States in Mind Anthony C. Lopez, Rose Mcdermott, and Michael

Home , Azar Gat, Donald Symons, John Tooby, Leda Cosmides, Mark Flinn, Mark van Vugt

States in Mind States in Mind Anthony C. Lopez, Rose McDermott, and Evolution, Coalitional Psychology, and Michael Bang International Politics Petersen

One of the most commonly studied puzzles in international politics is the recurrence of coalitional competition and aggression between political groups such as states. Indeed, this pattern constitutes an enduring and central feature of all politics. Yet despite the tragic endurance of this leitmotif throughout history, its manifestation varies through time and space. Some wars are fought for honor or revenge, whereas others are ignited for mere opportunism or as a consequence of various misperceptions, whatever their source. We argue that evolutionary theory provides a theoretical framework that can explain both the stubborn endurance and dynamic diversity of coalitional behavior. Debate on the relevance of “human nature” and biological factors for explaining political behavior is not new.1 Yet the comprehensive value of evolutionary theory for explaining important aspects of international politics has not been adequately explicated. As we discuss below, this has in part been a consequence of general skepticism about the validity and scope of evolutionary theory for explaining political behavior. We argue, however, that evolutionary psychology can generate falsiªable ex ante predictions that are of central interest to the study of international politics, and we offer several hypotheses derived from this model to illustrate the depth of this approach. Evo- lutionary psychologists have already generated a large body of work that suggests that the human brain contains webs of psychological mechanisms, or adaptations, each designed to operate in domains relevant to modern politics, and which emerged as a product of natural selection. Furthermore, researchers have begun to realize that humans come equipped with an evolved “coali-

Anthony C. Lopez is a Ph.D. candidate in Political Science at Brown University. Rose McDermott is Profes- sor of Political Science at Brown University. Michael Bang Petersen is Associate Professor of Political Sci- ence and Government at Aarhus University.

The authors would like to thank Leda Cosmides, Andrew Delton, Max Krasnow, Aaron Sell, John Tooby, and the participants of the research seminar at the Center for Evolutionary Psychology at the University of California, Santa Barbara, for critical feedback on concepts developed in this article. For helpful comments on earlier drafts, the authors are indebted to Benjamin Cohen, Jonathan Cowden, Jonathan Mercer, and the anonymous reviewers.

1. John R. Alford and John R. Hibbing, “The Origin of Politics: An Evolutionary Theory of Politi- cal Behavior,” Perspectives on Politics, Vol. 2, No. 4 (December 2004), pp. 707–723; Bradley A. Thayer, “Bringing in Darwin: Evolutionary Theory, Realism, and International Politics,” Interna- tional Security, Vol. 25, No. 2 (Fall 2000), pp. 124–151; and Duncan S.A. Bell and Paul K. MacDon- ald, “Correspondence: Start the Evolution without Us,” International Security, Vol. 26, No. 1 (Summer 2001), pp. 187–194.

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tional psychology,” as a consequence of adaptive problems faced by our ancestors related to social and political life such as collective action, coalition formation and maintenance, cheater detection, resource division, the negotia- tion of status hierarchies, and war.2 Note that all of these problems have obvious modern analogues that leaders and countries confront daily and that constitute the central themes of the study of international politics. Thus, we argue that evolutionary psychology provides a necessary framework for explaining the puzzling endurance of many types of international behavior, such as coalitional aggression and its modern manifestation, war. We aim to show that evolutionary psychology can indeed offer useful and falsi- ªable hypotheses for international politics, and that misgivings regarding such an approach have no theoretical merit. Furthermore, this approach is dynamic enough to encompass disparate motives and preference structures—egoism and cooperativeness; rational and “irrational” behavior—under the same explanatory rubric that can help to solve old puzzles and shed light on new discoveries. These goals are accomplished in three sections. First, we introduce the theoretical framework of evolutionary psychology. Second, we respond to what we identify as two major misconceptions about the use of evolutionary theory for explaining political behavior. The ªrst misconception argues that evolutionary models are “politically indeterminate,” and the second argues that evolutionary theory cannot be used to generate predictions in the realm of social or political behavior. In the third section, we develop and present speciªc hypotheses within three areas of inquiry: (1) perception and representation of political coalitions such as states; (2) the facilitation of action within and between coalitions; and (3) sex differences in political attitudes and behavior. These three areas make up a signiªcant aspect of what we refer to as human “coalitional psychology.” This coalitional psychology represents the set of underlying psychological mechanisms, designed by natural selection, that enables and generates behavior among and within coalitions. As we discuss in detail below, this coalitional psychology is active in the management of internal coali-

2. John Tooby, Leda Cosmides, and Michael E. Price, “Cognitive Adaptations for n-Person Ex- change: The Evolutionary Roots of Organizational Behavior,” Managerial and Decision Economics, Vol. 27, Nos. 2–3 (March–May 2006), pp. 103–129; Azar Gat, War in Human Civilization (Oxford: Ox- ford University Press, 2006); Christopher Boehm, Hierarchy in the Forest: The Evolution of Egalitarian Behavior (Cambridge, Mass.: Harvard University Press, 1999); Michael E. Price, Leda Cosmides, and John Tooby, “Punitive Sentiment as an Anti-Free Rider Psychological Device,” Evolution and Human Behavior, Vol. 23, No. 3 (May 2002), pp. 203–231; Steven Pinker, How the Mind Works (New York: W.W. Norton, 1997); and Richard W. Wrangham, “Evolution of Coalitionary Killing,” Year- book of Physical Anthropology, Vol. 42 (1999), pp. 1–30.

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tion dynamics such as leadership and cooperation, as well as in the external dynamics of competition and aggression (war) among coalitions.

Evolutionary Psychology: A Theoretical Introduction

Evolutionary psychology is an approach to understanding behavior that argues that the functional structure of the human brain has been designed by natural selection to respond reliably and efªciently to adaptive problems in our ancestral social and ecological environments.3 An “adaptive problem” is any challenge, threat, or opportunity faced by an organism in its environment that is evolutionarily recurrent (i.e., not a onetime or otherwise novel problem) and affects reproductive success. For example, coalitional aggression, or war, has been a persistent social challenge faced by humans over the course of their evolution.4 Researchers have provided theoretical and empirical support for the existence of evolved psychological mechanisms in humans designed by natural selection to navigate the challenge of coalitional conºict.5 In this article, we use the word “mechanism” to refer to psychological adaptations that have been designed by natural selection. These psychological mechanisms, as our main unit of analysis, are physically instantiated systems in the brain that take a range of input from within and around the organism, and transform

3. Leda Cosmides and John Tooby, “From Evolution to Behavior: Evolutionary Psychology as the Missing Link,” in John Dupré, ed., The Latest on the Best: Essays on Evolution and Optimality (Cam- bridge, Mass.: MIT Press, 1987), pp. 276–306; Jerome H. Barkow, Leda Cosmides, and John Tooby, eds., The Adapted Mind: Evolutionary Psychology and the Generation of Culture (New York: Oxford University Press, 1992); and David M. Buss, ed., The Handbook of Evolutionary Psychology (Hoboken, N.J.: John Wiley and Sons, 2005). Our discussion of evolutionary psychology follows the adaptationist approach of evolutionary biology’s “modern synthesis.” See George C. Williams, Ad- aptation and Natural Selection: A Critique of Some Current Evolutionary Thought (Princeton, N.J.: Princeton University Press, 1966); and Ernst Mayr, “How to Carry Out the Adaptationist Pro- gram?” American Naturalist, Vol. 121, No. 3 (March 1983), pp. 324–334. 4. Lawrence H. Keeley, War before Civilization: The Myth of the Peaceful Savage (New York: Oxford University Press, 1996); Keith F. Otterbein, “The Origins of War,” Critical Review, Vol. 11, No. 2 (Spring 1997), pp. 251–277; Azar Gat, “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-Gatherer Fighting, Pt. 1: Primary Somatic and Reproductive Causes,” Anthropological Quarterly, Vol. 73, No. 1 (January 2000), pp. 20–34; and Steven A. LeBlanc and Kath- erine E. Register, Constant Battles: The Myth of the Peaceful, Noble Savage (New York: St. Martin’s, 2003). 5. John Tooby and Leda Cosmides, “The Evolution of War and Its Cognitive Foundations,” Tech- nical Report, No. 88-1 (Santa Barbara: Institute for Evolutionary Studies, University of California, Santa Barbara, 1988); Richard W. Wrangham, “Is Military Incompetence Adaptive?” Evolution and Human Behavior, Vol. 20, No. 1 (January 1999), pp. 3–17; John D. Wagner, Mark V. Flinn, and Barry G. England, “Hormonal Response to Competition among Male Coalitions,” Evolution and Human Behavior, Vol. 23, No. 6 (November 2002), pp. 437–442; Dominic D.P. Johnson, Rose McDermott, Emily S. Barrett, Jonathan Cowden, Richard W. Wrangham, Matthew H. McIntyre, and Stephen Peter Rosen, “Overconªdence in Wargames: Experimental Evidence on Expectations, Aggression, Gender, and Testosterone,” Proceedings of the Royal Society B, June 20, 2006, pp. 2513–2520; and Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Exchange.”

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that input into output: distally in the form of behavior, motivation, and so on, and proximally in the form of, for example, physiological signals such as shifts in hormone levels or neurotransmitter patterns. Because this is essentially a process of information transfer and transformation, we also refer to these evolved mechanisms as “information-processing systems.” For example, evolutionary theorists have posited the existence of psychological mechanisms designed for the regulation of aggression in conºicts of interest.6 Because an important ancestral cue that would have helped to determine one’s leverage in such contests was pure physical strength, researchers predicted that self-assessment of strength would be one cue that would regulate one’s willingness to resort to force to resolve conºicts of interest. Not only was this the case, but physical strength on its own was a signiªcant predictor of support for the use of violence in international disputes as well.7 This is an example of an evolved psychological mechanism (the psychological calibration of aggression contingent on physical strength), designed by natural selection in response to an adaptive problem (conºicts of interest), that acts to transform input (self-assessments of relevant physical characteristics) into output (dominance displays, aggression, anger, testosterone increase, etc.) that would have achieved adaptive results in ancestral environments. This is also an example of an adaptation designed for an ancestral environment producing output that appears “irrational” in a modern international context—especially where mechanized weapons are available. A rational choice model would not predict that personal strength would track perceptions on the international use of force. Regarding the scope of selection pressures and resultant psychological mechanisms, it is important to recognize that adaptive problems cluster into “domains.” When a set of challenges shares an informational cue structure, or a set of environmental triggers, that allows content-laden psychological programs to reliably track and respond to these challenges with appropriately in- tegrated behavioral, emotional, cognitive, and physiological processes, we say that these challenges constitute a speciªc “domain.”8 For example, the problems of quickly and reliably detecting and differentiating allies from enemies share an informational cue structure that is distinct from problems such as

6. Geoff A. Parker, “Assessment Strategy and Evolution of Fighting Behavior,” Journal of Theoreti- cal Biology, Vol. 47, No. 1 (September 1974), pp. 223–243; and John Archer, The Behavioural Biology of Aggression (Cambridge: Cambridge University Press, 1988). 7. Aaron Sell, John Tooby, and Leda Cosmides, “Formidability and the Logic of Human Anger,” Proceedings of the National Academy of Sciences, Vol. 106, No. 35 (September 2009), pp. 15073–15078. 8. Leda Cosmides and John Tooby, “Origins of Domain Speciªcity: The Evolution of Functional Organization,” in Lawrence A. Hirshfeld and Susan A. Gelman, eds., Mapping the Mind: Domain Speciªcity in Cognition and Culture (New York: Cambridge University Press, 1994), pp. 85–116.

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distinguishing a potential mate from kin or locating food. Thus, adaptive psychological mechanisms are expected to be “domain speciªc” because each mechanism is designed to attend to speciªc cues related to a particular problem, and a basic principle of engineering is that the same tool rarely solves two distinct problems with equal efªciency.9 In this sense, psychological adaptations depend on combined information from both the external and internal environment (e.g., physiology, informational output from other psychological mechanisms, etc.) to generate a range of contingent and adaptively appropri- ate behavior. Speciªc emotions can be understood in these terms as well, given that they provide superordinate programs that can operate to either potentiate or dampen a whole host of reactions. For example, fear improves vision and hearing, whereas anger tends to make people more optimistic about their likelihood of victory.10 The value of an evolutionary psychological approach thus lies in its ability to set out, a priori, clear lines of evidence that must be met in order to identify an adaptive problem and derive hypotheses about the precise information- processing structure of the psychological mechanism designed to solve this adaptive problem.11 To accomplish these goals, evolutionary psychologists of-

9. Importantly, there is much theoretical debate about the extent of domain speciªcity that is char- acteristic of evolved psychological mechanisms. Many evolutionary psychologists acknowledge that in addition to the array of highly domain-speciªc adaptations in the brain, selection also could have favored certain domain-general mechanisms to deal with novel environmental challenges. Nevertheless, this debate distracts from the underlying agreement among scholars about the design of adaptations, which is our basic point: the ultimate constraint on the design of a biological adaptation is the selection pressure that favored its emergence. Therefore, it is often more precise for analysis to be driven by the question: How does an adaptation represent an efªcient so- lution to a particular reproductive challenge? It is the causal link between selection pressures and the adaptations they shape that is important, not a priori attachments to an arbitrary level of spe- ciªcity or generality. But because in a real sense there is no such thing as a “general” problem that an organism confronts, the convention among evolutionary theorists is to view adaptations as specialized solutions to speciªc reproductive challenges. See Dan Chiappe and Kevin MacDonald, “The Evolution of Domain-General Mechanisms in Intelligence and Learning,” Journal of General Psychology, Vol. 132, No. 1 (January 2005), pp. 5–40; and H. Clark Barrett, Leda Cosmides, and John Tooby, “The Hominid Entry into the Cognitive Niche,” in Steven W. Gangstead and Jeffry A. Simpson, eds., The Evolution of Mind: Fundamental Questions and Controversies (New York: Guilford, 2007), pp. 241–248. 10. Randolph M. Nesse, “Evolutionary Explanations of Emotions,” Human Nature, Vol. 1, No. 3 (1990), pp. 261–289; and Leda Cosmides and John Tooby, “Evolutionary Psychology and the Emo- tions,” in Michael Lewis and Jeanette M. Haviland-Jones, eds., Handbook of the Emotions, 2d ed. (New York: Guilford, 2000), pp. 91–115. 11. It should be noted that the better-known approach of behavior genetics is to be distinguished from evolutionary psychology, which we focus on here. Although both approaches investigate the biological bases of behavior, the questions they ask are fundamentally different. Behavior genetics and related methods explain behavioral variation as a consequence of underlying genetic differences among individuals in a population. An adaptationist approach such as evolutionary psychology, however, explains behavior as the functional output of a species-typical evolved psychology interacting with variable internal and external environments. The latter, which we focus on in this article, has received less attention in political science generally.

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ten investigate the environment of evolutionary adaptedness (EEA). The EEA represents a statistical composite of the environmental regularities faced by humans in the environment in which a particular adaptation evolved.12 Just as the past is never perfectly accessible to modern scientists, neither is our evolutionary history entirely unknowable. If it were, many disciplines in addition to evolutionary theory, such as geology and archaeology, would be stillborn. In addition to reliance on evidence from paleontology, archaeology, and accumu- lated knowledge of ancestral habitats, evolutionary theorists also make use of evidence from modern-day hunter-gatherer societies and comparisons with primate systems.13 The identiªcation of an adaptive problem through an empirical investigation of ancestral environments can be combined with a “task analysis,” which establishes the evolvability criteria of a psychological adaptation. This is a way of asking: If a mechanism was favored by selection to solve an adaptive problem, what features must it logically possess if it is to do so successfully? To use the above example of the “aggression system,” if such a psychological adaptation was favored by selection, it must be able to compute relatively accurate and adaptively useful assessments of the ªghting ability of oneself and others based on cues that carry this information.14 Researchers subsequently vali- dated this hypothesis by showing that people are extraordinarily good at assessing the ªghting ability of men based on cues such as physical size, facial characteristics, and voice.15 One can easily extend this set of hypotheses to the coalitional level, and expect to see systems designed for the regulation of aggression between coalitions that depend on endogenous cues such as relative numbers and physical size, and exogenous cues such as geographical location and proximity to other coalitions.16 From this analysis, we can see that psychological adaptations reºect and literally embody the structure of the adaptive problems they were designed to solve. In effect, therefore, our evolved psycho-

12. John Tooby and Leda Cosmides, “The Psychological Foundations of Culture,” in Barkow, Cosmides, and Tooby, The Adapted Mind, pp. 19–136. 13. David M. Buss, Evolutionary Psychology: The New Science of the Mind, 2d ed. (Boston: Allyn and Bacon, 2004); and John Tooby and Irven DeVore, “The Reconstruction of Hominid Behavioral Evo- lution through Strategic Modeling,” in Warren G. Kinzey, ed., The Evolution of Human Behavior: Pri- mate Models (Albany: State University of New York Press, 1987), chap. 10. 14. Parker, “Assessment Strategy and Evolution of Fighting Behavior”; and Archer, The Behav- ioural Biology of Aggression. 15. Aaron Sell, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Rueden, and Mi- chael Gurven, “Human Adaptations for the Visual Assessment of Strength and Fighting Ability from the Body and Face,” Proceedings of the Royal Society B, February 2009, pp. 575–584; and Aaron Sell, Gregory A. Bryant, Leda Cosmides, John Tooby, Daniel Sznycer, Christopher von Reuden, Andre Krauss, and Michael Gurven, “Adaptations in Humans for Assessing Physical Strength from the Voice,” Proceedings of the Royal Society B, June 2010, pp. 3509–3518. 16. Richard Wrangham and Dale Peterson, Demonic Males: Apes and the Origins of Human Violence (Boston: Houghton Mifºin, 1996); and Wrangham, “Evolution of Coalitionary Killing.”

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logical architecture contains an embedded “map” of the reproductively sig- niªcant events and objects of the world in which humans evolved, including, as is most relevant for this article, our coalitional environment. This model is not deterministic or wholly internally driven as some misun- derstand; rather, our evolved psychology has been designed to operate ºexibly to take advantage of speciªc environmental (both internal and external) cues in order to determine how best to respond to particular reproductively sig- niªcant challenges. Adaptations are often facultative, meaning that the optimality of behavior varies with changes in the informational structure of the environment. Thus, models that posit environmental causes are not rendered obsolete by this approach; rather, such variables constitute critical input into the psychological mechanisms that are triggered by such forces. In this regard, the strength of the evolutionary psychological approach lies in its engineering analysis of information-processing systems in the brain. As mentioned above, this is accomplished by examining the environmental input that the system is designed to rely on, and by examining the link between this environmental input and speciªc behavioral output. In this sense, learning is not an alternative to biological models of behavior; rather, it remains an integral part of the process. Indeed, learning itself is enabled by and requires a suite of psychological mechanisms that allows humans to represent and recall the associations that allow identiªcation and categorization to take place.17 Applying evolutionary psychology to the study of politics requires one to specify how psychological mechanisms that were adapted to ancestral milieus function in modern mass-level society. In this regard, a number of observations need to be stressed. First, we would not expect mechanisms to have evolved for problems that did not occur repeatedly in our evolutionary past, or whose successful resolution did not confer a reproductive beneªt. Second, we would not expect mechanisms that proved successful in human evolutionary history to necessarily be at all adaptive under current environmental conditions.18 Indeed, we would often expect the reverse: for example, individuals who survived in the past because of their differential ability to retain body fat suffer premature morbidity and mortality in a modern world of fast food and sedentary lifestyles. Third, we expect structural similarities between modern political phenomena (e.g., war) and the informational cue structure of ancestral challenges (e.g., coalitional aggression) to automatically induce us to rep-

17. Charles R. Gallistel, The Organization of Learning (Cambridge, Mass.: MIT Press, 1990); and Dan Sperber, Explaining Culture: A Naturalistic Approach (Oxford: Blackwell, 1996). 18. Donald Symons, “On the Use and Misuse of Darwinism in the Study of Human Behavior,” in Barkow, Cosmides, and Tooby, The Adapted Mind, pp. 137–162.

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resent and interpret the former through the psychological processes selected in response to the latter.19 When taken together, these observations imply that many “irrational” decisions are not necessarily the result of general constraints on human cognition (such as bounded rationality). Rather, they can reºect the activation of highly sophisticated information-processing mechanisms that operate on assumptions that may no longer remain valid in modern environments. As we argue in more detail below, Homo sapiens evolved in small-scale social groups, and thus most, if not all, of our species-typical psychological mechanisms, and the intuitions they give rise to, operate on the assumptions relevant in this kind of environment. This remains true even as we now reason about modern war between societies composed of millions, which can lead to a number of seemingly irrational behaviors in international relations—behaviors that nonetheless were adaptive under ancestral conditions. Therefore, it is important to remember that human behavior is not the result of constant and conscious striving at every moment to maximize utility or reproductive success. Instead, humans and other organisms designed by natural selection can be thought of as “adaptation executors” rather than “ªtness maximizers” or “utility maximizers.” Thus, evolutionary psychology offers political scientists an account of the origins of psychological information-processing structures and the range of preferences and behaviors that they help to generate. This approach can also help to explain seemingly “irrational” behavior as often the result of a “mismatch” between the world a mechanism was designed to confront and the world it actually meets. Before presenting speciªc hypotheses that render these dynamics explicit, we address two important misconceptions about evolutionary theory in political science. Once these are addressed, we then turn to a discussion of our evolved coalitional psychology and the hypotheses of representation and behavior derived from this model for international politics.

Evolution and Behavior: Two Misconceptions

We have argued that one reason for the lacunae of evolutionary theory in the study of international relations is that the theoretical means for conducting such research has yet to be fully articulated. This situation often leads scholars to spend undue time arguing why a particular path should be taken instead of showing how that path might be taken. This article aims to correct this theoret-

19. Michael Bang Petersen, “Public Opinion and Evolved Heuristics: The Role of Category-Based Inference,” Journal of Cognition and Culture, Vol. 9, No. 3 (2009), pp. 367–389.

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ical gap by outlining evolutionary psychology and providing examples of how speciªc hypotheses can be derived from this approach. Some scholars, however, may question the usefulness and validity of applying evolutionary theory at all to generate predictions and hypotheses in the realm of political behavior. It is to these criticisms in general that we turn before exploring our hypotheses.

political indeterminacy Duncan Bell has argued that evolutionary psychology is “politically indeterminate.” For example, in his critique of evolutionary approaches to international relations, Bell argues that ªndings from evolutionary psychology are “open to multiple and contradictory readings.”20 Similarly, in their critique of Bradley Thayer’s application of Darwinist thinking to international relations, Bell and Paul MacDonald argue that this perspective “cannot tell us when individual humans will behave egoistically, submissively, or altruistically.”21 Furthermore, the argument proceeds, evolutionary dynamics have been uti- lized to show not only that egoism and dominance are “product[s] of the evolutionary process,”22 but also that humans are “cooperative, but not altruistic; competitive, but not exclusively so.”23 So are humans selªsh or cooperative? Are states condemned to endure never-ending security dilemmas fueled by perennial distrust and structurally insurmountable incentives to misrepresent, or are states ultimately cooperative and led by an underlying harmony of interest to seek gains from trade and live happily on the Pareto frontier? The perceived “political indeterminacy” of applications of evolutionary psychology to international relations is a consequence of the failure of previous scholarship to clearly and accurately elucidate the key unit of analysis that has earned evolutionary psychologists great theoretical and empirical traction in their own research: the information-processing structure of evolved psychological mechanisms. This is important to recognize because natural selection does not shape behavior directly; instead, psychological design features are re- tained by selection to the extent that they promote the reproductive success of their bearers by generating effective solutions (i.e., environmentally contingent adaptive behavior) to recurrent problems. Thus, it is not evolution or natural selection but evolved psychological mechanisms that generate behavioral out-

20. Duncan Bell, “Beware of False Prophets: Biology, Human Nature, and the Future of Interna- tional Relations Theory,” International Affairs, Vol. 82, No. 3 (May 2006), p. 504. 21. Thayer, “Bringing in Darwin”; and Bell and MacDonald, “Correspondence: Start the Evolution without Us,” p. 192. 22. Thayer, “Bringing in Darwin,” p. 125. 23. Alford and Hibbing, “The Origin of Politics,” p. 709.

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comes in interaction with the environment. By avoiding a direct engineering analysis of these systems and instead making the leap from evolution to behavior while leaving the necessary intermediate step (mechanism design) am- biguous, previous scholarship has left itself vulnerable to an erroneous inference. Bell and others are led to believe that the same blanket “evolutionary process” is being invoked to explain opposing outcomes; that is, a constant is being used to explain a variable—both aggression and altruism. As we show, however, it is not the “evolutionary process” that causes behavior; rather, various “proximate” psychological mechanisms designed in response to a range of “ultimate” adaptive challenges (regulating aggression, engaging in cooperation, etc.) are responsible for generating myriad behavioral outcomes in interaction with the environment. The adaptations we describe are psychologically instantiated conditional strategies that determine adaptively relevant output given a range of contextual cues. Indeed, effective systems should prove ºexible in nature, especially where reproductive challenges are dynamic rather than static. An individual who is universally egoistic or altruistic (i.e., invariant egoism or altruism across contextual domains, or, what evolutionary game theorists would refer to as an “unconditional strategy”) would likely have been at a ªtness disad- vantage relative to peers entrained with contextually dependent strategies for being egoistic in certain circumstances (e.g., when confronting enemies) and altruistic in others (e.g., when interacting with kin or one’s in-group). For example, evolutionary game theory has shown how the strategy “cooperate ªrst, then do what your opponent did on their last round” (TIT-FOR- TAT) is superior to the strategies “always defect” or “always cooperate.”24 Subsequently, evolutionary psychologists have found evidence that humans possess motivational circuitry specialized for detecting cheaters,25 and that dedicated motivational systems designed for punitive sentiment toward free- riders in collective action exist.26 This is consistent with the position argued by John Alford and John Hibbing that humans are “wary” (or, more precisely, conditional) cooperators, or, as John Orbell and his colleagues have argued, “Machiavellian” under some circumstances.27 Thus, Thayer’s arguments about egoism and dominance are not incompatible or inconsistent with Alford and

24. Robert Axelrod and William D. Hamilton, “The Evolution of Cooperation,” Science, March 27, 1981, pp. 1390–1396. 25. Leda Cosmides and John Tooby, “Neurocognitive Adaptations Designed for Social Exchange,” in Buss, The Handbook of Evolutionary Psychology, chap. 20. 26. Price, Cosmides, and Tooby, “Punitive Sentiment as an Anti-Free Rider Psychological Device.” 27. John Orbell, Tomonori Morikawa, Jason Hartwig, James Hanley, and Nicholas Allen, “‘Machi- avellian’ Intelligence as a Basis for the Evolution of Cooperative Dispositions,” American Political Science Review, Vol. 98, No. 1 (February 2004), pp. 1–15.

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Hibbing’s arguments about wary cooperation. These dispositions are products of mechanisms designed for separate domains of interaction (e.g., navigating dominance hierarchies and negotiating cooperation) that are related and may overlap, but yet remain psychologically distinct and are triggered by divergent environmental stimuli. One can now clearly see the problems inherent in asking whether humans are naturally hawkish or dovish. The answer depends on the expression of the conditional strategies embedded in psychological information-processing systems, which can generate a range of hawkish or dovish behaviors depending on a range of adaptively relevant contextual cues. It is imprecise to ask then, generally, whether humans are egoistic or cooperative; indeed, this question is indeterminate. As Azar Gat notes, “[I]nsistence on deªning a primary motive within the human motivational complex” has little point, and the question is as indeterminate as asking: “What is really the thing people are after in going to the supermarket: bread, meat or cheese?”28 A closer look at evolutionary theory helps to resolve this perceived ambiguity. Importantly, we are not merely claiming that behavior is conditional. Such a claim is neither insightful nor original. Instead, we argue that the structure of this conditionality is provided by innate information-processing systems in the human brain. Human behavior is not governed by an ultimate motive such as egoism, nor is behavior the result of a domain-general learning function applied universally across contexts that merely soaks up identities and preferences through, for example, reinforcement and path dependence. We argue that a proper evolutionary analysis of behavior must ask speciªcally about how a particular psychological mechanism is designed to generate certain types of output (e.g., egoism, altruism, etc.) in certain domains given the presence of ancestrally recurrent and adaptively relevant environmental cues. Evolved psychological mechanisms are the “proximate” manifestations of solutions to enduring, or “ultimate,” selection pressures.29 The end result is a vast array of species-typical conditional strategies that generates behavior that is marvelously varied across time and space.

prediction We have shown that evolutionary models of behavior are far from indeterminate in their explanations of behavior, so the next logical step is to inquire di-

28. Azar Gat, “The Causes and Origins of ‘Primitive Warfare’: Reply to Ferguson,” Anthropological Quarterly, Vol. 73, No. 3 (July 2000), p. 167 (emphasis in original). 29. The distinction between proximate and ultimate evolutionary explanations comes from Niko Tinbergen, “On Aims and Methods of Ethology,” Animal Biology, Vol. 55, No. 4 (December 2005), pp. 297–321.

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rectly about their ability to generate predictions. The theory of evolution by natural selection is commonly believed to have great explanatory power, yet little if any predictive power.30 This depends, however, on what is entailed by “prediction.” To illustrate, we brieºy present three classes of prediction that are often conºated in practice. The ªrst class of prediction regards timing. For example, when will war occur between two enemies, when will depression hit, or when will a state col- lapse? A second class concerns the contingent emergence or outcome of an event, person, or action. For example, who will win the election, which state will win the war? A third class of prediction relates to patterns of events and behavior. For example, do states tend to balance against gathering power over time? In this last class of predictions, the “when” or “who” of the process is often not speciªed. These three classes of prediction, needless to say, are neither exhaustive nor mutually exclusive, but rather illustrative. It has been difªcult for many social scientists to understand that evolutionary models do indeed offer predictions about behavior, and this difªculty likely results from the fact that prediction in these models rests on different on- tological bases. Evolutionary psychology offers predictions about the functional structure of psychological mechanisms that have been designed by natural selection in response to adaptive problems. On a broad level, therefore, evolutionary psychology predicts what mechanisms ought to exist given that a clearly deªned selection pressure was evolutionarily recurrent. For example, given that war has been relatively constant throughout human history, what mechanisms might have evolved to help participants discern friends from enemies, and respond to threat? On a more speciªc level, “mapping” the information-processing structure of psychological mechanisms allows evolutionary psychologists to predict a range of outputs (e.g., behavior and motivation) given the presence of adaptively relevant inputs.31 In this way, evolutionary psychology is able to offer

30. Michael Scriven, “Explanation and Prediction in Evolutionary Theory,” Science, August 28, 1959, pp. 477–482; and Robert Henry Peters, “Letter to the Editors: Predictable Problems with Tau- tology in Evolution and Ecology,” American Naturalist, Vol. 112, No. 986 (July–August 1978), pp. 759–762. 31. In a general sense, there are two major sources of behavioral variability. The ªrst is outlined exclusively in this article, in which we describe behavior as the contingent product of the interaction of evolved information-processing systems with their internal and external environments. In other words, variation in behavior is explained largely as a consequence of universal psychological mechanisms interacting with variable environments. A second type of explanation is often provided by approaches that examine those sets of biological features that are not universal and not designed by natural selection, but are found in some individuals and not in others as a consequence of other evolutionary processes, such as genetic mutation and drift. An example would be variation in the presence of a particular gene or “allele” throughout a population, which corre-

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clear, falsiªable, ex ante predictions of human political behavior. These predictions are essentially of the third above-mentioned class (i.e., predictions about patterns of behavior), and not so much about the speciªc timing or emergence of events. Importantly, although one could simply assume the existence of psychological mechanisms in a manner similar to the way rational choice models assume preferences, the logic of natural selection allows one to interrogate the origin and operation of evolved mechanisms in the brain. The evolutionary approach here is superior in that it is ecologically valid and descriptively accurate. For example, evolutionary psychology allows scholars to unite rational and apparently irrational behavior under one explanatory rubric: the calibration of aggression based on physical strength in contests between individuals can be rational in a strict utility sense, yet the calibration of support for an aggressive foreign policy based on this same cue, though ancestrally rational and adaptive (in the context of small-scale coalitional aggression), becomes irrational in a modern context.32 Consequently, evolutionary psychological and rationalist predictions are expected to converge only when the latter are consistent with strategies that would have enhanced reproductive success on average over evolutionary time. Thus, when political scientists assert that evolutionary models of behavior lack predictive power, what they are really saying is that they lack a particular kind of predictive power, which is neither surprising nor unique to evolutionary models. Indeed, as Bruce Bueno de Mesquita has argued, the mistaken no- tion that evolution lacks predictive power and is therefore not falsiªable “confuses evolutionary theory’s focus on time and the emergence of speciªc characteristics with the belief that predictions must therefore be about timing and those characteristics.”33 We are not predicting which countries will be at war in ªve years or where the next suicide bomber will strike, and we are most

sponds to variation in some phenotypic trait, such as aggressiveness. Although these two sources of variability are distinct, they are not irreconcilable. For an elaboration of these approaches, see John Tooby and Leda Cosmides, “On the Universality of Human Nature and the Uniqueness of the Individual: The Role of Genetics and Adaptation,” Journal of Personality, Vol. 58, No. 1 (March 1990), pp. 17–67; David M. Buss and Heidi Greiling, “Adaptive Individual Differences,” Journal of Personality, Vol. 67, No. 2 (April 1999), pp. 209–243; and Anthony C. Lopez and Rose McDermott, “Adaptation, Heritability, and the Emergence of Evolutionary Political Science,” Political Psychol- ogy, forthcoming. 32. Note that we do not inquire into the present-day adaptiveness of any particular trait or feature. Whether a trait is adaptive in modern environments is not an indicator that it was designed by natural selection in the past, and it is therefore not an indicator that the trait in question is an adaptation. In addition, we avoid the “naturalistic fallacy” by recognizing that the mere fact that a trait or system was favored by selection does not mean that this trait or system is normatively “good” in a moral or ethical sense. 33. Bruce Bueno de Mesquita, “The Beneªts of a Social-Scientiªc Approach to Studying Interna- tional Affairs,” in Ngaire Woods, ed., Explaining International Relations since 1945 (New York: Ox- ford University Press, 1996), p. 58.

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certainly not predicting what the “human race” will look like in a hundred or a million years. Most other models in political science are similarly deªcient with respect to timing in their predictions, and clearly evolutionary models should not be held to a higher standard than others in international relations. We have endeavored to show that misgivings about the relevance of evolutionary theory for explaining and predicting political behavior often rest on an incomplete understanding of this theory, as well as terminological imprecision regarding what exactly one means by, for example, “prediction.” Indeed, there are always constraints on the depth and breadth of domains in which prediction can be made, but with some theoretical precision, we can see that these misgivings are largely misplaced. We now turn toward a discussion of the set of psychological mechanisms that enables politically relevant coalitional dynamics. We argue that this human “coalitional psychology” is of central importance for researchers attempting to explain the patterns and novelty of international politics.

Coalitional Psychology

Modern politics, and international relations especially, is group based and or- ganized along an array of formal and informal group boundaries and identities relating to class, partisanship, age, sex, race, ethnicity, citizenship, religion, region, and ideology, among other categories. Such identiªcations prove highly inºuential in how citizens represent and think about politics at the domestic and international levels.34 For example, in explaining one of the assumptions of realism, Robert Gilpin tellingly describes such coalitions as the “essence of social reality”; in a world of scarcity and conºict, humans as a “tribal species” confront one another ªrst as coalitions.35 There is no doubt that group living has persistently constituted a fundamental feature of the evolutionary history of our species. For millions of years, Homo sapiens have lived, cooperated, and competed in groups, predomi- nantly as relatively nomadic hunter-gatherers. From archaeology, anthropology, and primatology, one can piece together some of the features of ancestral group life on the Pleistocene savannah. First, groups existed in small-scale communities consisting of between 25 and 200 individuals.36 Second, modern

34. Angus Campbell, Philip E. Converse, Warren E. Miller, and Donald E. Stokes, The American Voter (New York: John Wiley and Sons, 1960); and Alexander Wendt, “The State as Person in Inter- national Theory,” Review of International Studies, Vol. 30, No. 2 (April 2004), pp. 289–316. 35. Robert G. Gilpin, “The Richness of the Tradition of Political Realism,” International Organiza- tion, Vol. 38, No. 2 (Spring 1984), p. 44. 36. Robert L. Kelly, The Foraging Spectrum: Diversity in Hunter-Gatherer Lifeways (Washington, D.C.: Smithsonian Institution Press, 1995).

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hunter-gatherers are seldom highly hierarchical, and there are reasons to believe that power in ancestral groups was also relatively decentralized.37 Third, at the same time, groups contained individuals with elevated status, unique privileges, and special roles in the initiation of collective action such as war.38 Our understanding of the evolutionary origins of social status is expanding, and signiªcant evidence supports the “strong relation between social rank and ªtness or well-being” in ancestral environments.39 As Phyllis Lee points out, “When social status or dominance is associated with success in ‘priority of access’ competition, behavioral mechanisms to maximize status can be key de- terminants of reproductive success.”40 Fourth, coalitions played a signiªcant role in the determination of within-group hierarchies in the sense that ambi- tious individuals teamed up with others to secure or increase their standing within the group. Fifth, groups were most likely multilayered, and overarching tribes were composed of a number of hunter-gatherer bands that fused and ªssioned during the season.41 Sixth, between-tribe social interaction could be peaceful and involve long-distance trading.42 Seventh, war between tribes has not been evolutionarily uncommon and can most likely be traced back to the last common ancestor between humans and chimpanzees.43 Eighth, war—at least, offensive war—was most likely the exclusive domain of males.44 Ninth, violent conºict was not an infrequent cause of death. Death as a result of weapon-inºicted trauma can be traced back to the Middle Paleolithic with the discovery of pre-Holocene mass graves. For all known hunter-gatherer bands, the rates of violent death far exceed the rates for the United States, the most violent modern society in terms of domestic murder rates.45 Tenth, given the risks associated with warfare, it most likely took the form of hit-and-run

37. Christopher Boehm, “Conºict and the Evolution of Social Control,” Journal of Consciousness Studies, Vol. 7, Nos. 1–2 (2000), pp. 79–101. 38. Mark van Vugt and Rob Kurzban, “Cogntive and Social Adaptations for Leadership and Followership: Evolutionary Game Theory and Group Dynamics,” in Joseph P. Forgas, Martie G. Haselton, and William von Hippel, eds., Evolution and the Social Mind: Evolutionary Psychology and Social Cognition (New York: Psychology Press, 2007), chap. 14. 39. Joey T. Cheng, Jessica L. Tracy, and Joseph Henrich, “Pride, Personality, and the Evolutionary Foundations of Human Social Status,” Evolution and Human Behavior, Vol. 31, No. 5 (September 2010), p. 334. 40. Phyllis C. Lee, “Evolution and Ecological Diversity in Animal Mating and Parenting Systems,” in Peter T. Ellison and Peter B. Gray, eds., Endocrinology of Social Relationships (Cambridge, Mass.: Harvard University Press, 2009), p. 21. 41. Kelly, The Foraging Spectrum. 42. Robert Boyd and Joan B. Silk, How Humans Evolved, 5th ed. (New York: W.W. Norton, 2009). 43. Wrangham and Peterson, Demonic Males. 44. Martin Daly and Margo Wilson, Homicide (New York: Aldine de Gruyter, 1988); and Wrangham, “Evolution of Coalitionary Killing.” 45. Keeley, War before Civilization; LeBlanc and Register, Constant Battles; and Gat, War in Human Civlization.

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skirmishes carried out when numerical superiority and surprise could be achieved. This attack strategy is widespread among chimpanzees and modern hunter-gatherers.46 Eleventh, though risky, warfare involved signiªcant beneªts to the victors in the form of increased mating opportunities and increased social standing. For example, in a number of modern foraging societies, there is a direct link between a male’s success in violent combat and number of offspring. In fact, evolutionary models suggest that this is the reason war evolved in the ªrst place.47 Given the evolutionary endurance and reproductive signiªcance of these social dynamics, we argue that selection has favored sophisticated psychological machinery to enable and regulate behavior both within and between groups.48 In other words, human beings seem to be endowed with a “coalitional psychology” designed to manage and negotiate coalitional dynamics within and between tribes. To the extent that cues related to modern-day group politics tap into and trigger these mechanisms, we should expect the mechanisms to help structure modern political behavior as if modern politics were, in fact, played out in the ancestral social environment sketched above. Coalitional behavior encompasses interaction in which individuals come together to achieve a common goal and share the beneªts. This overarching domain consists of a range of more speciªc domains relating to many of the challenges listed above, such as detecting cheaters within groups, recruiting la- bor for collective action, distributing beneªts acquired through group efforts, as well as within- and between-group competition, status rivalry, and violence. We expect that each of these domains will have distinct yet often overlapping cue structures. Speciªc mechanisms will have been designed to process and respond to these challenges, resulting in behavior that, over evolutionary time, contributed on average to reproductive success. This remains true even if it results in behavior that appears “irrational” or maladaptive in modern evolutionarily novel environments. The existence of qualitatively distinct adaptive problems and solutions related to group (as compared to individual) behavior suggests that coalitional behavior represents more than the mere aggregation of individual behavior. For example, although individual-level aggression is zoologically common, co-

46. Joseph H. Manson and Richard W. Wrangham, “Intergroup Aggression in Chimpanzees and Humans,” Current Anthropology, Vol. 32, No. 4 (August–October 1991), pp. 369–390. 47. Tooby and Cosmides, “The Evolution of War and Its Cognitive Foundations”; and Gat, “The Human Motivational Complex.” 48. Forgas, Haselton, and Hippel, Evolution and the Social Mind; and Mark Schaller, Jeffry A. Simpson, and Douglas T. Kenrick, eds., Evolution and Social Psychology (New York: Psychology Press, 2006).

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alitional aggression is less so.49 Coalitional behavior, in general, seems to require specialized information-processing systems designed to integrate complex multi-individual coordination, tracking, and competition, which relatively few species possess. Thus, coalitional activity itself signals the presence of an array of specialized mechanisms designed both to adaptively reason about, and to behave, within and between groups. It is also necessary to distin- guish coalitions from alliances. When we refer here to coalitional psychology, we are using the term “coalitional” in its broadest sense to refer to n-person coordination, cooperation, and competition. This includes the dynamics in both within-tribe and between-tribe interactions. Although there might be differences between these two kinds of social interactions, we expect that much of the underlying cognitive machinery is shared.50 It is also important to note, however, that primatologists studying coalitional behavior have restricted the term “coalition” to refer to competitive and relatively short-lived intergroup exchanges, whereas “alliances” are referred to as sustained interactions that do not necessarily occur in the backdrop of intergroup competition and threat (e.g., the U.S.-led “coalition of the willing” during the 2003 Iraq War vs. the enduring transatlantic alliance between Great Britain and the United States, respectively). We believe the distinction is valid and reºected in our evolved psychology; however, for purposes of simplicity, we refer here to “coalitional psychology” as encompassing the set of evolved psychological mechanisms that oversees both of these dimensions.51 Clearly, the modern coalitional world is in many ways drastically different from that of ancestral times. In addition to generating behavior that appears irrational in a subjective-utility sense, the “mismatch” between ancestral and modern environments can result in widespread coalitional behaviors that appear to be deeply rooted, but may actually not be. For example, psychologists have long believed that the psychological categorization of race was instinc-

49. Tooby and Cosmides, “The Evolution of War and Its Cognitive Foundations”; Frans B.M. de Waal and Alexander H. Harcourt, “Coalitions and Alliances: A History of Ethological Research,” in de Waal and Harcourt, eds., Coalitions and Alliances in Humans and Other Animals (New York: Ox- ford University Press, 1992), chap. 1; and Lee Alan Dugatkin, Cooperation among Animals: An Evolu- tionary Perspective (New York: Oxford University Press, 1997). 50. Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Exchange.” 51. De Waal and Harcourt, “Coalitions and Alliances.” The choice of the label “coalitional” psychology is favored because it is the convention among evolutionary psychologists. See Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Exchange.” Note that many of the claims we will make about coalitional psychology will be speciªc to coalitions, per se, and not alliances, or vice versa. It is an empirical question, however, whether and to what extent the structure of evolved mechanisms designed to navigate coalitions differs from those designed to navigate alliances. We leave this as an open and important empirical question for future research in international relations.

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tual because it appeared to be automatic and almost impossible to “turn off.” Robert Kurzban and his colleagues, however, have argued that it would be highly unlikely for humans to possess a psychological mechanism designed by natural selection for the speciªc purpose of detecting and encoding race.52 This is primarily because, ancestrally, humans would rarely if ever have encountered individuals belonging to a different race. In the Pleistocene hunter- gatherer world of our ancestors, individuals traveled primarily by foot and would not have covered great distances. Given that the structure of the environment in which we evolved was not one in which our ancestors would have commonly encountered individuals from other races (indeed, there were no other races to encounter on the East African savannah), it is implausible to expect natural selection to have favored the emergence of psychological mechanisms designed for the detection and categorization of race. Instead, as Kurzban and his colleagues argue, the psychological encoding of race is a by-product of mechanisms designed for another purpose: the tracking and representation of coalitional afªliation. In other words, race encoding can be understood as a consequence of the interaction between a psychology designed to track cues indicating coalitional allegiance and the existence of racial segregation in modern domestic and international politics. These researchers provided the ªrst empirical demonstration of subjects failing to encode the race of others, which took place when subjects were presented with a social interaction in which racial cues were irrelevant to the target the mechanism was designed to seek—coalitional afªliation. There are many reasons why this example is signiªcant for the study of international politics. First, the mismatch between ancestral and modern environments can produce surprising and counterintuitive results that would be difªcult to predict without the beneªt of an evolutionary lens. Second, such an approach provides a source of optimism about the ºexibility of human nature: although many coalitional patterns emerge as the product of an innate psychology designed to navigate the challenges of group living, this does not mean that humans are doomed to a future of racism and war. Indeed, by learning more about the evolutionary forces that shaped the human brain, we learn

52. Robert Kurzban, John Tooby, and Leda Cosmides, “Can Race Be Erased? Coalitional Computa- tion and Social Categorization,” Proceedings of the National Academy of Sciences, December 18, 2001, pp. 15387–15392; Leda Cosmides, John Tooby, and Robert Kurzban, “Perceptions of Race,” Trends in Cognitive Sciences, Vol. 7, No. 4 (April 2003), pp. 173–179; Francisco J. Gil-White, “Are Ethnic Groups Biological ‘Species’ to the Human Brain?” Current Anthropology, Vol. 42, No. 4 (August– October 2001), pp. 515–554; Lawrence A. Hirschfeld, “On a Folk Theory of Society: Children, Evo- lution, and Mental Representations of Social Groups,” Personality and Social Psychology Review, Vol. 5, No. 2 (2001), pp. 107–117; and Robert Kurzban and Steven Neuberg, “Managing Ingroup and Outgroup Relationships,” in Buss, The Handbook of Evolutionary Psychology, chap. 22.

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more about why and how these systems operate, which enables us to take action to mitigate certain outcomes.53 Third, this example demonstrates the deeply embedded way in which humans categorize coalitional politics, and it demonstrates how the product of this categorization is also shaped by cultur- ally speciªc and contingent content. Clearly, an understanding of the environments in which we evolved, as well as how natural selection operates to build adaptations, is relevant for understanding the range of political behavior that we as humans manifest, as well as the conditionality of this behavior. Below we offer ªve hypotheses on the existence and operation of psychological adaptations within our evolved human coalitional psychology that produce and respond to politically relevant coalitional events. We present three categories of hypotheses, each of which we consider key elements of our evolved coalitional psychology: (1) coalitional representation; (2) facilitation of coalitional behavior; and (3) sex differences in coalitional behavior.

coalitional representation How do evolved systems in the brain interpret and represent coalitions in the environment? Political scientists often assume that political coalitions are represented, or at least can be modeled, as unitary actors. For example, much literature in international relations treats states as unitary actors; the public policy literature treats organizations as unitary actors; and the parliamentary literature treats political parties as unitary actors.54 In many ways, this is un- surprising. Given the existence of massive codiªed institutional structures that constrain the behavior of individual members and leaders, many collective actors are relatively unitary and can experience shifts in, for example, leadership without changing their orientations. At the same time, however, we suggest that the pressures of ancestral group living likely favored mechanisms for group representation that attribute varying levels of unity to groups, depend-

53. Robert M. Sapolsky, “A Natural History of Peace,” Foreign Affairs, Vol. 85, No. 1 (January/ February 2006), pp. 104–120. 54. In international relations, neorealists are of course most famous for treating states as unitary actors, but they are hardly alone. Some constructivists, even while stressing the importance of de- constructing the state, nevertheless recognize that states are often at least perceived as unitary actors and may assume relevant characteristics. Liberals as well, although tending to emphasize dynamics speciªc to the “second image” of domestic politics and regimes, utilize game-theoretic models to explain international cooperation for which it is often convenient to treat the state as a unitary actor. We do not argue that this is a fault; rather, that it is an important human tendency. Our argument here is to show how the content and variability of these representations affect behavior. On the unitary actor assumption in international politics, see Kenneth N. Waltz, Theory of International Politics (Reading, Mass.: Addison-Wesley, 1979); Wendt, “The State as Person in Inter- national Theory”; and Helen Milner, “International Theories of Cooperation among Nations: Strengths and Weaknesses,” World Politics, Vol. 44, No. 3 (April 1992), pp. 466–496.

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ing on the social and political contexts. Thus, the ªrst hypothesis seeks to outline one aspect of the information-processing structure of adaptive mechanisms designed for the cognitive representation of coalitions and their dynamics. We investigate the ways in which these representations shape behavior within and toward political coalitions. h1. unitary actor heuristic. Humans represent groups as if they were a special category of individual, relatively unstable and with a relatively short shadow of the future. It is very likely that our evolved psychology possesses heuristics that re- duce groups to unitary actors for the sake of cognitive simplicity.55 Indeed, humans in general often psychologically represent and respond to groups such as states, organizations, parties, and ethnicities in anthropomorphic ways, treating each as if it were a single person. At the same time, however, groups are systematically and fundamentally different from individuals in behavior and composition, and cooperation among individuals and groups poses separate adaptive problems. By implication, the cues that promote cooperation among individuals may not always promote cooperation among groups. For example, the expectation of long horizons of interaction—or, the “shadow of the future”—may be a better predictor of discount rate for individuals than it is for groups, because group composition can change quickly. Relatively stable tem- peraments enable individuals with a lengthy shadow of the future to build trust and cooperation based on these relatively stable interpersonal expectations:56 if a person honors an agreement today, she is likely to do so tomorrow. Because of the relative stability of personal reputations over time, lengthy shadows of the future more easily translate into low discount rates among individuals.57 Ancestrally, groups have been subject to relatively quick, sudden, and unpredictable shifts in leadership and orientation. Studies of chimpanzees have shown that internal coalitions are relatively unstable and that individuals shift coalitional partners when it is opportune to do so.58 This implies that leaders occasionally change as a result of within-group coalition dynamics. Similarly, anthropological researchers have described how Big Men (i.e., usually individ-

55. Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Exchange.” 56. Robert M. Axelrod, The Evolution of Cooperation, rev. ed. (New York: Basic Books, 2006). 57. We are well aware of the psychological literature suggesting that individuals may not display stable personality traits across situations; however, the personality psychology literature is clear that individuals remain stable in their characteristics within a given situation over time (i.e., tem- poral stability remains greater than cross-situational consistency). See Walter Mischel and Philip K. Peake, “In Search of Consistency: Measure for Measure,” in E. Tory Higgins, C. Peter Herman, and Mark P. Zanna, eds., Consistency in Social Behavior: The Ontario Symposium (Mahwah, N.J.: Law- rence Erlbaum Associates, 1982). 58. Frans B.M. de Waal, Chimpanzee Politics: Power and Sex among Apes (Baltimore, Md.: Johns Hopkins University Press, 1989).

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uals of great, though not necessarily formal, inºuence) in human foraging groups are occasionally overthrown by coalitions composed of lower-status individuals.59 Such within-group dynamics not only create an unstable internal coalitional environment but, potentially, also create instability in the relations between tribes. Hence, according to the archaeological record, between-tribe orientation could take a range of forms spanning from trading to war. It is most likely that leaders have played a role in framing the speciªc orientation toward other tribes and, most certainly, in the initiation of collective action.60 Without codiªed institutions to constrain behavior, the orientation of one tribe vis-à-vis another would be dependent on the speciªc leader.61 Frequent shifts in leadership would therefore have made ancestral tribes less than stable unitary actors. Somewhat paradoxically, this would have been accentuated by the limited nature of the leader’s power compared to the rest of the tribe. That is, because hierarchies were relatively ºat,62 leaders could ªnd it difªcult to en- force peace agreements with neighboring tribes (e.g., involving intermar- riage).63 For instance, the anthropological literature contains examples of how raiding parties are formed by young males against the wishes of the elders.64 Given these dynamics, our evolved coalitional psychology should be designed to attend to subtleties in loyalty shifts and recognize cues speciªc to group (as opposed to individual) longevity and stability, and then use such assessments to base expectations and build future relations—even though group stability is presumably greater today than it was ancestrally. For example, although U.S. Vice President Joseph Biden had hoped that the United States and Russia could “press the reset button” on their relationship (thus signaling a sudden reversal of policy), former Russian President Vladimir Putin astutely looked to more stable cues indicating long-term American intentions by not- ing, “The U.S. is a very big ship that cannot change its course dramatically in a few months.” Putin further noted that President Barack Obama would be around for “only eight years maximum.”65 Although the Obama administra-

59. Boehm, Hierarchy in the Forest; and Boehm, “Conºict and the Evolution of Social Control.” 60. Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Exchange”; and van Vugt and Kurzban, “Cogntive and Social Adaptations for Leadership and Followership.” 61. Johan van der Dennen, The Origin of War: The Evolution of a Male-Coalitional Reproductive Strat- egy (Groningen, Netherlands: Origin, 1995); Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Exchange”; and van Vugt and Kurzban, “Cogntive and Social Adaptations for Lead- ership and Followership.” 62. Boehm, Hierarchy in the Forest. 63. Van der Dennen, The Origin of War. 64. Wayne E. Lee, “Peace Chiefs and Blood Revenge: Patterns of Restraint in Native American Warfare, 1500–1800,” Journal of Military History, Vol. 71, No. 3 (July 2007), pp. 701–741. 65. Quoted in Ellen Barry, “Putin Sounds Warning on Arms Talks,” New York Times, December 29, 2009.

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tion has signaled greater cooperativeness, both the recent swings in policy orientation coming from previous administrations as well as the longer history of distrust alluded to by Putin suggest that such dramatic and sudden overtures of “friendship” may do little to allay distrust from some states. The problem of cooperation among groups and the problem of cooperation among individuals may indeed share a similar cue structure and thus represent somewhat overlapping domains. Some cues are likely to be shared between individuals and groups as indicators of stability.66 The task, therefore, is to form hypotheses that test where domains overlap and how they separate. For example, how often are treaties and agreements concluded and abandoned (i.e., commitment, trustworthiness)? Whether promises are kept is also an important indicator of trustworthiness both for individuals and for groups. Other cues, however, may not be shared between individuals and groups. For example, how quickly does a given political group experience abrupt changes in leadership? Also, are changes in leadership sudden and unpredictable, or reg- ular, according to some perceptible cue (e.g., timing, internal divisions, or heredity)? In fact, there is some evidence suggesting that such a cue structure exists. David Leblang and Shanker Satyanath have demonstrated that variables such as whether a government is divided, or whether there is frequent turnover in political power, tend to increase the variance of expectations held by international investors, precipitating the likelihood of currency crises in these countries.67 This is entirely consistent with our prediction. Groups that (inten- tionally or not) send costly-to-fake signals that indicate that they are prone to sudden shifts in behavior, ceteris paribus, should be perceived as riskier partners, whether for political alliance or economic relationships. Evolutionarily, as well as today, groups have been relatively more susceptible than individuals to sudden and quick shifts in reputation and behavior. As a consequence, our evolved psychology should be designed to recognize that the cues that es- tablish reputational stability are both quantitatively and qualitatively different for groups than they are for individuals. To be clear, we argue that groups are generally unstable relative to individuals in terms of, for example, their reputational features. This does not mean that groups must always be relatively unstable, only that they have tended to be so compared to individuals, which implies that there is variation in the range of instability represented by

66. Stability is emphasized because the reputation that enables cooperation given a low discount rate is relatively difªcult if that reputation is subject to change quickly and suddenly. 67. David Leblang and Shanker Satyanath, “Institutions, Expectations, and Currency Crises,” In- ternational Organization, Vol. 60, No. 1 (Winter 2006), pp. 245–262.

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groups. The mean of that variation, however, is greater for groups than for individuals. Thus, consistent with the research we cite above, political coalitions such as states assess one another on the basis of variations in their perceived reputational stability, which may be at least partly a function of leadership dynamics. Our argument is that this tendency is a direct consequence of the operation of underlying psychological mechanisms designed for a world in which the coalitional landscape displayed at least three certain reproductively signiª- cant and evolutionarily recurrent regularities: (1) coalitions displayed behavioral and reputational cues that were distinct (quantitatively and qualitatively) from those displayed by individuals; (2) individuals with psychological design features that allowed them to quickly and efªciently track and respond to such cues would have potentiated success in intercoalitional situations that place premiums on quick and coordinated action such as warfare; and (3) the endurance of these challenges and the beneªts of their successful resolution would have favored the accumulation of such design features into information- processing systems that tied these adaptively useful strategies to these coalitional domains. Although some may object that the tendency to treat groups different from individuals could be predicted by a rationalist formulation, such an approach would again underappreciate much of the apparently “irrational” output generated in modern environments by mechanisms designed for a small-scale coalitional environment. For example, modern nation-states are far more stable than ancestral hunter-gatherer coalitions, which is likely to lead humans in many situations to routinely underestimate the reputational stability of modern nation-states. A rationalist computation would take full consideration of institutional features that an evolved psychology may tend to overlook by instead privileging the coalitional cues that were causally relevant to the adaptive challenge in ancestral environments. For example, the removal of one leader through a coup, or a sanction on that leader’s power, should not promote the sort of pandemonium that it often does; rationally, individuals should be more concerned with legislation that affects institutional design rather than changes in leadership or its constituent features, yet these latter cues loom largest for individuals when appraising the stability of a political entity. To use a warfare analogy, the loss of a leader in battle is an irrationally crippling blow to morale and the will to ªght despite the presence of succes- sors and the survival of institutional structures, particularly in a highly mechanized context. In international relations, the recognition that humans are designed to

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psychologically represent groups as a special category of individual has impli- cations for theories of cooperation and conºict among states. Such research might investigate the ways in which evolved mechanisms for the representation of salient groups interact with modern institutions, particularly regime type or party structure, to produce predictable patterns of behavior among groups. We thus argue that the international relations literature on cooperation under anarchy at least partially misappropriates analyses drawn from evolutionary models of cooperation.68 In such models, the relevant unit is the individual acting in a dyad. We hypothesize that the conditions that promote cooperation among individuals may be similar to, but are by no means identical with, the conditions that favor cooperation among groups, such as states. In particular, as noted above, lengthy shadows of the future between political coalitions should, by themselves, be relatively poor predictors of their discount rate toward each other because group reputation and behavior are relatively less stable. This claim ªts in well with existing literature on reputation, which indicates that reputation may not be as inºuential as observers assume.69 The reason for this may not lie solely in the attributional bias noted by Jonathan Mercer, but also in an evolved psychology, which recognizes that, however accurate when formed, behavior in groups may not remain consistent over time, and so reputational stability often represents little more than an illu- sion. Thus, it is insufªcient to assume that a lengthy shadow of the future will lower the discount rate among groups merely because this is the experience of individuals. This hypothesis would seem to lend support to the realist claim that states cannot trust one another because of uncertainty in the political environment. In our formulation, however, this uncertainty and instability is not a constant, as it is sometimes portrayed, but rather contingent on such cues as the nature of the opposition (i.e., individual or group). We have argued that the reputational and behavioral cues displayed by individuals and coalitions were distinct from each other in ancestral environments, which has direct conse- quences for how we perceive coalitions today. This does not mean, however, that strategies may not vary within these two domains; we are not saying that individuals always trust each other and that coalitions never do. This will be- come clearer especially in our discussion of hypothesis 3 below on the nature

68. Kenneth A. Oye, ed., Cooperation under Anarchy (Princeton, N.J.: Princeton University Press, 1986); and Milner, “International Theories of Cooperation among Nations.” 69. Jonathan Mercer, Reputation and International Politics (Ithaca, N.Y.: Cornell University Press, 1996).

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of coalitional competition itself. We will show that intercoalitional dynamics can demonstrate a range of cooperative or competitive behavior depending on other relevant sets of coalitional cues.

facilitation of coalitional behavior Whereas mechanisms designed for coalitional representation provide a cognitive framework for the identiªcation, representation, and interpretation of coalitional objects and events, the facilitation of coalitional behavior speaks to questions of motivation, action, and coalitional maintenance. Although the two domains (representation and facilitation) are analytically distinct, they obviously inform and respond to each other in important ways. Psychological mechanisms designed to facilitate coalitional behavior govern motivations and decisionmaking related to participation in collective action and engagement in coalitional violence against rival groups. h2. coalitional entrepreneurship. Political entrepreneurs seek opportunities to strategically manipulate the coalitional environment, often using emotional devices such as “outrage” to inspire collective action. According to the anthropological and primate literature, the relative size of one’s coalition was a highly important factor in ancestral decisions regarding whether to engage in collective aggression or not. Attacks would most often have been initiated when one’s coalition outnumbered the enemy. From an adaptationist perspective, this makes perfect sense: larger coalitions can inºict more costs and, hence, are more likely to prevail in combat. In the case of forming a raiding party, the lack of power centralization in ancestral tribes implied that individuals had to be convinced to take part.70 Here, it is likely that potential participants in an aggressive act took stock of the number of coalitional allies before deciding whether to participate. For an entrepreneur who stood to gain from the initiation of coalitional aggression, a key problem therefore was to put together an initial critical mass of willing individuals to facilitate further recruitment. An- other key problem would have related to the orchestration of attention. In most cases of coalitional behavior, coalitions did not have to be assembled de novo because the bonds of solidarity to would-be allies preexisted (e.g., in the form of friendships or kinship). Hence, the problem of coalitional entrepreneurship related speciªcally to activating one’s coalition, which would be the case regarding both within- and between-tribe coalitional dynamics. For example, when forming a raiding party to retaliate in response to an attack by another tribe, the participants would most likely be kin or friends of the

70. R. Brian Ferguson, “Violence and War in Prehistory,” in Debra L. Martin and David W. Frayer, eds., Troubled Times: Violence and Warfare in the Past (Amsterdam: Gordon and Breach, 1997), p. 336.

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victims.71 This would also be the case when using a coalition to back up one’s claims in nonviolent within-tribe disputes.72 To coordinate the attention of a coalition, the entrepreneur would need to direct the members’ attentions to a problem and convincingly broadcast it as shared—that is, signify this is the group’s problem. Because of these adaptive problems, evolved psychological machinery should therefore remain especially sensitive to the strategic manipulation of the coalitional environment, and should contain dedicated information-processing systems designed to actively participate in what we term “coalitional entrepreneurship.” Human coalitional psychology should not only respond to the coalitional environment, but also seek opportunities to manipulate and exploit it, as we mentioned above. Much of the attempt to manipulate the coalitional environment emerges from the desire to increase the number and strength of alliance partners.73 Leaders will search the environment for useful alliance partners who can beneªt the coalition by the number, strength, and quality of the resources, as well as the knowledge, skills, and associations, they possess and bring to bear. Such resources not only increase the probability of victory should conºict occur, but also increase status in times of peace. Power and status increase the ability of alliance members to act unilaterally without undue concern about opposition. And, in turn, because beneªts unambiguously accrue to the winning side, uncommitted bystanders who see a winning coalition possess increased incentives to join, further heightening the probability of victory in the event of conºict. An evolutionary analysis helps scholars to understand why leaders might strategically invoke emotion to manipulate a constituency, by highlighting the downstream effects that are cued by such triggers, entraining a sequence of responses designed to heighten in-group solidarity. In this regard, an important example of coalitional entrepreneurship is the opportunistic exploitation of outrage (“Look at what they have done to us!”) by actual and would-be leaders to signal one’s real and potential allies that a

71. Napoleon A. Chagnon, “Life Histories, Blood Revenge, and Warfare in a Tribal Population,” Science, February 26, 1988, pp. 985–992. 72. Christopher von Rueden, Michael Gurven, and Hillard Kaplan, “The Multiple Dimensions of Male Social Status in an Amazonian Society,” Evolution and Human Behavior, Vol. 29, No. 6 (Novem- ber 2008), pp. 402–415. 73. The strategic manipulation of the coalitional environment does not simply mean that humans expand their coalition whenever possible. Coalitions cannot expand indeªnitely, given mounting problems of coordination as size increases. Therefore, strategic manipulation is not merely about maximizing size; it is also about the ability to inºuence coalitional composition and the distribu- tion of resources. See Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Ex- change”; and Anthony C. Lopez, “Evolution, Coalitional Psychology, and War,” in H-Diplo ISSF Roundtable on “Biology and Security,” Vol. 1, No. 1 (2010), pp. 35–52, http://www.h-net.org/ ϳdiplo/ISSF/PDF/ISSF-Roundtable-1-1.pdf.

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call to arms may prove necessary. Research in social psychology, for example, indicates that individuals in positions of leadership, to the extent that they highly identify with a group, should be particularly sensitive to group threats.74 Outrage, therefore, is likely triggered in response to displays (inten- tional or not), which can be framed as suggesting that a potential or perceived status rival undervalues one’s status, thereby threatening current or future welfare. The experience of outrage has been hypothesized by evolutionary psychologists to function as an emotional focal point around which supporters can coalesce and motivate action against an out-group.75 In this way, outrage fuels the engine of intragroup coordination and cooperative action against out- groups. Evidence of this dynamic abounds throughout human history. This is perhaps most dramatically evidenced by Adolf Hitler’s rise to power after the burning of the Reichstag in Germany, following inequitable treatment at the hands of British and French victors after World War I, which most Germans considered patently unfair. As a recent example, emotional outrage was instrumental in precipitating a wide coalition of support for U.S. military action in Afghanistan after the attacks on the World Trade Center in 2001. Ab- sent such outrage, the administration of George W. Bush failed to manifest a coalition as deep or as wide in the lead-up to the Iraq War in 2003. Indeed, it is often much easier to build outrage in response to an assault that is both deadly and symbolic—as the September 11 attacks were—than in response to the vio- lation of United Nations resolutions. The successful exploitation and manipulation of outrage shifts and consolidates the structure of coalitions in a given environment by soliciting and enlisting new members (especially those who might have otherwise stayed on the sidelines of action), strengthening the resolve of existing members, and promoting coalitional status and solidarity. Importantly, “outrages” represent acts of social construction when singular events are framed as indicative of a larger coalitional conºict in which “they” threaten or undervalue “us” in a way that suits the interest of particular entrepreneurs. Given the ancestral importance of status, even seemingly minor events can take on massive effects through such framing. For example, although few took notice in September 2005 when Danish cartoons depicted the ªgure of Mohammed in a daily newspaper, suddenly in February 2006 (half a year after the publications), enormous riots erupted in response throughout the Muslim world, thousands marched in the streets, and embassies were

74. See Russell Spears, Bertjan Doosje, and Naomi Ellemers, “Self-Stereotyping in the Face of Threats to Group Status and Distinctiveness: The Role of Group Identiªcation,” Personality and So- cial Psychology Bulletin, Vol. 23, No. 5 (May 1997), pp. 538–553. 75. Tooby, Cosmides, and Price, “Cognitive Adaptations for n-Person Exchange.”

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burned. This sensitivity to seemingly minor displays of status disparagement can seem irrational from a modern perspective. Yet, the underlying psychological mechanism evolved in ancestral small-scale groups where the current anthropological evidence suggests that individuals’ (in particular, males’) reproductive success was directly linked to their social status, and hence, selection would have designed our psychology to be highly attentive to status displays, deliberate or not.76 As shown by a number of modern events (e.g., the cartoon crises, the intifada following Israeli Prime Minister Ariel Sharon’s visit to the Temple Mount, and the sinking of a South Korean ship by a North Korean submarine), the psychological mechanisms designed by these ancestral selection pressures continue to shape international relations. h3. relative versus absolute gains. Relative gains dominate in relations with enemies, whereas absolute gains characterize relations with allies. Are groups driven by relative or absolute gains? This question has persisted and remained unresolved within such diverse literatures as international relations and social psychology. For example, neorealists have tended to emphasize the ubiquitous primacy of relative gains concerns, whereas institutionalists and neoliberals have been inclined to investigate the conditions under which absolute gains may trump relative gains concerns.77 The current archaeological and anthropological evidence, however, suggests that both types of orientations would have been important under ancestral social conditions. The archaeological record suggests that long-distance trading was a feature of prehistoric societies.78 As with other forms of social exchange, an emphasis on absolute gains can allow for the scope and depth of trade possibilities to expand in ways that it otherwise would not, and hence, the archaeological record suggests that psychological machinery facilitating this stance vis-à-vis other coalitions (including other tribes) existed among our Pleistocene ancestors.79 At the same time, all evidence suggests that war and other forms of violent conºict have also been ancestrally frequent.80 As relative capabilities are obviously of great import in violent clashes, this clearly suggests that psychological machinery designed to produce a relative gains orientation is present among our species-typical psy-

76. Cheng, Tracy, and Henrich, “Pride, Personality, and the Evolutionary Foundations of Human Social Status.” 77. We should acknowledge that there have indeed been efforts to “conditionalize” the debate, and thus we obviously agree that the impact of relative gains is “highly conditional” and that it does not necessarily and logically follow from anarchy alone. See, for example, the nuanced discussion in David A. Baldwin, ed., Neorealism and Neoliberalism: The Contemporary Debate (New York: Columbia University Press, 1993). 78. Boyd and Silk, How Humans Evolved. 79. Cosmides and Tooby, “Neurocognitive Adaptations Designed for Social Exchange.” 80. Wrangham, “Evolution of Coalitionary Killing”; and Phillip L. Walker, “A Bioarchaeological Perspective on the History of Violence,” Annual Review of Anthropology, Vol. 30 (2001), pp. 573–596.

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chological mechanisms. The immediate insight of an evolutionary approach to the debate on relative versus absolute gains is that psychological mechanisms regulating attention to, and the subsequent privileging of, either relative or absolute gains, similar to those governing cooperation versus aggression, depend on environmental cues indicative of particular domains. Speciªcally, such a mechanism or set of mechanisms must be facultative. A simple example is that relative gains achieve signiªcance between enemies, whereas absolute gains matter more within the context of cooperative coalitional relationships. What previous debates in international relations often fail to fully appreciate and adequately theorize is the signiªcance of context in deªning the nature of the relationship and how such alliances deªne goals.81 The effect of context follows directly from the ancestrally adaptive logic inherent in identifying the in- group, where cooperation remains essential, and striving to dominate (or at least remain undominated by) the out-group, which can also prove critical for survival.82 Thus, to the extent that conditions between groups such as states shift relations from out-group to in-group orientation, groups ought to privi- lege absolute over relative gains naturally and automatically. If actors want to move from emphasizing relative gains to concentrating on absolute gains, changing the nature of the larger relationship may constitute the essential ªrst step. In an illustrative indication of this dynamic, John Wagner, Mark Flinn, and Barry England ªnd that the hormonal response to male coalitional competition varies depending on whether the competitive context is within or between coalitions.83 Speciªcally, Wagner and his colleagues found that testosterone and cortisol levels were higher for males during between-coalition rather than within-coalition competitions. The authors point out that if testosterone levels are associated with dominance activity, then in situations of within-coalition competition, “coalition [stability] may necessitate inhibiting overt dominance strivings that could otherwise weaken a coalition....Con- versely, when competition occurs between distinct groups or coalitions, the opposite response seems advantageous.”84 In other words, the activation of

81. Joseph M. Grieco, “Anarchy and the Limits of Cooperation: A Realist Critique of the Newest Liberal Institutionalism,” International Organization, Vol. 42, No. 3 (Summer 1988), pp. 485–507; and Joseph M. Grieco, Robert Powell, and Duncan Snidal, “Controversies: The Relative-Gains Problem for International Cooperation,” American Political Science Review, Vol. 87, No. 3 (September 1993), pp. 729–743. 82. Henry Tajfel and John C. Turner, “The Social Identity Theory of Intergroup Behavior,” in Ste- phen Worchel and William G. Austin, eds., Psychology of Intergroup Relations (Chicago: Nelson Hall, 1986), pp. 7–24; and Jonathan Mercer, “Anarchy and Identity,” International Organization, Vol. 49, No. 2 (Spring 1995), pp. 229–252. 83. Wagner, Flinn, and England, “Hormonal Response to Competition among Male Coalitions.” 84. Ibid., p. 441.

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these endocrine mechanisms during within-coalition competitions may be in- hibited because hurting one’s brethren would tend to erode intracoalitional stability, despite its advantageous effects during intercoalition competition. In this instance, psychophysiological mechanisms are sensitive to cues indicating the relevant alliance conditions. Absolute gains should be privileged to the extent that interaction with coalitional members triggers motivations and dynamics speciªc to intracoalitional domains, whereas relative gains concerns should be emphasized during intercoalitional competitive interactions. We argue that the relative-absolute gains debate (as well as many other debates in international relations) is necessarily indeterminate if scholars insist on identifying a primary, exclusive, or inºexible motive. Instead, political groups will emphasize relative or absolute gains as a consequence of the particular relational cues perceived within the coalitional environment.

sex differences in coalitional behavior All sexually reproducing species have at least two sexual morphs. Sexual dimorphism is a biological regularity (though not a necessity) throughout the animal kingdom, and where this dimorphism exists, selection can be expected to have favored mechanisms for each sex contingent on the unique reproductive problems each faces.85 All functional sex differences result from adaptive challenges in the environment that are unique to, or differentially faced by, one sexual morph. Some of these functional sex differences can be explained by sexual selection as a consequence of their beneªcial effects in directly aiding in the competition for mates. The peacock’s tail is the classic example of a trait favored by sexual selection—although its length and brilliance may cause the peacock to be more vulnerable to detection and capture by predators, this cost is outweighed by its beneªcial ability to attract a mate.86 As Donald Symons points out, “The occurrence and intensity of sexual selection are determined by the ‘parental investment’ each sex typically makes in its offspring.”87 According to parental investment theory, the sex with greater parental investment will constitute a limiting (i.e., scarce) resource on the ªtness of the opposite sex, relegating the sex that invests less to compete, often aggressively, over access to reproductive resources.88 There tends to be an

85. Martin Daly and Margo Wilson, Sex, Evolution, and Behavior, 2d ed. (Boston: Willard Grant, 1983). 86. Amotz Zahavi, “Mate Selection—Selection for a Handicap,” Journal of Theoretical Biology, Vol. 53, No. 1 (September 1975), pp. 205–214. 87. Donald Symons, The Evolution of Human Sexuality (New York: Oxford University Press, 1979), p. 23. 88. Robert Trivers, “Parental Investment and Sexual Selection,” in Bernard Campbell, ed., Sexual Selection and the Descent of Man, 1871–1971 (Chicago: Aldine de Gruyter, 1972), pp. 136–207.

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early obligate asymmetry in parental investment: the gametes of one sex tend to be larger than the gametes of the other sex.89 Thus, from the beginning, one sex possesses a relatively larger and structurally obligate parental investment. Because sex is determined with respect to gamete size, it is the case that females, all things equal, tend to have higher relative levels of parental investment than males. This is the case with humans, as it is with most primates and mammals in general. Because human male parental investment has evolutionarily been low relative to females, inducing male competition over relatively scarce reproductive resources, male reproductive success is subject to wider variance than that of females. As Symons notes, “The more the males and females of a species differ in their typical parental investments, the more intense is the reproductive competition among members of the sex with the lesser investment, the greater is the variance in reproductive success among members of the competitive sex, and the more intensely sexual selection favors structures and behaviors of use in the competition.”90 Sexual selection will then act on males, favoring traits that promote intrasexual competition over mates, such as greater muscle mass. Sexual selection will also act on females in corresponding ways.91 In many domains, the adaptive problems faced by both sexes will be relatively identical, and thus males and females will posses the same adaptations for solving these problems (e.g., color constancy in vision). Where one sex is differentially ex- posed to a particular reproductive constraint, however, selection will reºect this by designing that sex to be differentially well adapted for solving that problem.92 Based on sexually speciªc selection pressures, we offer the following prelim- inary hypotheses on adaptive sex differences with relevance for human coalitional psychology. h4. coalitional size and strength. Coalitional size and male, but not female, physical strength will positively predict individual support for aggressive foreign policies. In primates, chimpanzees will run away if they encounter a member of an enemy group in the forest; once the imbalance of power ratio increases to three to one, the chimpanzee and his coalition will then seek to over-

89. There is the rare case of isogamy in some species in which male and female gamete size is equal. 90. Symons, The Evolution of Human Sexuality, p. 23. 91. William D. Lassek and Steven J.C. Gaulin, “Waist-Hip Ratio and Cognitive Ability: Is Gluteofemoral Fat a Privileged Store of Neurodevelopmental Resources?” Evolution and Human Behavior, Vol. 29, No. 1 (January 2008), pp. 26–34. 92. Joshua New, Max M. Krasnow, Danielle Truxaw, and Steven J.C. Gaulin, “Spatial Adaptations for Plant Foraging: Women Excel and Calories Count,” Proceedings of the Royal Society B, November 7, 2007, pp. 2679–2684.

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take and kill the opponent; these contests are always among males.93 In human societies, the ethnographic record clearly shows that coalitional aggression is carried out by males to a much larger extent than by females, and the evidence strongly suggests that male psychology contains psychological mechanisms designed for ancestral warfare, including adaptive forms of overconªdence.94 This sex difference is far from unimportant even in modern societies. For example, quite remarkably, one of the strongest predictors in explaining the severity of modern wars is the frequency of young males in the relevant populations.95 As the frequency of young males increases, so does the severity of the war. During our evolutionary past as hunter-gatherers, warfare was a small-scale phenomenon involving contests between small raiding parties. In such situations, even small numerical or qualitative asymmetries between coalitions would prove a vital determinant of outcome. As with chimpanzees, coalitional size constitutes a central component determining one’s individual willingness to participate in aggression. The likelihood of prevailing in such competitions would have been directly related to increases in coalitional size (though, ultimately, a range of other factors, such as maintaining intragroup cooperation, might limit the adaptive size of coalitions as well). This, of course, gives new meaning to Joseph Stalin’s famous dictum that quantity may have a quality all its own. This may also partly explain the tendency, in modern military contexts, to irrationally overemphasize coalitional factors such as relative capabilities at the expense of more nuanced and effective emphasis on force structure and employment.96 For example, the U.S. war in Vietnam involved a decisive military advantage for the United States, but traditional victory remained elusive because insufªcient attention was paid to the tenacity and endurance of the local population. Leaders in any combat operation that strug- gles against an insurgency understand that sheer strength alone often proves insufªcient to achieve decisive victory. Yet, ancestrally, relative capabilities would have proved more decisive than in modern conºicts that take place above the militarized threshold. Another important factor would be the individual coalition member’s physical strength. Ancestrally, individual physical strength would have been highly

93. Wrangham, “Evolution of Coalitionary Killing.” 94. Johnson et al., “Overconªdence in Wargames”; and Wrangham, “Evolution of Coalitionary Killing.” 95. Christian G. Mesquida and Neil I. Wiener, “Male Age Composition and Severity of Conºicts,” Politics and the Life Sciences, Vol. 18, No. 2 (September 1999), pp. 181–189. 96. Stephen D. Biddle, Military Power: Explaining Victory and Defeat in Modern Battle (Princeton, N.J.: Princeton University Press, 2004).

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correlated with the ability to inºict costs and hence survive and prevail in combat. Given that victorious individuals were more likely to reproduce, the aggressive characteristics that brought them reproductive success were more likely to be passed on to a greater number of progeny, and this process would be expected to continue iteratively across many generations.97 Thus, the importance of individual physical strength is rather obvious in dyadic interactions, but given the relatively small size of ancestral coalitions, this psychology would also have come to be applied to group interactions. Thus, a strong male could signiªcantly boost the formidability, and prospects for victory, of his overall group. Given the small scale of intergroup conºict, even a small addition could tip the balance; ever the more so if that addition is formidable. We argue that one of the fundamental insights gleaned from evolutionary psychology regards the way in which modern citizens appraise mass-level political phenomena through evolved psychological mechanisms designed to navigate the small-scale environments of our ancestors. This implies that parameters such as coalitional size and individual male physical strength automatically and unconsciously guide modern individuals’ decisions regarding aggressive foreign policy within a much larger modern nation-state context. Ancestrally, male coalitions would be composed of both kin and non-kin; and in modern societies, this might imply that a male’s physical strength, number of close male friends, and number of brothers and close male cousins would regulate the extent to which he unconsciously estimates probabilities of prevailing in battle. In addition, prospects for victory may decisively inºuence interest in undertaking such action. Thus, for males, personal physical strength and coalition size should, ceteris paribus, predict both individual support for, and conªdence in, aggressive foreign policy programs.98 Research has al-

97. For a dramatic example, see Tatiana Zerjal et al., “The Genetic Legacy of the Mongols,” Ameri- can Journal of Human Genetics, Vol. 72, No. 3 (March 2003), pp. 717–721. 98. John Tooby, Leda Cosmides, Aaron Sell, Debra Lieberman, and Daniel Sznycer, “Internal Reg- ulatory Variables and the Design of Human Motivation: A Computational and Evolutionary Ap- proach,” in Andrew J. Elliot, ed., Handbook of Approach and Avoidance Motivation (Mahwah, N.J.: Lawrence Erlbaum, 2007), chap. 15. One should be careful not to derive explanations of particulars from causal claims about averages. This hypothesis does not tell you that the more you bench- press, the more you will unequivocally be inclined to support aggressive foreign policies. The human aggression system is computationally complex, and many other features play a causal role in shaping the proªle of human aggression. We argue only that strength represents one of the factors that enter into such a calculation. See Azar Gat, “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter-Gatherer Fighting, Pt. 2: Proximate, Subordinate, and Derivative Causes,” Anthropological Quarterly, Vol. 73, No. 2 (April 2000), pp. 74–88; John Archer, “Testoster- one and Human Aggression: An Evaluation of the Challenge Hypothesis,” Neuroscience and Biobehavioral Reviews, Vol. 30, No. 3 (2006), pp. 319–345; Rose McDermott, Dustin Tingley, Jonathan Cowden, Giovanni Frazetto, and Dominic D.P. Johnson, “Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation,” Proceedings of the National Academy of Sci- ences, February 17, 2009, pp. 2118–2123; and Sell, Tooby, and Cosmides, “Formidability and the Logic of Human Anger.”

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ready demonstrated the validity of this expectation.99 For example, the study by Aaron Sell and his colleagues mentioned above found that stronger men display greater support for aggressive foreign policy action, as predicted from this perspective.100 As coalition size and strength would have been generic predictors of the ability to inºict costs and achieve victory ancestrally, these parameters would also likely inºuence a range of other modern issues that relate to internal societal conºict involving criminal justice and economic redistribution. h5. reproduction status. Individuals with children, particularly women, will adopt differing positions concerning aggressive foreign policies than those without progeny. Individuals without children, particularly men, may differentially support such policies. Depending on how an issue is framed, people with children will be disproportionately less willing to risk costs than those without children in wars of aggression. For example, John Mueller’s data show that age correlates negatively with support for wars.101 Younger people obviously face the choice of participation in coalitional aggression based on their own in- terests and incentives. Older people with children, however, may ªnd offensive (as opposed to defensive) wars more costly if combat risks the possibility that they would lose their children in conºict. This will be particularly true if parents are too old to have additional children. This constraint will exert its biological effect on the reproductive capacity of women long before it affects men, thus placing pressure on women to oppose such wars earlier in their life- span. In line with this, anthropological studies have found that women often act to restrain collective aggression.102 The mirror image of female opposition to wars that risk the lives of their children arises in men who may want children but are unable to ªnd suitable mates within their own group, either because the majority of women are already taken by higher-status or wealthier men, or because their own social position does not yet warrant access to mates. Success in battle may beneªt such men in at least two distinct ways. First, men who achieve heroic status through courage on the battleªeld, and who may be able to bring beneªts back to their community, gain status and wealth that may help them to increase their access and attractiveness to suitable mates. In addition, ancestrally, men were also able to ªnd or kidnap brides from conquered territory, and secure mates in

99. Aaron Sell, “Regulating Welfare Tradeoff Ratios: Three Tests of an Evolutionary-Computa- tional Model of Human Anger,” Ph.D. dissertation, University of California, Santa Barbara, Sep- tember 2005. 100. Sell, Tooby, and Cosmides, “Formidability and the Logic of Human Anger.” 101. John E. Mueller, War, Presidents, and Public Opinion (New York: John Wiley and Sons, 1973). 102. Lee, “Peace Chiefs and Blood Revenge.” For a counterexample, see Napoleon A. Chagnon, Yanomamö: The Fierce People, 3d ed. (New York: Holt, Rinehart, and Winston, 1983).

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such a fashion.103 Given these selection pressures acting over human evolutionary history, male psychology should have adapted to implicitly regulate the willingness to engage in collective aggression based on the within-group availability of mates. Although this might seem irrational from the perspective of modern large-scale warfare where the possibility of capturing mates is limited (not least because of international conventions), human psychology may nonetheless be designed to operate on the basis of those assumptions that would have produced “best bets” in the environment of evolutionary adaptedness. And even though a mate-seeking motivation might not be explicit in relation to modern wars, evidence suggests that sexuality can still play a role. Capture of brides, for example, persists in limited pastoral and clan conºicts in places such as Central Asia, and rape is a frequent aspect of war both histori- cally and in the modern context.104 In this way, young men may have personal incentives to ªght offensive wars that go beyond the imperatives put forth by their leaders. Thus, such males with high status aspirations, who have not yet achieved high status, will remain the most dangerous opponents in conºict.105

Conclusion

Taken together, the hypotheses we present within the preceding areas of inquiry are derived from the framework of evolutionary psychology, which investigates the ªt between the structure of ancestrally recurrent adaptive problems and evolved psychological mechanisms in the human brain. Our aim in this article has been to show that evolutionary psychology offers a via- ble model with which to analyze and explain political behavior, to dispel false impressions of the inability of evolutionary models to offer ex ante predictions and hypotheses, and to outline speciªc hypotheses for a research program in evolutionary political science that focuses, in particular, on the central role of our evolved coalitional psychology. In addition, insights derived from this perspective promise to develop and correct many of the problematic assumptions about human nature embedded in extant models of social and political behavior. Speciªcally, evolutionary psychology can provide an explanation of the origin of preferences. Such preferences are shaped by our evolved psychological architecture, which remains plastic precisely because its mechanisms depend irrevocably on a range of environmental cues (both internal and external) to

103. Gat, “The Human Motivational Complex: Evolutionary Theory and the Causes of Hunter- Gatherer Fighting, Pt. 1.” 104. Mia Bloom, “Death Becomes Her: Women, Occupation, and Terrorist Mobilization,” PS: Politi- cal Science and Politics, Vol. 43, No. 3 (July 2010), pp. 445–450. 105. Stephen Peter Rosen, War and Human Nature (Princeton, N.J.: Princeton University Press, 2007).

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function. Through examination of the localized political environments in which humans evolved to cooperate and compete, we can better understand the patterns and novelty of international political behavior. Any investigation into the structure of our coalitional psychology must have two components. First, how are coalitions represented? For example, what is the process by which we psychologically attribute intentionality, reputation, and history to coalitions? Second, the way people think about coalitions in- variably informs how they act toward and within coalitions. Thus, while the process of coalitional representation sets the framework for interpretation and evaluation of coalitional objects and events, the facilitation of coalitional behavior takes the analysis a step further and inquires into processes of motivation and action. In addition to these two components, and because of the evolutionarily enduring differential reproductive constraints between the sexes, we expect that in certain domains, natural selection will have favored psychological adaptations for coalitional behavior that are unique to each sex. This is, of course, notwithstanding the fact that across many domains, the adaptive problems faced by both sexes will be relatively identical, and thus both sexes will posses the same adaptations for solving these similar problems. We have argued that evolutionary psychology offers students of international political behavior a useful integrative framework for reconciling disparate motives and for explaining the persistence of seemingly irrational biases that appear difªcult to mitigate. We do not, however, aim to replace existing theories of international politics such as realism, liberalism, or constructivism; instead, we wish to show that each offers a piece of a puzzle that should not be examined in isolation. This is more than an appeal for greater discussion among theoretical traditions; it is an appeal to recognize that each tradition is, in effect, examining a different aspect of our evolved coalitional psychology. Additionally, rationalist models may also be improved by theoretically grounding these models in ecologically valid assumptions. This attempt at establishing a model of ecological rationality can only broaden scholars’ understanding of political behavior. A growing body of research across ªelds as diverse as neuroscience, cognitive science, behavioral economics, behavior genetics, and biological anthropology suggests that we are political animals quite literally “designed” to negotiate the complex world of coalitional living. Evolved psychological mechanisms in these and other domains are the bridge between the theory of natural selection and the behavior we seek to explain. This evolutionary perspective on international politics reveals a world in which the enduring ca- dence of coalitional behavior represents not the repetitive drumbeat of blind determinism, but rather the unique rhythm of a particularly human history.

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