real or imagined) existence of a public good severs the link between participation and expected personal benefit, such that even non-participants can expect benefits, and

125 when they do, should act to reward participants to the extent that the value of their donation does not outweigh their on average gain. It is noteworthy, however, that willingness to participate strongly and independently predicted motivations to reward participants only in offense, even when controlling for expected benefit, as predicted.

Discussion

Hypotheses 1 and 2 were fully supported by the data. One’s willingness to participate in coalitional aggression was conditional upon the expected benefit of group action. In offense, the greater the expectation of personal benefit, the more likely subjects were willing to participate, independent of expectations of group benefit. But the reverse was not true: expectation of group benefit was not an independent predictor of willingness to participate in offensive scenarios.

In defense, the reverse was true: group benefit predicted motivations to participate, independent of one’s expectations of personal benefit. But expectations of person benefit did not independently predict motivations to participate in defense.

Hypothesis 3–that men would be more willing to participate than women—was also supported by the data. However, these questions measured willingness to participate in ways that emphasized physically joining the war effort. There is evidence that sex differences in aggression are pronounced especially on measures of direct participation in aggression (Van Vugt 2009; McDonald, Navarrete, and Van Vugt 2012). I expect that if questions were asked more broadly about willingness to contribute to the war effort in more general or indirect ways (e.g. providing material support) that sex differences would be less striking or even disappear – but only in defense. This may partly explain the

126 smaller sex difference on the measure of one’s willingness to contribute in defense. In contrast, I expect sex differences to remain statistically significant in offense, even on measures of less direct pathways of support toward the war effort. Although this was not tested in either study 1 or study 2, future research could easily test this conjecture.

Hypotheses 4 and 5 were also confirmed; men expect greater benefits than women from offensive aggression but not from defensive aggression.

Hypotheses 6 was only partially supported. I predicted that punitive sentiment toward non-participants would be triggered by willingness to participate in defense, and this was supported. But I also predicted that willingness to participate would fail to predict punitive sentiments in the offensive scenario. For example, no matter how willing you are to participate in offensive aggression, nonparticipants are not free riders and there is no fitness differential between you: nonparticipants do not pay the cost of participation, but they also do not benefit, as they would in defense. The question, therefore, is the following: If non-participants in offense are not encoded by the mind as

“free riders,” then why would participants seek to punish them? There are two possible explanations for this.

One explanation is that successful offensive coalitional aggression confers many types of benefits, some of which are less “public” than others. Indeed, it is more likely the case that defensive and offensive coalitional aggression both confer some types of public goods when successful (e.g. elevated status, deterrence, etc.), but offensive coalitional aggression comes with the added premium of privatized benefits to the

127 participants.19 Thus, this study does not sufficiently distinguish between offense and defense as privatized vs. public good, respectively, in order to make a clear prediction about punitive sentiment. However, the validation of the previous hypotheses based on this distinction suggests that the distinction, however imperfect, may prove useful.

A second explanation accepts the logic that if nonparticipants in the offensive scenario are not psychologically encoded as “free riders,” then participants should not seek to punish them; however, it adds the consideration that labor recruitment may be one function of punitive sentiment. The above hypotheses assumed that punishment is designed only for eliminating adverse fitness differentials (Price, Cosmides, and Tooby

2002). It could be the case, however, at least in offense, that punitive sentiment toward nonparticipants serves the additional function of labor recruitment, especially due to the greater complexity of the labor recruitment problem in offense as discussed in chapter 1.

The second round of experimentation will test this conjecture more directly. For now, one additional piece of evidence we can examine is whether the absolute levels of punitive sentiment toward non-participants vary by domain. For example, a paired t-test for differences in means reveals that both men and women were more likely to experience punitive sentiment toward non-participants in defense than in offense (males, r = .68, females, r = .60; both p-values < .001). This outcome flows directly from the logic of the public/private goods distinction between offense and defense, suggesting that this distinction may not be as problematic as previously considered. Nevertheless, these data still do not help us to know why the motivation to punish nonparticipants is linked

19 It may be more appropriate to consider these types of benefits as club goods – excludible and nonrival – rather than, or in addition to private goods.

128 with one’s level of participation in both domains. This will be a question addressed in the second study.

Lastly, hypothesis 7 was also supported (reward sentiment is predicted by expected benefit to self in defense, but by willingness to participate in offense), but with the additional finding that reward sentiment is also independently predicted by expected benefit in offense. In other words, in defense, only expected benefit and not willingness to participate, predicts reward sentiment toward non-participants. But in offense, both expected benefit and willingness to participate independently predict reward sentiment.

Study 2

Although the hypotheses were mostly supported in Study 1, the most significant question remaining is the role of punitive sentiment toward non-participants in coalitional aggression. I found that, for both offense and defense, punitive sentiment toward non- participants was best predicted by one’s willingness to participate, despite the fact that I expected that this relationship would hold only in defense and not in offense. Again, if non-participants in offense are not free riders, then punitive sentiment – as an anti-free riding mechanism – should not be triggered by cues in this domain indicating non- participation by others, regardless of one’s participation level. This hypothesis was formed on the assumption that the exclusive function of punitive sentiment in this domain is to eliminate the adverse fitness consequences generated by free riders specifically.

Therefore, in this study, I will adjust this assumption to allow that punitive sentiment may also serve the function of labor recruitment. In other words, the psychological adaptations that regulate the expression of punitive sentiment may be sensitive not only

129 to information the mind receives regarding whether one has participated (in order to eliminate free riders), but should also be sensitive to information regarding how much labor is necessary and available for the task (in order to allocate punishment for the sake of incentivizing participation). The second study tests the extent to which punitive sentiment serves not only the function of eliminating free riders, but also the function of recruiting labor.

In order to understand the effect of perceived labor levels on punitive sentiment toward non-participants, we must consider how these cues might be interpreted differently in the two domains of offense and defense, which requires a return to fundamentals. I have previously emphasized the ancestral importance of relative numbers for coalitional aggression. In both humans and chimpanzees, offensive raids are often conducted only once numerical superiority can be established; chimpanzees tend to engage their enemy once the ratio of attackers-to-victim reaches three-to-one (Manson and Wrangham 1991). However, in the case of chimpanzee raids, the central fitness outcome of such raids is territorial and greater relative numerical superiority, both of which are public goods. Expanded territory combined with fewer antagonists in the ranks of enemy groups is a benefit that inheres to the group at large and is not privatized among the few raiding chimpanzees. Thus, in chimpanzee coalitional aggression, the benefits from defensive and offensive raids are largely public.

The benefits of human offensive raids also include territory and greater relative numbers. However, humans are particularly good at monopolizing material resources, which means that plunder becomes a unique and significant benefit in human offensive raiding. This establishes a distinction between offense and defense in humans that does

130 not exist in chimpanzee coalitional aggression. For example, as discussed above, the benefits of successful defensive coalitional aggression are public. In this environment, punitive sentiment toward non-participants should remain high because the fitness relevant game theoretic structure of this situation is one in which non-participants, as free riders, generate fitness consequences for evolved strategies that pay the cost of participating but do not punish free riding. Furthermore, given that the benefits of defense are public, every additional unit of labor added to the effort only further decreases the cost:benefit ratio faced by each participating individual, meaning that in defense, more labor is always better. In defense, therefore, it should be the case that even if punitive sentiment toward non-participants is an anti-free rider device and a labor recruitment device, punitive sentiment should always be high among participants toward non-participants, because more labor only serves to reduce costs in an environment in which benefits are public (H8).20

In offense, however, additional units of labor to the collective action do not reduce the cost:benefit ratio experienced by participants. When labor is insufficient for the successful execution of offensive coalitional aggression, participants (initiators) have a unique and powerful interest in recruiting labor since they have identified that the initiation of offensive aggression would benefit them. However, when labor is sufficient for the execution of offensive coalitional aggression, each additional unit of labor actually increases the cost:benefit ratio given that the benefits are privatized and

20 I do not claim that this will be true of any collective action that yields public goods; rather, this may be particularly true of collective actions that involve violence, since, as noted in chapter 1, one of the hallmarks of successful coalitional violence is a combination of low risk and a high probability of success.

131 materially fixed.21 For example, if there are 50 units of resources to be plundered from out-group X, and 10 individuals are required in order to surprise and overwhelm outgroup X and steal away with those resources, then each individual potentially receives 5 units as reward (plunder) on average.22 However, if 15 more individuals are added to the effort, then the cost:benefit ratio is effected in the following way. On the cost side, the fact that the raiders have more than doubled in size dramatically reduces the risk to which each is exposed, while also dramatically increasing the probability of success. However, on the benefit side, with 25 total individuals participating in the raid, each individual now only receives 2 resource units on average.

Therefore, if one’s willingness to participate in offensive aggression is tied to one’s personal (not group) expectation of benefit (as confirmed in Study 1), then it should be the case that there is a quadratic relationship between one’s willingness to participate and perceived labor levels, instead of the monotonic relationship predicted in defense. In other words, at very low labor levels, it may make little sense to invest the time and effort necessary to build a coalition; however, as labor levels increase, it becomes increasingly worthwhile to engage in the endeavor until a critical threshold is reached, after which point the coalition members experience diminishing marginal returns per capita as more participants join.23 It is because of this dynamic that punitive sentiment, if it is designed to recruit labor, should be heightened in offense only when labor is insufficient, and less

21 This is compounded by the fact that each additional member added to the coalition increases the cognitive complexity of the task of coalitional coordination (Tooby, Cosmides, and Price 2006). 22 There are many caveats here. For example, individuals may share these rewards with others upon returning to the group; however, even in this case, this sharing is likely to occur non-randomly. Specifically, sharing is likely to occur within kin and alliance networks and not within the group as a whole. In any event, the acquisition of the resource by the individual only enhances that individual’s inclusive fitness, regardless of whether it is ultimately shared with others. 23 Importantly, this dynamic applies with special force in the context of the initiation of raids, rather than the decision to engage in pitched battles.

132 so when labor is perceived as sufficient (H9).24 However, in defense, punitive sentiment toward non-participants should remain high regardless of perceived labor levels.

It is important to remember that, under this revised view of punitive sentiment, one’s willingness to participate should trigger punitive sentiment in both offense and in defense (as was observed in study 1), but for different reasons. In defense, it is because of the asymptotically decreasing cost:benefit ratio faced by group members (more labor is always better, but with decreasing marginal returns at very high levels); in offense, it is because the labor recruitment problem must be tailored to an optimum labor level. To reiterate, in humans such mechanisms should operate to according to distinct rules: In defense, more is always better; in offense, coalition size should be especially sensitive to the balance between shared risk and personal benefit.

As before, it is likely the case that the selection pressures faced by each sex are unique and that adaptations that regulate behavior and motivation operate differently in males than they do in females. As discussed previously, males are more willing to participate in both offensive and defensive aggression. Given that coalitional aggression has ancestrally – for both humans and chimpanzees – been largely a male endeavor, it is likely that the effects of perceived labor levels on punitive sentiment will be unique to each sex. In study 1, males were more willing to participate in both offense and defense; however, I did note that in defense, this sex difference is likely most prominent on measures of physical participation, and less prominent on measures of less direct forms of contribution and support.

24 Again, given the previous footnote, this should be especially true when labor levels fall slightly short of levels that are perceived to be necessary for success.

133 Based on this analysis, I expect that in defense, the willingness of males to participate will be insensitive to perceived labor levels (H10), while the willingness of females to participate will be increased by the perception that labor is insufficient

(H14).25 In other words, the prospect of foreign incursion will be sufficient to trigger a high level of participation from males, regardless of perceived labor levels, but females are more likely to physically engage when the stakes are greater.26 For this same reason, it is likely that females will be especially punitive toward non-participants in defense when labor is insufficient; conversely, in offense, we would expect females to refrain from engaging in labor recruitment for offense in the form of punitive sentiment toward non-participants (H12 and H13).

We observed in study 1 that in offense, males are more willing than females to participate, and males also expect greater benefit from offense than females. However, the preceding theoretical discussion suggests that too much labor in offense can backfire.

Consequently, I expect that when males perceive that labor is sufficient for the task, they will be less likely to want to join offensive aggression; when perceived labor levels are nearly, but not quite sufficient for the task, males will be more likely to want to join the campaign (H11). I expect that females will remain uninterested in joining offensive

25 The “insensitivity” to labor levels of male willingness to participate in defense should be qualified. In fact, there is a dual selection pressure in the context of participation in public defense. On the one hand, the cost-benefit fitness analysis described above suggests that more labor is always better, particularly in the context of defense of kin-based groups. On the other hand, however, given that the structure of the problem is of course a public good, there should be contravening selection pressure to free ride. It may be the case that the emotion of shame or guilt is an emotion that participants seek to manipulate in non- participants for the sake of mitigating the psychological incentives to free ride. However, future research must test this conjecture. 26 The caveat here is that at extremely low labor levels (e.g. everyone runs for the hills) willingness to participate will indeed erode, regardless of domain of aggression, and regardless of the quality of the benefit in question.

134 coalitional aggression, regardless of labor levels (H15). Given these considerations, I offer the following hypotheses:

Male Subjects, Punitive Sentiment:

H8: In defense, punitive sentiment toward non-participants will be insensitive to perceived labor conditions.

H9: In offense, punitive sentiment toward non-participants will be higher when labor is perceived as insufficient for the task than when labor is perceived as sufficient, and punitive sentiment (as labor recruiting device) will be directed toward males and not females.

Willingness to Participate:

H10: In defense, willingness to participate will remain high independent of perceived labor conditions.

H11: In offense, willingness to participate will be higher when labor is perceived to be insufficient (yet near levels necessary to succeed).

Female Subjects, Punitive Sentiment:

H12: In defense, punitive sentiment toward non-participants will be greater when labor is insufficient than when it is sufficient

H13: In offense, punitive sentiment toward non-participation will remain low regardless of perceived labor levels.

Willingness to Participate:

H14: In defense, willingness to participate will be greater when perceived labor levels are insufficient than when they are perceived as sufficient.

H15: In offense, willingness to participate will be insensitive to perceived labor levels.

135 Design

I tested the second round of hypotheses by incorporating a between-subjects manipulation into the previous design. 188 undergraduate subjects participated in this study, mostly psychology majors, of which 74 were men and 114 were women. All subjects read the same offense and defense vignettes, followed by the same survey questions soliciting willingness to participate, punitive sentiment, etc. The new between- subjects manipulation altered the design in the following way. Although all subjects read an offense and a defense vignette, each subject read vignettes in which either: 1) success was unlikely if more people do not join, or; 2) success was likely even if more people do not join. This was accomplished by adding a couple of sentences to the end of each vignette describing one or the other labor condition. For example, half of the subjects received a survey in which both vignettes (offense and defense) described coalitional aggression that was unlikely to succeed if more people did not join, while the other half received a survey in which both vignettes (offense and defense) described coalitional aggression that would probably succeed even if more people did not join. The manipulations added to the end of the vignettes are:

136 Defense: Labor Insufficient: Although a large war party can be successful against the invaders, if many of the reluctant people do not join the war party, it current size may be insufficient and therefore unlikely to repel the invaders. This may result in your tribe’s collective defeat at the hands of the foreigners.

Labor Sufficient: Although many are reluctant to join the war party, the current amount of committed volunteers should be enough to repel the invaders.

Offense: Labor Insufficient: Although a large war party can be successful in seizing a city, if many of the reluctant people do not join the war effort, your war party, at its current size, will be unlikely to seize a city. Instead, it will probably be repelled by the foreigners and be forced to return empty-handed.

Labor Sufficient: Although some are reluctant, the current amount of eager volunteers should be enough to seize a city, even if the reluctant people do not join the war party.

Results

To begin, it may be useful to observe the direct effects of the between-subjects manipulation of labor levels to determine whether they had the anticipated effect. For example, given the repeated discussion above in which greater numbers translates in to greater prospects for success, it should be the case that where labor is insufficient, subjects rate the probability of success lower than they do when they perceive labor to be sufficient. I take this as a manipulation check to observe whether the labor manipulation is operating in the expected way. Graphs 4 and 5 present interesting results.

137 Graphs 4 and 5

138 Graphs 4 and 5 graphically depict the relationship between sex and labor condition upon subjects’ appraisal of the probability of success. The y-axis represents a reported probability of success on a 0-100% scale. In offense, greater labor levels lead to a greater reported probability of success for both males and females (males: r = .28, p =

.01; females: r = .33, p < .001, respectively).27 However, in defense there is a surprising interaction; that is, the effect of labor condition upon the subjective probability of success depends on the sex of the subject. Greater perceived labor levels translated into a higher subjective probability of success for males (r = .36, p < .001), but females’ reported probability of success remained entirely unaffected by perceived labor levels (r = .04, p =

.69). This surprising result is best discussed alongside a further anomaly relating to sex differences below; therefore, I postpone discussion of these results until then. I present the results relating to the hypotheses in the following two clusters. First, I discuss results pertaining to the hypotheses about punitive sentiment; second, I discuss results pertaining to the hypotheses about willingness to participate.

PUNITIVE SENTIMENT: MALES

H8: In defense, male punitive sentiment toward male and female non-participants will be insensitive to perceived labor conditions.

H9: In offense, male punitive sentiment toward non-participants will be higher when labor is perceived as insufficient for the task than when labor is perceived as sufficient, and punitive sentiment (as labor recruiting device) will be directed toward males and not females.

27 Results from t-test for differences in means assuming unequal variances

139 Tables 3 and 4 below contain results relating to H8 and H9. Results are obtained through t-tests for differences in means computed using R programming software (v.

2.15.0). I also computed OLS multiple regression models that included the interaction terms as an independent check on the results and achieved identical results. In defense

(H8), male punitive sentiment toward both male and female non-participants was NOT affected by perceived labor levels (toward males: r = .14, p = .22; toward females: r =

.12, p = .29). In offense (H9), male punitive sentiment toward non-participating males was affected by perceived labor levels (r = .26, p = .02), but male punitive sentiment toward non-participating females was NOT affected by perceived labor levels (r = .14, p

= .27). Both hypotheses 8 and 9 are thus confirmed.

PUNITIVE SENTIMENT: FEMALES

H12: In defense, female punitive sentiment toward male and female non- participants will be greater when labor is insufficient than when it is sufficient.

H13: In offense, female punitive sentiment toward male and female non- participation will remain low regardless of perceived labor levels.

Tables 5 and 6 below contain results relating to H12 and H13. In defense (H12), female punitive sentiment toward both male and female non-participants was greater when labor was insufficient (toward males: r = .22, p = .02; toward females: r = .24, p =

.01). However, in offense (H13), contrary to prediction, female punitive sentiment toward non-participants was greater toward males, but not females, when labor was insufficient (toward males: r = .18, p = .05; toward females: r = .01, p = .26). Thus, H12 is supported, but H13 is only partially supported.

140

Table 3 Male Punitive Sentiment Toward Non-Participant Males

Male Subjects Only Offense Defense Labor Sufficient 1.89 2.84 Mean (sd) (sd = 1.17) (sd = 1.71) Labor Insufficient 2.76 3.35 Mean (sd) (sd = 1.95) (sd = 1.87) Effect Size (r)* r = .26 r = .14 (p-value) (p = .02) (p = .22) *Effect size calculated as r = √[t2 / (t2+df)].

Table 4 Male Punitive Sentiment Toward Non-Participant Females

Male Subjects Only Offense Defense Labor Sufficient 1.43 1.89 Mean (sd) (sd = .77) (sd = 1.05) Labor Insufficient 1.68 2.19 Mean (sd) (sd = 1.08) (sd = 1.35) Effect Size (r) r = .14 r = .12 (p-value) (p = .27) (p = .29)

Table 5 Female Punitive Sentiment Toward Non-Participant Males

Female Subjects Only Offense Defense Labor Sufficient 1.88 2.59 Mean (sd) (sd = 1.18) (sd = 1.40) Labor Insufficient 2.34 3.29 Mean (sd) (sd = 1.40) (sd = 1.75) Effect Size (r) r = .18 r = .22 (p-value) (p = .05) (p = .02)

Table 6 Female Punitive Sentiment Toward Non-Participant Females

Female Subjects Only Offense Defense Labor Sufficient 1.70 2.02 Mean (sd) (sd = 1.06) (sd = 1.07) Labor Insufficient 1.95 2.64 Mean (sd) (sd = 1.29) (sd = 1.56) Effect Size (r) r = .01 r = .24 (p-value) (p = .26) (p = .01)

141

Willingness to Participate (H10, H11 & H14, H15). Graphs 5 and 6 below graphically represent the relationship between sex and labor condition for both offense and defense upon one’s willingness to participate. Interactions are generated using OLS multiple regression computed with R programming software. All hypotheses are supported. I find that the willingness of men to participate in defense is insensitive to perceived labor labels in defense (H10), but willingness of men to participate in offense is greater when labor levels are perceived as insufficient for the task (H11).

Graphs 5 and 6

142

In offense, there is a statistically significant effect of labor condition on men (b =

.84, p = .04), but not women (b = -.17, p = .61). For defense, these effects are reversed: the effect of labor condition on women just misses significance (b = -.58, p = .07), but there is no such effect of labor condition on men in defense (b = .19, p = .63).

Discussion

Punitive sentiment in men. Given that defense is a public good, and given the consideration that more labor only reduces the cost:benefit fitness ratio, I predicted and observed that punitive sentiment by men toward non-participants would be unaffected by perceived labor levels in defense. This is due to the fact that it is almost always profitable to add more individuals in defensive coalitional aggression. In offense, however, punitive sentiment by men toward non-participants was greater when perceived

143 labor levels were insufficient for the task, and, as predicted, the effect of labor condition on the punitive sentiment of men toward non-participants was directed at men. In other words, when labor was insufficient for the task, men increased their punitive sentiment toward non-participating men, but not toward non-participating women (Tables 3 and 4).

Punitive sentiment in Women. The results regarding the punitive sentiment of women toward non-participants were slightly puzzling. I will start with defense and then discuss offense.

In defense, I predicted and found that punitive sentiment by women toward non- participants in defense was greater when labor was insufficient (H12). If it has been the case ancestrally, as it has been among modern hunter-gatherer groups (Van der Dennen

1995; Potts and Hayden 2008; Van Vugt 2009), that women are often captured and raped in war, then women will have a special interest in motivating participation when labor is insufficient; in contrast, when labor is sufficient, a woman loses nothing but gains a great deal by withholding punishment from males who do not participate, especially if those males are kin. Problematically, however, one could equally argue that her own kin and mates are better off the more men participate, because the cost to them is lower when there are more participants. There is a tension between selection in favor of withholding costly punishment when labor is sufficient, and selection in favor of costly punishment for the sake of motivating additional labor that could reduce the risk faced by participating kin. Future research should seek to investigate the effects of this dual selection pressure in mechanism design. It is likely that female punitive sentiment in defense may be tied greatly to variables such as the age, quantity, and sex of offspring.

144 One potential explanation for the surprising finding that female appraisals of the probability of success remained unaffected by labor levels in defense is the role of self- deception. We have seen that in defense, men have a general interest in participating and recruiting labor, which is independent of extant labor levels. In contrast, women have a conditional interest in participation and labor recruitment in defense (i.e. their interest in participation is greater when labor levels are lower), despite the fact that women appear generally pessimistic of their chances of victory. As mentioned above, women bear a unique cost in war, and it may be that pessimism is a form of negative illusion designed to compel male participation. Of course, these negative illusions find their analogue in positive illusions, or overconfidence, as discussed above. In this regard, it is noteworthy that men are more prone to overconfidence than women in conflict scenarios (Johnson et al. 2006; Johnson and Fowler 2011), and it may be the case that defense – the warfare domain most threatening to women – uniquely triggers this form of deception. Relatedly, it may also be the case that the sex difference in appraisal in the context of defense may be facilitated by differences in mood. For example, Lerner and Keltner (2001) found that anger facilitates risk-seeking and overconfidence, fear tends to facilitate risk-avoidance and pessimism. Unfortunately, these data do not allow me to test this explanation, but there is cause for further examination.

Moving forward to offense, I predicted that punitive sentiment by women toward non-participants would be insensitive to labor levels; in other words, the perception that labor was insufficient for the task would not trigger punitive sentiment by women toward non-participants (if this punitive sentiment is in part designed for labor recruitment). The assumption here is that females have no stake in a coalitional endeavor in which the

145 participants are largely, if not exclusively, male, and where the participants keep the spoils. The fitness consequences of expending effort for no gain are obviously negative.

However, I observed that punitive sentiment by women toward male (but not female) non-participants was greater when labor was insufficient (Tables 5 and 6). One possible explanation for this was mentioned in passing above; namely, although the benefits of offensive coalitional aggression are privatized among participants, those participants may share the spoils with others. To the extent that this sharing occurs preferentially toward one’s immediate family, the results in this study are no longer surprising; indeed, females should actively recruit labor when labor is insufficient, and these efforts should be directed at males.

Taken together, these findings lend support to the general hypothesis that punitive sentiment does indeed serve the additional function of labor recruitment, and that the design of this aspect of the labor recruitment mechanism operates differently in males and females. Furthermore, there is reason to believe that psychological adaptations designed to regulate participation, eliminate free-riding, and recruit labor operate in distinct ways depending on the domain of warfare. I also find evidence to support sex differences in the operation of these systems.

In the next chapter, I consider the strengths and weakness of the current design, discuss its contribution to existing research on the evolution of warfare and coalitional competition, and I investigate options for further study.

146

CHAPTER THREE: GENERAL DISCUSSION

I have argued that warfare – or more broadly, coalitional aggression – has constituted a set of evolutionarily recurrent selection pressures, such that it is likely that psychological adaptations exist as the product of natural selection for regulating behavior and motivation in this context. Thus, in the introductory chapter I reviewed theory and evidence relating to the existence, distribution, frequency, and intensity of coalitional aggression in human and primate evolutionary history. Although the direct and indirect evidentiary record is incomplete, I argued that there is sufficient evidence to test hypotheses regarding an evolved psychology of warfare given what is known or inferred about ancestral environments. Indeed, as previously mentioned, if such ancestral selection pressures existed, then evidence of this fact resides in the architecture of human psychology. This is because the functional structure of adaptations mirrors the selective pressures that gave rise to them. Therefore, following the adaptationist program, hypothesis formation is guided by expectation of the necessary fit between ancestral selection pressures and the behavior-regulatory design of evolved psychological mechanisms.

Applying this adaptationist framework led to the question: If there are psychological adaptations that regulate behavior in the context of warfare, and if these adaptations are facultative, then what are the conditions under which: 1) An individual should be motivated to participate in coalitional aggression, and 2) the participants are

147 able to successfully enforce each other’s participation? Thus, I outlined the “risk contract of war,” which represents the set of psychological conditions that must be fulfilled in order for coalitional aggression to be successfully initiated. As Tooby and Cosmides

(1988) point out, natural selection should favor a willingness to participate in coalitional aggression when, for example, the probability of success is great, there is a random distribution of risk among the participants, and a “fair” allocation of the benefits of victory. However, the benefits of victory, for example, may have been systematically different between certain types of warfare, namely, offense and defense. As a result, although the evaluation of expected benefit is an important cue that psychological adaptations should track in any instance of coalitional aggression, it is likely the case that this cue will have different effects on behavior and motivation in the two domains of warfare.

Thus, I hypothesized that offensive and defensive warfare represent two types of coalitional aggression that have been distinct and reproductively significant in human evolutionary history, such that it is reasonable to expect that humans possess distinct psychological information-processing systems that are activated in each domain. Taking the risk contract of war as a starting point, I expect that: 1) psychological adaptations exist that regulate behavior and motivation in coalitional aggression; 2) these adaptations track specific adaptively relevant and evolutionarily recurrent cues (e.g. the quality/quantity of benefits) that are used to calibrate relevant behavioral/motivational outputs (e.g. willingness to participate, punitive sentiment toward others who do not participate, etc.), and; 3) the particular way that these adaptations calibrate outputs based on specific cues will depend on the particular domain (e.g. offense or defense?).

148 Study 1 tested a set of hypotheses generated using this framework. As hypothesized, expected benefit was an important cue regulating willingness to participate in coalitional aggression, but the type of benefit that triggered willingness to participate depended upon the domain of aggression (H1 & H2). Thus, expectations of group benefit upregulated one’s willingness to participate in defensive, but not offensive, coalitional aggression; in offense, willingness to participate was upregulated by expectations of personal benefit, not group benefit. As discussed earlier, this flows directly from the public/private goods distinction between defense and offense, respectively. Given that our ancestors evolved in small-scale hunter-gatherer bands, which consisted largely of kin and extended kin networks, and given that the benefits of successful defense are largely public, the prospect of a shared fitness threat (loss of territory, capture of reproductive resources, etc.) should be an important cue that would increase one’s willingness to participate in defense.

Incidentally, this defense psychology may play an important role in modern notions of “collective security” in international relations, which institutionalizes the concept of the indivisibility of threat by asserting that a threat to one is a threat to all.

Although the evolutionary calculus is that shared threat motivates individual willingness, modern security institutions essentially exploit defense psychology by reversing the calculus and convert a dyadic non-shared threat into a shared threat. Collective security is effective if defense psychology is triggered among the members such that: 1)

Collective action is facilitated, and; 2) Deterrence against external threats is enhanced.

Of course, institutions alone cannot “dictate” the experience of a shared threat to its members, which of course suggests that institutions that are built on pre-existing shared

149 group boundaries and identities are more successful at coordinating collective action than institutions that are built for the purpose of creating shared group boundaries. This is evident, for example, in the very different historical trajectories experienced by the North

Atlantic Treaty Organization (NATO) on the one hand, and the Southeast Asian Treaty

Organization (SEATO) on the other. In other words, institutions are successful when they are the products of shared identities, rather than when they are designed in order to produce them.

The prospect of shared threat is sufficient to trigger one’s motivation to participate in collective defense, yet when the question is the initiation of offensive aggression against another coalition, even though success may confer benefits to the group as a whole, the relevant question becomes, “how much will I personally benefit?”

Of course, the phenomenon of cycles of violence complicates this dynamic because one coalition can “initiate” violence against an adversary that has been perceived to present a future danger (e.g. preemptive or preventive war), or in response to previous aggression

(e.g. revenge). In these situations, a defense psychology may very much be at work, despite the fact that one has initiated aggression. Thus, it is possible that one important difference between proponents of war and those who reject the need for it is the extent to which a given individual perceives the war as defensive or offensive. The 2003

American invasion of Iraq may serve as modern example in this regard.

To illustrate, U.S. President George W. Bush made the case for preventive war

(despite his inappropriate use of the label “preemptive”) by making the case that Saddam

Hussein intended to acquire and use weapons of mass destruction (WMD), and that Iraq was a hotbed of terrorist activity – which was an alarming prospect in the context of the

150 recent 9/11 attacks. National Security Advisor Condoleeza Rice’s manipulation of the

“smoking gun/mushroom cloud” analogy only further provoked the specter that inaction would be fatal for the in-group. In short, the threat was imminent and indivisible.

Opponents of war argued instead that Hussein could be contained and that there was no evidence of WMD or Hussein’s intentions of using them. War was not inevitable, war opponents claimed, and its threat was not shared. Furthermore, and quite tellingly, opponents of war accused the proponents of war of seeking to initiate war for the sake of private interests, such as oil. This is exactly how an evolved coalitional psychology should operate in the prelude to war: If we are initiating, the mind should actively scan for information relating to whether the benefit is public or private, since the answer to this question intimately and powerfully determines both one’s willingness to participate in and support warfare, as well as the fitness consequences of doing so.

Ancestrally, to have joined offensive aggression under the pretext that it is actually defensive would have had negative fitness consequences to the extent that the actual benefits were incommensurate with expected benefits; conversely, to have stayed on the sidelines of defense in the context of an invasion, having falsely categorized aggression as offensive, would risk not only your group’s defeat, but also your own survival and reproductive future. As my results show, our evolved coalitional psychology should be particularly active during the prelude to war by scanning for relevant cues indicating the proper domain of warfare. Additionally, one important corollary that follows from the analysis above is that the labor recruitment problem is generally more easily overcome for defensive than for offensive aggression. For example, both men and women are more willing to participate in defensive rather than

151 offensive coalitional action. This establishes an interesting dynamic: given exogenous labor recruitment challenges, and where the privatized benefits to initiators is great, those more willing to participate in offensive aggression should, all things equal, differentially act to misrepresent offensive aggression as defensive for the sake of “cheating” the problem of labor recruitment. This misrepresentation on behalf of initiators may even occur through self-deception, in which the greater the benefit perceived by those who would seek to initiate aggression, the more likely they are to truly believe that the initiation of aggression is necessary, either for the sake of preventing future aggression or defending the status of the group, for example. Such self-deceivers should be especially susceptible to outrage at actions of the out-group that appear to derogate the in-group’s status position (Tooby, Cosmides, and Price 2006). Furthermore, given the central importance of the perceived probability of success for the initiation of aggression and lethal raids, it is likely this form of self-deception would co-occur with positive illusions regarding the probability of victory, as discussed in the introduction (Wrangham 1999a;

Johnson, Wrangham, and Rosen 2002).

Thus, in practice it can be quite difficult to discern whether any given instance of warfare is “actually” defensive or offensive. However, this is likely the consequence of the collective interplay of individuals attempting to resolve and enforce the risk contract of war. In this sense, a distinction between offense and defense is indeed subjective, but the content of this subjectivity is provided by the interplay of: 1) A species-typical evolved coalitional psychology designed to operate according to privileged hypotheses specific to the domain of warfare; 2) Unique situation-specific variables relating to intra- coalition variables (size of one’s coalition) and inter-coalition variables (proximity to

152 other coalitions, past history of conflict) and; 3) Unique individual level variables such as sex, personal formidability, number of siblings, personal prior history in aggression, status position relative to others, etc.

Regarding the third point above, another important individual-level variable that should impact one’s willingness to participate and one’s expected benefit from coalitional violence is whether the individual is male or female. Because the selection pressures faced by our human ancestors in warfare were unique for each sex, it is the case that: 1)

An evolved psychology of warfare should regulate willingness to participate as well as perceptions of benefit in ways that are sex-specific, and; 2) These sex differences should be further contingent upon the domain of warfare. Thus, I hypothesized (H3), in accordance with sexual selection and parental investment theory, primate evidence, and human experimental and cross-cultural evidence, that men should generally be more willing to participate than women in coalitional aggression. However, I noted the caveat that this is likely a consequence of the fact that the questions I asked emphasized physical participation. Empirical evidence from other studies notes that this sex difference is mitigated on measures of less direct forms of participation (Van Vugt 2009; Ginges and

Atran 2011). Nevertheless, I expect that this sex difference should remain significant in offense, regardless of the measure of participation. This has not yet been tested by the literature, but if this expectation were borne out, it would further support the framework here. Other hypotheses regarding sex differences in Study 1 were also supported; namely, that males should expect greater benefit from offensive aggression than females

(H4), but that this sex difference should disappear in defense (H5). In short, although warfare represents an evolutionarily recurrent and adaptively significant set of selection

153 pressures for our human ancestors, the fitness consequences of these challenges are contingent upon sex, and thus, the psychological mechanisms designed to regulate behavior and motivation in these domains will operate in distinct ways depending on this variable.

Hypothesis 6 predicted that if punitive sentiment is designed specifically for the elimination of adverse fitness differentials between participants and free riders, that one’s willingness to participate should predict punitive sentiment in defense, but not in offense.

In offense, non-participants are not free riders and therefore punitive sentiment should not be directed at them if it is designed for this purpose. Results, however, indicated that willingness to participate predicted punitive sentiment in both defense and offense, leaving several possibilities: 1) The mind does encode non-participants in offensive aggression as free riders; 2) Punitive sentiment may also be designed for labor recruitment. Given that the other hypotheses based on the public/private goods distinction of defense and offense were validated, I proceeded with the assumption that it is unlikely that subjects encoded non-participants in offense as free riders. Instead, I investigated the second possibility that punitive sentiment may also function as a labor recruitment device. There is experimental evidence that the mere existence of punishment in public goods games is sufficient elicit higher levels of participation from group members (Boyd and Richerson 1992). Thus, it may be the case non-participants do indeed pose a fitness consequence on initiators to the extent that their non-participation hinders the viability of the offensive campaign. In other words, in defense, non- participants are free riders; in offense, non-participants are, from the perspective of only

154 the initiators, a hindrance to what would otherwise be a (reproductively) successful campaign.

In study 2, I investigated this question further. Specifically, I hypothesized that if punitive sentiment were designed also for labor recruitment, then it should be particularly active when labor levels are perceived to fall short of what is necessary for victory.

Again, however, this relationship depends on whether the coalitional aggression is offensive or defensive, and furthermore depends upon the sex of the subject. What is the logic by which punitive sentiment toward non-participants will be contingent upon domain of warfare and sex of the subject? The central issue of consideration here for both men and women is the evolutionarily recurrent risk-to-benefit ratio faced by each sex in each domain of warfare. Starting with men, in defense, where benefits are public, more participants only reduces per capita risk, while holding benefits constant. Thus, labor recruitment is just as important when labor is sufficient as when labor is insufficient.28 All things equal, the relevant motivational dynamic is maximally reducing the risk-to-benefit ratio, and in defense this is accomplished with more labor, regardless of current participating labor (H8). For women in defense, and because the costs of failure were likely greater for women than for men, women should be particularly

28 In my defensive scenario, the size of the foreign coalition was left deliberately ambiguous. One might object that if a clearly smaller foreign coalition were to attempt invasion, labor recruitment might not be as vital, and punitive sentiment toward non-participants could be muted. However, the outlined calculus is likely to hold even in the face of invasion by a relatively smaller coalition. As mentioned above, one component of the motivational dynamic that has not been considered in this study is shame. Fear of shame in the face of scorn by peers is likely an additional feature that operates to motivate participation. In the context of the present study, it is possible that an individual is more likely to receive shame from his peers if he does not participate in defense when the threat is small rather than when the threat is great. Again, sex differences are likely such that women are perhaps less likely to be the targets of shame (although they actively direct it) when the threat is small, but perhaps more likely to be the targets of shame when the threat is very large.

155 punitive toward non-participants when labor is insufficient than when it is sufficient, if punitive sentiment is indeed designed as a labor recruitment mechanism (H12).

However, this situation is not that straightforward. In defeat, females may still reproduce, while males are likely to be reproductively isolated, so an additional consideration is the question of whether there are female-specific costs due to infanticide, for example. Additionally, given the surprising finding that female estimates of the probability of success remained low in defense independent of perceived labor levels, it may be the case that female punitive sentiment in the service of labor recruitment may be less about achieving success and more about spreading the risk incurred by related males involved in the coalitional effort. Future studies are required to examine female efforts toward labor recruitment, as well as how these efforts interact with various life history variables, such as number of offspring and reproductive status in general.

For men in offense, the risk-to-benefit ratio is as follows. Given that the benefits of success are subject to privatization among the participants (as reproductive opportunities would have been), punitive sentiment on behalf of initiators toward non- participants should be greater when labor is insufficient than when it is sufficient (H9).

When labor is sufficient, more labor only decreases the risk-to-benefit ratio by reducing the benefit side of the equation in per capita terms. Offensive aggression and raids have evolutionarily been perpetrated by males given that sexual selection has uniquely equipped them for combat and competition (Wrangham 1999; Archer 2006; Sell, Tooby, and Cosmides 2009; Puts, Apicella, and Cárdenas 2012). For these reasons I expected that women would be generally uninterested in recruiting labor for offensive aggression, such that punitive sentiment toward non-participants would be insensitive to perceived

156 labor levels (H13). Although hypotheses 8, 9, and 12 were supported, hypothesis 13 was not. I explained that one reason that women feel more punitive in offense when labor is insufficient is that they expect participants from offensive aggression will share the spoils of war. These data do not allow testing this conjecture, however.

Lastly, hypotheses 10, 11, 14, and 15 dealt with the question of how one’s willingness to participate is affected by not only the domain of warfare, but also the sex of the subject and the perceived labor levels. If the analysis regarding the adaptively relevant risk-to-benefit ratio described above is valid, then it should be the case that, for men, willingness to participate should be high and remain high in defense, regardless of perceived labor levels, which was indeed the case (H10). Women, however, approach defense conditionally; direct physical participation is greater when perceived labor levels are insufficient. In other words, in the face of likely defeat, where additional labor could tip the balance in your coalition’s favor, women become more likely to participate in defensive coalitional aggression (H14). An important caveat here is that this outcome hinges critically on the type of participation being measured. Obviously various forms of participation entail different fitness consequences, so this should not be surprising. Thus, were I to have explicitly measured indirect forms of participation, I expect that women, as well as men, would be “at ceiling” in terms of their willingness to participate in defense, regardless of perceived labor levels.

Turning to offense, I predicted and found that the participation of men was conditional upon perceived labor levels: when labor was insufficient, willingness to participate was greater (H11). Again, given that the risk-to-benefit ratio is sub-optimal from the perspective of initiators, evolved mechanisms should motivate participation and

157 labor recruitment in the face of evidence that a larger coalition would help to establish the conditions in which it is reproductively advantageous to initiate coalitional aggression: namely, a low-risk/high-benefit endeavor. Again due to the differential selection pressures faced by women over evolutionary time, I found that female willingness to participate in offensive aggression remained low and was relatively insensitive to perceptions regarding perceived labor levels, as predicted (H15).

These data lend support to extant evolutionary models that explain coalitional aggression as primarily the product of a male coalitional reproductive strategy (Van der

Dennen 1995; Wrangham 1999; McDonald, Navarrete, and Van Vugt 2012). However, my results clearly indicate that participation in coalitional aggression is not the exclusive domain of males (especially in defense), even if males appear, in general, more eager to participate in (especially physically) and more likely to perceive benefit from certain forms of warfare (i.e. offense). The results above indicate that men and women both possess psychological mechanisms specialized to regulate behavior in warfare in a way that has been adaptively useful over evolutionary time given the unique reproductive challenges faced by each sex.

Three conclusions follow from this that are relevant given the discussion regarding the evolution of war surveyed in the introduction. First, although we do not have complete information regarding the ancestral past, we can formulate hypotheses regarding how a mechanisms ought to logically operate if a given selection pressure was present. If we cannot reject these hypotheses, we are justified in the belief that, absent a superior alternative explanation, these psychological systems likely owe their design to the selection pressures that this design reflects. Second, support for these hypotheses

158 specifically also lends credence to the wider claim, that humans have evolved in a coalitional environment characterized by periodic aggressive encounters, which seems to have resulted in selection favoring psychological mechanisms designed for the successful navigation of these adaptive challenges. Third, the existence of psychological adaptation for warfare does not allow the inference that humans are naturally war-prone and that warfare is inevitable. Instead, we have discovered that humans seem to possess specialized psychological design that regulates the conditional expression of behavior in response to environmental contingencies. Social scientists have long investigated the ways in which behavior is a response to the environment, and I do the same here. The key difference is that I postulate psychological adaptations that are responsible for structuring behavioral response to the environment. This should be as true in the case of warfare, as I have discussed above, as well as in other domains such as social learning and cultural transmission (Gallistel 1990; Sperber 1996; Morgan et al. 2011).

Psychological adaptations and the rationalist critique

Two important points require elaboration regarding the operation of psychological adaptations. The first is a statement regarding their role in conscious decision-making, and the second is a statement regarding why it is necessary to study them. I discuss each in turn.

We experience the consequences, not the processing, of psychological mechanisms. Although evolved mechanisms in the brain regulate behavior according to adaptively useful privileged hypotheses, we do not experience mechanism processing; we experience mechanism outcomes. In my discussion of the operation of these

159 mechanisms, I have argued, for example, that adaptations exist that regulate one’s willingness to participate in coalitional aggression. I have argued that these adaptations are designed to scan the environment for adaptively relevant cues such as the type of benefit, the probability of success, and extant and required labor levels, and that these inputs calibrate the resultant willingness to participate. However, it is a fallacy that therefore humans consciously regulate their behavior based on these cues, or that they experience this processing in a conscious manner. For example, although psychological mechanisms exist that regulate altruism in the context of cues such as genetic relatedness, we do not experience love for our parents as the result of a conscious deliberation consisting of careful computation of variables that we have realized are in our reproductive interests. To see why, we must recognize that there is a distinction between:

1) The subjective experiences generated in part by the operation of underlying psychological mechanisms, and; 2) The instantiated logic by which these mechanisms regulate various output (e.g. behavior, motivation, cognitive processing, etc.) which ancestrally had the on-average effect of generating outcomes that correlated with reproductive fitness.

The complex internal computation of evolved mechanisms is outwardly expressed and experienced as the desires and motivations of our subjective phenomenology: the threat of attack from abroad triggers outrage and inspires action – it does not trigger deliberative and explicit calculation of Pareto-optimal or fitness-optimal strategies. The gulf between the unconscious operation of these Darwinian algorithms and the conscious experience of motivation is perhaps most obvious in those domains in which there have been significant fitness premiums on quick and efficient responses to environmental

160 adaptive challenges. Thus, as I have discussed previously, the prospect of war itself is sufficient to trigger a host of recalibrational consequences in the brain that effect behavior, motivation, and cognition, such as in-group loyalty and out-group suspicion

(Gneezy and Fessler 2011; McDonald, Navarrete, and Van Vugt 2012). Despite the fact that the operation of these mechanisms is experienced more often as merely “the right thing to do,” rather than as the conscious computational evaluation of relevant variables, some may nevertheless argue that phenomena such as in-group pro-sociality in the face of inter-group competition can just as easily be explained through a rationalist framework. Yet, in the context of modern mass-level nation-states with professional military institutions, these types of motivational biases seem increasingly atavistic, irrational, and downright unnecessary. We have now traversed into a discussion of the rationalist critique.

Humans are not utility-maximizers; we are adaptation-executors. As a consequence of our evolutionary history, humans are endowed with an evolved psychological architecture composed of adaptations designed to solve adaptive problems in ancestral environments. Human behavior reflects the operation of these adaptations, and the operational rules that are instantiated into these adaptations represent the privileged hypotheses that over evolutionary time correlated with reproductive fitness.

The ultimate currency that determines the perpetuity of these adaptations is on-average reproductive fitness; therefore, it will often, but not always, be the case that these adaptations generate behavior that appears to be contrary to the individual’s best interests. Thus, rationalist models face inherent limits in explanatory ability, even if they may occasionally succeed at prediction. Furthermore, adaptationism allows for the

161 generation of hypotheses that would be difficult if not inherently impossible to generate from a rationalist framework, or any other framework that neglected ancestral selection pressures.

For example, I have made the case that the benefits of successful defensive coalitional aggression represent a public good. However, one of the most striking findings of behavioral economics is that collective action, from a rationalist perspective, is impossible without sanctioning mechanisms to sustain participation (Olson 1965).

Given that defense is a public good, why should individuals – especially males – be effectively “at ceiling” in terms of their motivations to participate, even in the face of evidence that there is sufficient labor for successful defense? This is especially surprising since subjects were responding to hypothetical scenarios and the design offered no form of financial incentive.29 This seems irrational from the perspective of the immediate interests of the individual; however, given the fact that ancestral hunter- gatherer bands were organized around kin structures, it would have been reproductively disastrous to ignore the call of collective defense.30 Adaptations designed to regulate willingness to participate in this kind of ancestral coalitional environment should indeed increase one’s willingness to participate in the face of shared threat. The modern consequence of the operation of these mechanisms is the highly irrational nationalism that erupts when a foreign adversary threatens one’s nation-state, which is composed

29 Indeed, this likely underestimates the real effect size of the prospect of invasion on willingness to participate in defense, although this can only be confirmed by replication. 30 Information economics suggests an alternative explanation: perhaps it is the case that each individual participates because no one individual can be sure that others will participate. However, this fails to explain why males but not females operate according to this logic. Furthermore, this alternative explanation presumes a priori that participation on behalf of one’s group is normatively good. Otherwise, uncertainty regarding the participation of others should generate panic and route, not eager willingness to participate, sacrifice, and risk one’s life – especially in the context of modern nation-states composed overwhelmingly of strangers.

162 mostly of genetically unrelated strangers – If the United States is attacked, why shouldn’t

I just move to Canada? Yet, we are irrevocably endowed with a psychological architecture that interprets modern phenomena through the lens of information- processing systems designed to expect evolutionarily recurrent ancestral environments.

Inevitably, we interpret the world we encounter with the psychology we inherit.

To further appreciate the value-added of the adaptationst approach, consider the case of sex differences in motivation for coalitional aggression: why should it be the case that men seem to be more eager to engage in coalitional aggression than women?

Analysis of the selection pressures differentially faced by each sex provides an explanation that is unique to an adaptationist approach. On the one hand, sexual selection and parental investment theory explain why males, given lower levels of parental investment, have been equipped by natural selection with the phenotypic weapons of aggressive inter-sexual (male v. male) competition (Trivers 1972; Symons 1979). On the other hand, it is a direct consequence of this investment asymmetry that coalitional aggression has been reproductively advantageous for men more than for women (Tooby and Cosmides 1988; McDonald, Navarrete, and Van Vugt 2012). As explained in

Chapter 1, males stand to reap great reproductive benefits from coalitional aggression even when combat claims the lives of many males; females, however, stand to lose in direct proportion to lives lost in combat.

163 relating to behavior and motivation in coalitional aggression, and explained how the operation of these mechanisms is further contingent on whether aggression is offensive or defensive. Given that: 1) Coalitional aggression (especially offense) represents the manifestation of a male reproductive strategy that produced on-average fitness benefits for men but not women, and; 2) The initiation of offensive aggression represents benefits that are subject to privatization, while the benefits of defense are more public; the following results were predicted and observed: men are on average more willing to physically engage in coalitional violence (though this sex difference may disappear in defense, but not offense, on less direct forms of participation); men expect greater benefit than women from offense, but not from defense; male willingness to participate in defense did not depend on existing labor levels, while females were especially likely to participate when labor was perceived as insufficient; male willingness to participate in offense depended on cues establishing a favorable risk-to-benefit ratio, while female willingness to participate remained unconditionally low.

Neither rational choice nor socialization offers an adequate alternative explanation of these dynamics. Rationally, both men and women should be increasingly unwilling to participate if labor levels are perceived as sufficient for the task; yet in defense, men were highly willing regardless of this perception. Rationally, both men and women should be increasingly willing to engage in offensive aggression when labor levels are sufficient given increasing certainty of victory; yet, women were unaffected by perceived labor levels in offense, and men displayed the opposite reaction, being motivated by insufficient rather than sufficient labor levels. This dynamic makes sense as the product of strategies that were designed to generate outcomes that ancestrally

164 correlated with reproductive success. Socialization fares no better as an alternative explanation. If males are socialized to be aggressive and females socialized to be submissive, then women should be unwilling to participate in coalitional aggression in general; instead, they were increasingly willing to participate in defense when labor levels were perceived as insufficient, and there is empirical evidence to support the claim that in defense – but not offense – women are just as willing as men to participate in coalitional aggression in indirect non-physical ways. Additionally, we live in a world of cultural norms that strongly proscribe support for and participation in offensive aggression31; yet, men displayed greater expected benefit from offensive aggression, and also displayed an increased willingness to participate in offense when environmental cues indicated a risk-to-benefit ratio that would have ancestrally correlated with reproductive success.

Of course, there are no existing rational choice or socialization theories to explain offensive and defensive psychology, so I am left to infer what these frameworks might expect. Nevertheless, given the brief discussion above, it does seem to be the case that an adaptationist framework uniquely explains the range of outcomes observed in this study.

Importantly, adaptationist analysis explains the range of human behavior in terms of evolved systems that were selected as a consequence of their on average fitness enhancing effects. Consequently, it may be the case that these evolved systems – or psychological adaptations – may generate behavior that occasionally maximizes the

31 The presence of warfare internationally is not evidence against the prevalence of norms against offensive warfare. As mentioned above, critics of the American invasion of Iraq in 2003 argued that it was unprovoked and therefore unjustified. Although proponents couched the justifications for war in the language of prevention, which by definition involves a first-strike, the initiation of violence was viewed as necessary to forestall an increasingly inevitable attack in the future. In other words, opponents of war argued that the invasion was purely offensive, while proponents argued that the invasion was ultimately defensive. The common thread here is an adherence to the belief that war is especially justified when it is in defense against a real or expected threat.

165 welfare of the individual person. However, as we have seen above, it will also be the case that such adaptations will motivate behavior that appears irrational from the individual’s perspective. As social scientists, were are therefore faced with a choice: 1)

We can accept rationalist models as the norm, while continuing to amend the general framework when we notice that individuals make systematic errors, or; 2) We can abandon the rationalist framework as an explanatory model in place of ecologically valid models that explain both rational and irrational behavior as the product of a psychology that is not designed to maximize individual utility but on average reproductive success in ancestral environments. Rationalist models offer a tool that is occasionally useful for prediction; ecologically valid adaptationist models offer a tool that allows investigation into the real and complex design of the human brain.

Limits of design

Every study faces methodological shortcomings that limit both internal and external validity. I outline the specific ways in which my study faces such limits.

Internal validity. The main manipulation (offensive vs. defensive domains) was within-subjects, meaning that each subject received both manipulations, but the order of the manipulations was randomly varied in order to mitigate ordering effects. Within- subjects designs are weaker in terms of internal validity than between-subjects designs, in which subjects are randomly allocated to either a treatment or control group.

Furthermore, within-subjects designs face the difficulty of differentiating effects between manipulations, as well as a greater likelihood of committing type II errors, in which one fails to reject a null hypothesis (no relationship) that is false. In the context of these

166 difficulties, it is noteworthy that my hypotheses regarding the main manipulation were largely supported.

External validity. As is the case with the overwhelming majority of social psychological studies, my dissertation uses subjects that were drawn exclusively from an undergraduate population, which of course limits one’s ability to generalize beyond the population of which the sample is representative. Importantly, however, this student population is in fact the same age as most individuals in active combat, and therefore may be ecologically valid for these reasons. Nevertheless, research must proceed in stages, in which initial tests establish proof of concept, and future studies aim to replicate findings with sounder design and greater generalizability. The two studies reported here indeed establish proof of concept, and the next stages of this research should be to replicate findings, for example, with cross-cultural sample populations.

Construct validity. My main manipulation concerns the differentiation between offensive and defensive warfare. I focus on this distinction as it relates to the initiation of violence, and I utilize an operational definition that is accepted both by scholars of international relations (Jervis 1978) and ethologists (Durham 1976). This distinction is that defense represents aggressive reaction to foreign attempts to take territory or resources, while offense represents the aggressive initiation of attempts to seize territory or resources, where resources are broadly defined as material or non-material. Vignettes representing each domain were constructed with attention to establishing the cues, which ancestrally were likely to have correlated with each domain. For example, the defensive domain involves the imminent arrival of a foreign coalition of unknown size and strength,

167 while the offensive domain involves the opportunity to attack and seize resources from a weak outgroup/coalition.

The choice of a tribal context instead of a modern context represents the attempt to decouple modern moral pre-conceptions regarding the use of force. However, one might object that in such a “tribal” environment in the absence of moral constraints, why shouldn’t men, for example, jump at the opportunity to engage in violence with reckless abandon? Obviously my results indicate that this was not the case, and the fact that the hypothesized conditional strategies were supported suggests that the tribal context did not have the effect of implicitly signaling that aggression was less reprehensible or more sanctioned in general. Nevertheless, it is useful to experiment with different warfare contexts to examine the ways in which the hypothesized psychological mechanisms interact with modern contexts and institutions to regulate behavior. Indeed, evolutionary psychology argues that we interpret the modern world through the lens of a Stone Age mind; this being the case, a useful next step, upon identifying the existence and operation of psychological adaptations, is to form hypotheses regarding the ways in which these adaptations interpret modern environmental cues.

For example, one important institution that may interact with our coalitional psychology in important ways is democracy. Under democratic regimes in which the scope of political enfranchisement is relatively wide, war-minded democratic executives face an acute labor recruitment problem when they seek to initiate offensive violence.32

This magnifies the motivation (self-deceived or actual) to misrepresent offensive aggression as defensive, particularly where their expected privatized benefits are great.

32 Although in the context of military institutions leaders do not necessarily face the challenge of recruiting soldiers, the labor recruitment problem is manifested in the challenge of recruiting support for violence. Ancestrally as well as today, political support must anchor the success of coalitional violence.

168 This dynamic may lead to interesting system wide effects as well, as the spread of democracy may indeed be accompanied to a certain degree by an ostensible norm against the initiation of offensive aggression and the competitive framing of aggression of any type as defensive. Thus, it should come as no surprise given the significant downstream motivational consequences of war framing, that one of the most hotly debated considerations in any conflict, ranging from civil to international war, is the rather parochial question: “Who started it?”

Final remarks

I argue that humans possess “separate psychologies” for offensive and defensive warfare. I began in the introduction by evaluating the evidence that warfare has indeed constituted an ancestrally recurrent and reproductively significant adaptive challenge.

Although the evidence is inconclusive, I argue that it is possible to test hypotheses regarding the design of putative psychological adaptations for warfare given what is known or inferred regarding the character of ancestral warfare. In chapter one I outlined evolutionary psychology, which is an adaptationist framework for explaining the design of adaptations in the brain designed by natural selection to solve specific adaptive challenges. Evolutionary psychologists have outlined the “risk contract of war,” which outlines the conditions under which natural selection would favor the initiation of coalitional aggression (Tooby and Cosmides 1988; McDonald, Navarrete, and Van Vugt

2012). This conditionality is instantiated into psychological adaptations as decision- rules, for example, that regulate behavioral, motivational, and cognitive processes during warfare.

169 The risk contract of war suggests that, given the zero-sum allocational distribution of reproductive resources, selection would favor mechanisms that upregulated male willingness to participate in coalitional aggression when, for example, the probability of success is great, risk is randomly distributed and minimal, and benefits are “fairly” distributed (Tooby and Cosmides 1988). One’s own willingness to participate, however, only fulfills one dimension of the risk contract. Once the suite of psychological mechanisms in any given individual processes the interaction of individual-level variables (e.g. personal formidability, ingroup status) in conjunction with situation- specific variables (e.g. offense vs. defense, labor sufficient vs. insufficient) such that motivation to participate is upregulated, the new question becomes the enforcement of the risk contract on others. This second dimension deals with the twin problems of building and maintaining the coalition. In defense, given that the benefits have tended to take the form of a public good, the main adaptive problem from the perspective of participants is the elimination of free-riders; in offense, given the privitazation of spoils, the main adaptive problem from the perspective of initiators is labor recruitment.

Using the risk contract of war as a general framework, I argue that psychological adaptations designed by natural selection to regulate the two components of the risk contract of war (regulating one’s own participation & enforcement of the risk contract on others) operate in a distinct fashion depending on whether the context of warfare is offensive or defensive. For example, I show that the evaluation of prospective benefit from coalitional aggression is one cue that such adaptations ought to track, but that in offense the adaptively relevant cue is expected personal benefit, while in defense the adaptively relevant cue is expected group benefit. Additionally, I demonstrate sex

170 differences in willingness to participate, as well as expected benefit, from coalitional aggression.

The observation of sex differences is noteworthy because although it is true that offensive coalitional aggression likely evolved as the product of a male reproductive strategy, it is nevertheless true, as the saying goes, that “war affects us all” – especially in the case of defense. It would be strange indeed for males, but not females, to be endowed with a psychology designed to regulate behavior in the context of warfare. Indeed, there is evidence that both men and women possess behavior-regulatory adaptations for warfare, but they operate according to sexually dimorphic information-processing pathways.

Study 2 revealed evidence to support the claim that punitive sentiment is in part designed to serve the function of labor recruitment, in addition to the function of eliminating the fitness differential generated between participants and free riders. In addition, I predicted and found that one’s willingness to participate was adaptively contingent upon whether the domain of warfare was offensive or defensive; whether labor was sufficient for the task; and whether the prospective participant was male or female.

Although previous research has examined the effect of inter-group conflict on within-group cooperation (Burton-Chellew, Ross-Gillespie, and West 2010; Gneezy and

Fessler 2011), this dissertation is the first to examine the effect of type of inter-group conflict (offense vs. defense) on behavior and motivation. Although international relations scholars have examined the effect of offensive and defensive military capabilities on the likelihood and character of warfare (Quester 2002; Biddle 2001), my

171 research is the first to essentially reverse the analytical framework by asking how offensive and defensive warfare affects political psychology. Finally, my research contributes to a growing area of interest by evolutionary psychologists generally referred to as the study of human “coalitional psychology,” which represents the suite of adaptations built by natural selection for navigating ancestral coalitional dynamics. In this regard, evolutionary psychologists have been most active in the areas of leadership and inter-group conflict (Kurzban and Neuberg 2005; Van Vugt and Ahuja 2011;

McDonald, Navarrete, and Van Vugt 2012). My research adds to this tradition by outlining and expanding the risk contract of war, and particularly by investigating the psychological dimensions of offensive and defensive warfare from an adaptationist perspective.

Evolutionary psychology offers an important tool for investigating the existence of psychological adaptations and explaining their design. Of the myriad adaptations that humans likely possess as a consequence of ancestral selection pressures, the set of adaptations that together comprise our “coalitional psychology” is of particular relevance to the study of political behavior. Indeed, we are coalitional animals, and examination of the selection pressures that have shaped the human brain can only shed greater light on both the enduring patterns and surprising novelties of international politics.

In the concluding chapter, I consider the application of evolutionary theory toward questions of interest in political science in general, yet focusing on the question of inter-group conflict in international politics.

172 Adams, Karen Ruth. 2004. “Attack and Conquer? International Anarchy and the Offense- Defense-Deterrence Balance.” International Security 28 (3): 45–83. doi:10.1162/016228803773100075. Aiello, Leslie C., and R. I. M. Dunbar. 1993. “Neocortex Size, Group Size, and the Evolution of Language.” Current Anthropology 34 (2) (April 1): 184–193. Albert, D J, R H Jonik, and M L Walsh. 1992. “Hormone-dependent Aggression in Male and Female Rats: Experiential, Hormonal, and Neural Foundations.” Neuroscience and Biobehavioral Reviews 16 (2): 177–192. Alcock, John. 1975. Animal Behavior: An Evolutionary Approach. Sunderland, Mass.: Sinauer Associates. ———. 2005. Animal Behavior: An Evolutionary Approach, Eighth Edition. 8th ed. Sinauer Associates. Alexander, Richard D. 1979. Darwinism and Human Affairs. Seattle: University of Washington Press. ———. 1987. The Biology of Moral Systems. Hawthorne, N.Y.: A. de Gruyter. Alford, J R, C. L. Funk, and J R Hibbing. 2005. “Are Political Orientations Genetically Transmitted?” American Political Science Review 99 (2): 153–167. Alford, John R., and John R. Hibbing. 2004. “The Origin of Politics: An Evolutionary Theory of Political Behavior.” Perspectives on Politics 2 (4): 707–723. Archer, J. 2006. “Testosterone and Human Aggression: An Evaluation of the Challenge Hypothesis.” Neuroscience & Biobehavioral Reviews 30 (3): 319–345. Archer, John. 1988. The Behavioural Biology of Aggression. Cambridge: Cambridge University Press. http://www.loc.gov/catdir/enhancements/fy0906/87021792- d.html. ———. 2006. “Testosterone and Human Aggression: An Evaluation of the Challenge Hypothesis.” Neuroscience & Biobehavioral Reviews 30 (3): 319–345. doi:10.1016/J.Neubiorev.2004.12.007. Axelrod, Robert, and William D. Hamilton. 1981. “The Evolution of Cooperation.” Science 211 (4489): 1390–1396. Axelrod, Robert M. 1984. The Evolution of Cooperation. New York: Basic Books. http://www.loc.gov/catdir/enhancements/fy0831/83045255-d.html. Barkow, Jerome H., Leda Cosmides, and John Tooby. 1992. The Adapted Mind: Evolutionary Psychology and the Generation of Culture. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0636/91025307- d.html. Barnett, Michael. 2009. “Evolution Without Progress? Humanitarianism in a World of Hurt.” International Organization 63 (04): 621–663. Bell, D. 2006. “Beware of False Prophets: Biology, Human Nature and the Future of International Relations Theory - BELL - 2006 - International Affairs - Wiley Online Library.” International Affairs. http://onlinelibrary.wiley.com/doi/10.1111/j.1468-2346.2006.00547.x/full. Bell, DSA, and PK MacDonald. 2001. “Start the Evolution Without Us.” International Security 26 (1): 187–194. Bennett, John W. Wheeler. 2011. The Pipe Dream Of Peace The Story Of The Collapse Of Disarmament. Nabu Press.

173 Betzig, Laura L. 1986. Despotism and Differential Reproduction: a Darwinian View of History. New York: Aldine Pub. Biddle, Stephen. 2001. “Rebuilding the Foundations of OffenseDefense Theory.” Journal of Politics 63 (3) (August 1): 741–774. doi:10.1111/0022-3816.00086. Boehm, Christopher. 1984. Blood Revenge: the Anthropology of Feuding in Montenegro and Other Tribal Societies. Lawrence, Kan.: University Press of Kansas. ———. 1999. Hierarchy in the Forest: The Evolution of Egalitarian Behavior. Cambridge, Mass.: Harvard University Press. Bowles, S. 2009. “Did Warfare Among Ancestral Hunter-gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932): 1293. Bowles, Samuel. 2009. “Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932) (June 5): 1293–1298. doi:10.1126/science.1168112. Boyd, R., and P. J. Richerson. 1992. “Punishment Allows the Evolution of Cooperation (or Anything Else) in Sizable Groups.” Ethology and Sociobiology 13 (3): 171– 195. Boyd, Robert, and Peter J. Richerson. 1988. “The Evolution of Reciprocity in Sizable Groups.” Journal of Theoretical Biology 132 (3) (June 7): 337–356. doi:10.1016/S0022-5193(88)80219-4. Brown, Michael E., Owen R. Coté Jr, Sean M. Lynn-Jones, and Steven E. Miller, eds. 2004. Offense, Defense, and War. 1st ed. The MIT Press. Burt, Austin, and Robert Trivers. 2006. Genes in Conflict: The Biology of Selfish Genetic Elements. Belknap Press of Harvard University Press. Burton-Chellew, Maxwell N., Adin Ross-Gillespie, and Stuart A West. 2010. “Cooperation in Humans: Competition Between Groups and Proximate Emotions.” Evolution and Human Behavior 31 (2): 104–108. Buss, D. M., and D. P. Schmitt. 1993. “Sexual Strategies Theory - an Evolutionary Perspective on Human Mating.” Psychological Review 100 (2): 204–232. Buss, D. M., and T. Shackelford. 1997. “Human Aggression in Evolutionary Psychological Perspective.” Clinical Psychology Review 17: 605–619. Buss, David M. 2004. Evolutionary Psychology: The New Science of the Mind. Boston: Allyn and Bacon. Campbell, Bernard, ed. 1972. Sexual Selection and the Descent of Man: 1871-1971. Aldine Transaction. Carroll, Sean B. 2006. The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. New York, N.Y.: W.W. Norton & Co. Chagnon, Napoleon A. 1983. Yanomamö: the Fierce People. New York: Holt, Rinehart and Winston. ———. 1988. “Life Histories, Blood Revenge, and Warfare in a Tribal Population.” Science 239 (4843): 985–992. Charney, Evan. 2008. “Genes and Ideologies.” Perspectives on Politics 6 (02). doi:10.1017/S1537592708080626. http://www.journals.cambridge.org/abstract_S1537592708080626. Choi, J K, and S Bowles. 2007. “The Coevolution of Parochial Altruism and War.” Science 318 (5850): 636–640. doi:10.1126/science.1144237.

174 Cikara, Mina, Emile G. Bruneau, and Rebecca R. Saxe. 2011. “Us and Them.” Current Directions in Psychological Science 20 (3) (June 1): 149 –153. doi:10.1177/0963721411408713. Cohen, Ronald. 1978. Origins of the State: The Anthropology of Political Evolution. Ed. Elman Rogers Service. Inst for the Study of Human Is. Confer, Jaime C., Judith A. Easton, Diana S. Fleischman, Cari D. Goetz, David M. G. Lewis, Carin Perilloux, and David M Buss. 2010. “Evolutionary Psychology: Controversies, Questions, Prospects, and Limitations.” American Psychologist 65 (2): 110–126. Cosmides, Leda, H. Clark Barrett, and John Tooby. 2010. “Adaptive Specializations, Social Exchange, and the Evolution of Human Intelligence.” Proceedings of the National Academy of Sciences (May 5). doi:10.1073/pnas.0914623107. http://www.pnas.org/content/early/2010/05/04/0914623107.abstract. Cosmides, Leda, and John Tooby. 1981. “Cytoplasmic Inheritance and Intragenomic Conflict.” Journal of Theoretical Biology 89 (1) (March 7): 83–129. doi:10.1016/0022-5193(81)90181-8. ———. 1987. “From Evolution to Behavior: Evolutionary Psychology as the Missing Link.” In The Latest on the Best: Essays on Evolution and Optimality, 276–306. Cambridge, Mass.: MIT Press. ———. 1994a. “Origins of Domain Specificity: The Evolution of Functional Organization.” In Mapping the Mind: Domain Specificity in Cognition and Culture, 85–116. New York: Cambridge University Press. ———. 1994b. “Better Than Rational - Evolutionary Psychology and the Invisible Hand.” American Economic Review 84 (2): 327–332. ———. 2005. “Neurocognitive Adaptations Designed for Social Exchange.” In The Handbook of Evolutionary Psychology, 584–627. Hoboken, NJ: Wiley. Crawford, Neta C. 2009. “Human Nature and World Politics: Rethinking `Man’.” International Relations 23 (2) (June 1): 271–288. doi:10.1177/0047117809104639. Curley, Tyler M. 2009. “Social Identity Theory and EU Expansion.” International Studies Quarterly 53 (3) (September 1): 649–668. doi:10.1111/j.1468- 2478.2009.00550.x. Daly, Martin, and Margo Wilson. 1983. Sex, Evolution, and Behavior. Boston: Willard Grant Press. ———. 1988. Homicide. New York: A. de Gruyter. Dawkins, Richard. 1976. The Selfish Gene. Oxford: Oxford University Press. ———. 1980. “Good Strategy or Evolutionarily Stable Strategy?” In Sociobiology: Beyond Nature/Nurture?, 331–367. Boulder: Westview Press. ———. 1983. The Extended Phenotype: the Long Reach of the Gene. Oxford; New York: Oxford University Press. ———. 1986. The Blind Watchmaker. New York: Norton. Delton, Andrew W., Max M. Krasnow, Leda Cosmides, and John Tooby. 2011. “Evolution of Direct Reciprocity Under Uncertainty Can Explain Human Generosity in One-shot Encounters.” Proceedings of the National Academy of Sciences 108 (July 25): 13335–13340. doi:10.1073/pnas.1102131108.

175 Van der Dennen, J.M.G. 1995. The Origin of War: The Evolution of a Male-coalitional Reproductive Strategy. Groningen: Origin Press. Dennett, Daniel. 1995. Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York: Simon & Schuster. Dunbar, Robin I. M. 1993. “Coevolution of Neocortical Size, Group Size, and Language in Humans.” Behavioral and Brain Sciences 16 (4): 681–735. Durham, W. H. 1976. “Resource Competition and Human Aggression .1. Review of Primitive War.” Quarterly Review of Biology 51 (3): 385–415. Dyson-Hudson, Rada, and Eric Alden Smith. 1978. “Human Territoriality: An Ecological Reassessment.” American Anthropologist 80 (1): 21–41. Eaves, L., P. Hatemi, N. Gillespie, and N. Martin. 2008. “Looking for Politically Relevant Genes.” Behavior Genetics 38 (6): 623–623 101. Eldakar, Omar Tonsi, and David Sloan Wilson. 2011. “Eight Criticisms Not to Make About Group Selection.” Evolution 65 (6) (June 1): 1523–1526. Ember, C. R. 1978. “Myths About Hunter-Gatherers.” Ethnology 17 (4): 439–448. Ermer, E., L Cosmides, and J Tooby. 2008. “Relative Status Regulates Risky Decision Making About Resources in Men: Evidence for the Co-evolution of Motivation and Cognition.” Evolution and Human Behavior 29 (2): 106–118. doi:10.1016/J.Evolhumbehav.2007.11.002. Van Evera, S. 1998. “Offense, Defense, and the Causes of War.” International Security 22 (4): 5–43. Van Evera, Stephen. 1984. “The Cult of the Offensive and the Origins of the First World War.” International Security 9 (1): 58–107. Fearon, J. D. 1995. “Rationalist Explanations for War.” International Organization 49 (3): 379–414. Feldstein, Martin. 1999. “A Self-Help Guide for Emerging Markets.” Foreign Affairs, March 1. http://www.foreignaffairs.com/articles/54801/martin-feldstein/a-self- help-guide-for-emerging-markets. Flinn, M. V., D. C. Geary, and C. V. Ward. 2005. “Ecological Dominance, Social Competition, and Coalitionary Arms Races: Why Humans Evolved Extraordinary Intelligence.” Evolution and Human Behavior 26 (1): 10–46. doi:10.1016/J.Evolhumbehav.2004.08.005. Forgas, Joseph P., Martie Haselton, and William von Hippel. 2007. Evolution and the Social Mind: Evolutionary Psychology and Social Cognition. New York, NY: Psychology Press. Fowler, J H, and D Schreiber. 2008. “Biology, Politics, and the Emerging Science of Human Nature.” Science 322 (5903): 912–914. doi:10.1126/science.1158188. Fowler, James H, and Christopher T Dawes. 2008. “Two Genes Predict Voter Turnout.” The Journal of Politics 70 (03). doi:10.1017/S0022381608080638. http://www.journals.cambridge.org/abstract_S0022381608080638. Fry, Douglas P. 2007. Beyond War: The Human Potential for Peace. 1St ed. Oxford University Press, USA. Gallistel, Charles R. 1990. The Organization of Learning. Cambridge, Mass.: MIT Press. Gat, Azar. 2000a. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-gatherer Fighting, Part II. Proximate, Subordinate, and Derivative Causes.” Anthropological Quarterly 73 (2): 74–88.

176 ———. 2000b. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-Gatherer Fighting. Part I. Primary Somatic and Reproductive Causes.” Anthropological Quarterly 73 (1): 20–34. ———. 2006. War in Human Civlization. Oxford: Oxford University Press. http://www.loc.gov/catdir/toc/ecip0614/2006017223.html. Gazzaniga, Michael S. 2000. Cognitive Neuroscience: a Reader. Malden, Mass.: Blackwell. Gazzaniga, Michael S., Diana Steen, and Bruce T. Volpe. 1979. Functional Neuroscience. New York: Harper & Row. Gigerenzer, Gerd. 2000. Adaptive Thinking: Rationality in the Real World. New York: Oxford University Press. Gigerenzer, Gerd, and Reinhard Selten. 2001. Bounded Rationality: the Adaptive Toolbox. Cambridge, Mass.: MIT Press. Ginges, J, and S Atran. 2011. “War as a Moral Imperative (not Just Practical Politics by Other Means).” Proceedings of the Royal Society B: Biological Sciences 278 (1720): 2930–2938. doi:10.1098/rspb.2010.2384. Glaser, Charles L., and Chaim Kaufmann. 1998. “What Is the Offense-defense Balance and Can We Measure It?” International Security 22 (4): 44–82. Gneezy, Ayelet, and Daniel M. T. Fessler. 2011. “Conflict, Sticks and Carrots: War Increases Prosocial Punishments and Rewards.” Proceedings of the Royal Society B: Biological Sciences (June 8). doi:10.1098/rspb.2011.0805. http://rspb.royalsocietypublishing.org/content/early/2011/06/03/rspb.2011.0805.a bstract. Godfrey-Smith, Peter, and Jon F. Wilkins. 2008. “Adaptationism.” In A Companion to the Philosophy of Biology, Chapter 11. Oxford: Blackwell. Goodall, Jane. 1986. The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Mass.: Belknap Press of Harvard University Press. Goodwin, Adam. 2010. “Evolution and Anarchism in International Relations: The Challenge of Kropotkin’s Biological Ontology.” Millennium - Journal of International Studies 39 (2): 417–437. doi:10.1177/0305829810384676. Green, Donald, and Ian Shapiro. 1996. Pathologies of Rational Choice Theory: A Critique of Applications in Political Science. Yale University Press. Hagen, Edward H, and Peter Hammerstein. 2006. “Game Theory and Human Evolution: a Critique of Some Recent Interpretations of Experimental Games.” Theoretical Population Biology 69 (3) (May): 339–348. doi:10.1016/j.tpb.2005.09.005. Hamilton, W. D. 1964a. “Genetical Evolution of Social Behaviour I.” Journal of Theoretical Biology 7 (1): 1–16. ———. 1964b. “Genetical Evolution of Social Behaviour 2.” Journal of Theoretical Biology 7 (1): 17–52. Harcourt, A. H., and F. B. M. de Waal. 1992. Coalitions and Alliances in Humans and Other Animals. Oxford [England]; New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0639/91004285-d.html. Haselhuhn, Michael P, and Elaine M Wong. 2011. “Bad to the Bone: Facial Structure Predicts Unethical Behaviour.” Proceedings of the Royal Society B: Biological Sciences (July 6). doi:10.1098/rspb.2011.1193. http://rspb.royalsocietypublishing.org/content/early/2011/06/29/rspb.2011.1193.

177 Hatemi, P K, J R Alford, J R Hibbing, N G Martin, and L J Eaves. 2009. “Is There a ‘Party’ in Your Genes?” Political Research Quarterly 62 (3): 584–600. doi:10.1177/1065912908327606. Heckhausen, Jutta, and Heinz Heckhausen. 2010. Motivation and Action. Cambridge University Press. Henrich, Joseph. 2004. “Cultural Group Selection, Coevolutionary Processes and Large- scale Cooperation.” Journal of Economic Behavior & Organization 53 (1) (January): 3–35. doi:10.1016/S0167-2681(03)00094-5. Henrich, Joseph, Jean Ensminger, Richard McElreath, Abigail Barr, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2010. “Markets, Religion, Community Size, and the Evolution of Fairness and Punishment.” Science 327 (5972) (March 19): 1480–1484. doi:10.1126/science.1182238. Henrich, Joseph, Richard McElreath, Abigail Barr, Jean Ensminger, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2006. “Costly Punishment Across Human Societies.” Science 312 (5781) (June 23): 1767–1770. doi:10.1126/science.1127333. Hooper, Paul L., Hillard S. Kaplan, and James L. Boone. 2010. “A Theory of Leadership in Human Cooperative Groups.” Journal of Theoretical Biology 265 (4) (August 21): 633–646. doi:10.1016/j.jtbi.2010.05.034. Hudson, Valerie M., and Andrea Den Boer. 2002. “A Surplus of Men, A Deficit of Peace: Security and Sex Ratios in Asia’s Largest States.” International Security 26 (4): 5–38. doi:10.1162/016228802753696753. Huntington, Samuel P. 1993. The Third Wave: Democratization in the Late 20th Century. University of Oklahoma Press. Jervis, R. 1978a. “Cooperation Under the Security Dilemma.” World Politics: A Quarterly Journal of International …. http://www.jstor.org/stable/2009958. ———. 1978b. “Cooperation Under Security Dilemma.” World Politics 30 (2): 167–214. ———. 2003. “Understanding the Bush Doctrine.” Political Science Quarterly. http://www.ingentaconnect.com/content/taps/psq/2003/00000118/00000003/art00 001. Johnson, Dominic D. P., and James H. Fowler. 2011. “The Evolution of Overconfidence.” Nature 477 (7364): 317–320. doi:10.1038/nature10384. Johnson, Dominic D. P., Rose McDermott, Emily S. Barrett, Jonathan Cowden, Richard W. Wrangham, Matthew H. McIntyre, and Stephen Peter Rosen. 2006. “Overconfidence in Wargames: Experimental Evidence on Expectations, Aggression, Gender and Testosterone.” Proceedings of the Royal Society of London Series B-Biological Sciences: 2513–2520. doi:10.1098/Rspb.2006.3606. Johnson, Dominic D. P., Richard W. Wrangham, and Steven P. Rosen. 2002. “Is Military Incompetence Adaptive? An Empirical Test with Risk-taking Behaviour in Modem Warfare.” Evolution and Human Behavior 23 (4): 245–264. Johnson, Dominic D.P., and Dominic Tierney. 2011. “The Rubicon Theory of War: How the Path to Conflict Reaches the Point of No Return.” International Security 36 (1): 7–40. doi:i: 10.1162/ISEC_a_00043

. Kahler, Miles. 1998. “Rationality in International Relations.” International Organization 52 (04): 919–941. doi:10.1162/002081898550680.

178 Kameda, T., M. Takezawa, R. S. Tindale, and C. M. Smith. 2002. “Social Sharing and Risk Reduction - Exploring a Computational Algorithm for the Psychology of Windfall Gains.” Evolution and Human Behavior 23 (1): 11–33. Kanai, Ryota, Tom Feilden, Colin Firth, and Geraint Rees. 2011. “Political Orientations Are Correlated with Brain Structure in Young Adults.” Current Biology 21 (8) (April 26): 677–680. doi:10.1016/j.cub.2011.03.017. Kaplan, H., and K. Hill. 1985. “Food Sharing Among Ache Foragers - Tests of Explanatory Hypotheses.” Current Anthropology 26 (2): 223–246. Keeley, Lawrence H. 1996. War Before Civilization: The Myth of the Peaceful Savage. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0638/94008998-d.html. Kelly, Raymond C. 2000. Warless Societies and the Origin of War. University of Michigan Press. Kratochwil, Friedrich, and John Gerard Ruggie. 1986. “International Organization: A State of the Art on an Art of the State.” International Organization 40 (04): 753– 775. doi:10.1017/S0020818300027363. Kurzban, Robert, and Daniel Houser. 2005. “Experiments Investigating Cooperative Types in Humans: A Complement to Evolutionary Theory and Simulations.” Proceedings of the National Academy of Sciences of the United States of America 102 (5): 1803–1807. Kurzban, Robert, and Steven Neuberg. 2005. “Managing Ingroup and Outgroup Relations.” In The Handbook of Evolutionary Psychology, 653–675. Hoboken: John Wiley & Sons. Kurzban, Robert, John Tooby, and L Cosmides. 2001a. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences 98 (26): 15387–15392. Kurzban, Robert, John Tooby, and Leda Cosmides. 2001b. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences of the United States of America 98 (26): 15387–15392. LeBlanc, Steven A., and Katherine E. Register. 2003. Constant Battles: The Myth of the Peaceful, Noble Savage. New York: St. Martin’s. http://www.loc.gov/catdir/bios/hol052/2002036880.html. Lehmann, Laurent, Laurent Keller, Stuart West, and Denis Roze. 2007. “Group Selection and Kin Selection: Two Concepts but One Process.” Proceedings of the National Academy of Sciences 104 (16) (April 17): 6736 –6739. doi:10.1073/pnas.0700662104. Lerner, J S, and D Keltner. 2001. “Fear, Anger, and Risk.” Journal of Personality and Social Psychology 81 (1) (July): 146–159. Levy, Jack S. 1984. “The Offensive/defensive Balance of Military Technology: A Theoretical and Historical Analysis.” International Studies Quarterly 28 (2): 219– 238. Levy, Jack S., and William R. Thompson. 2011. The Arc of War: Origins, Escalation, and Transformation. University Of Chicago Press. Lieberman, D., J Tooby, and L Cosmides. 2007. “The Architecture of Human Kin Detection.” Nature 445 (7129): 727–731. doi:10.1038/Nature05510.

179 Lieberman, Matthew D., Darren Schreiber, and Kevin N. Ochsner. 2003. “Is Political Cognition Like Riding a Bicycle? How Cognitive Neuroscience Can Inform Research on Political Thinking.” Political Psychology 24 (4) (December): 681– 704. doi:10.1046/j.1467-9221.2003.00347.x. Lopez, Anthony C. 2010. Evolution, Coalitional Psychology, and War. H-Diplo ISSF Roundtable on “Biology and Security.” Lopez, Anthony C., and Rose McDermott. “Adaptation, Heritability, and the Emergence of Evolutionary Political Science.” Political Psychology. Lopez, Anthony C., Rose McDermott, and Michael Bang Petersen. 2011. “States in Mind: Evolution, Coalitional Psychology, and International Politics.” International Security 36 (2): 48–83. Lorenz, Konrad. 1966. On Aggression. London,: Methuen. Manson, Joseph H., and Richard W. Wrangham. 1991. “Intergroup Aggression in Chimpanzees and Humans.” Current Anthropology 32 (4): 369–390. Martin, N G, L J Eaves, A C Heath, R. Jardine, L M Feingold, and H J Eysenck. 1986. “Transmission of Social Attitudes.” Proceedings of the National Academy of Sciences 83 (12) (June 1): 4364–4368. Masters, Roger D. 1989. The Nature of Politics. New Haven: Yale University Press. Mathew, Sarah, and Robert Boyd. 2011. “Punishment Sustains Large-scale Cooperation in Prestate Warfare.” Proceedings of the National Academy of Sciences. http://www.pnas.org/content/108/28/11375.short. Maynard Smith, J. 1976. “Group Selection.” Quarterly Review of Biology 51: 277–283. Maynard Smith, John. 1982. Evolution and the Theory of Games. Cambridge; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam022/81021595.html. ———. 1993. The Theory of Evolution. Cambridge [England]; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam025/93020358.html. ———. 1998. Evolutionary Genetics. Oxford; New York: Oxford University Press. ———. 1999. Shaping Life: Genes, Embryos, and Evolution. New Haven: Yale University Press. Mayr, Ernst. 1983. “How to Carry Out the Adaptationist Program?” The American Naturalist 121 (3): 324–334. ———. 2001. What Evolution Is. New York: Basic Books. McDermott, R, D Tingley, J Cowden, G Frazzetto, and D D P Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. doi:10.1073/pnas.0808376106. McDermott, Rose. 2004. “The Feeling of Rationality: The Meaning of Neuroscientific Advances for Political Science.” Perspectives on Politics 2 (4): 691–706. McDermott, Rose, James H Fowler, and Oleg Smirnov. 2008. “On the Evolutionary Origin of Prospect Theory Preferences.” The Journal of Politics 70 (02). doi:10.1017/S0022381608080341. http://www.journals.cambridge.org/abstract_S0022381608080341. McDermott, Rose, Dustin Tingley, Jonathan Cowden, Giovanni Frazetto, and Dominic D. P. Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral

180 Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. McDonald, Melissa M., Carlos David Navarrete, and Mark Van Vugt. 2012. “Evolution and the Psychology of Intergroup Conflict: The Male Warrior Hypothesis.” Philosophical Transactions of the Royal Society B: Biological Sciences 367 (1589) (March 5): 670 –679. doi:10.1098/rstb.2011.0301. Mead, M. 1940. “Warfare Is Only an Invention—not a Biological Necessity.” Asia 40 (8): 402–405. Mehta, Pranjal H, Amanda C Jones, and Robert A Josephs. 2008. “The Social Endocrinology of Dominance: Basal Testosterone Predicts Cortisol Changes and Behavior Following Victory and Defeat.” Journal of Personality and Social Psychology 94 (6): 1078–1093. doi:10.1037/0022-3514.94.6.1078. Mercer, Jonathan. 1995. “Anarchy and Identity.” International Organization 49 (2): 229– 252. ———. 2005. “Rationality and Psychology in International Relations.” International Organization 59 (Winter): 77–106. Mesquida, C. G., and N. I. Wiener. 1999. “Male Age Composition and Severity of Conflicts.” Politics and the Life Sciences 18 (2): 181–189. Milner, Helen. 1992. “International Theories of Cooperation Among Nations: Strengths and Weaknesses.” World Politics 44 (3): 466–496. Mitani, John C., David P. Watts, and Sylvia Amsler J. 2010. “Lethal Intergroup Aggression Leads to Territorial Expansion in Wild Chimpanzees.” Current Biology 20 (12) (June 22): R507–R508. Mitchell, Gregory, Philip E Tetlock, Daniel G Newman, and Jennifer S Lerner. 2003. “Experiments Behind the Veil: Structural Influences on Judgments of Social Justice.” Political Psychology 24 (3) (September 1): 519–547. doi:10.1111/0162- 895X.00339. Morgan, T. J. H, L. E Rendell, M. Ehn, W. Hoppitt, and K. N Laland. 2011. “The Evolutionary Basis of Human Social Learning.” Proceedings of the Royal Society B: Biological Sciences (July 27). doi:10.1098/rspb.2011.1172. http://rspb.royalsocietypublishing.org/content/early/2011/07/21/rspb.2011.1172.a bstract. Morgenthau, Hans Joachim, and Kenneth W. Thompson. 1993. Politics Among Nations: The Struggle for Power and Peace. McGraw-Hill. Nettleship, Martin A., R. Dale Givens, and Anderson Nettleship. 1975. War, Its Causes and Correlates. The Hague Chicago: Mouton; distributed by Aldine. Nowak, Martin A, Corina E Tarnita, and Edward O Wilson. 2010. “The Evolution of Eusociality.” Nature 466 (7310): 1057–1062. doi:10.1038/nature09205. Nowak, Martin A. 2006. “Five Rules for the Evolution of Cooperation.” Science 314 (5805) (December 8): 1560 –1563. doi:10.1126/science.1133755. Olson, Mancur. 1965. The Logic of Collective Action; Public Goods and the Theory of Groups. Cambridge, Mass.,: Harvard University Press. Orbell, John, and Tomonori Morikawa. 2011. “An Evolutionary Account of Suicide Attacks: The Kamikaze Case.” Political Psychology 32 (2): 297–322. doi:10.1111/j.1467-9221.2010.00808.x. Otterbein, Keith F. 2004. How War Began. 1st ed. TAMU Press.

181 Oxley, D R, K B Smith, J R Alford, M V Hibbing, J L Miller, M Scalora, P K Hatemi, and J R Hibbing. 2008. “Political Attitudes Vary with Physiological Traits.” Science 321 (5896): 1667–1670. doi:10.1126/science.1157627. Panchanathan, Karthik, and Robert Boyd. 2004. “Indirect Reciprocity Can Stabilize Cooperation Without the Second-order Free Rider Problem.” Nature 432 (7016) (November 25): 499–502. doi:10.1038/nature02978. Parker, Geoff. 1974. “Assessment Strategy and the Evolution of Fighting Behaviour.” Journal of Theoretical Biology 47 (1) (September): 223–243. Petersen, Michael Bang. 2009. “Public Opinion and Evolved Heuristics: The Role of Category-Based Inference.” Journal of Cognition and Culture 9 (3): 367–389. doi:10.1163/156770909X12518536414376. ———. 2012. “Social Welfare as SmallScale Help: Evolutionary Psychology and the Deservingness Heuristic.” American Journal of Political Science 56 (1) (January 1): 1–16. doi:10.1111/j.1540-5907.2011.00545.x. Pinker, Steven. 2011. The Better Angels of Our Nature: Why Violence Has Declined. Viking Adult. Potts, Malcolm, and Thomas Hayden. 2008. Sex and War: How Biology Explains Warfare and Terrorism and Offers a Path to a Safer World. BenBella Books. Powell, Robert. 2006. “War as a Commitment Problem.” International Organization 60 (1): 169–203. Price, Michael. 2012. “Group Selection Theories Are Now More Sophisticated, but Are They More Predictive? A Review of Samuel Bowles and Herbert Gintis, A Cooperative Species: Human Reciprocity and Its Evolution.” Evolutionary Psychology 10 (1): 45–49. Price, Michael E, Leda Cosmides, and John Tooby. 2002. “Punitive Sentiment as an Anti-Free Rider Psychological Device.” Evolution and Human Behavior 23 (3): 203–231. Puts, David A, Coren L Apicella, and Rodrigo A Cárdenas. 2012. “Masculine Voices Signal Men’s Threat Potential in Forager and Industrial Societies.” Proceedings of the Royal Society B: Biological Sciences 279 (1728) (February 7): 601–609. doi:10.1098/rspb.2011.0829. Puurtinen, Mikael, and Tapio Mappes. 2009. “Between-group Competition and Human Cooperation.” Proceedings of the Royal Society B: Biological Sciences 276 (1655) (January 22): 355 –360. doi:10.1098/rspb.2008.1060. Quester, George H. 2002. Offense and Defense in the International System. 3rd ed. Transaction Publishers. Rand, David G., Samuel Arbesman, and Nicholas A. Christakis. 2011. “Dynamic Social Networks Promote Cooperation in Experiments with Humans.” Proceedings of the National Academy of Sciences 108 (48) (November 29): 19193 –19198. doi:10.1073/pnas.1108243108. Richerson, Peter J., and Robert Boyd. 2006. Not by Genes Alone: How Culture Transformed Human Evolution. University Of Chicago Press. Ridley, Mark. 2004. Evolution. Malden, MA: Blackwell Pub. Ridley, Matt. 1994. The Red Queen: Sex and the Evolution of Human Nature. New York: Maxwell Macmillan International.

182 ———. 1997. The Origins of Virtue: Human Instincts and the Evolution of Cooperation. New York: Viking. Rosen, Stephen Peter. 2005. War and Human Nature. Princeton, N.J.: Princeton University Press. http://www.loc.gov/catdir/enhancements/fy0654/2003065590- d.html. Sapolsky, Robert M. 2006. “A Natural History of Peace.” Foreign Affairs. Schultheiss, O, and M Wirth. 2009. “Biopsychological Aspects of Motivation”: 1–91. Sell, Aaron, Gregory A. Bryant, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Reuden, Andre Krauss, and Michael Gurven. 2010. “Adaptations in Humans for Assessing Physical Strength from the Voice.” Proceedings of the Royal Society B: Biological Sciences: 3509–3518. Sell, Aaron, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Rueden, and Michael Gurven. 2009. “Human Adaptations for the Visual Assessment of Strength and Fighting Ability from the Body and Face.” Proceedings of the Royal Society of London Series B-Biological Sciences 276 (1656): 575–584. doi:10.1098/rspb.2008.1177. Sell, Aaron, John Tooby, and Leda Cosmides. 2009. “Formidability and the Logic of Human Anger.” Proceedings of the National Academy of Sciences 106 (35): 15073–15078. Sellers, JG, MR Mehl, and RA Josephs. 2007. “Hormones and Personality: Testosterone as a Marker of Individual Differences.” Journal of Research in Personality 41 (1): 126–138. Sharansky, Natan, and Ron Dermer. 2004. The Case for Democracy: The Power of Freedom to Overcome Tyranny and Terror. 1ST ed. PublicAffairs. Short, Lindsey A., Catherine J. Mondloch, Cheryl M. McCormick, Justin M. Carré, Ruqian Ma, Genyue Fu, and Kang Lee. 2012. “Detection of Propensity for Aggression Based on Facial Structure Irrespective of Face Race.” Evolution and Human Behavior 33 (2) (March): 121–129. doi:10.1016/j.evolhumbehav.2011.07.002. Sidanius, Jim, and Robert Kurzban. 2003. “Evolutionary Approaches to Political Psychology.” In Oxford Handbook of Political Psychology. New York: Oxford University Press. Silverberg, James, and J. Patrick Gray. 1992. Aggression and Peacefulness in Humans and Other Primates. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0604/91020318-d.html. Simmons, Beth A, Frank Dobbin, and Geoffrey Garrett. 2006. “Introduction: The International Diffusion of Liberalism.” International Organization 60 (4): 781– 810. Smith, Kevin B, Christopher W Larimer, Levente Littvay, and John R Hibbing. 2007. “Evolutionary Theory and Political Leadership: Why Certain People Do Not Trust Decision Makers.” The Journal of Politics 69 (2): 285–299. doi:10.1111/j.1468- 2508.2007.00532.x. Smith, Kevin B, Douglas R Oxley, Matthew V Hibbing, John R. Alford, and John R. Hibbing. 2011a. “Linking Genetics and Political Attitudes: Reconceptualizing Political Ideology.” Political Psychology 32 (3): 369–397. doi:10.1111/j.1467- 9221.2010.00821.x.

183 Smith, Kevin B., Douglas Oxley, Matthew V. Hibbing, John R. Alford, and John R. Hibbing. 2011b. “Disgust Sensitivity and the Neurophysiology of Left-Right Political Orientations.” PLoS ONE 6 (10) (October 19): e25552. doi:10.1371/journal.pone.0025552. Sober, Elliott, and David Sloan Wilson. 1999. Unto Others: The Evolution and Psychology of Unselfish Behavior. Harvard University Press. Somit, A., and S. A. Peterson. 1998. “Review Article: Biopolitics After Three Decades - A Balance Sheet.” British Journal of Political Science 28: 559–571. Somit, Albert, and Steven A. Peterson. 1997. Darwinism, Dominance, and Democracy: the Biological Bases of Authoritarianism. Westport, Conn.: Praeger. Sperber, Dan. 1996. Explaining Culture: a Naturalistic Approach. Oxford: Blackwell. Stanton, SJ, and OC Schultheiss. 2007. “Basal and Dynamic Relationships Between Implicit Power Motivation and Estradiol in Women.” Hormones and Behavior 52 (5): 571–580. Sumner, William Graham. 1970. War and Other Essays. Ams Pr Inc. Symons, Donald. 1979. The Evolution of Human Sexuality. New York: Oxford University Press. ———. 1992. “On the Use and Misuse of Darwinism in the Study of Human Behavior.” In The Adapted Mind: Evolutionary Psychology and the Generation of Culture, 137–160. New York: Oxford University Press. Tajfel, Henry, and John C. Turner. 1986. “The Social Identity Theory of Intergroup Behavior.” In Psychology of Intergroup Relations. Chicago: Nelson Hall. Takezawa, Masanori, and Michael E Price. 2010. “Revisiting ‘The Evolution of Reciprocity in Sizable Groups’: Continuous Reciprocity in the Repeated N-person Prisoner’s Dilemma.” Journal of Theoretical Biology 264 (2) (May 21): 188–196. doi:10.1016/j.jtbi.2010.01.028. Thayer, BA. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security. http://www.mitpressjournals.org/doi/pdf/10.1162/016228800560471. Thayer, Bradley A. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security 25 (2): 124–151. ———. 2001. “Correspondence: Start the Evolution Without Us.” International Security 26 (1): 194–198. ———. 2004. Darwin and International Relations: On the Evolutionary Origins of War and Ethnic Conflict. Lexington: University Press of Kentucky. Thayer, Bradley A, and Valerie M Hudson. 2010. “Sex and the Shaheed: Insights from the Life Sciences on Islamic Suicide Terrorism.” International Security 34 (4): 37–62. Thompson, William R. 2001. Evolutionary Interpretations of World Politics. New York: Routledge. http://www.loc.gov/catdir/toc/fy022/00066485.html. Tiger, Lionel. 2004. Men in Groups. Revised. Transaction Publishers. Tooby, John, and Leda Cosmides. 1988. “The Evolution of War and Its Cognitive Foundations.” Institute for Evolutionary Studies Technical …. http://www.psych.ucsb.edu/research/cep/papers/EvolutionofWar.pdf.

184 ———. 1990. “On the Universality of Human Nature and the Uniqueness of the Individual: The Role of Genetics and Adaptation.” Journal of Personality 58 (1): 17–67. Tooby, John, Leda Cosmides, and Michael E Price. 2006. “Cognitive Adaptations for N- person Exchange: The Evolutionary Roots of Organizational Behavior.” Managerial and Decision Economics 27 (2-3): 103–129. Trivers, Robert. 1971. “The Evolution of Reciprocal Altruism.” The Quarterly Review of Biology 46 (1): 35–57. ———. 1972. “Parental Investment and Sexual Selection.” In Sexual Selection and the Descent of Man. Chicago: Aldine Publishing. ———. 2000. “The Elements of a Scientific Theory of Self-Deception.” Annals of the New York Academy of Sciences 907 (April): 114–131. ———. 2011. The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life. 1st ed. Basic Books. Turney-High, Harry Holbert. 1949. Primitive War: Its Practice and Concepts. Columbia,: Univ. of South Carolina Press. Van Vugt, Mark. 2009. “Sex Differences in Intergroup Competition, Aggression, and Warfare: The Male Warrior Hypothesis.” Annals of the New York Academy of Sciences 1167 (June): 124–134. doi:10.1111/j.1749-6632.2009.04539.x. Vugt, Mark Van, and Anjana Ahuja. 2011. Naturally Selected: The Evolutionary Science of Leadership. HarperCollins. van Vugt, Mark, and Rob Kurzban. 2007. “Cogntive and Social Adaptations for Leadership and Followership: Evolutionary Game Theory and Group Dynamics.” In Evolution and the Social Mind: Evolutionary Psychology and Social Cognition, 229–243. New York: Psychology Press. Wagner, John D., Mark V. Flinn, and Barry G. England. 2002. “Hormonal Response to Competition Among Male Coalitions.” Evolution and Human Behavior 23 (6): 437–442. Waytz, Adam, and Liane Young. 2011. “The Group-Member Mind Trade-Off.” Psychological Science 22 (12) (December 8): 1–9. doi:10.1177/0956797611423546. Wendt, A. E. 1987. “The Agent-Structure Problem in International-Relations Theory.” International Organization 41 (3): 335–370. Williams, George C. 1966. Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought. Princeton, N.J.: Princeton University Press. Wilson, D.S., and E. Sober. 1994. “Reintroducing Group Selection to the Human Behavioral Sciences.” Behavioral and Brain Sciences 17 (4): 585–607. Wilson, Edward O. 1980. Sociobiology. Cambridge, Mass.: Belknap Press of Harvard University Press. ———. 2000. Sociobiology: the New Synthesis. Cambridge, Mass.: Belknap Press of Harvard University Press. Wilson, M, and M Daly. 2002. “An Evolutionary Psychological Perspective on the Modulation of Competitive Confrontation and Risk Taking.” Hormones. http://134.83.117.117/3518/PDF/PoundetalEvolutionaryPsychPerspective.pdf. Wrangham, Richard. 1999a. “Evolution of Coalitionary Killing.” Yearbook of Physical Anthropology 42: 1–30.

185 ———. 1999b. “Is Military Incompetence Adaptive?” Evolution and Human Behavior 20 (1): 3–17. Wrangham, Richard, and Dale Peterson. 1996. Demonic Males: Apes and the Origins of Human Violence. Boston: Houghton Mifflin. Wrangham, Richard W, and Luke Glowacki. 2012. “Intergroup Aggression in Chimpanzees and War in Nomadic Hunter-Gatherers: Evaluating the Chimpanzee Model.” Human Nature (March 3). doi:10.1007/s12110-012-9132-1. http://www.ncbi.nlm.nih.gov/pubmed/22388773. Wright, Quincy. 1983. A Study of War, 2nd Edition. 2nd ed. University Of Chicago Press. Wright, Robert. 2000. NonZero: the Logic of Human Destiny. New York: Pantheon Books. http://www.loc.gov/catdir/bios/random059/99040859.html. Wynne-Edwards, V. C. 1967. Animal Dispersion in Relation to Social Behaviour. Hafner Publishing Company. Yamagishi, Toshio, and Nobuhiro Mifune. 2009. “Social Exchange and Solidarity: In- group Love or Out-group Hate?” Evolution and Human Behavior 30 (4) (July): 229–237. doi:10.1016/j.evolhumbehav.2009.02.004. Yamagishi, Toshio, Shigehito Tanida, Rie Mashima, Eri Shimoma, and Satoshi Kanazawa. 2003. “You Can Judge A Book by Its Cover: Evidence That Cheaters May Look Different From Cooperators.” Evolution and Human Behavior 24 (4): 290–301.

186

CHAPTER FOUR: EVOLUTIONARY POLITICS

This dissertation investigates the general hypothesis that humans possess psychological adaptations that regulate behavior, motivation, and cognition in warfare. I find evidence to support the existence of such adaptations, and further, I show that the behavior-regulatory logic of these adaptations is distinct depending on whether warfare is offensive or defensive. Drawing upon sexual selection and parental investment theory, I also show that these evolved mechanisms exhibit important sex differences. In this concluding chapter, I explore the wider implications of the application of evolutionary theory for our understanding of political behavior. This will place my current findings in the larger context of such evolutionary approaches, and will help to illuminate the ways in which such findings contribute to existing knowledge in political science.

In the first section of this chapter, I review previous research in the area I that define as “political ethology” – the study of political behavior from an ethological perspective. Ethology is the study of animal behavior through both ultimate

(evolutionary) and proximate explanations, and it incorporates various lines of inquiry for understanding behavior, only one of which I have emphasized here – adaptationism. A survey of this research area will serve as an orientation to the current state of integration between the study of politics and evolutionary science.33 In the second section, I address the question of individual variability in the context of human universals, which will help

33 What I am referring to as political ethology is otherwise known as “biopolitics,” but I avoid this latter term because it is too subject to confusion with the same term that is employed with different meaning in philosophy and public policy.

187 to clarify misunderstandings that exist regarding genes and the structure of adaptations.

The third section explores the question of how to study evolved systems in the context of the institutions of modern politics.

Political Ethology

As an active research area within political science, the application of theory and evidence from the life sciences began in earnest by around the middle of the 20th century, and was relatively well established by the time of the creation within political science of the Association for Politics and the Life Sciences. This expanding interest among political scientists in evolutionary theory was particularly inspired by emergence of sociobiology (Wilson 1980), and given force within political science by Wahlke’s 1979 presidential address to the American Political Science Association. Early proponents of what became known as “biopolitics” sought to show that many of the behaviors of central interest to political scientists – such as inter-group conflict and leadership – were also potentially well-explained by evolutionary theory.

Early notable works in this interdisciplinary endeavor were Roger Master’s The

Nature of Politics (1989), Laura Betzig’s Despotism and Differential Reproduction

(1986), and Richard Alexander’s The Biology of Moral Systems (1987). Al Somit and

Steven Peterson were also particularly active in urging political scientists to turn to the life sciences for greater understanding of political behavior (1998), and in their own research they explored the possibility that power relations among and within states were rooted in the dominance hierarchies familiar to ethologists and primatologists (1997).

Despite interesting and innovative empirical work conducted by these scholars, political

188 ethology remained largely theoretical had yet to “break through” into mainstream political science.

By the turn of the century, a group of scholars, trained especially but not exclusively in the methods of behavior genetics, began to research the heritability of political attitudes. In a seminal paper, Martin et al. (1986) demonstrated a significant genetic component to the transmission of social attitudes, and these data were later reanalyzed by Alford, Funk, and Hibbing (2005) who showed that a substantial amount of the variation in political attitudes could be accounted for by genetic variation among individuals. These scholars recognized that all aspects of human behavior are a result of gene-environment interactions, and they sought to identify the nature of genetic variation that contributed to a fuller picture of individual political differences (Alford and Hibbing

2004). In many ways, this was the “second birth” of political ethology, which forced greater attention not only by political scientists, but also by the scientific community in general (Fowler and Schreiber 2008). Although this second generation of scholars reinvigorated the application of theory and evidence from the life sciences toward the study of political behavior, many scholars applied these insights to voting behavior and domestic politics specifically (Fowler and Dawes 2008; Eaves et al. 2008; Hatemi et al.

2009; Smith et al. 2011a). In addition to the use of behavior genetics and allelic association studies, many scholars increasingly turned to physiology and neuroscience to explore the biological dimensions of political attitudes, especially relating to the cleavage between liberal and conservative ideologies (Lieberman, Schreiber, and Ochsner 2003;

Oxley et al. 2008; Kanai et al. 2011; Smith et al. 2011b).

189 Despite the fact that international relations, as a sub-field of political science, has been very eager to engage in debates regarding human nature (Axelrod 1984; Milner

1992; Morgenthau and Thompson 1993; Mercer 1995), epistemology, and ontology

(Kratochwil and Ruggie 1986; Wendt 1987), direct applications of evolutionary theory to international political behavior have been relatively infrequent. Again, however, by the turn of the century, scholars began to increasingly turn to evolutionary theory to explain aspects of international politics. Bradley Thayer argued that the egoism at the heart of realism could be placed on firmer scientific footing by incorporating findings – especially from sociobiology – that explained inter-group conflict in the context of dominance contests (Thayer 2000; Thayer 2004). Crawford, however, uses modern findings from neuroscience to rightly challenge the view of static view of human nature embedded in realism (Crawford 2009). Steven Rosen explored endocrinology research to investigate ways in which social institutions may interact with individual-level variation in phenotypic traits such as testosterone levels (Rosen 2005). Dominic Johnson and colleagues have shown that overconfidence, especially prominent in males, operates to lead individuals and groups to overestimate their probability of success, especially in warfare, and was likely favored by natural selection for the purpose of deterrence

(Johnson, Wrangham, and Rosen 2002; Johnson et al. 2006; Johnson and Fowler 2011;

Johnson and Tierney 2011). McDermott explored the promise of findings from neuroscience for political behavior in general, has utilized evolutionary theory to explain the structure of prospect theoretic preferences, and has also found evidence of a genetic basis for individual variation in aggressiveness (McDermott 2004; McDermott, Fowler, and Smirnov 2008; McDermott et al. 2009).

190 Despite these findings, resistance to political ethology in political science continues (Bell 2006; Charney 2008). Some of these critiques are necessary in order for this area of inquiry to become more robust. Indeed, both the further development of theoretical frameworks and the replication of findings are necessary for political ethology to further entrench itself within the mainstream. The latter has occurred in earnest, especially regarding the genetic bases of political attitudes, and knowledge in this area has matured greatly, even though there is much room for further study. Unfortunately, however, theoretical frameworks that explain the connections between various approaches within political ethology are relatively absent. For example, imagine three distinct studies: First, a behavior genetics study that demonstrates that a political attitude has a heritable component; Second, a study presenting evidence that individuals with a certain gene tend to be more aggressive than those without it; Third, a study revealing the operation of a bias such as overconfidence, which seems to operate differently in males than in females. Each of these studies is an example of research within political ethology, but what are the differences between them, and what are the similarities? How do they relate to each other and help paint a broader portrait of human political nature?

No theoretical framework in political science exists to offer any semblance of an answer to these questions. A theoretical framework that unites political ethology research must begin with an evolutionary model that explains both the presence of individual biological uniqueness as well as the existence of universal human adaptations. It is to this framework that I now turn.

191 Uniqueness and Universality in Political Behavior

All research in political ethology essentially examines two kinds of biological systems (Lopez and McDermott, forthcoming). First, every organism subject to natural selection possesses a range of adaptations that are species-typical. As explained in chapter 1, evolutionary psychology examines the set of species-typical adaptations in the human brain that regulate behavior, motivation, and cognition. It is the adaptations themselves that are species-typical. When such adaptations are facultative, they tend to produce behavior that is context-specific, and thus variable across time and space. In this sense, some cultural variation can be explained partly as a consequence of universal psychological adaptations in interaction with variable environments. Behavior is variable, yet the adaptations that generate behavior are nevertheless universal.

Ultimately, psychological adaptations transform environmental information within and external to the organism into behavior or other forms of output that would have been adaptively useful in ancestral environments. Thus, I also have also referred to these adaptations as information-processing mechanisms. These mechanisms are manifest in the human nervous system in various forms, from the structure of neural networks to the endocrine system that regulates hormone levels.

Second, every organism also possesses a range of genetically heritable features that are unique to the individual and that distinguish it from other organisms. In addition to the variation between individuals that is explained by universal adaptations in the context of environmental variation, there is variation between individuals that is due to genetic differences between them. Of course, these genetic differences may affect the operation of species-typical adaptations. For example, it is hypothesized that humans

192 possess species-typical psychological adaptations that regulate aggression (Sell, Tooby, and Cosmides 2009). However, it has also been found that genes present in some individuals but not in others correlate with differences in levels of aggression, and also that individual differences in testosterone levels correlate with stable personality differences (Sellers, Mehl, and Josephs 2007; McDermott et al. 2009). Thus, species- typical adaptations exist that regulate behavior, and heritable differences between individuals exist that affect the person-specific expression of these adaptations independent of environmental variation. These genetically heritable differences are often explained as a consequence of entropic processes such as genetic mutation, which is a necessary by-product of evolutionary processes.

It may be the case, however, that psychological adaptations exist that are in fact not species-typical, or that species-typical traits exist that are not adaptations. The latter are often explained as a consequence of processes such as genetic drift; however, the former can be explained through a few prominent mechanisms. To begin, and in general, when a heritable phenotypic trait helps an organisms solve an adaptive problem, natural selection tends to drive that feature to fixation in a population (Williams 1966; Mark

Ridley 2004). However, natural selection is a process in which such traits are selected relative to alternative traits.34 In some situations, it may be the case that the reproductive

34 Incidentally, it is this feature that allows biologically functionalist explanations to escape causal circularity. George Williams set out a list of criteria that help one to identify the existence of biological adaptation. For example, a putative adaptation must be reliably developing and operate with functional specialization toward the resolution of a problem that posed a recurrent reproductive challenge in ancestral environments (Williams 1966). However, it is not the case that where fitness benefits would accrue to an organism that possessed adaptation X, that therefore such an adaptation must exist. Natural selection operates as a physical sift that filters among existing alternatives; it does not positively “evoke” the fittest variants. In addition, there are phylogenic constraints on what selection can “engineer” in organisms (Maynard Smith 1999). For example, although it would confer a massive fitness benefit, there are no butterflies equipped with tiny machine guns in defense against predators (Dennett 1995, 251). Regarding coalitional aggression, there are a number of species in which parental investment dynamics and other

193 fitness of a given trait depends on the frequency of other traits in its environment – a situation known as frequency-dependent selection. For example, egoists do better the more altruists there are in a population, but as egoists become more populous, their relative fitness declines. Where this is the case, stable variation may exist in which sub- populations possess different sets of adaptations (Dawkins 1980; Kurzban and Houser

2005). Another explanation for non-universal adaptations is simply that different sub- populations exist in reliably distinct environments, such that selection has favored distinct adaptations in those sub-populations. This, of course, requires a degree of immobility between sub-populations (Maynard Smith 1993). Finally, sexual selection describes the process whereby two sexes experience distinct selection pressures, and consequently, natural selection shapes distinct adaptations in each sex in response to these pressures.

Nevertheless, in this unique case, such sex differences have a genetic basis that is universal due the nature of sexual recombination (Symons 1979; Matt Ridley 1994).

Despite these caveats, for the most part when we consider the operation of complex psychological adaptations, we can expect them to be species-typical and facultative in a manner that reflects the complexity and contingency of the adaptive problems they were designed to solve. We should expect that the operation of such psychological adaptations across individuals should vary as a consequence of environmental variation, as well as heritable variation within individuals that affects the operation of universal adaptations (Tooby and Cosmides 1990). Thus, most research in political ethology has examined heritable variation and not adaptation specifically. For example, behavior genetics examines the heritable variation that exists between

ecological factors would seem to favor the emergence of coalitional behavior, yet such behavior remains relatively rare (Tooby and Cosmides 1988).

194 individuals and explores the extent to which such variation correlates with variation in political traits, as well as considerations of how these traits interact with environmental factors. However, research on the role of testosterone in political behavior is a nice example of the integration of both approaches. Jon Archer has established the “challenge hypotheses,” which explains the operation of testosterone partly as a hormonal regulator of behavior and motivation in the context of threats to status (Archer 2006). In this sense, the endocrine regulation of testosterone based on its downstream affects on motivation and behavior is an example of a complex adaptation, and its operation has been shown to be a human universal. However, we also know that individuals are born with different basal levels of testosterone that affects the particular ways in which individuals respond to status threats (Stanton and Schultheiss 2007; Mehta, Jones, and Josephs 2008).

In sum, research in political ethology may examine the operation of adaptations and their by-products,35 or it may examine the heritable variation that exists between individuals that affects the operation of such adaptations. Most political ethology research has examined the latter, although adaptationist approaches are steadily becoming more common, especially in international relations (Johnson, Wrangham, and Rosen

2002; Gat 2006; Smith et al. 2007; Thayer and Hudson 2010; Lopez, McDermott, and

Petersen 2011; Petersen 2012). As both approaches mature, the next question that researchers must begin to address is the interaction between biological systems and social institutions.

35 On by-products of adaptations, see for example Kurzban, Tooby, and Cosmides (2001)

195 Evolution, Psychology, and Political Institutions

As I mentioned in chapter 3, humans interpret the world they encounter with the psychology they inherit. However, humans, perhaps more so than any other species, are cultural innovators. We evolved to live in small nomadic hunter-gatherer bands of about

50-200 individuals, yet we have slowly expanded our social networks and the reach of our institutions, and much of the world now lives in territorially fixed nation-states composed of hundreds of thousands to hundreds of millions of individuals (Wright 2000).

It is not my intention to describe or explain here how this transformation in the evolution of social complexity was possible, and in any event, it has been treated at length elsewhere (Cohen 1978; Alexander 1979; Wright 2000; Flinn, Geary, and Ward 2005).

Instead, I seek to explore the consequences of interactions between Stone Age minds and modern political environments and institutions in the domain of coalitional aggression, or warfare.

We begin with the observation that each society is composed of a group of individuals with the same set of adaptations, but with varying forms of heritable uniqueness. In addition, as a consequence of unique histories, individuals occupy distinct social positions, which differentially affect the operation of psychological adaptations in each of these individuals. For example, evolutionary psychologists have shown that humans possess adaptations designed to regulate social sharing, which proscribe the redistribution of wealth when the poverty of others is due to lack of effort versus unforeseeable circumstances (Kaplan and Hill 1985; Kameda et al. 2002), and also that humans possess adaptations to regulate behavior during conflicts of interest (Sell, Tooby, and Cosmides 2009). Thus, although poor and wealthy individuals possess the same set

196 of psychological adaptations for regulating conflicts of interest and resource distribution, individuals in these two groups may perceive “fairness” with respect to the division of resources in different ways as a consequence of different personal and social histories which have calibrated those universal adaptations in unique ways.

To continue with the example of resource distribution, it is hypothesized that adaptations exist that regulate sharing such that redistribution is favored when reversals of fortune are due to bad luck rather than poor effort (Kameda et al. 2002). Thus, political institutions that are designed to redistribute wealth among groups in some way often ultimately must face the issue of how the misfortune of a given group in-need was established; in other words, psychological adaptations that regulate resource sharing tie the response to misfortune to the cause of misfortune. Domestically, we see this most dramatically regarding social welfare programs; the relative popularity of a given social welfare program is often proportional to the degree to which it is perceived as helping those who have incurred unforeseen and unavoidable reversals of fortune – something that “could happen to any of us.” In short, institutions discriminate between luck and effort. Where misfortune is due to the former, sharing is seen as a social good; where it is due to the latter, sharing is seen as social malady (Petersen 2012).

Similarly, in international relations, this same dynamic emerges in a slightly different form in the case of financial crises. For example, during the Asian financial crisis of the 1990s, analysts who blamed economic misfortune on poor domestic policymaking were keen to withhold financial assistance absent some form of commitment toward changed policies. However, analysts who instead saw economic misfortune as an inevitable by-product of the cyclical nature of markets instead believed

197 that such “structural adjustment” was unnecessary and only served to create new problems on top of existing ones (Feldstein 1999). These examples do not show that humans follow evolved heuristics instead of conscious or rational deliberation. What they show is that conscious deliberation is likely shaped by evolved heuristics that privilege the consideration of certain forms of evidence over others. These cases above are examples of institutions that have developed in order to solve modern social problems that mirror the structure of recurrent ancestral social problems – the distribution of wealth and resources among groups. Adaptations were favored by natural selection to solve these problems, and the institutions we have created to solve them in modern contexts continue to reflect the logic of ancestral politics.

An understanding of the functional logic of psychological adaptations can help to offer an explanation for the design of institutions, and it can also help to explain why certain institutions become legitimate and spread, while others do not. For example, in international relations, constructivism has lacked an effective answer as to why particular ideas and institutions come to dominate over others, and this is in part because the cognitive model inherent in constructive frameworks does not take into consideration that decision-making and learning are guided by privileged hypotheses in the mind. Thus, constructivists are often left groping in the dark to identify clear selection criteria that guide the process of social institutionalization.

Emanuel Adler attempts to resolve this problem, but is again hamstrung by familiar theoretical problems. Adler’s model of “cognitive evolution” seeks to explain why “certain ideas and concepts acquire epistemic, discursive and institutional authority”

(1997: 340), and he suggests as part of his model that successful institutions (those that

198 “survive” and spread as a consequence of political selection) are those that “help produce a balance or temporary consensus between competing trends,” and that “may serve as a rallying point for the formation of dominant coalitions (1997: 340).” However, this only serves to beg the question: what is it about these institutions that make them rallying points? As suggested above, evolutionary psychology offers criteria by which to recognize which social cues may serve as rallying points in a given domain of social interaction.

For example, perhaps one of the biggest trends in the recent history of international politics has been the spread of democracy, and there is no shortage of explanations as to why this is the case and how it has occurred (Huntington 1993;

Simmons, Dobbin, and Garrett 2006). Democracy is an institution, and like most institutions, it establishes an incentive structure that systematically shapes the motives of those who participate in it. But what are those motives, and how are they shaped by the incentive structure that democracy provides? A fundamental human drive is to avoid exploitation and to prevent manipulation by others in an effort to preserve personal and social autonomy. Alford and Hibbing (2004) have suggested that because humans are

“wary cooperators” we seek socially cooperative settings, but we also seek to limit the influence of others who aim to control the direction and decisions of the group.

Similarly, Boehm (1999) has suggested that an important feature of almost all social systems, whether hierarchical or egalitarian, is a system of social sanctions against the exploitation of authority by an individual or group of individuals.

These drives are likely part of a psychological motivational system that is designed to reap the rewards of communal living while guarding and placing checks

199 against the emergence of free-riders and despots. It is no surprise that democracy, an institution premised upon checks and balances, and freedom from arbitrary rule, has become so popular, even if its implementation has been accompanied by economic and political difficulties. This suggests that it is not so much the positive liberties offered by democracy that make it so attractive, but especially the negative liberties that it provides.

Importantly, this is not an argument for democracy, per se, but the particular facets of democracy that happen to mesh well with the evolved structure of mechanisms designed, for example, to avoid exploitation and despotism. This is just a brief example of how understanding the selection pressures that accompany group living can help to illuminate the structure of psychological mechanisms that operate to form preferences over institutional types.

The discussion of democracy raises an especially intriguing problem. Despite the fact that its institutional structure is “naturally” appealing to evolved minds designed to avoid exploitation and preserve social voice and mobility, the decentralized nature of democracy paradoxically establishes many operational challenges. In other words, democracy, while almost universally desired in theory, remains stubbornly difficult to enact in practice. In part, this is due to a dynamic I mentioned in chapter 3; namely, that it is easier to build institutions on top of existing shared identities rather than to use institutions to build shared identities. The establishment of democracy is an exercise in civic trust – trust that others will follow the “rules of the game,” and trust in the ability of institutions to resolve conflict. This dual challenge is what makes democracy, despite its inherent allure, so difficult to enact in practice. Humans evolved in small-scale groups, relatively homogenous and with relatively decentralized power structures in the context

200 of asymmetries in the relative influence of group members. In this context, leadership was often personal and depended upon personal attributes such as charisma, skill, and formidability (Boehm 1999; Smith et al. 2007; Van Vugt and Ahuja 2011). Although democracy has a powerful natural appeal due to its institutional checks on exploitation, it can be devilishly challenging to enact at the level of massive nation-states, especially where national sub-groupings lack an over-arching shared identity, and have been subject to rule by despots or regimes centered on individual personalities.

For example, the “Rose Revolution” in the Republic of Georgia was a popular movement that ousted a Soviet-era leader in favor of democratic reform and government.

Yet, the substantive outcome of these efforts has been continued lack of trust in legal institutions, and the replacement of one strong-arm leader for another. Again, democracy is universally desired, but individuals struggle to build shared identity, and they struggle to build trust in institutions instead of personalities. When modern problems mirror ancestral challenges, certain solutions stand out relative to others (democracy vs. authoritarianism); however, when modern environments render the enactment of these solutions difficult or impossible in certain situations, we may nevertheless still strive for them. For example, the Bush administration viewed the expansion of democracy as an inherent good and inevitable progression, such that, where tyrants are removed democracies will naturally take their place (Jervis 2003; Sharansky and Dermer 2004).

So strong is the natural pull of democracy, that it is easy to underestimate the challenges to its development, or perhaps even its cultural inappropriateness as a form of government. These challenges are at the hart of democratic transitions the world over, and it is surprising, despite cultural variation among polities, that these simple and central

201 challenges should reproduce themselves across drastically different cultural and temporal contexts. Yet, if we understand these challenges as the product of adapted minds trying to impose ancestral solutions on modern environments, the universality of the challenge and its central dynamics become clearer.

In the context of warfare, we notice an array of relevant institutions as well, some more formal than others. For example, many states have institutions that compel participation in national militaries, as well penal law to enforce it. In this dissertation I have argued that humans possess psychological adaptations designed to recruit labor for coalitional aggression, or warfare. Yet, human societies also possess institutions designed for armed mobilization. How do these two systems interact to generate political outcomes? The answer, unsurprisingly, is that the outcome depends on the character of the institutional context. For example, in democratic states with standing militaries, a leader need not “build” an army; instead, one is available – a veritable coalition in waiting. What matters in this context is domestic congressional permission or other forms of popular support. In other words, despite the availability of military instruments, democratic leaders face deep constraints on their ability to initiate conflict, perhaps deeper than have ever existed in human history. First of all, the individual autonomy of democratic leaders is not as wide as it would have been ancestrally. Also, the degree of support that must be amassed, as well as the differences among a multitude of domestic groups that must be resolved, is significant indeed. This has the effect of magnifying the labor recruitment problem faced by leaders who would seek to initiate aggression.

Although, modern politics is an environment in which formal bureaucratic lobbying has replaced the informal contests for influence that prevailed ancestrally, leaders still face

202 the ages-old task of recruiting support, and I argue that the techniques that were most powerful then remain most powerful today. As I have suggested earlier, it may be the case that in democratic regimes especially, the institutional environment renders the initiation of offensive warfare exceedingly difficult, and in this context, initiators are especially likely to misrepresent offensive endeavors as defensive in nature.

Institutions are relevant to the operation of psychological adaptations in at least two prominent ways. First, their design and structure often represents a modern solution to ancestrally recurrent adaptive problems. Second, their design and structure systematically affect the distribution of incentives in a given group, which in turn affects the cues that these adaptations receive and use to regulate behavior and motivation.

Regarding the first point, we have seen that ancestrally adaptive logics governing sharing and the redistribution of wealth are mirrored in the structure of institutions for social welfare. Additionally, we have observed that democracy possesses a natural allure that is especially prominent in the context of large nation-states, yet it is tragically difficult to establish precisely because of the evolutionarily novelties peculiar to modern political landscapes (i.e. impersonal institutions, cultural heterogeneity). Regarding the second point, we have seen that democracy imposes steep hurdles on leaders who would seek to initiate warfare on behalf of parochial interests, and therefore democratic countries may be particularly susceptible to leader misrepresentations of offensive warfare as defensive in nature in order to circumvent these institutional hurdles. In this context, it is perhaps unsurprising, as I have mentioned in chapter 3, that the marketing of war to democratic audiences therefore revolves especially around questions such as “who started it,” and

203 “who benefits,” since modern political institutional environments may only enhance these evolutionarily relevant considerations.

The above discussion on the interaction between evolved psychology and modern institutions is not conclusive or definitive, but meant as an exploration of the ways in which the interaction may occur. In particular, future investigation must attend to the ways in which the privileged hypotheses in the adapted mind shape the degree of institutional variation in domains that closely map onto domains of ancestral adaptive problems, such as the distribution of resources among individuals and groups.

Reciprocally, attention must be given to how the culturally specific shape of such institutions in turn constrains, enables, magnifies, and attenuates the set of endogenous preferences generated by psychological adaptations. In short, psychological adaptations guide social production, yet the products of this creative process inevitably shape the environment within which adapted minds negotiate and compete.

Adapted Minds, Evolving Politics

This dissertation has investigated the existence of psychological adaptations designed in response to ancestral adaptive problems that operate in domains of political behavior. I have found evidence for the existence of information-processing systems in the brain that operate according to logic that would have been adaptive in ancestral environments, and that appears incongruent with expectations based purely on rationalist or constructivist considerations. Findings in this dissertation contribute to new knowledge in the following ways. First, in general, we learn that adaptations in the human brain exist that adaptively structure motivation and behavior in warfare contingent

204 upon the form of warfare. Second, it builds on and contributes to existing literature that has examined the relationship between inter-group conflict and within-group cooperation

(Puurtinen and Mappes 2009; Burton-Chellew, Ross-Gillespie, and West 2010; Gneezy and Fessler 2011) by showing that whether inter-group conflict is framed as offensive or defensive structures resulting patterns of within-group behavior. Third, it develops an entirely new psychological approach to the existing debate in international relations regarding the “offense-defense balance.” The psychological mechanisms that underpin warfare are of deep interest to a range of disciplines, and my findings promise to contribute to research in each of these disciplines in unique ways.

In general, this research comes on the heels of expanded interest in adaptationist approaches in international relations (Thayer and Hudson 2010; Lopez, McDermott, and

Petersen 2011). However, my contribution goes further than most others in this regard by specifically examining the operation of the psychological mechanisms that regulate behavior. Despite the fact that the “environment” of international politics is full of evolutionarily novelties, we should expect individuals to represent the international political landscape through the lens of an evolved coalitional psychology designed in the context of a small-scale hunter-gatherer environment. The operation of such mechanisms will be especially apparent in domains such as warfare, which continue to trigger adaptations designed for the regulation of reasoning about and participating in coalitional violence.

Although massive nation-states confront each other across continents and within fixed territories, the substance and patterns of these conflicts remain familiar to the mind’s eye. The central preoccupations of international politics are largely the same as

205 they have been for millions of years among competing political units: how to deter outgroup violence; how to win allies; how to divide and isolate adversaries; how to establish defensible borders; what policies to enact toward out-groupers who wish to become in- groupers (i.e. the question of immigration). As a discipline, political science has already made great strides toward explaining and understanding many of these dynamics.

However, I argue that by incorporating a deeper understanding of the psychological equipment that humans necessarily bring to bear on these and other considerations, we gain an indispensible tool with which to investigate the patterns and novelty of political behavior.

206 Archer, John. 1988. The Behavioural Biology of Aggression. Cambridge: Cambridge University Press. http://www.loc.gov/catdir/enhancements/fy0906/87021792- d.html. ———. 2006. “Testosterone and Human Aggression: An Evaluation of the Challenge Hypothesis.” Neuroscience & Biobehavioral Reviews 30 (3): 319–345. doi:10.1016/J.Neubiorev.2004.12.007. Axelrod, Robert, and William D. Hamilton. 1981. “The Evolution of Cooperation.” Science 211 (4489): 1390–1396. Axelrod, Robert M. 1984. The Evolution of Cooperation. New York: Basic Books. http://www.loc.gov/catdir/enhancements/fy0831/83045255-d.html. Barkow, Jerome H., Leda Cosmides, and John Tooby. 1992. The Adapted Mind: Evolutionary Psychology and the Generation of Culture. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0636/91025307- d.html. Barnett, Michael. 2009. “Evolution Without Progress? Humanitarianism in a World of Hurt.” International Organization 63 (04): 621–663. Bell, D. 2006. “Beware of False Prophets: Biology, Human Nature and the Future of International Relations Theory - BELL - 2006 - International Affairs - Wiley Online Library.” International Affairs. http://onlinelibrary.wiley.com/doi/10.1111/j.1468-2346.2006.00547.x/full. Bell, DSA, and PK MacDonald. 2001. “Start the Evolution Without Us.” International Security 26 (1): 187–194. Bennett, John W. Wheeler. 2011. The Pipe Dream Of Peace The Story Of The Collapse Of Disarmament. Nabu Press. Betzig, Laura L. 1986. Despotism and Differential Reproduction: a Darwinian View of History. New York: Aldine Pub. Biddle, Stephen. 2001. “Rebuilding the Foundations of OffenseDefense Theory.” Journal of Politics 63 (3) (August 1): 741–774. doi:10.1111/0022-3816.00086. Boehm, Christopher. 1984. Blood Revenge: the Anthropology of Feuding in Montenegro and Other Tribal Societies. Lawrence, Kan.: University Press of Kansas. ———. 1999. Hierarchy in the Forest: The Evolution of Egalitarian Behavior. Cambridge, Mass.: Harvard University Press. Bowles, S. 2009. “Did Warfare Among Ancestral Hunter-gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932): 1293. Bowles, Samuel. 2009. “Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?” Science 324 (5932) (June 5): 1293–1298. doi:10.1126/science.1168112. Boyd, R., and P. J. Richerson. 1992. “Punishment Allows the Evolution of Cooperation (or Anything Else) in Sizable Groups.” Ethology and Sociobiology 13 (3): 171– 195. Boyd, Robert, and Peter J. Richerson. 1988. “The Evolution of Reciprocity in Sizable Groups.” Journal of Theoretical Biology 132 (3) (June 7): 337–356. doi:10.1016/S0022-5193(88)80219-4. Brown, Michael E., Owen R. Coté Jr, Sean M. Lynn-Jones, and Steven E. Miller, eds. 2004. Offense, Defense, and War. 1st ed. The MIT Press.

207 Burt, Austin, and Robert Trivers. 2006. Genes in Conflict: The Biology of Selfish Genetic Elements. Belknap Press of Harvard University Press. Burton-Chellew, Maxwell N., Adin Ross-Gillespie, and Stuart A West. 2010. “Cooperation in Humans: Competition Between Groups and Proximate Emotions.” Evolution and Human Behavior 31 (2): 104–108. Buss, D. M., and D. P. Schmitt. 1993. “Sexual Strategies Theory - an Evolutionary Perspective on Human Mating.” Psychological Review 100 (2): 204–232. Buss, D. M., and T. Shackelford. 1997. “Human Aggression in Evolutionary Psychological Perspective.” Clinical Psychology Review 17: 605–619. Buss, David M. 2004. Evolutionary Psychology: The New Science of the Mind. Boston: Allyn and Bacon. Campbell, Bernard, ed. 1972. Sexual Selection and the Descent of Man: 1871-1971. Aldine Transaction. Carroll, Sean B. 2006. The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. New York, N.Y.: W.W. Norton & Co. Chagnon, Napoleon A. 1983. Yanomamö: the Fierce People. New York: Holt, Rinehart and Winston. ———. 1988. “Life Histories, Blood Revenge, and Warfare in a Tribal Population.” Science 239 (4843): 985–992. Charney, Evan. 2008. “Genes and Ideologies.” Perspectives on Politics 6 (02). doi:10.1017/S1537592708080626. http://www.journals.cambridge.org/abstract_S1537592708080626. Choi, J K, and S Bowles. 2007. “The Coevolution of Parochial Altruism and War.” Science 318 (5850): 636–640. doi:10.1126/science.1144237. Cikara, Mina, Emile G. Bruneau, and Rebecca R. Saxe. 2011. “Us and Them.” Current Directions in Psychological Science 20 (3) (June 1): 149 –153. doi:10.1177/0963721411408713. Cohen, Ronald. 1978. Origins of the State: The Anthropology of Political Evolution. Ed. Elman Rogers Service. Inst for the Study of Human Is. Confer, Jaime C., Judith A. Easton, Diana S. Fleischman, Cari D. Goetz, David M. G. Lewis, Carin Perilloux, and David M Buss. 2010. “Evolutionary Psychology: Controversies, Questions, Prospects, and Limitations.” American Psychologist 65 (2): 110–126. Cosmides, Leda, H. Clark Barrett, and John Tooby. 2010. “Adaptive Specializations, Social Exchange, and the Evolution of Human Intelligence.” Proceedings of the National Academy of Sciences (May 5). doi:10.1073/pnas.0914623107. http://www.pnas.org/content/early/2010/05/04/0914623107.abstract. Cosmides, Leda, and John Tooby. 1981. “Cytoplasmic Inheritance and Intragenomic Conflict.” Journal of Theoretical Biology 89 (1) (March 7): 83–129. doi:10.1016/0022-5193(81)90181-8. ———. 1987. “From Evolution to Behavior: Evolutionary Psychology as the Missing Link.” In The Latest on the Best: Essays on Evolution and Optimality, 276–306. Cambridge, Mass.: MIT Press. ———. 1994a. “Origins of Domain Specificity: The Evolution of Functional Organization.” In Mapping the Mind: Domain Specificity in Cognition and Culture, 85–116. New York: Cambridge University Press.

208 ———. 1994b. “Better Than Rational - Evolutionary Psychology and the Invisible Hand.” American Economic Review 84 (2): 327–332. ———. 2005. “Neurocognitive Adaptations Designed for Social Exchange.” In The Handbook of Evolutionary Psychology, 584–627. Hoboken, NJ: Wiley. Crawford, Neta C. 2009. “Human Nature and World Politics: Rethinking `Man’.” International Relations 23 (2) (June 1): 271–288. doi:10.1177/0047117809104639. Curley, Tyler M. 2009. “Social Identity Theory and EU Expansion.” International Studies Quarterly 53 (3) (September 1): 649–668. doi:10.1111/j.1468- 2478.2009.00550.x. Daly, Martin, and Margo Wilson. 1983. Sex, Evolution, and Behavior. Boston: Willard Grant Press. ———. 1988. Homicide. New York: A. de Gruyter. Dawkins, Richard. 1976. The Selfish Gene. Oxford: Oxford University Press. ———. 1980. “Good Strategy or Evolutionarily Stable Strategy?” In Sociobiology: Beyond Nature/Nurture?, 331–367. Boulder: Westview Press. ———. 1983. The Extended Phenotype: the Long Reach of the Gene. Oxford; New York: Oxford University Press. ———. 1986. The Blind Watchmaker. New York: Norton. Delton, Andrew W., Max M. Krasnow, Leda Cosmides, and John Tooby. 2011. “Evolution of Direct Reciprocity Under Uncertainty Can Explain Human Generosity in One-shot Encounters.” Proceedings of the National Academy of Sciences 108 (July 25): 13335–13340. doi:10.1073/pnas.1102131108. Van der Dennen, J.M.G. 1995. The Origin of War: The Evolution of a Male-coalitional Reproductive Strategy. Groningen: Origin Press. Dennett, Daniel. 1995. Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York: Simon & Schuster. Dunbar, Robin I. M. 1993. “Coevolution of Neocortical Size, Group Size, and Language in Humans.” Behavioral and Brain Sciences 16 (4): 681–735. Durham, W. H. 1976. “Resource Competition and Human Aggression .1. Review of Primitive War.” Quarterly Review of Biology 51 (3): 385–415. Dyson-Hudson, Rada, and Eric Alden Smith. 1978. “Human Territoriality: An Ecological Reassessment.” American Anthropologist 80 (1): 21–41. Eaves, L., P. Hatemi, N. Gillespie, and N. Martin. 2008. “Looking for Politically Relevant Genes.” Behavior Genetics 38 (6): 623–623 101. Eldakar, Omar Tonsi, and David Sloan Wilson. 2011. “Eight Criticisms Not to Make About Group Selection.” Evolution 65 (6) (June 1): 1523–1526. Ember, C. R. 1978. “Myths About Hunter-Gatherers.” Ethnology 17 (4): 439–448. Ermer, E., L Cosmides, and J Tooby. 2008. “Relative Status Regulates Risky Decision Making About Resources in Men: Evidence for the Co-evolution of Motivation and Cognition.” Evolution and Human Behavior 29 (2): 106–118. doi:10.1016/J.Evolhumbehav.2007.11.002. Van Evera, S. 1998. “Offense, Defense, and the Causes of War.” International Security 22 (4): 5–43. Van Evera, Stephen. 1984. “The Cult of the Offensive and the Origins of the First World War.” International Security 9 (1): 58–107.

209 Fearon, J. D. 1995. “Rationalist Explanations for War.” International Organization 49 (3): 379–414. Feldstein, Martin. 1999. “A Self-Help Guide for Emerging Markets.” Foreign Affairs, March 1. http://www.foreignaffairs.com/articles/54801/martin-feldstein/a-self- help-guide-for-emerging-markets. Flinn, M. V., D. C. Geary, and C. V. Ward. 2005. “Ecological Dominance, Social Competition, and Coalitionary Arms Races: Why Humans Evolved Extraordinary Intelligence.” Evolution and Human Behavior 26 (1): 10–46. doi:10.1016/J.Evolhumbehav.2004.08.005. Forgas, Joseph P., Martie Haselton, and William von Hippel. 2007. Evolution and the Social Mind: Evolutionary Psychology and Social Cognition. New York, NY: Psychology Press. Fowler, J H, and D Schreiber. 2008. “Biology, Politics, and the Emerging Science of Human Nature.” Science 322 (5903): 912–914. doi:10.1126/science.1158188. Fowler, James H, and Christopher T Dawes. 2008. “Two Genes Predict Voter Turnout.” The Journal of Politics 70 (03). doi:10.1017/S0022381608080638. http://www.journals.cambridge.org/abstract_S0022381608080638. Fry, Douglas P. 2007. Beyond War: The Human Potential for Peace. 1St ed. Oxford University Press, USA. Gallistel, Charles R. 1990. The Organization of Learning. Cambridge, Mass.: MIT Press. Gat, Azar. 2000a. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-gatherer Fighting, Part II. Proximate, Subordinate, and Derivative Causes.” Anthropological Quarterly 73 (2): 74–88. ———. 2000b. “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-Gatherer Fighting. Part I. Primary Somatic and Reproductive Causes.” Anthropological Quarterly 73 (1): 20–34. ———. 2006. War in Human Civlization. Oxford: Oxford University Press. http://www.loc.gov/catdir/toc/ecip0614/2006017223.html. Gazzaniga, Michael S. 2000. Cognitive Neuroscience: a Reader. Malden, Mass.: Blackwell. Gazzaniga, Michael S., Diana Steen, and Bruce T. Volpe. 1979. Functional Neuroscience. New York: Harper & Row. Gigerenzer, Gerd. 2000. Adaptive Thinking: Rationality in the Real World. New York: Oxford University Press. Gigerenzer, Gerd, and Reinhard Selten. 2001. Bounded Rationality: the Adaptive Toolbox. Cambridge, Mass.: MIT Press. Ginges, J, and S Atran. 2011. “War as a Moral Imperative (not Just Practical Politics by Other Means).” Proceedings of the Royal Society B: Biological Sciences 278 (1720): 2930–2938. doi:10.1098/rspb.2010.2384. Glaser, Charles L., and Chaim Kaufmann. 1998. “What Is the Offense-defense Balance and Can We Measure It?” International Security 22 (4): 44–82. Gneezy, Ayelet, and Daniel M. T. Fessler. 2011. “Conflict, Sticks and Carrots: War Increases Prosocial Punishments and Rewards.” Proceedings of the Royal Society B: Biological Sciences (June 8). doi:10.1098/rspb.2011.0805. http://rspb.royalsocietypublishing.org/content/early/2011/06/03/rspb.2011.0805.a bstract.

210 Godfrey-Smith, Peter, and Jon F. Wilkins. 2008. “Adaptationism.” In A Companion to the Philosophy of Biology, Chapter 11. Oxford: Blackwell. Goodall, Jane. 1986. The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Mass.: Belknap Press of Harvard University Press. Goodwin, Adam. 2010. “Evolution and Anarchism in International Relations: The Challenge of Kropotkin’s Biological Ontology.” Millennium - Journal of International Studies 39 (2): 417–437. doi:10.1177/0305829810384676. Green, Donald, and Ian Shapiro. 1996. Pathologies of Rational Choice Theory: A Critique of Applications in Political Science. Yale University Press. Hagen, Edward H, and Peter Hammerstein. 2006. “Game Theory and Human Evolution: a Critique of Some Recent Interpretations of Experimental Games.” Theoretical Population Biology 69 (3) (May): 339–348. doi:10.1016/j.tpb.2005.09.005. Hamilton, W. D. 1964a. “Genetical Evolution of Social Behaviour I.” Journal of Theoretical Biology 7 (1): 1–16. ———. 1964b. “Genetical Evolution of Social Behaviour 2.” Journal of Theoretical Biology 7 (1): 17–52. Harcourt, A. H., and F. B. M. de Waal. 1992. Coalitions and Alliances in Humans and Other Animals. Oxford [England]; New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0639/91004285-d.html. Haselhuhn, Michael P, and Elaine M Wong. 2011. “Bad to the Bone: Facial Structure Predicts Unethical Behaviour.” Proceedings of the Royal Society B: Biological Sciences (July 6). doi:10.1098/rspb.2011.1193. http://rspb.royalsocietypublishing.org/content/early/2011/06/29/rspb.2011.1193. Hatemi, P K, J R Alford, J R Hibbing, N G Martin, and L J Eaves. 2009. “Is There a ‘Party’ in Your Genes?” Political Research Quarterly 62 (3): 584–600. doi:10.1177/1065912908327606. Heckhausen, Jutta, and Heinz Heckhausen. 2010. Motivation and Action. Cambridge University Press. Henrich, Joseph. 2004. “Cultural Group Selection, Coevolutionary Processes and Large- scale Cooperation.” Journal of Economic Behavior & Organization 53 (1) (January): 3–35. doi:10.1016/S0167-2681(03)00094-5. Henrich, Joseph, Jean Ensminger, Richard McElreath, Abigail Barr, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2010. “Markets, Religion, Community Size, and the Evolution of Fairness and Punishment.” Science 327 (5972) (March 19): 1480–1484. doi:10.1126/science.1182238. Henrich, Joseph, Richard McElreath, Abigail Barr, Jean Ensminger, Clark Barrett, Alexander Bolyanatz, Juan Camilo Cardenas, et al. 2006. “Costly Punishment Across Human Societies.” Science 312 (5781) (June 23): 1767–1770. doi:10.1126/science.1127333. Hooper, Paul L., Hillard S. Kaplan, and James L. Boone. 2010. “A Theory of Leadership in Human Cooperative Groups.” Journal of Theoretical Biology 265 (4) (August 21): 633–646. doi:10.1016/j.jtbi.2010.05.034. Hudson, Valerie M., and Andrea Den Boer. 2002. “A Surplus of Men, A Deficit of Peace: Security and Sex Ratios in Asia’s Largest States.” International Security 26 (4): 5–38. doi:10.1162/016228802753696753.

211 Huntington, Samuel P. 1993. The Third Wave: Democratization in the Late 20th Century. University of Oklahoma Press. Jervis, R. 1978a. “Cooperation Under the Security Dilemma.” World Politics: A Quarterly Journal of International …. http://www.jstor.org/stable/2009958. ———. 1978b. “Cooperation Under Security Dilemma.” World Politics 30 (2): 167–214. ———. 2003. “Understanding the Bush Doctrine.” Political Science Quarterly. http://www.ingentaconnect.com/content/taps/psq/2003/00000118/00000003/art00 001. Johnson, Dominic D. P., and James H. Fowler. 2011. “The Evolution of Overconfidence.” Nature 477 (7364): 317–320. doi:10.1038/nature10384. Johnson, Dominic D. P., Rose McDermott, Emily S. Barrett, Jonathan Cowden, Richard W. Wrangham, Matthew H. McIntyre, and Stephen Peter Rosen. 2006. “Overconfidence in Wargames: Experimental Evidence on Expectations, Aggression, Gender and Testosterone.” Proceedings of the Royal Society of London Series B-Biological Sciences: 2513–2520. doi:10.1098/Rspb.2006.3606. Johnson, Dominic D. P., Richard W. Wrangham, and Steven P. Rosen. 2002. “Is Military Incompetence Adaptive? An Empirical Test with Risk-taking Behaviour in Modem Warfare.” Evolution and Human Behavior 23 (4): 245–264. Johnson, Dominic D.P., and Dominic Tierney. 2011. “The Rubicon Theory of War: How the Path to Conflict Reaches the Point of No Return.” International Security 36 (1): 7–40. doi:i: 10.1162/ISEC_a_00043

212 Kurzban, Robert, John Tooby, and L Cosmides. 2001a. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences 98 (26): 15387–15392. Kurzban, Robert, John Tooby, and Leda Cosmides. 2001b. “Can Race Be Erased? Coalitional Computation and Social Categorization.” Proceedings of the National Academy of Sciences of the United States of America 98 (26): 15387–15392. LeBlanc, Steven A., and Katherine E. Register. 2003. Constant Battles: The Myth of the Peaceful, Noble Savage. New York: St. Martin’s. http://www.loc.gov/catdir/bios/hol052/2002036880.html. Lehmann, Laurent, Laurent Keller, Stuart West, and Denis Roze. 2007. “Group Selection and Kin Selection: Two Concepts but One Process.” Proceedings of the National Academy of Sciences 104 (16) (April 17): 6736 –6739. doi:10.1073/pnas.0700662104. Lerner, J S, and D Keltner. 2001. “Fear, Anger, and Risk.” Journal of Personality and Social Psychology 81 (1) (July): 146–159. Levy, Jack S. 1984. “The Offensive/defensive Balance of Military Technology: A Theoretical and Historical Analysis.” International Studies Quarterly 28 (2): 219– 238. Levy, Jack S., and William R. Thompson. 2011. The Arc of War: Origins, Escalation, and Transformation. University Of Chicago Press. Lieberman, D., J Tooby, and L Cosmides. 2007. “The Architecture of Human Kin Detection.” Nature 445 (7129): 727–731. doi:10.1038/Nature05510. Lieberman, Matthew D., Darren Schreiber, and Kevin N. Ochsner. 2003. “Is Political Cognition Like Riding a Bicycle? How Cognitive Neuroscience Can Inform Research on Political Thinking.” Political Psychology 24 (4) (December): 681– 704. doi:10.1046/j.1467-9221.2003.00347.x. Lopez, Anthony C. 2010. Evolution, Coalitional Psychology, and War. H-Diplo ISSF Roundtable on “Biology and Security.” Lopez, Anthony C., and Rose McDermott. “Adaptation, Heritability, and the Emergence of Evolutionary Political Science.” Political Psychology. Lopez, Anthony C., Rose McDermott, and Michael Bang Petersen. 2011. “States in Mind: Evolution, Coalitional Psychology, and International Politics.” International Security 36 (2): 48–83. Lorenz, Konrad. 1966. On Aggression. London,: Methuen. Manson, Joseph H., and Richard W. Wrangham. 1991. “Intergroup Aggression in Chimpanzees and Humans.” Current Anthropology 32 (4): 369–390. Martin, N G, L J Eaves, A C Heath, R. Jardine, L M Feingold, and H J Eysenck. 1986. “Transmission of Social Attitudes.” Proceedings of the National Academy of Sciences 83 (12) (June 1): 4364–4368. Masters, Roger D. 1989. The Nature of Politics. New Haven: Yale University Press. Mathew, Sarah, and Robert Boyd. 2011. “Punishment Sustains Large-scale Cooperation in Prestate Warfare.” Proceedings of the National Academy of Sciences. http://www.pnas.org/content/108/28/11375.short. Maynard Smith, J. 1976. “Group Selection.” Quarterly Review of Biology 51: 277–283.

213 Maynard Smith, John. 1982. Evolution and the Theory of Games. Cambridge; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam022/81021595.html. ———. 1993. The Theory of Evolution. Cambridge [England]; New York: Cambridge University Press. http://www.loc.gov/catdir/description/cam025/93020358.html. ———. 1998. Evolutionary Genetics. Oxford; New York: Oxford University Press. ———. 1999. Shaping Life: Genes, Embryos, and Evolution. New Haven: Yale University Press. Mayr, Ernst. 1983. “How to Carry Out the Adaptationist Program?” The American Naturalist 121 (3): 324–334. ———. 2001. What Evolution Is. New York: Basic Books. McDermott, R, D Tingley, J Cowden, G Frazzetto, and D D P Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. doi:10.1073/pnas.0808376106. McDermott, Rose. 2004. “The Feeling of Rationality: The Meaning of Neuroscientific Advances for Political Science.” Perspectives on Politics 2 (4): 691–706. McDermott, Rose, James H Fowler, and Oleg Smirnov. 2008. “On the Evolutionary Origin of Prospect Theory Preferences.” The Journal of Politics 70 (02). doi:10.1017/S0022381608080341. http://www.journals.cambridge.org/abstract_S0022381608080341. McDermott, Rose, Dustin Tingley, Jonathan Cowden, Giovanni Frazetto, and Dominic D. P. Johnson. 2009. “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation.” Proceedings of the National Academy of Sciences 106 (7): 2118–2123. McDonald, Melissa M., Carlos David Navarrete, and Mark Van Vugt. 2012. “Evolution and the Psychology of Intergroup Conflict: The Male Warrior Hypothesis.” Philosophical Transactions of the Royal Society B: Biological Sciences 367 (1589) (March 5): 670 –679. doi:10.1098/rstb.2011.0301. Mead, M. 1940. “Warfare Is Only an Invention—not a Biological Necessity.” Asia 40 (8): 402–405. Mehta, Pranjal H, Amanda C Jones, and Robert A Josephs. 2008. “The Social Endocrinology of Dominance: Basal Testosterone Predicts Cortisol Changes and Behavior Following Victory and Defeat.” Journal of Personality and Social Psychology 94 (6): 1078–1093. doi:10.1037/0022-3514.94.6.1078. Mercer, Jonathan. 1995. “Anarchy and Identity.” International Organization 49 (2): 229– 252. ———. 2005. “Rationality and Psychology in International Relations.” International Organization 59 (Winter): 77–106. Mesquida, C. G., and N. I. Wiener. 1999. “Male Age Composition and Severity of Conflicts.” Politics and the Life Sciences 18 (2): 181–189. Milner, Helen. 1992. “International Theories of Cooperation Among Nations: Strengths and Weaknesses.” World Politics 44 (3): 466–496. Mitani, John C., David P. Watts, and Sylvia Amsler J. 2010. “Lethal Intergroup Aggression Leads to Territorial Expansion in Wild Chimpanzees.” Current Biology 20 (12) (June 22): R507–R508.

214 Mitchell, Gregory, Philip E Tetlock, Daniel G Newman, and Jennifer S Lerner. 2003. “Experiments Behind the Veil: Structural Influences on Judgments of Social Justice.” Political Psychology 24 (3) (September 1): 519–547. doi:10.1111/0162- 895X.00339. Morgan, T. J. H, L. E Rendell, M. Ehn, W. Hoppitt, and K. N Laland. 2011. “The Evolutionary Basis of Human Social Learning.” Proceedings of the Royal Society B: Biological Sciences (July 27). doi:10.1098/rspb.2011.1172. http://rspb.royalsocietypublishing.org/content/early/2011/07/21/rspb.2011.1172.a bstract. Morgenthau, Hans Joachim, and Kenneth W. Thompson. 1993. Politics Among Nations: The Struggle for Power and Peace. McGraw-Hill. Nettleship, Martin A., R. Dale Givens, and Anderson Nettleship. 1975. War, Its Causes and Correlates. The Hague Chicago: Mouton; distributed by Aldine. Nowak, Martin A, Corina E Tarnita, and Edward O Wilson. 2010. “The Evolution of Eusociality.” Nature 466 (7310): 1057–1062. doi:10.1038/nature09205. Nowak, Martin A. 2006. “Five Rules for the Evolution of Cooperation.” Science 314 (5805) (December 8): 1560 –1563. doi:10.1126/science.1133755. Olson, Mancur. 1965. The Logic of Collective Action; Public Goods and the Theory of Groups. Cambridge, Mass.,: Harvard University Press. Orbell, John, and Tomonori Morikawa. 2011. “An Evolutionary Account of Suicide Attacks: The Kamikaze Case.” Political Psychology 32 (2): 297–322. doi:10.1111/j.1467-9221.2010.00808.x. Otterbein, Keith F. 2004. How War Began. 1st ed. TAMU Press. Oxley, D R, K B Smith, J R Alford, M V Hibbing, J L Miller, M Scalora, P K Hatemi, and J R Hibbing. 2008. “Political Attitudes Vary with Physiological Traits.” Science 321 (5896): 1667–1670. doi:10.1126/science.1157627. Panchanathan, Karthik, and Robert Boyd. 2004. “Indirect Reciprocity Can Stabilize Cooperation Without the Second-order Free Rider Problem.” Nature 432 (7016) (November 25): 499–502. doi:10.1038/nature02978. Parker, Geoff. 1974. “Assessment Strategy and the Evolution of Fighting Behaviour.” Journal of Theoretical Biology 47 (1) (September): 223–243. Petersen, Michael Bang. 2009. “Public Opinion and Evolved Heuristics: The Role of Category-Based Inference.” Journal of Cognition and Culture 9 (3): 367–389. doi:10.1163/156770909X12518536414376. ———. 2012. “Social Welfare as SmallScale Help: Evolutionary Psychology and the Deservingness Heuristic.” American Journal of Political Science 56 (1) (January 1): 1–16. doi:10.1111/j.1540-5907.2011.00545.x. Pinker, Steven. 2011. The Better Angels of Our Nature: Why Violence Has Declined. Viking Adult. Potts, Malcolm, and Thomas Hayden. 2008. Sex and War: How Biology Explains Warfare and Terrorism and Offers a Path to a Safer World. BenBella Books. Powell, Robert. 2006. “War as a Commitment Problem.” International Organization 60 (1): 169–203. Price, Michael. 2012. “Group Selection Theories Are Now More Sophisticated, but Are They More Predictive? A Review of Samuel Bowles and Herbert Gintis, A

215 Cooperative Species: Human Reciprocity and Its Evolution.” Evolutionary Psychology 10 (1): 45–49. Price, Michael E, Leda Cosmides, and John Tooby. 2002. “Punitive Sentiment as an Anti-Free Rider Psychological Device.” Evolution and Human Behavior 23 (3): 203–231. Puts, David A, Coren L Apicella, and Rodrigo A Cárdenas. 2012. “Masculine Voices Signal Men’s Threat Potential in Forager and Industrial Societies.” Proceedings of the Royal Society B: Biological Sciences 279 (1728) (February 7): 601–609. doi:10.1098/rspb.2011.0829. Puurtinen, Mikael, and Tapio Mappes. 2009. “Between-group Competition and Human Cooperation.” Proceedings of the Royal Society B: Biological Sciences 276 (1655) (January 22): 355 –360. doi:10.1098/rspb.2008.1060. Quester, George H. 2002. Offense and Defense in the International System. 3rd ed. Transaction Publishers. Rand, David G., Samuel Arbesman, and Nicholas A. Christakis. 2011. “Dynamic Social Networks Promote Cooperation in Experiments with Humans.” Proceedings of the National Academy of Sciences 108 (48) (November 29): 19193 –19198. doi:10.1073/pnas.1108243108. Richerson, Peter J., and Robert Boyd. 2006. Not by Genes Alone: How Culture Transformed Human Evolution. University Of Chicago Press. Ridley, Mark. 2004. Evolution. Malden, MA: Blackwell Pub. Ridley, Matt. 1994. The Red Queen: Sex and the Evolution of Human Nature. New York: Maxwell Macmillan International. ———. 1997. The Origins of Virtue: Human Instincts and the Evolution of Cooperation. New York: Viking. Rosen, Stephen Peter. 2005. War and Human Nature. Princeton, N.J.: Princeton University Press. http://www.loc.gov/catdir/enhancements/fy0654/2003065590- d.html. Sapolsky, Robert M. 2006. “A Natural History of Peace.” Foreign Affairs. Schultheiss, O, and M Wirth. 2009. “Biopsychological Aspects of Motivation”: 1–91. Sell, Aaron, Gregory A. Bryant, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Reuden, Andre Krauss, and Michael Gurven. 2010. “Adaptations in Humans for Assessing Physical Strength from the Voice.” Proceedings of the Royal Society B: Biological Sciences: 3509–3518. Sell, Aaron, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Rueden, and Michael Gurven. 2009. “Human Adaptations for the Visual Assessment of Strength and Fighting Ability from the Body and Face.” Proceedings of the Royal Society of London Series B-Biological Sciences 276 (1656): 575–584. doi:10.1098/rspb.2008.1177. Sell, Aaron, John Tooby, and Leda Cosmides. 2009. “Formidability and the Logic of Human Anger.” Proceedings of the National Academy of Sciences 106 (35): 15073–15078. Sellers, JG, MR Mehl, and RA Josephs. 2007. “Hormones and Personality: Testosterone as a Marker of Individual Differences.” Journal of Research in Personality 41 (1): 126–138.

216 Sharansky, Natan, and Ron Dermer. 2004. The Case for Democracy: The Power of Freedom to Overcome Tyranny and Terror. 1ST ed. PublicAffairs. Short, Lindsey A., Catherine J. Mondloch, Cheryl M. McCormick, Justin M. Carré, Ruqian Ma, Genyue Fu, and Kang Lee. 2012. “Detection of Propensity for Aggression Based on Facial Structure Irrespective of Face Race.” Evolution and Human Behavior 33 (2) (March): 121–129. doi:10.1016/j.evolhumbehav.2011.07.002. Sidanius, Jim, and Robert Kurzban. 2003. “Evolutionary Approaches to Political Psychology.” In Oxford Handbook of Political Psychology. New York: Oxford University Press. Silverberg, James, and J. Patrick Gray. 1992. Aggression and Peacefulness in Humans and Other Primates. New York: Oxford University Press. http://www.loc.gov/catdir/enhancements/fy0604/91020318-d.html. Simmons, Beth A, Frank Dobbin, and Geoffrey Garrett. 2006. “Introduction: The International Diffusion of Liberalism.” International Organization 60 (4): 781– 810. Smith, Kevin B, Christopher W Larimer, Levente Littvay, and John R Hibbing. 2007. “Evolutionary Theory and Political Leadership: Why Certain People Do Not Trust Decision Makers.” The Journal of Politics 69 (2): 285–299. doi:10.1111/j.1468- 2508.2007.00532.x. Smith, Kevin B, Douglas R Oxley, Matthew V Hibbing, John R. Alford, and John R. Hibbing. 2011a. “Linking Genetics and Political Attitudes: Reconceptualizing Political Ideology.” Political Psychology 32 (3): 369–397. doi:10.1111/j.1467- 9221.2010.00821.x. Smith, Kevin B., Douglas Oxley, Matthew V. Hibbing, John R. Alford, and John R. Hibbing. 2011b. “Disgust Sensitivity and the Neurophysiology of Left-Right Political Orientations.” PLoS ONE 6 (10) (October 19): e25552. doi:10.1371/journal.pone.0025552. Sober, Elliott, and David Sloan Wilson. 1999. Unto Others: The Evolution and Psychology of Unselfish Behavior. Harvard University Press. Somit, A., and S. A. Peterson. 1998. “Review Article: Biopolitics After Three Decades - A Balance Sheet.” British Journal of Political Science 28: 559–571. Somit, Albert, and Steven A. Peterson. 1997. Darwinism, Dominance, and Democracy: the Biological Bases of Authoritarianism. Westport, Conn.: Praeger. Sperber, Dan. 1996. Explaining Culture: a Naturalistic Approach. Oxford: Blackwell. Stanton, SJ, and OC Schultheiss. 2007. “Basal and Dynamic Relationships Between Implicit Power Motivation and Estradiol in Women.” Hormones and Behavior 52 (5): 571–580. Sumner, William Graham. 1970. War and Other Essays. Ams Pr Inc. Symons, Donald. 1979. The Evolution of Human Sexuality. New York: Oxford University Press. ———. 1992. “On the Use and Misuse of Darwinism in the Study of Human Behavior.” In The Adapted Mind: Evolutionary Psychology and the Generation of Culture, 137–160. New York: Oxford University Press. Tajfel, Henry, and John C. Turner. 1986. “The Social Identity Theory of Intergroup Behavior.” In Psychology of Intergroup Relations. Chicago: Nelson Hall.

217 Takezawa, Masanori, and Michael E Price. 2010. “Revisiting ‘The Evolution of Reciprocity in Sizable Groups’: Continuous Reciprocity in the Repeated N-person Prisoner’s Dilemma.” Journal of Theoretical Biology 264 (2) (May 21): 188–196. doi:10.1016/j.jtbi.2010.01.028. Thayer, BA. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security. http://www.mitpressjournals.org/doi/pdf/10.1162/016228800560471. Thayer, Bradley A. 2000. “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics.” International Security 25 (2): 124–151. ———. 2001. “Correspondence: Start the Evolution Without Us.” International Security 26 (1): 194–198. ———. 2004. Darwin and International Relations: On the Evolutionary Origins of War and Ethnic Conflict. Lexington: University Press of Kentucky. Thayer, Bradley A, and Valerie M Hudson. 2010. “Sex and the Shaheed: Insights from the Life Sciences on Islamic Suicide Terrorism.” International Security 34 (4): 37–62. Thompson, William R. 2001. Evolutionary Interpretations of World Politics. New York: Routledge. http://www.loc.gov/catdir/toc/fy022/00066485.html. Tiger, Lionel. 2004. Men in Groups. Revised. Transaction Publishers. Tooby, John, and Leda Cosmides. 1988. “The Evolution of War and Its Cognitive Foundations.” Institute for Evolutionary Studies Technical …. http://www.psych.ucsb.edu/research/cep/papers/EvolutionofWar.pdf. ———. 1990. “On the Universality of Human Nature and the Uniqueness of the Individual: The Role of Genetics and Adaptation.” Journal of Personality 58 (1): 17–67. Tooby, John, Leda Cosmides, and Michael E Price. 2006. “Cognitive Adaptations for N- person Exchange: The Evolutionary Roots of Organizational Behavior.” Managerial and Decision Economics 27 (2-3): 103–129. Trivers, Robert. 1971. “The Evolution of Reciprocal Altruism.” The Quarterly Review of Biology 46 (1): 35–57. ———. 1972. “Parental Investment and Sexual Selection.” In Sexual Selection and the Descent of Man. Chicago: Aldine Publishing. ———. 2000. “The Elements of a Scientific Theory of Self-Deception.” Annals of the New York Academy of Sciences 907 (April): 114–131. ———. 2011. The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life. 1st ed. Basic Books. Turney-High, Harry Holbert. 1949. Primitive War: Its Practice and Concepts. Columbia,: Univ. of South Carolina Press. Van Vugt, Mark. 2009. “Sex Differences in Intergroup Competition, Aggression, and Warfare: The Male Warrior Hypothesis.” Annals of the New York Academy of Sciences 1167 (June): 124–134. doi:10.1111/j.1749-6632.2009.04539.x. Vugt, Mark Van, and Anjana Ahuja. 2011. Naturally Selected: The Evolutionary Science of Leadership. HarperCollins. van Vugt, Mark, and Rob Kurzban. 2007. “Cogntive and Social Adaptations for Leadership and Followership: Evolutionary Game Theory and Group Dynamics.”

218 In Evolution and the Social Mind: Evolutionary Psychology and Social Cognition, 229–243. New York: Psychology Press. Wagner, John D., Mark V. Flinn, and Barry G. England. 2002. “Hormonal Response to Competition Among Male Coalitions.” Evolution and Human Behavior 23 (6): 437–442. Waytz, Adam, and Liane Young. 2011. “The Group-Member Mind Trade-Off.” Psychological Science 22 (12) (December 8): 1–9. doi:10.1177/0956797611423546. Wendt, A. E. 1987. “The Agent-Structure Problem in International-Relations Theory.” International Organization 41 (3): 335–370. Williams, George C. 1966. Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought. Princeton, N.J.: Princeton University Press. Wilson, D.S., and E. Sober. 1994. “Reintroducing Group Selection to the Human Behavioral Sciences.” Behavioral and Brain Sciences 17 (4): 585–607. Wilson, Edward O. 1980. Sociobiology. Cambridge, Mass.: Belknap Press of Harvard University Press. ———. 2000. Sociobiology: the New Synthesis. Cambridge, Mass.: Belknap Press of Harvard University Press. Wilson, M, and M Daly. 2002. “An Evolutionary Psychological Perspective on the Modulation of Competitive Confrontation and Risk Taking.” Hormones. http://134.83.117.117/3518/PDF/PoundetalEvolutionaryPsychPerspective.pdf. Wrangham, Richard. 1999a. “Evolution of Coalitionary Killing.” Yearbook of Physical Anthropology 42: 1–30. ———. 1999b. “Is Military Incompetence Adaptive?” Evolution and Human Behavior 20 (1): 3–17. Wrangham, Richard, and Dale Peterson. 1996. Demonic Males: Apes and the Origins of Human Violence. Boston: Houghton Mifflin. Wrangham, Richard W, and Luke Glowacki. 2012. “Intergroup Aggression in Chimpanzees and War in Nomadic Hunter-Gatherers: Evaluating the Chimpanzee Model.” Human Nature (March 3). doi:10.1007/s12110-012-9132-1. http://www.ncbi.nlm.nih.gov/pubmed/22388773. Wright, Quincy. 1983. A Study of War, 2nd Edition. 2nd ed. University Of Chicago Press. Wright, Robert. 2000. NonZero: the Logic of Human Destiny. New York: Pantheon Books. http://www.loc.gov/catdir/bios/random059/99040859.html. Wynne-Edwards, V. C. 1967. Animal Dispersion in Relation to Social Behaviour. Hafner Publishing Company. Yamagishi, Toshio, and Nobuhiro Mifune. 2009. “Social Exchange and Solidarity: In- group Love or Out-group Hate?” Evolution and Human Behavior 30 (4) (July): 229–237. doi:10.1016/j.evolhumbehav.2009.02.004. Yamagishi, Toshio, Shigehito Tanida, Rie Mashima, Eri Shimoma, and Satoshi Kanazawa. 2003. “You Can Judge A Book by Its Cover: Evidence That Cheaters May Look Different From Cooperators.” Evolution and Human Behavior 24 (4): 290–301.

219

APPENDIX A: SURVEY 1

Script of instructions to be read to subjects: This is a survey designed to investigate people’s perceptions of group behavior. This survey consists of four parts. Please complete them in the order in which they are presented. Please try not to skip any questions. The survey is anonymous – do not write your name on it. If you are uncomfortable answering any of the questions for any reasons, do not answer them. During any part of the survey, if you have any questions, please feel free to ask. Thank you!

General information: You are being asked to participate in a survey that is anonymous and voluntary, and you may quit the survey at any time. The survey may take about 20- 30 minutes to complete. Terminating the survey and/or refusing to take the survey will not result in any form of penalty. If you have any questions regarding your rights as a research subject, please contact the Human Subjects Committee at 893-3807. If you have questions about this particular study, contact Anthony Lopez at [email protected], or (323) 868-7938.

220 Survey, Part I

Scenario 1: Imagine that you and your friends and kinsmen are members of a nomadic horse-riding people, the Pathans, in the year 1050. You and your group are tough and strong, but your life is meager. You cook over dung-fires, drink fermented mare’s milk, sleep in yurts under skins, and freeze every winter. Your ancestral territory is on the dry steppe, but you also border on the prosperous Chinese province of Sinkiang. You have heard that the governor of the province is ambitious, and intends to extend his control into your territory. If you lose your grasslands, you and your family will have nothing. The governor has assembled a war party, which has launched a series of night-time raids on your people. Some of your women have been kidnapped and some of your men were killed. You hear rumors that another raid is going to happen tonight. You and your friends and fellow tribesmen begin to discuss whether you should form a war party to repel the raiders.

Please read the following questions and circle the number that best corresponds to your answer.

1. I would participate in this war effort.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

2. If I chose to participate in this war effort, I would want to contribute a lot to help it succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

221 3. I would be willing to sacrifice a lot to help this war effort succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

4. If I chose to participate, I would be willing to risk my life.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

5. If one of my fellow tribesmen did not participate, I’d think they should be punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

6. If one of my fellow tribesmen did participate, I’d think they should be rewarded.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

222 7. If my group succeeded in repelling the invaders, I would feel very happy.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

8. If my group succeeded in repelling the invaders, it would benefit me personally.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

9. If my group succeeded in repelling the invaders, it would benefit us as a group.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

10. I expect that most of my fellow tribesmen will want to participate in this war effort.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

223 11. Our group could have avoided this war.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

224 Survey, Part II

Below is a list of eight countries in no particular order. Please re-order them according to their approximate distance from Washington, D.C. in the empty spaces below. For instance, given three countries, Argentina, Mexico, and Ecuador, they would be ranked in the following order: 1) Mexico; 2) Ecuador; 3) Argentina. Do the best you can, and please do not leave any blank.

1. Mongolia 2. Australia 3. France 4. Japan 5. South Africa 6. India 7. Italy 8. Madagascar

1. 2. 3. 4. 5. 6. 7. 8.

225 Survey, Part III

Scenario 2: Imagine that you and your friends and kinsmen are members of a nomadic horse-riding people, the Pathans, in the year 1050. You and your group are tough and strong, but your life is meager. You cook over dung-fires, drink fermented mare’s milk, sleep in yurts under skins, and freeze every winter. Your ancestral territory is on the dry steppe, but you also border on the prosperous Chinese province of Sinkiang. You sometimes enter these cities to trade, but the Chinese men and women laugh at your poor clothes, your dirt, and your lack of refinement. You do notice that the men are short, weak, and cowardly, despite the fact that they give themselves airs. The women are also beautiful, and dressed in the best silks. You and your friends have heard that the Mongols to the North had attacked and taken over several cities, and are now wealthy, powerful, and have substantial harems. The Chinese troops had run like rabbits. You and your friends and fellow tribesmen begin to discuss whether you should form a war party to seize one of the neighboring cities.

Please read the following questions and circle the number that best corresponds to your answer.

12. I would participate in this war effort.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

13. If I chose to participate in this war effort, I would want to contribute a lot to help it succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

226 14. I would be willing to sacrifice a lot to help this war effort succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

15. If I chose to participate, I would be willing to risk my life.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

16. If one of my fellow tribesmen did not participate, I’d think they should be punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

17. If one of my fellow tribesmen did participate, I’d think they should be rewarded.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

227 18. If my group succeeded in seizing a city, I would feel very happy.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

19. If my group succeeded in seizing a city, it would benefit me personally.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

20. If my group succeeded in seizing a city, it would benefit us as a group.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

21. I expect that most of my fellow tribesmen will want to participate in this war effort.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

228 22. Our group could have avoided this war.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

229 Survey, Part IV

23. The criminal justice system is too lenient with criminals and increased penalties will produce fewer crimes.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

24. Jail sentences are too light, criminals should be punished severely.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

25. People should be severely punished for their misdeeds.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

26. Most of those who advocate lenient treatment of criminals do not attach sufficient weight to the seriousness of the crimes they commit.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

230 27. More emphasis should be placed on keeping criminals behind bars.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

28. If lawmakers would make tougher laws against crime, we wouldn’t have so many criminals.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

Demographic Information:

Age:

Gender:

Year in School:

Major:

Transfer Student?: Yes/No (please circle one)

Thank you!

231

APPENDIX B: SURVEY 2

Script of instructions to be read to subjects: This is a survey designed to investigate people’s perceptions of group behavior. This survey consists of four parts. Please complete them in the order in which they are presented. Please consider each question carefully, and try not to skip any questions. The survey is anonymous – do not write your name on it. If you are uncomfortable answering any of the questions for any reasons, do not answer them. During any part of the survey, if you have any questions, please feel free to ask. Thank you!

232

Survey, Part I

Although a large war party can be successful against the invaders, if many of the reluctant people do not join the war party, it current size may be insufficient and therefore unlikely to repel the invaders. This may result in your tribe’s collective defeat at the hands of the foreigners.

Although many are reluctant to join the war party, the current amount of committed volunteers should be enough to repel the invaders.

Please read the following questions and circle the number that best corresponds to your answer.

233 1. Under the circumstances, I believe the war party has a ____% chance of repelling the invaders.

2. I would join this war party.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

3. I would want to contribute a lot to help this war party succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

4. I would be willing to sacrifice a lot to help this war party succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

5. I would be willing to risk my life to help this war party succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

234

6. If the war party succeeded in repelling the invaders, I would feel very happy.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

7. If the war party succeeded in repelling the invaders, it would benefit me personally.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

8. If the war party succeeded in repelling the invaders, it would benefit our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

9. Assuming that the war party is successful in repelling the invaders, I expect that if I did join the war party I would personally benefit just as much as if I did not join the war party.

1 2 3 4 5 6 7

Disagree Agree strongly strongly

235

10. I expect that most of the men in my tribe will want to join this war party.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

11. I expect that most of the women in my tribe will want to join this war party.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

12. Our tribe could have avoided this war.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

236 (Questions 13-22) Some of the men in your tribe were reluctant to join, despite being able bodied. If one of these men decided not to join this war party…

13. I believe he should be punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

14. I would be willing to expend time, effort and material resources to have him punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

15. I believe the group should expend time, effort and material resources to have him punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

237 16. I would feel angry towards him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

17. I would view him as a coward.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

18. I would view him as weak.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

19. I would have a lower opinion of him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

238 20. I would question his loyalty to the group as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

21. I would want him to be ostracized from out tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

22. I would want him to be kicked out of our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

239 (Questions 23-32) Some of the women in your tribe were reluctant to join, despite being able bodied. If one of these women decided not to join this war party…

23. I believe she should be punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

24. I would be willing to expend time, effort and material resources to have her punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

25. I believe the group should expend time, effort and material resources to have her punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

240 26. I would feel angry towards her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

27. I would view her as a coward.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

28. I would view her as weak.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

29. I would have a lower opinion of her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

241 30. I would question her loyalty to the group as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

31. I would want her to be ostracized from our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

32. I would want her to be kicked out of our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

242 (Questions 33-39) Some of the men in your tribe were reluctant to join the war party, despite being able bodied. If one of these men did join this war party…

33. I believe he should be rewarded.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

34. I would be willing to expend time, effort and material resources to reward him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

35. The group should expend time, effort and material resources to reward him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

243 36. I would feel grateful towards him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

37. I would believe he was brave.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

38. It would show that he is loyal to the tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

39. I would have a higher opinion of him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

244 (Questions 40-46) Some of the women in your tribe were reluctant to join the war party, despite being able bodied. If one of these women did join this war party…

40. I believe she should be rewarded.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

41. I would be willing to expend time, effort and material resources to reward her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

42. The group should expend time, effort and material resources to reward her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

245 43. I would feel grateful towards her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

44. I would believe she was brave.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

45. It would show that she is loyal to the tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

46. I would have a higher opinion of her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

246

Survey, Part II

Below is a list of eight countries in no particular order. Please re-order them according to their approximate distance from Santa Barbara, California in the empty spaces below. For instance, given three countries, Argentina, Mexico, and Ecuador, they would be ranked in the following order: 1) Mexico; 2) Ecuador; 3) Argentina. Do the best you can, and please do not leave any blank.

Canada Australia France Japan South Africa India

247 Survey, Part III

You and your friends have heard that the Mongols to the North had attacked and taken over several cities, and are now wealthy and powerful. The Chinese troops had run like rabbits. You and your friends and fellow tribesmen begin to discuss whether you should form a war party to seize one of the neighboring cities. Those who join the war party will be able to keep some of the spoils of war for themselves. Some are eager to join and have already committed to participating, but other able-bodied individuals in your tribe are reluctant.

Although a large war party can be successful in seizing a city, if many of the reluctant people do not join the war effort, your war party, at its current size, will be unlikely to seize a city. Instead, it will probably be repelled by the foreigners and be forced to return empty-handed.

Although some are reluctant, the current amount of eager volunteers should be enough to seize a city, even if the reluctant people do not join the war party.

Please read the following questions and circle the number that best corresponds to your answer.

248 1. Under the circumstances, I believe the war party has a ____% chance of seizing a city.

2. I would join this war party.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

3. I would want to contribute a lot to help this war party succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

4. I would be willing to sacrifice a lot to help this war party succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

5. I would be willing to risk my life to help this war party succeed.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

249

6. If the war party succeeded in seizing a city, I would feel very happy.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

7. If the war party succeeded in seizing a city, it would benefit me personally.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

8. If the war party succeeded in seizing a city, it would benefit our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

250 9. Assuming that the war party is successful in seizing a city, I expect that if I did join the war party I would personally benefit just as much as if I did not join the war party.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

10. I expect that most of the men in my tribe will want to join this war party.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

11. I expect that most of the women in my tribe will want to join this war party.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

12. Our tribe could have avoided this war.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

251 (Questions 13-22) Some of the men in your tribe were reluctant to join, despite being able bodied. If one of these men decided not to join this war party…

13. I believe he should be punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

14. I would be willing to expend time, effort and material resources to have him punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

15. I believe the group should expend time, effort and material resources to have him punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

252 16. I would feel angry towards him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

17. I would view him as a coward.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

18. I would view him as weak.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

19. I would have a lower opinion of him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

253

20. I would question his loyalty to the group as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

21. I would want him to be ostracized from out tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

22. I would want him to be kicked out of our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

254 (Questions 23-32) Some of the women in your tribe were reluctant to join, despite being able bodied. If one of these women decided not to join this war party…

23. I believe she should be punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

24. I would be willing to expend time, effort and material resources to have her punished.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

25. I believe the group should expend time, effort and material resources to have her punished.

1 2 3 4 5 6 7

Disagree Agree strongly strongly

255 26. I would feel angry towards her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

27. I would view her as a coward.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

28. I would view her as weak.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

29. I would have a lower opinion of her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

256 30. I would question her loyalty to the group as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

31. I would want her to be ostracized from our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

32. I would want her to be kicked out of our tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

257 (Questions 33-39) Some of the men in your tribe were reluctant to join the war party, despite being able bodied. If one of these men did join this war party…

33. I believe he should be rewarded.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

34. I would be willing to expend time, effort and material resources to reward him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

35. The group should expend time, effort and material resources to reward him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

258 36. I would feel grateful towards him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

37. I would believe he was brave.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

38. It would show that he is loyal to the tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

39. I would have a higher opinion of him.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

259 (Questions 40-46) Some of the women in your tribe were reluctant to join the war party, despite being able bodied. If one of these women did join this war party…

40. I believe she should be rewarded.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

41. I would be willing to expend time, effort and material resources to reward her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

42. The group should expend time, effort and material resources to reward her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

260 43. I would feel grateful towards her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

44. I would believe she was brave.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

45. It would show that she is loyal to the tribe as a whole.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

46. I would have a higher opinion of her.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

261 Survey, Part IV

1. The criminal justice system is too lenient with criminals and increased penalties will produce fewer crimes.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

2. Jail sentences are too light, criminals should be punished severely.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

3. People should be severely punished for their misdeeds.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

4. Most of those who advocate lenient treatment of criminals do not attach sufficient weight to the seriousness of the crimes they commit.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

262 5. More emphasis should be placed on keeping criminals behind bars.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

6. If lawmakers would make tougher laws against crime, we wouldn’t have so many criminals.

1 2 3 4 5 6 7 Disagree Agree strongly strongly

Demographic Information:

Age:

Sex: Male / Female

Year in School:

Major:

Political Affiliation: Democrat / Republican / Other: ______

Men only: I am stronger than ____% of other men.

263

Women only: I am stronger than _____% of other women.

Transfer Student: Yes / No (please circle one)

Thank you!

264

APPENDIX C: ADDITIONAL DATA for SURVEY 1

The following four tables contain the results from bivariate and multivariate OLS regressions on two dependent variables in defense and offense: Punitive Sentiment and

Reward Sentiment. Independent variables are four measures of participation, and three measures of expected benefit.

DEFENSE DV: Punitive Sentiment Independent Measures Bivariate Multivariate …willing to participate… .58*** .52* …want to contribute a lot… .50** -.49 …willing to sacrifice a lot... .49*** .47 …willing to risk my life… .34** -.003

DV: Reward Sentiment Independent Measures Bivariate Multivariate …feel very happy… .32 .23 …benefit me personally… .42** .40* …benefit us as a group… .29 -.11 p < .001 = *** p < .01 = ** p < .05 = * (non-standardized OLS regression coefficients reported)

OFFENSE DV: Punitive Sentiment Independent Measures Bivariate Multivariate …willing to participate… .56*** .43*** …want to contribute a lot… .34*** -.04 …willing to sacrifice a lot... .47*** .19 …willing to risk my life… .26** -.03

DV: Reward Sentiment Independent Measures Bivariate Multivariate …feel very happy… .73*** .55*** …benefit me personally… .73*** .39* …benefit us as a group… .63*** -.15 p < .001 = *** p < .01 = ** p < .05 = * (non-standardized OLS regression coefficients reported)

265 ADDITIONAL DATA for SURVEY 2

Sex Differences in Offense and Defense contingent upon perceived labor levels:

(Labor 1 = Labor Sufficient) (Labor 2 = Labor Insufficient) Offense Males Females p p Males Females p N = 37 N = 56 (m/w) N = 37 N = 58 ExpSeize % 62.95 63.48 .91 .01/.00 48.73 49.66 .84 PersBenef 5.11 5.16 .87 .10/.64 5.73 5.29 .18 BenefGroup 6 5.77 .39 .56/.58 6.16 5.90 .29 Happy 4.78 5.02 .52 .17/.45 5.35 4.78 .12

OffJoin 3.89 3.55 .40 .06/.59 4.73 3.72 .008 OffContrib 3.97 3.77 .61 .03/.42 4.95 4.02 .01 OffSacrifice 3.08 3.13 .89 .00/.32 4.41 3.41 .01 OffRiskLife 2.76 2.27 .16 .02/.27 3.84 2.57 .001

(Labor 1 = Labor Sufficient) (Labor 2 = Labor Insufficient) Defense Males Females p p Males Females p N = 37 N = 56 m/w N = 37 N = 58 ExpRepel 69.70 56.29 .007 .00/.69 52.68 54.74 .62 PersBenef 5.89 5.98 .77 .28/.16 6.24 6.28 .88 BenefGroup 6.16 6.52 .14 .13/.59 6.57 6.43 .50 Happy 6.11 6.25 .63 .20/.55 6.51 6.36 .50

DefJoin 5.43 4.79 .09 .65/.06 5.62 5.36 .45 DefContrib 5.62 5.52 .77 .29/.20 6.03 5.81 .40 DefSacrifice 5.35 5 .33 .23/.23 5.81 5.31 .09 DefRiskLife 4.86 3.86 .01 .22/.03 5.41 4.55 .02 • T-tests for differences in means

The tables above compile results of t-test for differences in means between various measures in offense and defense contingent upon labor levels. The far left column lists the measures within which differences between and within sex were measured. The tables can be interpreted according to the following example. The first line of the top table considers sex differences in the expected probability of success in offense.

Beginning from left to right, the t-test for differences in means between male and female average expected probability of success in offense when labor is sufficient revealed no

266 statistically significant difference (p = .91). Moving from left to right, it also shows that among men there is a statistically significant difference in expected probability of success between the two labor conditions (p < .01) and among females, there is also a statistically significant difference in expected probability of success between the two labor conditions

(p < .001). Moving further from left to right, the first column shows no statistically significant difference between male and female expected probability of success in offense when labor is insufficient (p = .84).

The variables in the far left column are the following, from top to bottom:

Expected probability of success; Expected personal benefit; Expected benefit to the group; Expected happiness upon success; Willingness to participate; Willingness to contribute; Willingness to sacrifice a lot; Willingness to risk one’s life.

The next six tables present the results of bivariate and multivariate OLS regressions of five independent variables on the dependent variable Willingness to participate. The six tables below are in two groups of three tables. The first group of three tables examines the effect of five variables on the dependent variable willingness to participate between offense and defense, and only when labor is sufficient. The second group of three tables examines the same relationships but only when labor is INsufficient.

The five independent measures, in order of top to bottom as listed, are: Expected probability of success; Expected personal benefit; Expected group benefit; Expectations that women are likely to participate; Expectations that men are likely to participate.

Within each group of three tables, the first table considers the subject population as a

267 whole and does not distinguish between males and females. The second table, examines only males, and the third table examines only females.

Labor Sufficient [Men+Women; N=93] Offense Defense Y = JOIN Bivariate Multiple Bivariate Multiple Seize/Repel .28** .08 .50*** .30** PersBenef .35*** .31^ .46*** .14 BenefTribe .27** -.13 .49*** .17 ExpWJoin .16 .02 .46*** .22* ExpMJoin .43*** .35** .50*** .14 p < .001 = *** p < .01 = ** p < .05 = * p < .10 = ^ (standardized OLS regression coefficients)

[Men; N=37] Offense Defense Y = JOIN Bivariate Multiple Bivariate Multiple Seize/Repel .36* .08 .55*** .10 PersBenef .45** .57* .64** .16 BenefTribe .26 -.27 .69*** .23 ExpWJoin -.07 -.23 .51*** .17 ExpMJoin .36* .33^ .72*** .29

[Women; N=56] Offense Defense Y = JOIN Bivariate Multiple Bivariate Multiple Seize/Repel .18 .07 .42** .29* PersBenef .27* .02 .30* .08 BenefTribe .29* .06 .33* .16 ExpWJoin .40** .25* .46*** .32* ExpMJoin .50*** .37** .30* .04

268 Labor Insufficient [Men+Women; N=95] Offense Defense Y = JOIN Bivariate Multiple Bivariate Multiple Seize/Repel .31** .21* .30** .11 PersBenef .55*** .39*** .39*** .21 BenefTribe .51*** .17 .45*** .11 ExpWJoin .35*** .27** .45*** .26** ExpMJoin .38*** .00 .43*** .16 p < .001 = *** p < .01 = ** p < .05 = * p < .10 = ^ (standardized OLS regression coefficients)

[Men; N=37] Offense Defense Y = JOIN Bivariate Multiple Bivariate Multiple Seize/Repel .24 .15 .32^ .27 PersBenef .70*** .48** .41 .47 BenefTribe .59*** .20 .34* -.11 ExpWJoin .36* .24^ .25 .25 ExpMJoin .39* .02 .07 -.26

[Women; N=58] Offense Defense Y = JOIN Bivariate Multiple Bivariate Multiple Seize/Repel .39** .21^ .29* .04 PersBenef .44*** .34* .47*** .13 BenefTribe .44*** -.00 .42** -.04 ExpWJoin .45*** .32** .59*** .39*** ExpMJoin .48*** .19 .64*** .41^

269