OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

PART 1 Prosocial Behavior at the Micro-Level

Schroeder251014OUS_PC.indb 35 12/12/2014 4:36:53 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

Schroeder251014OUS_PC.indb 36 12/12/2014 4:36:53 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

CHAPTER The Evolutionary Psychology of 2 Human Pro-sociality: Adaptations, Byproducts, and Mistakes Pat Barclay and Mark van Vugt

Abstract Evolutionary psychologists seek to understand prosocial behavior at four complementary levels of analysis: psychological mechanisms, development of those mechanisms (ontogeny), their adaptive or evolutionary function, and their evolutionary history (phylogeny). In terms of adaptive function, prosocial behavior is often costly to perform, so it is an evolutionary enigma. To evolve and be maintained, prosocial sentiment needs to bring corresponding fitness benefits. The authors outline a number of such evolutionary functions of prosocial behavior. Adaptive functions include direct benefits, mutualisms, stake or vested interests, kinship, reciprocity (direct and indirect), and costly signaling. Nonadaptive functions include mistakes, byproducts, and cultural learning. They provide a diagnostic tool for determining the likely function of any particular prosocial act and discuss three emerging perspectives in the study of prosocial behavior: scale of competition, multilevel selection, and biological markets. We conclude with future directions in evolutionary research on prosocial behavior. Key Words: altruism, cooperation, reciprocity, costly signaling, evolutionary psychology, levels of analysis

Introduction selected against because they cause us to perform Humans are a prosocial species. People make behaviors that may be costly. Nevertheless, proso- substantial sacrifices to help their kin and sup- cial sentiments persist such that prosocial behavior port their friends, rescue complete strangers in is ubiquitous in human interactions and in many bystander emergencies, make large financial dona- nonhuman interactions, too. Why? This is the tions to charities, and defend their in-groups question that this chapter addresses. against outsiders (Dovidio, Pilliavin, Schroeder, & In this chapter, we start by clarifying two major Penner, 2006). Yet human prosociality is an evolu- sources of confusion over evolutionary explana- tionary puzzle because over time natural selection tions: differences in (1) definitions and (2) the will ruthlessly winnow out any traits that reduce an types of questions that are being addressed. We individual’s fitness (i.e., someone’s relative repro- then introduce a flowchart outlining a number of ductive success). Thus, for any costly trait to evolve potential factors that could cause prosocial senti- and persist, there need to be some corresponding ment to emerge, either because they have been ultimate benefits in terms of spreading the actor’s directly selected for through natural selection or genes. A first-pass glance at natural selection would because they are byproducts of other adaptations. suggest that prosocial sentiments should have been We briefly discuss some new perspectives that

37

Schroeder251014OUS_PC.indb 37 12/12/2014 4:36:54 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

researchers are investigating and present some con- Researchers often get into unnecessary quarrels clusions and questions for future research. over the “causes” of prosocial behavior, without realizing that they may be providing valid answers Definitions to different questions (Barclay, 2011a; West et al., Prosocial behavior is defined as behavior “intended 2011). For example, one researcher may say “people to benefit one or more people other than oneself” help each other because they feel empathy.” A sec- (Batson & Powell, 2003, p. 463). This is a very broad ond researcher may say “people help each other term that includes many subcomponents, such as because they learn to help.” A third researcher will cooperation, mutualism, altruism, helping, and so say “people help each other because those who help on. Because different scientific disciplines use these tend to receive help.” A fourth research may say terms differently, we will simply provide the defini- “people help each other because we share this trait tions we are using and invite readers to substitute their with other apes and it evolved out of kin altruism.” preferred terms for these phenomena. That way, the What these researchers may not realize is that they focus is on the phenomena, not the semantics. We could all be right—or could all be wrong—because will use the term “prosocial behavior” to refer to any they are answering questions at different levels of actions that are intended to benefit others, regard- analysis. Nobel prize-winning ethologist Niko less of whether the actor also benefits in the process. Tinbergen (e.g., 1968) introduced his four levels of We will use the more popular word “helping” syn- analysis to clarify the different types of questions onymously with “prosocial behavior.” We will use the and avoid unproductive debates over explanations term “prosocial sentiment” to refer to any emotions at different levels. or psychological mechanisms that trigger this help- In our example, the first researcher is talking ing. Some types of prosocial behavior are costly to about proximate psychological mechanisms, that the actor, at least temporarily (“costly cooperation”), is, what is going on within the individual at the whereas other types of prosocial behavior carry no time he or she helps. The second research is talking costs or provide return benefits to the actor almost about development, that is, how that psychological immediately (“noncostly cooperation”). Biologists use mechanism (whatever it happens to be) develops the term “altruism” to refer to actions which decrease within the life span of an individual and how genes one’s lifetime reproductive success, and it is one form and environments interact. The third researcher of costly cooperation (West, El Moulden, & Gardner, is asking about ultimate function, that is, why an 2011). A mutualism is a form of (noncostly) coopera- individual would develop in such a way as to have tion when the actor and another agent both benefit that psychological mechanism, what the benefits of from something the actor does. This could include having it are, and what selective pressures cause it active coordination between the two of them but does to persist. The fourth research is addressing phylog- not need to. Those who disagree with our terminology eny or evolutionary history, that is, how and when should simply substitute their own where appropriate. the mechanism evolved in our evolutionary history, and what prior trait(s) it evolved from. Levels of Analysis: What Question(s) Are Our example shows how these four levels of We Addressing? analysis are complementary, not mutually exclu- Evolutionary psychology draws from many dis- sive: all behaviors require an explanation at all four ciplines, including but not limited to evolutionary of these levels of analysis to be fully understood. biology, experimental economics, mathematical The only fruitful scientific discussion is between game theory, anthropology, and of course psy- explanations within the same level. For example, chology (social, developmental, cognitive, etc.). researchers can debate whether the psychologi- It uses tools and methods from all of these to cal mechanism that triggers helping behavior is investigate behavior. As such, evolutionary psy- empathy versus “oneness with others” (e.g., Batson chology is not a field or subdiscipline in the tradi- et al., 1997, versus Cialdini et al., 1997). They can tional sense. Instead, it is a meta-theoretical stance also debate development by asking whether that which can be applied to any field, subdiscipline, psychological mechanism is learned versus innate or topic (Daly, 2011; Van Vugt & Schaller, 2008). (though this is actually a false dichotomy, see What often differentiates evolutionary researchers Ridley, 2003). When debating adaptive function, from nonevolutionary researchers is the types of researchers can argue over whether prosocial behav- questions they ask, and how those questions are ior serves to invite reciprocation or serves to signal interconnected. desirable qualities. For phylogeny, we can discuss

38 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 38 12/12/2014 4:36:54 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

whether our prosocial sentiments are unique to the being prosocial increases one’s inclusive fitness (i.e., human lineage versus evolutionarily ancient, and spread of one’s genes). Nonadaptive explanations are we can debate which other sentiments they evolved ways in which prosocial behavior could spread even from. However, we cannot, for example, say that if they do not increase one’s fitness: for example, the because prosociality is learned, it therefore does not behavior could be a byproduct of some other adap- function to invite reciprocation, because these are tive mechanism or it could be a mistake produced explanations at different levels (e.g., the reciproca- by a prosocial psychology that is adaptive on aver- tion could be the reinforcer that causes prosocial- age (or once was). Some of these explanations have ity to be learned). Much of the controversy over received more attention than others, but it does not evolutionary explanations of prosociality is because mean that they are more important, more interest- researchers mix up these levels of analysis, for ing theoretically, or even more common in nature example by assuming that people are consciously (Clutton-Brock, 2009; West et al., 2011). concerned with receiving benefits for helping or Figure 2.1 outlines these different explana- that all acts of helping are based on selfish personal tions in a flow chart. This figure is designed to motivations (Barclay, 2011a, 2012b; Van Vugt & roughly move from prosociality with obvious and Van Lange, 2006; West et al., 2011). We agree well-studied adaptive benefits to the less obvious or with evolutionary biologist Richard Dawkins who less-studied types of benefits associated with proso- argued that “selfish genes” can produce genuinely ciality. The flowchart could be used as a diagnos- selfless organisms (Dawkins, 1976/2006)—these tic tool for discovering the origins and functions are two different levels of analysis! of different types of helping in the real-world. For All four levels of analysis are important to study similar charts that distinguish between functions and can inform each other. Different researchers of helping behavior, see Bshary and Bergmüller focus on different levels, depending on their scien- (2008) or West et al. (2011). tific discipline. For example, this volume includes several chapters on proximate psychological mech- Adaptive Explanations anisms and their proximate neural underpinnings, Adaptive explanations are cases where the even- such as empathy (Batson et al.; Davis), mood tual benefits of helping outweigh the costs, either (Clark), mortality salience (Hirschberger), and the for the individual (direct fitness) or for copies of neuroscience underlying these (Grijalva and col- his/her genes residing in other bodies (indirect leagues). Some chapters focus on the development fitness)—together referred to as inclusive fitness of prosociality (Eisenberg), culture (Piliavin & (Hamilton, 1964). To help differentiate between Siegl), and we are happy to even see a chapter on them, we will illustrate each with the example of the phylogeny of prosociality (de Waal). In this hunting. Hunting is a common practice in the soci- chapter, we will primarily address the question of eties in which humans evolved, and hunted meat evolutionary function. If we can understand the is often shared. As such, hunting is very common evolutionary functions of prosociality, then we topic in evolutionary studies of cooperation, and can make better predictions about how to change the underlying principles can generalize to other social situations to foster prosociality. Paraphrasing forms of prosocial behavior. Please see Figure 2.2 the great evolutionary biologist George Williams for a visual depiction of each kind of explanation. (1966, p. 6) we believe that our understanding Each of these listed explanations for prosocial of human prosociality would be aided greatly by behavior could warrant an article unto itself, so we knowing the purpose for which it was designed. can give only a quick overview of each and refer the reader to the relevant literatures. Evolutionary Functions of Prosociality What selective pressures have caused proso- Direct Benefits and Byproduct Mutualism cial sentiment in the human lineage? While the Imagine a hunter who catches a large mammal answer is not yet completely certain, there are which ends up getting shared with others, even several intriguing possibilities as to the evolution- the nonhunters who scrounge from his kill. Many ary origins of prosocial behavior. We can roughly would consider this hunting to be prosocial behav- divide these evolutionary accounts into two cat- ior because others benefit, even though the actor egories: adaptive explanations versus nonadaptive may not have intended for them to benefit—he may explanations. Adaptive explanations are those that have simply been concerned with filling his own find some benefit to prosocial behavior, such that empty belly (Harpending, 1998). Hunting provides

Barclay, Van Vugt 39

Schroeder251014OUS_PC.indb 39 12/12/2014 4:36:54 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

Adaptive Explanations Does the actor automatically Yes benet directly? Mutualisms & byproduct mutualism (e.g. volunteer’s dilemma) No Stake or vested interest Will the actor personally benet Yes if the recipient receives help? (e.g. banker’s paradox, pseudo-reciprocity) No

Do kin benet? Yes „e “kin selection” component of inclusive tness No

Does helping increase the likelihood Yes From the recipient: direct reciprocity of the actor receiving help? From other: indirect reciprocity No

Does helping signal some hidden Yes quality like resources, abilities, or Costly signaling good character?

No Non-Adaptive Explanations

Is the helping caused by an error in Yes (a) Mistakes by an adaptive mechanism executing any of the stages above? (e.g. incomplete info, error management) (b) Outliers on a normal curve No (c) Pathology in an adaptive mechanism (d) Evolutionary mismatch (“lag”)

Is the helping linked with a trait which Yes Evolutionary byproduct is under strong selection pressure? (e.g. docility, learning via conformity) No

Does helping behaviour cause the Yes Memes & cultural “group” idea of helping to spread? (may or selection may not be benecial for the actor) No

Evolutionary psychology is currently unable to explain this helping

Fig. 2.1 Diagnostic flowchart of the functional causes of prosocial behavior. For any instance of prosocial behavior, one should start at the top and determine whether the benefits at that stage are sufficient to outweigh the costs of helping. If not, one should investi- gate lower stages. These explanations are ordered in an estimated order of parsimony (e.g., direct benefits are easiest to explain); we are not committed to the exact order, and some changes in order are expected with more research on each of these areas.

a direct benefit to the hunter because he gets to eat. is better off if someone hunts but they are person- Even if there is a cost to hunting, hunting is better ally best off if it is someoneelse who expends that than starving. Importantly, even sharing the meat effort. This sort of situation has received exten- may be directly beneficial if it stops others from sive theoretical work, but under different names, pestering the hunter for meat. Any benefits to oth- such as a Volunteer’s Dilemma (Diekmann, 1985; ers are a byproduct of the hunter doing what is in Murnighan et al., 1993; Myatt & Wallace, 2008), his best interest. In this sort of situation, prosocial producer/scrounger game (Barnard & Sibly, 1981; behavior is selected for, yet primarily because of the Vickery et al., 1991), Dragon-Slayer game (Bliss & direct benefits to the actor (think of a wealthy per- Nalebuff, 1984), Snowdrift Game (Doebeli & son purchasing a golf course to play on from which Hauert, 2005; Kümmerli et al., 2007), and Brave other golfers could profit too). Leader game (Shen et al., 2010). The names may Volunteering. A special case of direct ben- differ, but the logic of the game1 is the same: for efit prosociality is when a lone hunter volunteers each person, the worst situation is if no one pays the to catch food that others can scrounge. Everyone cost of volunteering to produce the food, slay the

40 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 40 12/12/2014 4:36:54 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

(a) Volunteer’s dilemma (b) Mutualism

Common Common resource resource

(c) Stake or vested interest (d) Kinship

Externality

(e) Direct reciprocity (f) Indirect reciprocity

(g) Costly signaling

Wow!

Fig. 2.2 Adaptive explanations for prosocial behavior (a) Volunteer’s Dilemma, where one individual produces a resource that oth- ers happen to also benefit from (byproduct mutualism); (b) mutualisms (including coordination) where multiple individuals benefit from working toward a common goal; (c) one individual has a vested interest of the well-being of someone else who produces posi- tive externalities; (d) individuals behave nicer to kin than to nonkin, because the former are more likely to carry copies of the same gene(s); (e) two individuals directly reciprocate prosocial acts, possibly with some time lag or in different currencies; (f) prosociality is reciprocated indirectly (i.e., by someone other than the recipient); and (g) costly signaling, where prosociality allows audiences to infer some difficult-to-observe trait about the actor. Solid arrows indicate direction of helping, dashed arrows indicate observation, hollow arrows indicate positive externalities flowing from one individual or resource to someone else, and arrows that are crossed out indicate an absence of helping (or at least less helping than with solid arrows).

dragon, or clear the snowdrift, and the best situa- There have been many theoretical and empiri- tion is if someone else (not oneself) does so. If others cal studies of Volunteer’s Dilemmas in humans are unlikely to volunteer, then one is best off to vol- and other animals. For example, Kümmerli and unteer oneself. Others will happen to benefit from colleagues (2007) show that people are much this, but that is a byproduct of an individual follow- more likely to cooperate with each other in this ing his/her best interests. This type of scenario has sort of situation than in the traditional Prisoner’s been used to explain to all sorts of situations includ- Dilemma game (where free-riding is the strategy ing bystander helping, food production, vigilance that maximizes individual payoff in any given against enemies, voting, and so on (Komorita & round). This result matches game theoretical pre- Parks, 1994). It has even been applied to the dictions by Doebeli and Hauert (2005). If only enforcement of group cooperation, in that people one (or a few) individual(s) need to volunteer in might take on the cost of punishing noncooperation such situations, then people will be less likely to if no one else does (O’Gorman, Henrich, & Van volunteer in larger groups because it is more likely Vugt, 2009; Raihani & Bshary, 2011). that someone else can do so (e.g., Archetti, 2009).

Barclay, Van Vugt 41

Schroeder251014OUS_PC.indb 41 12/12/2014 4:36:55 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

This prediction integrates evolutionary biology nice (e.g., Blurton-Jones, 1984; Fehr & Gächter, with the vast literature on “diffusion of respon- 2002; O’Gorman et al., 2009; Ostrom, 1990; sibility” in bystander helping, which shows that Yamagishi, 1986). When such coercion is pres- group size inhibits helping (for a meta-analysis, ent, there are direct benefits for helping others in see Fischer et al., 2011). Individual characteristics order to avoid the costs of punishment. We will not of group members are also relevant. For example, elaborate on this here, because many readers will Diekmann (1993) has empirically shown that if not consider coerced helping to be “prosocial,” but one person has greater ability to provide a pub- we mention briefly it because it fits the definition of lic good because he/she pays lower costs for doing prosocial behavior and seems to be relatively com- so, then that person is more likely to “volunteer” mon – think of a hunter being ostracized for not and others are more likely to refrain. Finally, the sharing his meat. costs of failure are also relevant: Archetti (2009) has mathematically shown that people are actu- Stake or Vested Interests ally better off when there is a high cost of no one In television show Survivor, the point is to vote volunteering, because people are more likely to people out of a group until one person remains, volunteer in such cases. Such counterintuitive while gathering food and surviving a hostile envi- predictions show how taking an evolutionary ronment (maybe much like the environment in approach can lead to novel predictions about pro- which humans evolved). In the show’s first season, social behavior. the candidate Richard Hatch became irreplace- Mutualisms. Sometimes hunting requires coor­ able to his group by becoming a good hunter. di­­nation: Individuals working together can accom- Although others may have wanted to vote him plish something that they could not accomplish alone. out, they also relied on the food he provided, such Each individual benefits from working with others, that they had a vested interest in keeping him in and this is the basis of mutualisms. Mutualisms the group and ensuring his “survival.” Reality are ubiquitous in nature (Clutton-Brock, 2009; television may border on fiction, but the principle Sachs et al., 2004), and are also ubiquitous among here is general: one person can have some stake humans, as exemplified in the classic Adam Smith or vested interest in the welfare of another, such quote that “it is not from the benevolence of the that the former person directly benefits from help- butcher, the brewer, or the baker that we expect our ing the latter. This principle carries many names, dinner, but from regard to their own interest.” Some including pseudoreciprocity (Connor, 1986, researchers do not find mutualisms as “theoretically 1995), stake (Roberts, 2005), the Banker’s Paradox interesting” as other forms of cooperation, but they (Tooby & Cosmides, 1996), and interdependence are arguably the most common kind of cooperation or Selective Investment Theory (Brown & Brown, in nature (Clutton-Brock, 2009; West et al., 2011). 2006). Studies in hunter-gatherers support the One party in a mutualism may benefit more than anecdote with Richard Hatch: those who pro- the other, but it is better for both parties to keep vide meat for their groups tend to receive more the mutually beneficial relationship than to break it food from others when they themselves are sick (e.g., Bergstrom & Lachmann, 2003). (Gurven et al., 2000, see also indirect reciprocity, A special form of prosocial behavior through later). mutualistic cooperation is leadership (Van Vugt, When people have a vested interest in the 2006). Two hunters might benefit from coordi- well-being of their friends and social partners, they nating their efforts to hunt down prey. Yet one benefit from helping those friends, even if the friend hunter might get hungrier quicker or he has a more is unaware of the help. People benefit from being impulsive or dominating personality so that he will part of groups, such that they directly benefit from always lead the hunt. Given the risks associated helping those groups survive (Barclay & Benard, with leading a hunt, he might be slightly worse off 2013; Kokko et al., 2001; Lahti & Weinstein, than to be the follower yet he still profits from the 2005; Reeve & Hölldobler, 2007). These vested presence of another hunter (King, Johnson, & Van interests in others’ welfare can explain much help- Vugt, 2009). ing toward individuals and even groups: if you will Coercion and punishment. Not all help is will- eventually benefit from the survival and well-being ingly provided. Researchers in many disciplines of your allies and in-group members, then you have have noted that people are nicer to each other when a vested interest in helping them (De Cremer & they could be punished or harassed for not being Van Vugt, 1999; West et al., 2007).

42 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 42 12/12/2014 4:36:55 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

Little empirical work has been done on the (Daly & Wilson, 1988; Gardner & West, 2004). psychological mechanisms that trigger vested Kinship is a major form of grouping in many interests prosocial behavior (though see Brown & pre-industrial societies, and appears to be a major Brown, 2006). We would predict that they will be factor affecting who shares food with whom in related to genuine concern of some sort toward the many societies (Gurven, 2004). In fact, the most recipients; after all, you do not want someone to persistent, long-term, selfless, and unreciprocated be incapacitated if you depend on them, and your help that we see people perform—namely paren- concern will motivate you to ensure that they keep tal care—is actually just a special case of kinship benefitting you. Tooby and Comides (1996) have because offspring carry copies of parental genes suggested that from the actor’s perspective such (Daly & Wilson, 1988; Dawkins, 1976/2006). situations will also be associated with a desire to Natural selection has crafted a psychology that be irreplaceable to others, because this gives those includes such powerful sentiments as parental love, people a stake in your welfare, and thus increases filial attachment, fraternal and sororal solidarity, their likelihood of helping you. and other such nepotistic emotions. These emo- tions are the proximate psychological mechanisms Kinship that function to promote nepotism toward kin. All The vast majority of the more costly forms of told, kinship appears to be one of the most power- helping in both humans and nonhumans are ful causes of prosocial behavior for most humans directed toward kin. Why is this? Imagine that you on the planet. are a gene trying to propagate copies of yourself. The great evolutionary theorist William Hamilton Reciprocity (1964) noted that there are at least two ways you Hunting food is difficult, and hunters often can do this: by increasing the reproduction of your come home empty-handed. This means that each current body (direct fitness), or by increasing the hunter is at risk of going hungry some days and reproduction of other bodies that carry a copy of having a bonanza of food on others days when he yourself (indirect fitness).Inclusive fitness is the catches something. To resolve the problem of being sum of these effects—direct fitness plus indirect hungry on some days, two or more hunters could fitness—and is what organisms have evolved to agree to help each other. Each hunter will share maximize.2 For any given gene, close kin are sta- with the other(s) when he has plenty, and gets a tistically likely to carry identical copies. Any gene share when he is hungry. This way, each has fewer that causes an individual to help close kin will often hungry days and is more likely to survive. cause help to be targeted toward copies of itself. There is a risk associated with this type of pro- Thus, we should predict that psychological mecha- sociality because sharing is costly: Sharing involves nisms that cause nepotism will evolve in many spe- giving up meat (or time, effort, money, etc.). If one cies, and that this nepotism should depend in part person received meat from others without giving on the closeness of kinship (as well as the fitness anything in return, then he would be better off costs and benefits). This prediction has been abun- than someone who paid the cost of sharing. This dantly confirmed in many species (for a review, see strategy of “free-riding” on others would be ben- Alcock, 1993); the fact that it has even been stud- eficial if people are willing to give to anyone. One ied in plants (e.g., Dudley & File, 2007) suggests solution is for people to preferentially help those that inclusive fitness is a powerful idea that applies who have provided help in return: this is the basis across all of life. of reciprocity (Axelrod, 1984; Trivers, 1971; Van Much research has shown that—all else being Vugt & Van Lange, 2006). In this way, the helpers equal—people are nicer to kin than nonkin: they tend to receive help and the nonhelpers tend to not are more likely to help kin, less likely to harm receive anything. Reciprocity comes in two basic kin, and more willing to tolerate injustices from forms—direct and indirect reciprocity—which kin (e.g., Burnstein, Crandall, & Kitayama, differ in whether the help is repaid by the recipient 1994; Daly & Wilson, 1988; DeBruine, 2002; or by others in the community. Grayson, 1993; Hames, 1987; Krupp et al., 2008; Direct reciprocity. People often get involved in Stewart-Williams, 2007). Of course, all else is exchange relationships where they take turns help- never equal, but even when people are in compe- ing each other. In our meat example, two hunters tition with others, they will compete less sharply might share with each other as long as each of them with kin than with nonkin in the same situations has given in the past. Colloquially, we have such

Barclay, Van Vugt 43

Schroeder251014OUS_PC.indb 43 12/12/2014 4:36:55 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

expressions as “you scratch my back and I’ll scratch getting increasingly prosocial when one’s partner yours,” which carry the implicit condition that “I reciprocates. This accurately models what people will not scratch your back unless you scratch mine.” actually do in experimental games (Roberts & Is this kind of prosocial behavior beneficial Renwick, 2003; Van den Bergh & Dewitte, 2006), for the actor? Most readers of this chapter will be especially with strangers with whom they have familiar with Axelrod’s computer simulations of not yet built up a trusting relationship (Majolo the Prisoner’s Dilemma Game (Axelrod, 1984). et al., 2006). A Prisoner’s Dilemma is a two-person game where Contrary to popular belief, the existence of each player has the binary choice either “cooperat- reciprocity does not require calculations or strict ing” or “defecting” in each of a number of rounds bookkeeping of past acts (recall from the intro- (iterations). Axelrod conducted computer simu- duction to this chapter that an act may be self- lated tournaments with different strategies for play- ish at the gene level but genuinely selfless at the ing iterated Prisoner’s Dilemmas, and the strategy level of the individual actor). Instead, reciproc- that consistently survived the best was Tit-for-Tat. ity explains why people are capable of possessing Tit-for-Tat is a simple strategy of initially cooperat- genuine warmth toward others like friends. If ing with one’s partner, and thereafter simply imitat- I genuinely value your welfare, it will cause me ing the partner’s action on the previous interaction. to help you, which can cause you to genuinely Tit-for-Tat is a remarkably good strategy because it help me when I need it, which causes me to value cooperates with other cooperators and does not get your welfare more, and so on. In other words, “suckered” for long by those who do not cooperate. reciprocity is the adaptive evolutionary cause of As such, it tends to do better than many other strat- prosocial behavior, whereas empathy and feelings egies (Axelrod, 1984; Boyd & Lorberbaum, 1987; of warmth are potential proximate psychological Dawkins, 1976/2006; Wilson, 1971). causes (e.g., Barclay, 2012b; de Waal, 2000; de There are conditions that limit the effectiveness Waal & Suchak, 2010; Frank, 1988; West et al., of Tit-for-Tat, of course. Tit-for-Tat only works if 2011). What reciprocity does require are the cog- the “shadow of the future” is long enough such that nitive abilities to detect when others might fail the future benefits of one’s partner’s reciprocation to reciprocate (Cosmides et al., 2010), remember will outweigh the cost of immediate helping (much who has and has not reciprocated (Barclay, 2008; subsequent work shows decreased cooperation in Mealey et al., 1996), and delay gratification in the last round of a cooperative task, a.k.a., “end- order to reap the long-term gains of reciproca- game effects”). Tit-for-Tat requires enough other tion (Harris & Madden, 2002; Stevens & Hauser, reciprocators around to make it worth initiating a 2004; Van Vugt & Van Lange, 2006). reciprocal relationship. Also, Tit-for-Tat must not Indirect reciprocity. People do not only help be directly competing against its partners, because their immediate friends and reciprocal partners. this decreases the benefits of prosocial behavior Human prosociality is much broader than that. (West et al., 2006; see “Scale of Competition”, People regularly help those who will not have the later). Under some conditions, Tit-for-Tat can be opportunity to reciprocate. Imagine one hunter beaten by more forgiving strategies that overlook who is known to regularly share with others, and accidental failures to cooperate, or by strategies that a second hunter who is known for stinginess. exploit unconditional cooperators (e.g., Brembs, When the generous hunter gets sick and is unable 1996; Klapwijk & Van Lange, 2009; Nowak & to hunt for himself, others are likely to give him Sigmund, 1992, 1993). Although Tit-for-Tat is not meat, whereas the stingy hunter is much less likely always the best reciprocal strategy to follow, the net to receive meat when sick (Gurven et al., 2000). sum of years of theory is that some willingness to This is an example of indirect reciprocity, which reciprocally exchange help can be a highly success- is when prosocial acts are reciprocated by some- ful strategy. one other than the recipient (Alexander, 1987; for Recent work has moved beyond the simple a review see Nowak & Sigmund, 2005). Under Prisoner’s Dilemma by allowing people to use graded indirect reciprocity, people acquire a good reputa- levels of prosociality instead of a binary choice. tion when they help others, and this makes them Roberts and Sherratt (1998; Sherratt & Roberts, more likely to receive help when they themselves 1999) have mathematically shown that the best need it. People who refuse to help good people get strategy in such situations is “Raise-the-Stakes,” a bad reputation, which reduces their likelihood of which means starting out moderately prosocial and receiving help.

44 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 44 12/12/2014 4:36:56 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

Wedekind and Milinski (2000) had partici- (Hawkes, 1991; Smith & Bliege Bird, 2000; Smith, pants play an experimental game where they could 2004). This is an example of costly signaling, which give money to other participants and could gain a is a way to broadcast information about oneself in reputation for giving or refusing. The experiment- a way which constrains it to be honest (Searcy & ers ensured that there was no possibility of direct Nowicki, 2007; Zahavi & Zahavi, 1997). reciprocation from the recipient because partici- Individual A benefits from sending signals to pants would never be paired with the same person convince Individual B that A has certain qualities again. Despite this, participants tended to give (e.g., abilities, resources, cooperative intent), and B money to others who had given in the past, such benefits from determining whether A honestly does that people with a good reputation were more likely possess those qualities. How does B know if A’s sig- to receive money. This result has been replicated in nals are honest or if A is bluffing? Signals can be several other similar experiments (Milinski et al., constrained to be honest if they carry a potential 2001; Semmann et al., 2004; Seinen & Schram, fitness cost which is only worthwhile for someone 2006; Wedekind & Braithwaite, 2002). People who honestly possesses the quality (Gintis et al., seem to use a combination of personal experience 2001; Searcy & Nowicki, 2007). For example, it and social information about others when deciding is fairly easy for Bill Gates to donate $1 billion to whether to help them (Roberts, 2008; Sommerfeld charity. As such, Bill Gates pay a relatively low et al., 2007). Evolutionary game theorists are cur- fitness cost for such large donations, and this can rently investigating what types of acts will result in be outweighed by any reputational benefits he obtaining a good versus bad reputation, and how receives. For most other folks, the reputational ben- a refusal to help a “bad” person might or might efits would not outweigh the crippling cost of sac- not harm one’s own reputation (Bolton et al., rificing that much money, so the fitness cost is too 2005; Milinski et al., 2001; Ohtsuki & Iwasa, high and therefore not worth it. As a result of these 2004, 2007). This research has implications for differing fitness costs, audiences can infer that Bill the genetic or cultural evolution of moral systems Gates is very rich because he has over a billion dol- (Alexander, 1987). lars to spare. Bill Gates thus receives status, respect, Indirect reciprocity can also be used to sup- mating opportunities (if he were so inclined), and a port large-scale cooperation. People who provide host of other social benefits. public goods that benefit the whole group tend Costly signaling theory has explained many forms to receive more help from others (Milinski et al., of prosociality like philanthropy (Harbaugh, 1998), 2002; Panchanathan & Boyd, 2004). As a result, large public feasts and potlatches (e.g., Boone, 1998; reputational forces like indirect reciprocity can be Smith & Bliege Bird, 2000; Van Vugt & Hardy, harnessed to support prosocial actions like the fight 2010; reviewed by Barclay, 2010a), peer-to-peer against climate change, because people who work file-sharing (Lyle & Sullivan, 2007), blood donations against climate change tend to benefit in terms (Lyle et al., 2009, volunteering (Van Vugt & Iredale, of indirect reciprocity (Milinski et al., 2006; Van 2012), and even organizational citizenship behavior Vugt, 2009). (Engelhardt & Van Vugt, unpublished data). In addition to signaling talents, abilities and Costly Signaling resources, prosocial behavior also signals coopera- Hunting big game is challenging, and hunters tive intent: “You know that I am unlikely to cheat regularly come home empty-handed. It takes a lot you because any short-term benefits I would gain of skill to catch big game with any regularity. If are not enough to outweigh the cost of the signal” you see someone who is often sharing meat from (André, 2010; Barclay, 2010a). This principle has big game that he has caught, what do you conclude successfully predicted various forms of prosocial about him? Probably that he has resources and activities such as apologies (Ohtsubo & Watanabe, skills. These can include talents such as athletic abil- 2009), commitment to relationships (Seymour & ity, physical strength, coordination, intelligence, Sozou, 2009), contributions to charities and public perseverance, leadership, and commitment—all goods (Iredale et al., 2008; Van Vugt & Iredale, of which are desirable traits in a sexual mate or in 2012), and religious rituals (Sosis, 2004) by look- a coalitional partner and undesirable traits in an ing at them as types of costly signals of cooperative enemy. As such, hunting (and sharing) large game intent. Much laboratory research shows that people may be a way of signaling qualities about oneself treat prosocial behavior as though it signaled future that may otherwise be difficult to observe directly cooperative intent (reviewed by Barclay, 2010a).

Barclay, Van Vugt 45

Schroeder251014OUS_PC.indb 45 12/12/2014 4:36:56 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

In animal behavior, costly signaling theory due to evolutionary lag. Each of these could cause has been particularly useful in investigating sex- instances of prosocial behavior that do not yield ual selection and mate choice. Given that people benefits. have a vested interest in choosing prosocial mates, Adaptive on Average. Suppose that one day you and helping behavior can be one way of signaling have successfully hunted meat, but you would pre- that trait, costly signaling may also be involved fer not to share with the rest of the group because in sexual selection for prosociality (Barclay, 2010; you and your family are hungry. You could try to Van Vugt & Iredale, 2012) and moral virtue smuggle it back to your family or consume it on the (Miller, 2007). spot, but what if others catch you? You would risk losing your reputation, getting punished, and hav- Summary of Adaptive Explanations ing others not share with you in the future. That The previous section gives several ways in which would be really bad. It looks like you would get away individuals may benefit from prosocial behavior with it and you could defect on your group anony- (direct benefits from an outcome, stake or vested mously, but is it really worth the risk? It is easy to interests in the recipient, direct or indirect reci- say with hindsight whether you could have gotten procity, and costly signaling of hidden traits). In away with it, but you cannot tell this in advance. addition, any genes influencing prosociality could Perhaps it is safer to share, just in case someone spread if they cause an organism to help kin who comes along. That way, you are guaranteed to keep are statistically most likely to carry copies of those your reputation and avoid punishment. Sure, you genes. These benefits would result in the evolution will sometimes end up helping others when you and maintenance of prosocial sentiment. However, did not strictly need to, but that may be a small not all instances of prosocial behavior bring ben- cost compared with the risk of reputational loss. efits, so the next section deals with such instances. Natural selection might even favor a psychology that makes people want to share, because someone Nonadaptive Explanations who genuinely wants to share will be guaranteed to Contrary to popular belief, evolutionary theory keep their reputation (Delton et al., 2011; Frank, does not predict that every instance of prosocial 1988; Simpson & Willer, 2008). behavior will bring benefits and increase inclusive Our psychological mechanisms have evolved fitness. For example, prey species sometimes get to be adaptive on average, in that they bring more eaten because they mistake where predators are benefits than costs when averaged across all situa- (e.g., a zebra running toward a hidden lion) and tions. All mechanisms occasionally make mistakes several bird species are tricked into raising cuckoo because errors are inevitable in any decision-making chicks. These animals clearly produce a benefit to process (Haselton & Buss, 2000; Nesse, 2005). the other animals, such that these behaviors fit Prosocial sentiments, like empathy, cause us to some definitions of prosociality. Clearly, such mis- help others (Batson et al., 1997; de Waal & Suchak, takes and manipulations frequently occur in nature 2010). In a world with reciprocity and reputation, but they are not adaptive. What evolutionary the- this usually results in prosocial people receiving ory can do is make predictions about when such benefits for helping, even if those people do not nonadaptive outcomes might result, and why. intend to receive such benefits. As long as those benefits outweigh the costs of occasionally helping Mistakes the “wrong” people (e.g., those who will not recip- No one would suggest that all behavior is rocate) or in the “wrong” situations (e.g., when we perfectly executed or that all consequences are are anonymous) then it would still be adaptive to intended. Or at least, no one with any experience have prosocial sentiments (Barclay, 2011a; Delton of the world should suggest this. Humans have et al., 2011; Frank, 1988). imperfect information, limited time, and many What predictions does this nonadaptive other such constraints (Todd, 2001). Mechanisms hypothesis allow us to make? Firstly, we would break down. There are at least four types of mis- explicitly predict that possession of prosocial takes that are worth mentioning regarding pro- sentiments tends to bring benefits on average. sociality (a) mistakes from mechanisms that are Secondly, we can use evolutionary principles to “adaptive on average,” (b) outliers on a normal predict when people will err on the side of help- curve, (c) pathologies or breakdowns of adaptive ing versus err on the side of not-helping. This is mechanisms, and (d) mismatched environments a classic example of signal detection, also known

46 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 46 12/12/2014 4:36:56 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

as the “smoke-detector principle” (Nesse, 2005) Fessler, 2005; Mifune et al., 2010; Rigdon et al., or “error management” theory (Haselton & Buss, 2009; but see Sparks, 2011). As another example, 2000). Basically, we really want to avoid making facial resemblance is one cue that people use to the more costly or more frequent errors, like having detect kinship (DeBruine, 2005), and participants our smoke detector fail to detect a real fire. In this in experimental games are more cooperative when context, the optimal decision rule depends on the they are playing with people whose faces have been costs and benefits of helping versus not helping, in morphed to slightly resemble the participant’s own situations when one “should help” (i.e., when there face (DeBruine, 2002, 2005; Krupp et al., 2008). are benefits) versus in situations where one “need In both of these examples, an adaptive psychologi- not help” (i.e., when there are no benefits) (Delton cal mechanism is being “tricked” to produce a pro- et al., 2011). social response even when the participant does not All else being equal, biases toward helping benefit from being helpful to others. This mistake will be strong (1) when there are large benefits for hypothesis has some interesting implications for helping when one “should help” (e.g., if audiences how societies can encourage prosocial behavior, respond very favorably to helpers); (2) when there for instance, providing cues of being watched in are high costs of not-helping when one “should anonymous public spaces. have helped” (e.g., if audiences react unfavor- Outliers. Imagine that in any selection envi- ably to nonhelpers); and (3) if the most common ronment, there is an “optimal” level of helping situations are ones where one “should help” (e.g., behavior where one receives the most inclusive fit- truly anonymous situations are rare, and interac- ness benefits per unit of cost. The optimum will tions that appear anonymous are usually not actu- inevitably vary with social and ecological circum- ally anonymous). By helping in such situations, stances, including the local norms, the cooperation one receives high social benefits and avoids high of others, the possibilities for reputation, proxim- social costs, so it is worthwhile to “err on the side ity to kin, the “shadow of the future,” and so on. of helping.” Conversely, all else being equal, people Ideally, if one wants to maximize inclusive fitness, should be biased against helping (1) when there one would help exactly that much, but no more. are high costs for helping when one “need not” do Helping less than the optimum would result in so (e.g., embarrassment, unnecessary exposure to reaping fewer benefits, and helping more would risk); (2) when there are large benefits for avoiding result in needlessly incurring costs (e.g., Barclay, unnecessary helping (e.g., avoiding helping when it 2011b; Baumard et al., 2013). is costly relative to the potential gains); and (3) if Of course, almost no one will ever hit this opti- one is most likely to encounter situations where one mum exactly. Individuals will differ in their com- “need not” actually help (e.g., if most interactions binations of genes, their developmental histories, that appear anonymous actually are anonymous). their past learning experiences, their accuracies in By avoiding helping in such situations, one avoids assessing the situation, and so on. This will all cause paying the costs of helping when it is unnecessary deviations around the optimum, such that some to do so. The overall bias toward helping—and the people help others less than would be optimal for frequency of “unnecessary” help—will depend on them to do, and other people help more than would the relative magnitude of these average costs and be optimal. This is inevitable, because all traits are benefits and the frequency of each type of situation. expected to have some deviations around the opti- We can also predict that people will be more mum (Tooby & Cosmides, 1990). We can imag- cooperative when presented with cues that they ine a bell-curve, with most people being somewhat might benefit from helping. In other words, we can close to the optimum, some people being further design experiments to cause participants to make away from optimality in either direction, and a few “mistakes” by helping when they receive no ben- rare people deviating so far from optimality that efits for doing so, as long as we trigger cues that their helping seriously oversteps (or understeps) the would normally indicate the presence of benefits. bounds of utility.3 For example, the presence of eyes is normally a It is interesting to ask what maintains such vari- cue that one is being observed, and many experi- ation, but lengthy discussion of this is beyond the ments have shown that people are more generous scope of this chapter (see Buss & Greiling, 1999; with their money when they can observe eye-like Tooby & Cosmides, 1990). For present purposes, stimuli on a computer or on a poster (Bateson we need only know that variation exists, and some- et al., 2006; Burnham & Hare, 2007; Haley & times, when prosociality carries no benefits, it

Barclay, Van Vugt 47

Schroeder251014OUS_PC.indb 47 12/12/2014 4:36:56 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

might just be because the person is at the tail end current generations. If the environment stays rela- of the optimality bell curve. For instance, people tively constant, then those traits will function well might be on the extreme tail of the empathizing in the current environment. However, if the envi- trait and as a result they might be more prone to ronment has changed recently, then traits which help across a wide range of situations even when were once adaptive may no longer be adaptive. there are no adaptive benefits—the extreme female In other words, the “old” adaptations might not brain hypothesis (Baron-Cohen, 2003). yet have been selected out of a population if the Pathologies. When Phineas Gage had a metal selection pressures have recently changed. This bar accidentally driven through his skull in 1848, idea is known as “evolutionary lag” or “mismatch,” it radically changed his personality and he became because the changes in genes lag slightly behind more irreverent, profane, and impulsive. One would the changes in environments (Laland & Brown, never ask, “What is the function of his impulsive- 2006; Van Vugt & Ahuja, 2010). The classic ness?,” because it is obvious that something had example of evolutionary lag is our preferences for gone seriously wrong with Gage’s brain, namely sweets, salts, and fats: it was adaptive to crave these that part of it had been blasted outside of his skull. when they were rare, because they were valuable On a less severe note, developmental accidents can sources of energy and nutrients. People still crave easily happen when building or maintaining any them even though they are overabundant in mod- organ as complex as a brain. Any slight perturba- ern environments and lead to obesity and other tions during development can cause deviations health problems. from optimality. With modern machines, some car Social environments have changed dramatically or computer owners discover this upon purchasing in the last several centuries and millennia. As such, a “lemon.” In human development, pathologies can some prosocial sentiments that were once adap- be caused by physical trauma, pathogens, senes- tive might no longer be adaptive. For example, we cence, genetic mutations, or chemicals and other have gone from living in small kin-based groups to teratogens. If there is evidence that something has much larger groups of mostly nonkin. In the for- gone “wrong” in someone’s development or that mer circumstances, a psychology with the decision something is “broken,” then we should not expect rules such as “feel warmth toward all group mem- all of their behavior to be adaptive. All bets are off bers” and “help someone who needs aid” would in such cases. result in prosocial behavior mostly targeted toward Some pathologies will result in less prosocial kin or to reciprocal partners, whereas in modern behavior rather than more. For example, it is well circumstances it would not. Thus, prosocial senti- known that head trauma can cause antisocial ments that once increased inclusive fitness may no behavior (e.g., Andrews et al., 1998). However, it is longer do so. at least theoretically possible that some breakdowns In addition to changes in the scale and kin com- could result in heightened prosocial behavior. For position of groups, we now also have many more example, a breakdown in the brain areas respon- opportunities for anonymity and movement between sible for self-interested behavior could possibly groups. This means that people can now get away with result in more decision weight being placed on the more selfish behavior than they could have in small interests of others. If a developmental perturbation bands, and it is now easier to move to a new group caused someone to feel less hunger, then that per- and run from one’s bad reputation. Accordingly, son would be more willing to share food because he reputation may be less important in modern envi- or she would not want it as much. We know of no ronments than in past environments—though this research on whether heightened prosociality can be requires empirical testing. If so, then it would not be caused by pathologies, but such studies would be as beneficial as it once was to possess social emotions very interesting if found. Perhaps people have not like guilt and shame. Such emotions help people investigated this topic because excessive generos- maintain their reputations and make amends for any ity is seen as “nice” rather than pathological, and damage they have done to cooperative relationships therefore not in need of “fixing.” (Frank, 1988; Ketelaar & Au, 2003). Mismatches and evolutionary lag. Natural When people can simply run from a bad repu- selection does not plan ahead. Our current adap- tation or simply gain new partners to replace any tations are “designed” to work well in past envi- partners they have estranged then these emo- ronments: Those who had more offspring in past tions are no longer functional. This situation may environments tended to pass their traits on to be changing with the advent of the internet and

48 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 48 12/12/2014 4:36:56 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

social media technologies such as Facebook and growth—there is little selection pressure against Twitter as people are now able to spread infor- them if the selection for fast growth is so strong. mation about others’ reputation—for good or for On a more positive note, some types of proso- ill—quickly and efficiently. As it stands now, it is ciality may be developmentally linked with each currently unknown whether evolutionary lag is a other. Over 40 years ago, Dmitri Belyaev began major factor in explaining human prosociality. breeding foxes for one single trait: tameness. This Yet it is worth investigating prosocial behavior in has resulted in a number of other changes in his smaller and largely kin-based social networks that breeding population, including floppy ears, shorter were the norm until fairly recently to see if humans tails and legs, light patches of fur, altered fear and still apply the same decision rules in large, modern corticosteroid responses, “feminized” head shape, and complex societies (Dunbar et al., 2012; West and altered reproductive patterns (Trut, 1999). et al., 2011). These are all developmentally linked with tame- ness, such that they increase in frequency when Evolutionary byproducts tameness is selected for. Most interesting are the Not every trait we see was specifically selected behavioral changes regarding sociability, which for in evolution. Some traits exist as incidental have resulted in foxes who “seek out human contact byproducts of other traits (spandrels; Gould & and lick experimenters’ hands and faces” (Trut, Lewontin, 1979). For example, we should not ask 1999, p. 169). “What is the advantage of birds’ bones being so How does this apply to human prosociality? brittle?” because brittleness is a necessary conse- Humans have likely been under strong selection for quence of being light, and lightness has presum- the ability to get along with fellow group members, ably been selected for because of its importance because some degree of mutual tolerance pays better in flight. Thus, brittleness is a byproduct of selec- than constant hostility. This “self-domestication” tion for lightness. To what extent could prosocial of humans could have had other effects on human behavior be a nonadaptive byproduct of other traits evolution, because the ability to get along is devel- that are adaptive themselves? opmentally linked with other traits (Ridley, 2003). Developmental byproducts. Natural selection As such, prosocial sentiment could have arisen as is a very blunt instrument. It is very hard to select a byproduct of natural selection for “tameness” for one single trait without accidentally selecting or tolerance in humans (Hare et al., 2007). Just for other traits. Different traits can be correlated like the foxes who were bred for tameness toward if they are caused by the same gene (“pleiotropy”), humans and now behave very nicely toward their if they are caused by genes that share the same handlers, natural selection for mutual tolerance region of a chromosome (“linkage”), or if the same in humans could have resulted in humans who brain regions or pathways are involved in multiple now actively behave very nicely toward each other behavioral traits. In such cases, strong selection for and show strong affiliative needs (Baumeister & one feature will result in any correlated features Leary, 1995). “piggybacking” along and also increasing in fre- Byproducts of other adaptations. Some types quency. These correlated features are not selected of prosocial behavior may be byproducts of other for directly, but their existence is a byproduct of adaptive mechanisms. For example, Richerson and something that was selected for. Boyd (2005) argue that people could learn cooper- The best examples of byproducts come from ative behavior through “conformist transmission,” animal breeding. For example, the poultry indus- which means copying whatever behaviors are most try intensively breeds their chickens for things common within a population. Copying common like fast growth, but sometimes other correlated behaviors is normally an adaptive way of learning traits end up increasing in frequency also. This how to do things because others may have already has resulted in what Temple Grandin calls “rap- figured out the best way of doing things. However, ist roosters” who attempt to forcefully mate with it can also cause people to make systematic errors the hens, and often end killing them in the process when they also copy behaviors that turn out to not (Grandin & Johnson, 2005). Because of the intense be optimal—an effect that has been triggered in selection pressure that is being applied for fast dozens of articles on conformity (for a review, see growth, other traits that would normally be mal- Cialdini & Goldstein, 2004). Given that humans adaptive can increase in frequency if they happen rely so much on socially learned behaviors, this to be genetically correlated with genes controlling bias toward conformist transmission is probably

Barclay, Van Vugt 49

Schroeder251014OUS_PC.indb 49 12/12/2014 4:36:57 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

adaptive on average, even if it occasionally causes us the benefits of one adaptation without any of the to learn maladaptive behaviors. Thus, it is possible costly byproducts. For these reasons, it is unwise to that our tendency to copy prosocial behavior could simply assume that costly forms of prosociality are be a maladaptive byproduct of our adaptive ten- byproducts of something else, unless we can dem- dency to copy common behaviors. Herbert Simon onstrate that there has been recent strong selection (1990, 1993) has made a similar argument about for a correlated trait. And of course, any byproduct our disposition to learn from others, which he calls explanations must be subjected to empirical testing “docility.” This is a highly advantageous trait yet of their predictions, just as we would do for adap- it allows other people to occasionally manipulate tive explanations. us into learning altruistic behaviors which do not benefit us. Propagation of Ideas: Memes and Cultural On a much more speculative note, social emo- Group Selection tions like empathy may be evolutionary byproducts Most people think of evolution as dealing of selection for our ability to copy others. Humans mostly with genes, but cultural traits can also are extraordinarily good at imitation and other evolve. If a cultural trait is better at propagat- forms of social learning (Herrmann et al., 2007), ing itself and attracting new bearers, then it will and we rely on these abilities in order to survive spread in a population at the expense of alterna- (Bandura, 1962). The ability to imitate seems to tive cultural traits. The study of such transmission involve specialized neurons called “mirror neu- is known as “memetics” after Richard Dawkins’ rons.” These mirror neurons allow us to form an concept of “memes”—units of culture which jump internal representation of others’ actions in order from one mind to the next (Dawkins, 1976/2006), to replicate those actions ourselves (Keysers, or Dual-Inheritance Theory, because of the fact 2006). These mirror neurons may also be involved that humans inherit traits both genetically and in empathy, which is the ability to share others’ culturally (Boyd & Richerson, 2002; Richerson & emotional states, and may possibly be involved in Boyd, 2005).4 Theory-of-Mind (Keysers & Gazzola, 2006). It is One trick for a cultural trait to spread is to be highly likely that imitation and Theory-of-Mind good for the bearer: others will see that the bearer are adaptive traits which have been under strong is doing well and will imitate that cultural trait selection pressure. This would cause an increase (Richerson & Boyd, 2005). In such cases, the cul- in mirror neurons (or whatever else happen to be tural trait and the genetic trait are in a symbiotic the neurological mechanisms), which could pos- mutualism; both benefit from such arrangements. sibly have side effects like causing the presence of However, a cultural trait need not necessar- empathy. Under this hypothesis, empathy—and ily be good for its bearer to spread. If a cultural the prosocial behavior it triggers—is not adaptive trait is exceptionally good at getting itself copied itself, but exists because of strong selection for imi- by new minds, then it will spread even if it has tative abilities and theory-of-mind. no net effect—or even a negative effect—on its Evolutionary byproduct hypotheses can explain bearer’s fitness (Dawkins, 1976/2006). Thus, cul- how costly behaviors arise if they happen to be tural traits can also be like parasites in that they incidentally caused by other adaptations or if they can manipulate their hosts to increase their own piggyback on selection for other traits. Byproducts propagation at the expense of their bearer’s fitness can only explain prosocial behavior with relatively (Dennett, 2006). low costs because the selection against the “pro- When it comes to prosocial behavior, public acts social byproduct” would have to be weaker than of generosity attract attention, not least because the selection pressures favoring the correlated trait. others want to receive a share of that generosity For example, if conformist transmission caused too (Blackmore, 2000). As such, public generosity is many people to imitate suicidal self-sacrifice, then likely to be observed by many people. All else being conformist transmission would be selected against equal, this visibility increases the likelihood that unless the benefits for imitation were so large those behaviors will be imitated. After all, an act as to outweigh the cost of suicidal self-sacrifice needs to be noticed to be imitated. In this way, the (Mesoudi, 2009). Furthermore, given enough meme of “go out and help others” turns its bearer generations, natural selection should tend to sever into what Susan Blackmore has called a “meme any genetic or developmental links that cause fountain”—someone who broadcasts memes that costly byproducts, so that organisms could get others can then pick up (Blackmore, 2000). This

50 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 50 12/12/2014 4:36:57 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

may or may not be good for the bearer, but it does if there is only one position, then any help you give aid the propagation of the meme for helping. to him will directly harm you because it increases By definition, prosocial behavior benefits others the likelihood that he will get the job instead of in one’s group, so members of a prosocial group are you. All of your competition is against this one better off than members of less prosocial groups. person, and this “local” competition undermines This means that there are advantages of being part your incentives to cooperate with each other. If of a prosocial group, even if helping others is per- you are interviewing for different jobs, then you sonally costly. This can lead to cultural change as are not in competition, and you could both benefit more prosocial (and thus more successful) groups from helping each other to compete against your replace less prosocial groups and bring their cul- respective competitors. In this case, you have no tural norms with them, or by less-successful groups local competition, because you are both competing imitating the prosocial norms of more successful against separate pools. How about an intermediate groups (Boyd & Richerson, 2002). People may situation? If you are both competing for a position, also “vote with their feet” by joining groups with but there are many positions, then you could still norms fostering prosocial behavior (Gürerk et al., benefit from helping each other because this puts 2006). For example, this may have been a factor in you both in a better position to compete with the the spread of early Christianity because there were larger pool of candidates. You would still be partly large benefits for joining a group which had strong in competition with each other, and this would norms about helping others (Wilson, 2002). This somewhat suppress your incentives to cooperate, process of cultural change has been called “cultural but most of the competition is with others. group selection” (Richerson & Boyd, 2005), as This example illustrates the principle of “scale successful cultural norms spread at the expense of of competition,” which evolutionary biologists have less successful norms. In previous writing, one of started to apply to cooperative interactions among us has noted that a better name is simply “cultural kin and nonkin alike (West et al., 2002, 2006). selection,” because groups are neither necessary Competition is said to be “local” when people are nor sufficient for this process to happen (Barclay, in direct competition with their partners, such that 2010a). Regardless of the name, it is clear that cul- they are in a zero-sum relationship. Competition is ture evolves, and that norms about prosociality can “global” when this local competition does not exist. spread through cultural evolution. Local competition will tend to suppress coopera- tion, and may even cause spite because people will Summary of Nonadaptive Explanations have an incentive to harm their partners (Gardner & These examples demonstrate that in addition to West, 2004). explaining adaptive instances of prosociality, evo- West and colleagues (2006) demonstrated this lution can also explain the existence of nonadap- principle in an elegant experiment using an iterated tive prosocial behavior. Such behavior could be a Prisoner’s Dilemma game. Participants were divided mistake by an adaptive mechanism, a breakdown into groups of three from within a larger class. They of an adaptive mechanism, an outlier on a normal would play separate Prisoner’s Dilemmas games curve, a case of evolutionary lag, an evolutionary with each of their two partners, and would earn or developmental byproduct, or an idea spreading points from each set of games. Prizes were either at the expense of its bearer. Importantly, evolution- given to the highest earners in the class (global ary theory makes novel predictions in each of these competition) or to the highest earner in each group cases. In the next section, we discuss some new per- of three (local competition). When prizes went to spectives that may (or may not) prove useful. the highest earners in the class, there was an incen- tive to cooperate with one’s partners in order to earn Emerging Evolutionary Perspectives on a higher score than others in the class, and people Prosocial Behavior cooperated about 45% of the time. When prizes Scale of Competition went to the highest earner in each group of three, Suppose that you and another candidate are cooperating with one’s partners would help them interviewing for a job at a company. If this other win against oneself, so cooperation rates plummeted candidate makes a mistake that you can easily cor- to less than 20%. This experiment shows how the rect for him, do you help him out? Your willingness scale of competition affects prosocial behavior and to do so will probably be affected by whether you are how changes in this structural factor can enhance both interviewing for the same job. If you are, and or inhibit cooperation (e.g., in workplaces). This

Barclay, Van Vugt 51

Schroeder251014OUS_PC.indb 51 12/12/2014 4:36:57 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

research group has also demonstrated the impor- the confusion over multilevel selection. Multilevel tance of scale of competition on prosocial behavior selectionists define “altruism” as behavior that in other species such as fig wasps (West et al., 2001) decreases one’s fitnessrelative to the local group, and bacteria (Griffin et al., 2004), demonstrating whereas inclusive fitness theorists define “altru- that scale of competition is an important factor ism” as behavior that decreases one’s fitness rela- across all taxa of life. tive to the global population or relative to what one would have gotten if one had not taken action (Kerr et al., 2004; Reeve, 2000; West et al., 2007, Multilevel Selection 2011). By the former definition, “a positive effect In this chapter, we have largely focused on how on self . . . can be altruistic if the effects on others prosocial behavior can increase inclusive fitness. are even greater” (Wilson, 1990, p. 135, emphasis Inclusive fitness theory examines how one’s behav- added). This means that a hunter would be defined ior affects one’s own reproduction and one’s kin’s as “altruistic” if he catches big game solely because reproduction (Hamilton, 1964). However, this is he is hungry but others happen to receive an equal not the only perspective one can take when seek- share of his meat (Harpending, 1998). ing adaptive explanations for behavior. Inclusive The big question is: Is it useful to look at fitness theory is simply one method of counting fit- group fitness when looking at prosocial behavior? ness, and alternative methods exist. For example, Evolutionary researchers disagree on this, as do one can use “neighbor-modulated fitness.” Instead the two authors of this chapter. Some research- of examining one’s effects on oneself and on kin ers (including one of us) have written about how (as in inclusive fitness theory), neighbor-modulated human groups can function as single reproduc- fitness examines only one’s own reproduction and tive units, much like beehives, and have arguably includes kin’s effects on oneself (Queller, 2011; done so for much of human evolutionary history West et al., 2011). These two methods are math- (Wilson, Van Vugt, & O’Gorman, 2008). This ematically equivalent; they only differ in whether would involve heritable group-level adaptations for kin effects are counted when going from oneself promoting altruism and cooperation within groups toward kin or when coming from kin to oneself. as well as suppressing intragroup aggression and Another common—though more controver­- competition, fostering coordination, making group sial—­alternative is multilevel selection (e.g., Boyd decisions, and dealing with intergroup conflict. et al., 2003; O’Gorman et al., 2008; Sober & These heritable group-level adaptations may include Wilson, 1998; Wilson, 1979, 1990, 1998, 2004). means of inculculating others with a set of moral Some types of cooperation will decrease one’s fit- rules (e.g., religion, the practice of monogamy), ness relative to one’s group but will increase the punishing norm violators and noncooperators, cre- fitness of that group relative to other groups. ating roles of leadership and followership, and cre- Multilevel selection looks at how one’s actions ating symbolic social identities (e.g., Bowles, 2006; affect group fitness versus individual fitness, and Wilson et al., 2008). Through these mechanisms, whether between-group selection for cooperation within-group selection forces have significantly is stronger than the within-group selection against weakened compared with between-group selec- costly cooperation; cooperation will arise when the tion forces, allowing for these group adaptations to latter is stronger than the former. spread. One conducive factor to this kind of group It is important to stress that multilevel selec- selection is the rate and scale of deadly intergroup tion and inclusive fitness theory are mathemati- conflict among ancestral hunter-gatherer societies cally equivalent (e.g., Foster et al., 2006; Queller, (Bowles, 2009), which allowed for the emergence 2011; Reeve, 2000; Sober & Wilson, 1998; West of prosocial traits such as altruism, bravery, and 5 et al., 2007, 2011). This is no longer under any heroism toward in-groups as well as aggression serious debate. All multilevel selection models can and prejudice toward out-groups (the male warrior be translated into inclusive fitness models and vice hypothesis; Van Vugt et al., 2007). versa. Rather than being a “new selective force,” Other researchers (including the other one of us) multilevel selection is simply another way of look- emphasize that all alleged examples of group selec- ing at fitness, much like a different way of looking tion can be viewed much more effectively from an at a Necker cube (Sober & Wilson, 1998; Reeve, inclusive fitness perspective (e.g., Barclay, 2010a; 2000). This involves defining some words like Reeve, 2000; West et al., 2011). Group selection “altruism” differently, which has caused much of is invoked when an act increases the group’s fitness

52 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 52 12/12/2014 4:36:57 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

but decreases one’s reproduction relative to that development of prosocial behavior because it creates group average. Some things are called “group selec- a selection pressure for fairness and cooperation. If tion” but are actually directly beneficial because you are not receiving a “fair” deal then you can an individual receives a share of whatever public simply find someone else who will offer that deal good he/she provides for others (see the different (André & Baumard, 2011; Baumard et al., 2013). definitions of “altruism” earlier; see also the section In a biological market, the best way to get a good on volunteering); groups are neither necessary nor partner is to be a good partner. As long as there are sufficient for prosocial behavior in such situations. enough opportunities for reputation building or Other situations are called “group selection” when there are costs for being abandoned then this will an organism has a stake in the well-being of fel- cause an escalation of prosocial behavior, in a pro- low group members, for example because it benefits cess known as “runaway social selection” (Nesse, from being part of large groups (see “Stake or vested 2007) or “competitive altruism” (Barclay, 2004, interests” earlier). Finally, other things are called 2011b; Barclay & Willer, 2007; Hardy & Van “group selection,” which are actually a disguised Vugt, 2006; Roberts, 1998; Van Vugt & Hardy, form of kin altruism because the group members 2010).). are all descended from recent common ancestors. The theory of biological markets combines asp­ Because it is often unclear which of these situa- ects of mutualisms, reciprocity and costly signaling tions is being referred to whenever someone says in explaining prosociality. For example, traditional “group selection,” it creates great confusion to lump evolutionary perspectives predict that people will them together under that banner (Barclay, 2010a; be more prosocial when they are being observed, see also West et al., 2011). These three situations but biological markets go further by predict- involve distinct selective pressures and psycho- ing that people will be even more generous when logical mechanisms and should thus be kept dis- competing over access to partners (Barclay & tinct. Furthermore, these situations usually do not Willer, 2007; Sylwester & Roberts, 2011; Van Vugt & involve group-level adaptations, that is, the adapta- Iredale, 2012); similar results are found in cleaner tion is a heritable property of individuals instead fish (Bshary & Grutter, 2005). Such competition of the group (Gardner & Grafen, 2009). This is pays off because high contributors gain status for not to say that these situations are not interesting; helping others (Hardy & Van Vugt, 2006), and they are all extremely interesting, though for differ- are more likely to be chosen as partners (Barclay & ent reasons. Indeed, some of these situations (e.g., Willer, 2007) and mates (Barclay, 2010b). In bio- stake) have unfortunately been under-researched logical markets, prosociality is affected by factors by inclusive fitness theorists until recently. like the supply and demand of different currencies Ultimately, the question will be whether it is of help, and one’s market value and outside options useful to look at groups as single units when inves- (Barclay & Reeve, 2012; Noë & Hammerstein, tigating prosocial behavior. This will be decided by 1994, 1995). whether this perspective tends to generate enough testable and accurate predictions about prosocial Conclusions and Future Directions behavior that researchers using standard inclusive Evolutionary psychology is inherently interdis- fitness theory do not generate, and whether it can ciplinary and draws from all of the behavioral sci- do so without creating semantic confusion over ences. In addition, by investigating the evolutionary redefinitions of altruism. function (this chapter) and phylogenetic history of behavior (e.g., de Waal, this volume), evolutionary Biological Markets and approaches help link the behavioral sciences with Competitive Altruism the natural sciences. By investigating prosocial Humans can choose many of their social part- behavior from all four levels of analysis—proximate ners and leave uncooperative partners if there are psychological mechanisms, individual develop- better options available (comparison level of alter- ment, ultimate function, and evolutionary history natives; Kelley & Thibaut, 1978). The presence (phylogeny)—we can get a more complete under- of partner choice creates a market for social part- standing of the causes of prosocial behavior, and ners (Noë & Hammerstein, 2004, 2005). In such we can use explanations at one level to inform markets, people choose the best partners they can our research on the other levels (Daly, 2011; Van obtain, given their own value in this market. This Vugt & Schaller, 2008). Different fields and sub- perspective has implications for the evolution and disciplines will simply address different levels. In

Barclay, Van Vugt 53

Schroeder251014OUS_PC.indb 53 12/12/2014 4:36:57 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

this chapter, we have focused largely on ultimate behavior if they receive direct benefits from being function because other authors in this volume have prosocial (Barclay & Willer, 2007; Mulder et al., covered the other three levels. 2006). Other pressures may enhance each other, By investigating prosocial behavior at all four such as when moralistic punishers benefit from levels of analysis, evolutionary psychology is thus raising their group’s cooperation and as a result a useful framework for uniting all the work on they receive reputational benefits for punishing prosocial behavior found in this volume. Rather (Barclay, 2006). We need more theoretical and than being seen as a specific discipline or subdis- empirical work on integrating these different selec- cipline unto itself, evolutionary psychology should tive pressures. thus been seen as a perspective that can be applied 3) What psychological mechanisms would be to any field or subdiscipline (e.g., Daly, in press). selected for by each selection force? Throughout Thus, there can, and should be, evolutionary social this chapter, we have made some comments about psychology, evolutionary cognitive psychology, evo- the psychologies that each pressure would likely lutionary economics, evolutionary sociology, and select for (e.g., a vested interest in someone result- so on. We would encourage researchers in all of ing in a genuine concern for their welfare). Some these areas to incorporate evolutionary thinking of this work has already been done, but some is into their current disciplines. still just hypothesized (e.g., empathy as adaption Where do we go from here? Evolutionary psy- or byproduct of cultural learning). By examining chology shows the potential functions of different the psychological mechanisms, and their develop- forms of prosocial behavior and helps to elaborate ment, we can better integrate across the four levels what neurological, cognitive and emotional mecha- of analysis. nisms will underlie them. Nevertheless, there are 4) How do the dynamics of reputation-based many remaining questions about how exactly these prosociality work? There are a number of ques- selection pressures work, how they interact, and tions here that are still unknown. How do people how they have shaped our psychology. Here is a list come to believe that certain acts are prosocial of questions which could shape the future research and are thus worthy of reward (Barclay, 2011a; agenda on prosocial behavior. Panchanathan & Boyd, 2004)? How does proso- 1) What is the relative importance of dif- cial behavior come to signal certain traits such as ferent selective pressures? How do we know if honesty, intelligence, resources, and commitment a prosocial act is adaptive? We have presented a (Jensen-Campbell et al., 1995; Van Vugt & Iredale, number of factors that could select for prosocial 2012)? What exact traits are being signaled, and sentiment (see Figure 2.1). No single one of them when? By answering such questions, it can help us will explain all prosocial behavior, because differ- to create reputational systems to support prosocial ent situations call for different behaviors (e.g., help- goals (Barclay, 2011a). ing kin versus friends). Prosocial behavior is not 5) Why (and when) is prosocial behavior an a unitary phenomenon and should not be treated honest cue of future cooperative intent? People as such (Barclay & Reeve, 2012). Because of this, have an incentive to present themselves as more we need to investigate different situations to see cooperative than they actually are. Nevertheless, what types of prosocial behavior are best explained prosocial behavior at time A does appear to predict by each of the pressures listed. Furthermore, the prosocial behavior at time B, at least under some importance of each selective pressure may vary conditions—this is the basis of an agreeable per- with time and with socioecological environment sonality (Graziano et al., 1996). Why and when (e.g., reputation may be less important in today’s is there such consistency of behavior across situa- large groups, see “Evolutionary Lag”); this varia- tions, and why are not more people deceptive about tion requires investigation. their future intent (e.g., Barclay & Willer, 2007)? 2) How do these different selective pres- How is the honesty of such prosocial signals main- sures interact with each other? These pressures tained? If honesty is maintained by the cost of are not necessarily mutually exclusive, and more being prosocial, then how could it pay off for hon- than one may apply in any particular case (e.g., estly prosocial people but not pay off for deceptive Barclay, 2010a). Some may counteract each other. Machiavellians who are just trying to appear nice? For example, strict reciprocity is not needed among How do other extrinsic incentives undermine the close kin (Hames, 1987), and it is harder to infer validity of cues of prosociality (e.g., Mulder et al., people’s cooperative intent from their prosocial 2006)? Answering these questions is important

54 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 54 12/12/2014 4:36:58 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

for predicting others’ behavior and for any reputa- 2. Inclusive fitness theory is sometimes erroneously called tional system that relies on predicting others’ coop- “kin selection.” This latter term is potentially misleading because it can cause researchers to forget that inclusive fit- erative intent. ness includes benefits to self. Inclusive fitness is the broader 6) To what extent is prosociality an in-group term because it equals kin selection (indirect benefits) plus phenomenon (shaped by intergroup conflict)? individual selection (direct benefits). Intergroup conflict gives people a stake in the 3. Instead of a single bell-curve, there may actually be a well-being of group members and changes the scale bimodal distribution with two optima, one for cooperators and one for cheaters (e.g., psychopaths) who persist in low of competition. Given the presence of intergroup frequencies (Mealey, 1995; Harris et al., 1994). This does competition in human history (Bowles, 2009), not change our basic logic, because there will be deviations how has this shaped our prosociality and morality from either optimum. through both genetic and cultural evolution? 4. Proponents of Dual-Inheritance Theory appear to want 7) Why are there individual differences to distance themselves from any associations with the in prosocial behavior? idea of memes (Richerson & Boyd, 2005; Henrich et al., If prosocial behavior is 2008). We see these theories as having many underlying so adaptive, why are not all people prosocial to philosophical similarities despite the superficial differences. the same degree? Do these individual differences Rather than engage in this debate or speculate on its root represent different strategies (e.g., Mealey, 1995), causes, we will merely state that both theories agree that or adaptive responses to differences in costs and cultural norms can evolve and can spread even if they do not increase the genetic fitness of their bearers. benefits for prosociality (Barclay & Reeve, 2012; 5. For interested readers, Reeve (2000) gives a very simple Diekmann, 1993, Takahashi et al., 2006)? Why mathematical demonstration of why these perspectives are and when are there sex differences in prosocial mathematical equivalent. behavior (Balliet et al., 2011)? Evolutionary theory can inform the study of individual dif- References ferences and their development (e.g., Buss & Alcock, J. (1993). Animal behavior: An Evolutionary approach. Greiling, 1990; Sih et al., 2004; Tooby & Sunderland, MA: Sinauer Associates. Alexander, R. D. (1987). The biology of moral systems. New York Cosmides, 1990). Aldine de Gruyter. 8) Why are there cultural differences in pro- Andrews, T. K., Rose, F. D., & Johnson, D. A. (1998). Social social behavior? How do differences in social and and behavioural effects of traumatic brain injury in chil- ecological environments result in cultural differ- dren. Brain Injury, 12, 133–138. ences in prosociality? How and why are cultures André, J.-B. (2010). The evolution of reciprocity: Social types or social incentives? The American Naturalist, 175, 197–210. affected by factors such as market integration André, J.-B., & Baumard, N. (2011). Social opportunities and (Henrich et al., 2006), group size (Marlowe & the evolution of fairness. Journal of Theoretical Biology, 289, Berbesque, 2008), and partner mobility (Barclay, 128–135. 2011b)? The evolutionary study of cultural differ- Archetti, M. (2009). Cooperation as a volunteer’s dilemma and ences is a new and exciting field. the strategy of conflict in public goods games. Journal of Evolutionary Biology, 22, 2192–2200. Such questions can open up many new lines of Axelrod, R. (1984). The evolution of cooperation. New York research and help clarify why different prosocial Basic Books. sentiments exist, when each one acts, and how and Balliet, D., Li, N., Macfarlan, S., & Van Vugt, M. (2011). Sex why they are triggered by different situations. Such differences in cooperation: A meta-analytic review of social an understanding would help us understand how dilemmas. Psychological Bulletin, 137, 881–909. Bandura, A. (1962). Social learning through imitation. In R. to structure situations to increase prosocial behav- M. Jones (Ed.), Nebraska Symposium of Motivation. (pp. ior (Barclay, 2012a). As such, we look forward to 211–274). Oxford, UK: Nebraska Press. this and other research in the future. Finally, we Barclay, P. (2004). Trustworthiness and competitive altruism hope that this outline of evolutionary approaches can also solve the “tragedy of the commons. Evolution & will inspire other researchers to use evolutionary Human Behavior, 25, 209–220. Barclay, P. (2006). Reputational benefits for altruistic punish- thinking to inform their understanding of proso- ment. Evolution and Human Behavior, 27, 325–344. ciality at all four levels of analysis. Barclay, P. (2008). Enhanced recognition of defectors depends on their rarity. Cognition, 107, 817–828. Notes Barclay, P. (2010a). Reputation and the evolution of generosity. 1. The term “game” refers to an interaction between multiple Hauppauge, NY: Nova Science Publishers. parties (“players”), each of whose behaviors affect each oth- Barclay, P. (2010b). Altruism as a courtship display: Some er’s payoffs. Such “games” are used as simplified models for effects of third-party generosity on audience perceptions. more complex situations, and are amenable to mathemati- British Journal of Psychology, 101, 123–135. cal and empirical analysis by designating payoffs for differ- Barclay, P. (2011a). The evolution of charitable behaviour ent actions and outcomes. and the power of reputation. In C. Roberts (Ed.), Applied

Barclay, Van Vugt 55

Schroeder251014OUS_PC.indb 55 12/12/2014 4:36:58 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

evolutionary psychology (pp. 149–172). Oxford: Oxford Boyd, R., & Lorberbaum, J. P. (1987). No pure strategy is evo- University Press. lutionarily stable in the repeated Prisoner’s Dilemma game. Barclay, P. (2011b). Competitive helping increases with the Nature, 327, 58–59. size of biological markets and invades defection. Journal of Boyd, R., & Richerson, P. J. (2002). Group beneficial norms Theoretical Biology, 281, 47–55. can spread rapidly in a structured population. Journal of Barclay, P. (2012a). Harnessing the power of reputa- Theoretical Biology, 215, 287–296. tion: Strengths and limits for promoting cooperative Brembs, B. (1996). Chaos, cheating, and cooperation: behaviours. Evolutionary Psychology, 10, 868-883. Potential solutions to the Prisoner’s Dilemma. Oikos, Barclay, P. (2012b). Proximate and ultimate causes of punish- 76(1), 14–24. ment and strong reciprocity. Behavioral and Brain Sciences, Brown, S. L., & Brown, M. (2006). Selective investment the- 35(1), 16 –17. ory. Psychological Inquiry, 17, 1–29. Barclay, P., & Benard, S. (2013). Who cries wolf, and Bshary, R., & Bergmüller, R. (2008). Distinguishing four fun- when: Manipulation of perceived threats to preserve rank damental approaches to the evolution of helping. Journal of in cooperative groups. PLOS ONE, 8, e73863. Evolutionary Biology, 21, 405–420. Barclay, P., & Reeve, H. K. (2012). The varying relationship Bshary, R., & Grutter, A. (2005). Punishment and partner between helping and individual quality. Behavioral Ecology, switching cause cooperative behaviour in a cleaning mutu- 23, 693–698. alism. Biology Letters, 1, 396–399. Barclay, P., & Willer, R. (2007). Partner choice creates com- Burnham, T., & Hare, B. (2007). Engineering human coop- petitive altruism in humans. Proceedings of the Royal Society eration: Does involuntary neural activation increase public of London Series B, 274, 749–753. goods contributions? Human Nature: An Interdisciplinary Baron-Cohen, S. (2003). The essential difference: Male and female Biosocial Perspective, 18, 88–108. brains and the truth about autism. London: Penguin Books. Burnstein, E., Crandall, C., & Kitayama, S. (1994). Some Barnard, C. J., & Sibly, R. M. (1981). Producers and neo-Darwinian decision rules for altruism: Weighing cues scroungers: A general model and its application to captive for inclusive fitness as a function of biological importance flocks of house sparrows.Animal Behaviour, 29, 543–550. of the decision. Journal of Personality and Social Psychology, Bateson, M., Nettle, D., & Roberts, G. (2006). Cues of being 67, 773–789. watched enhance cooperation in a real-world setting. Buss, D. M., & Greiling, H. (1999). Adaptive individual differ- Biology Letters, 2, 412–414. ences. Journal of Personality, 67, 209–243. Batson, C. D., Sager, K., Garst, E., Kang, M., Rubchinsky, Cialdini, R. B., Brown, S. L., Lewis, B. P., Luce, C., & Neuburg, K., & Dawson, K. (1997). Is empathy-induced helping S. L. (1997). Reinterpreting the empathy-altruism rela- due to self-other merging? Journal of Personality and Social tionship: When one into one equals oneness. Journal of Psychology, 73, 495–509. Personality and Social Psychology, 73, 481–494. Baumard, N., André, J.-B., & Sperber, D. (2013). A mutual- Cialdini, R. G., & Goldstein, N. J. (2004). Social influence: istic approach to morality. Behavioral and Brain Sciences, Compliance and conformity. Annual Reviews of Psychology, 36, 59-122. 55, 591–621. Baumeister, R., & Leary, M. (1995). The need to belong: Desire Clutton-Brock, T. (2009). Cooperation between non-kin in for interpersonal attachments as a fundamental human animal societies. Nature, 462, 51–57. motivation. Psychological Bulletin, 117, 497–529. Connor, R. C. (1986). Pseudo-reciprocity: Investing in mutu- Bergstrom, C. T., & Lachmann, M. (2003a). The Red King alisms. Animal Behaviour, 34, 1562–1584. effect: When the slowest runner wins the coevolutionary Connor, R. C. (1995). Altruism among non-relatives: race. PNAS, 100, 593–598. Alternatives to the “Prisoner’s Dilemma.” Trends in Ecology Blackmore, S. J. (2000). The meme machine. Oxford, and Evolution, 10(2), 84–86. UK: Oxford University Press. Cosmides, L., Barrett, H. C., & Tooby, J. (2010). Adaptive spe- Bliss, C., & Nalebuff, B. (1984). Dragon-slaying and ballroom cializations, social exchange, and the evolution of human dancing: The private supply of a public good. Journal of intelligence. PNAS, 107, 9007–9014. Public Economics, 25, 1–12. Daly, M. (2011). How evolutionary thinking inspires and dis- Blurton Jones, N. G. (1984). A selfish origin for human food ciplines psychological hypotheses. In X. T. Wang & Y. J. sharing: Tolerated theft. Ethology and Sociobiology, 5, 1–3. Su (Eds.), Thus spake evolutionary psychologists (pp. 15–22). Bolton, G. E., Katok, E., & Ockenfels, A. (2005). Cooperation Beijing: Peking University Press. among strangers with limited information about reputa- Daly, M., & Wilson, M. (1988). Homicide. New York Aldine tion. Journal of Public Economics, 89, 1457–1468. de Gruyter. Boone, J. L. (1998). The evolution of magnanimity: When Dawkins, R. (1976/2006) The selfish gene (30th Anniversary is it better to give than to receive? Evolution and Human Ed.). New York: Oxford University Press. Behavior, 9, 1–21. DeBruine, L. (2002). Facial resemblance enhances trust. Bowles, S. (2006). Group cooperation, reproductive leveling, Proceedings: Biological Sciences, 269, 1307–1312. and the evolution of human altruism. Science, 1569–1572. DeBruine, L. M. (2005). Trustworthy but not lust-worthy: Bowles, S. (2009). Did warfare among ancestral Context-specific effects of facial resemblance. Proceedings: hunter-­gatherers affect the evolution of human social Biological Sciences, 272, 919–922. behaviors? Science, 324, 1293–1298. De Cremer, D., & Van Vugt, M. (1999). Social identification Boyd, R., Gintis, H., Bowles, S., & Richerson, P. J. (2003). The effects in social dilemmas: A transformation of motives. evolution of altruistic punishment. PNAS, 100, 3531–3535. European Journal of Social Psychology, 29, 871–893.

56 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 56 12/12/2014 4:36:58 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

Delton, A. W., Krasnow, M. M., Cosmides, L., & Tooby, J. the Ache of Paraguay. Evolution and Human Behaviour, 21, (2011). Evolution of direct reciprocity under uncertainty 263–282. can explain human generosity in one-shot encounters. Haley, K. J., & Fessler, D. M. T. (2005). Nobody’s watching? PNAS, 108, 13335–13340. Subtle cues enhance generosity in an anonymous economic Dennett, D. C. (2006) Breaking the spell. New York Viking. game. Evolution and Human Behavior, 26, 245–256. Diekmann, A. (1985). Volunteer’s Dilemma. Journal of Conflict Hamilton, W. D. (1964). The genetical evolution of social Resolution, 29, 605–610. behaviour (I and II). Journal of Theoretical Biology, 7, 1–52. Diekmann, A. (1993). Cooperation in an asymmetric vol- Hames, R. (1987). Garden labor exchange among the unteer’s dilemma: Theory and experimental evidence. Ye’kwana. Ethology and Sociobiology, 8, 259–284. International Journal of Game Theory, 22, 75–85. Harbaugh, W. T. (1998). What do donations buy? A model of Doebeli, M., & Hauert, C. (2005). Models of cooperation philanthropy based on prestige and warm glow. Journal of based on the Prisoner’s Dilemma and the Snowdrift game. Public Economics, 67, 269–284. Ecology Letters, 8, 748–766. Hardy, C., & Van Vugt, M. (2006). Nice guys finish first: The Dovidio, J. F., Pilliavin, J. A., Schroeder, D. A., & Penner, L. competitive altruism hypothesis. Personality and Social (2006). The social psychology of prosocial behavior. Mahwah, Psychology Bulletin, 32, 1402–1413. NJ: Lawrence Erlbaum Associates. Hare, B., Melis, A. P., Woods, V., Hastings, S., & Wrangham, Dudley, S. A., & File, A. L. (2007). Kin recognition in an R. (2007). Tolerance allows baboons to outperform annual plant. Biology Letters, 3, 435–438. chimpanzees on a cooperative task. Current Biology, 17, Dunbar, R, Baron, R., Frangou, A., Pearce, E., van leeuwen, 619–623. E., Stow, J., . . . van Vugt, M. (2012). Social laughter is cor- Harpending, H. (1998). Comment on D. S. Wilson’s “Hunting, related with an elevated pain threshold. Proceedings of the sharing, and multilevel selection: the tolerated-theft model Royal Society of London Series B, 279, 1161–1167. revisited.” Current Anthropology, 39, 88–89. Fehr, E. & Gächter, S. (2002) Altruistic punishment in Harris, A. C., & Madden, G. J. (2002). Delay discounting humans. Nature, 415, 137–140. and performance on the Prisoner’s Dilemma game. The Fischer, P., Krueger, J. I., Greitemeyer, T., Vogrincic, C., Psychological Record, 52, 429–440. Kastenmüller, A., Frey, D., . . . Kainbacher, M. (2011). Harris, G. T., Rice, M. E., & Quinsey, V. L. (1994). The bystander-effect: A meta-analytic review on bystander Psychopathy as a taxon: Evidence that psychopaths are a intervention in dangerous and non-dangerous emergencies. discrete class. Journal of Consulting and Clinical Psychology, Psychological Bulletin, 137, 517–537. 62, 387–397. Foster, K. R., Wenseleers, T., Ratnieks, F. L. W., & Queller, D. Hawkes, K. (1991). Showing off: Tests of an hypothesis C. (2006). There is nothing wrong with inclusive fitness. about men’s foraging goals. Ethology and Sociobiology, 12, Trends in Ecology and Evolution, 21, 599–600. 29–54. Frank, R. H. (1988). Passions within reason. New York Norton. Haselton, M. G., & Buss, D. M. (2000). Error management Gardner, A., & Grafen, A. (2009). Capturing the superor- theory: A new perspective on biases in cross-sex mind read- ganism: A formal theory of group adaptation. Journal of ing. Journal of Personality and Social Psychology, 78, 81–91. Evolutionary Biology, 22, 659–671. Henrich, J., Boyd, R., Bowles, S., Camerer, C., Fehr, E., Gintis, Gardner, A., & West, S. A. (2004). Spite and the scale of com- H., . . . Tracer, D. (2005). “Economic man” in cross-cultural petition. Journal of Evolutionary Biology, 17, 1195–1203. perspective: Behavioral experiments in 15 small-scale soci- Gintis, H., Smith, E. A., & Bowles, S. (2001). Cooperation and eties. Behavioral and Brain Sciences, 28, 795–855. costly signaling. Journal of Theoretical Biology, 213, 103–119. Henrich, J., Boyd, R., & Richerson, P. J. (2008). Five misun- Gould, S. J., & Lewontin, R. C. (1979). The spandrels of San derstandings about cultural evolution. Human Nature: An Marco and the Panglossian paradigm: A critique of the Interdisciplinary Biosocial Perspective, 19, 119 –137. adaptationist paradigm. Proceedings of the Royal Society of Herrmann, E., Call, J., Hernández-Lloreda, M. V., Hare, B., & London B, 205, 581–598. Tomasello, M. (2007). Humans have evolved specialized Grandin, T., & Johnson, C. (2005). Animals in transla- skills of social cognition: The cultural intelligence hypoth- tion: Using the mysteries of autism to decode animal behav- esis. Science, 317, 1360–1366. iour. New York Scribner. Iredale, W., Van Vugt., M., & Dunbar, R. (2008). Showing Grayson, D. K. (1993). Differential mortality and the Donner off in humans: Male generosity as mate signal. Evolutionary Party disaster. Evolutionary Anthropology, 2, 151–159. Psychology, 6, 386–392. Graziano, W., Jensen-Campbell, L., & Hair, E. C. (1996). Jensen-Campbell, L., Graziano, W., & West, S. (1995). Perceiving interpersonal conflict and reacting to it: The Dominance, prosocial orientation, and female prefer- case for agreeableness. Journal of Personality and Social ences: Do nice guys really finish last? Journal of Personality Psychology, 70, 820–835. and Social Psychology, 68, 427–440. Griffin, A. S., West, S. A., & Bucklin, A. (2004). Cooperation Kelley, H. H., & Thibaut, J. W. (1978). Interpersonal rela- and competition in pathogenic bacteria. Nature, 430, tions: A theory of interdependence. New York: Wiley. 1024–1027. Kerr, B., Godfrey-Smith, P., & Feldman, M. W. (2004). Gurven, M. (2004). To give and to give not: The behavioral What is altruism? Trends in Ecology and Evolution, 19(3), ecology of human food transfers. Behavioral and Brain 135–140. Sciences, 27, 543–583. Ketelaar, T., & Au, W. T. (2003). The effects of feelings of Gurven, M., Allen-Arave, W., Hill, K., & Hurtado, A. M. guilt on the behaviour of uncooperative individuals in (2000). “It’s a Wonderful Life”: Signaling generosity among repeated social bargaining games: An affect-as-information

Barclay, Van Vugt 57

Schroeder251014OUS_PC.indb 57 12/12/2014 4:36:58 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

interpretation of the role of emotion in social interaction. Milinski, M., Semmann, D., Krambeck, H.-J., & Marotzke, Cognition and Emotion, 17, 429–453. J. (2006). Stabilizing the Earth’s climate is not a losing Keysers, C. (2006). Quick guide: Mirror neurons. Current game: Supporting evidence from public goods experiments. Biology, 19, R971–R973. PNAS, 103, 394–3998. Keysers, C., & Gazzola, V. (2006). Towards a unifying theory Mulder, L. B., van Dijk, E., De Cremer, D., & Wilke, H. A. M. of social cognition. Progress in Brain Research, 156, 379–401. (2006). Undermining trust and cooperation: the para- King, A. J., Johnson, D. D. P., & Van Vugt, M. (2009). The dox of sanctioning systems in social dilemmas. Journal of origins and evolution of leadership. Currrent Biology, Experimental Social Psychology, 42, 147–162. R911–R916. Murnighan, J. K., Kim, J. W., & Metzger, A. R. (1993). The Klapwijk, A., & Van Lange, P. A. M. (2009). Promoting Volunteer Dilemma. Administrative Science Quarterly, 38, cooperation and trust in noisy situations: The power of 515–538. generosity. Journal of Personality and Social Psychology, 96, Myatt, D. P., & Wallace, C. (2008). An evolutionary analysis 83–103. of the volunteer’s dilemma. Games and Economic Behavior, Kokko, H., Johnstone, R. A., & Clutton-Brock, T. H. (2001). 62, 67–76. The evolution of cooperative breeding through group aug- Nesse, R. M. (2005). Natural selection and the regulation of mentation. Proceedings of the Royal Society of London Series defenses: A signal detection analysis of the smoke detector B, 268, 187–196. principle. Evolution & Human Behavior, 26, 88–105. Komorita, S. S., & Parks, C. D. (1994). Social dilemmas. Nesse, R. M. (2007). Runaway social selection for displays of Madison, WI: Brown & Benchmark. partner value and altruism. Biological Theory, 2, 143 –155. Krupp, D. B., DeBruine, L. M., & Barclay, P. (2008). A cue Noë, R., & Hammerstein, P. (1994). Biological mar- of kinship promotes cooperation for the public good. kets: Supply and demand determine the effect of partner Evolution and Human Behavior, 29, 49–55. choice in cooperation, mutualism and mating. Behavioral Kümmerli, R., Colliard, C., Fiechter, N., Petitpierre, B., Ecology & Sociobiology, 35, 1–11. Russier, F., & Keller, L. (2007). Human cooperation in Noë, R., & Hammerstein, P. (1995). Biological markets. Trends social dilemmas: Comparing the Snowdrift game with the in Ecology & Evolution, 10, 336–339. Prisoner’s Dilemma. Proceedings: Biological Sciences, 274, Nowak, M. A. (2006). Five rules for the evolution of coopera- 2965–2970. tion. Science, 314, 1560 –1563. Lahti, D. C., & Weinstein, B. S. (2005). The better angels of Nowak, M. A., & Sigmund, K. (1992). Tit for tat in heterog- our nature: Group stability and the evolution of moral ten- enous populations. Nature, 355, 250–253. sion. Evolution and Human Behavior, 26, 47–63. Nowak, M. A., & Sigmund, K. (1993). A strategy of win-stay, Laland, K., & Brown, G. (2006). Niche construction, human lost-shift that outperforms tit-for-tat in the Prisoner’s behavior, and the adaptive-lag hypothesis. Evolutionary Dilemma game. Nature, 364, 56–58. Anthropology, 15, 95–104. Nowak, M. A., & Sigmund, K. (2005). Evolution of indirect Lyle, H. F., III, Smith, E. A., & Sullivan, R. J. (2009). Blood reciprocity. Nature, 437, 1291–1298. donations as costly signals of donor quality. Journal of O’Gorman, R. O., Henrich, J., & Van Vugt, M.(2008). Evolutionary Psychology, 4, 263–286. Constraining free-riding in public goods games: Designated Lyle, H. F., III, & Sullivan, R. J. (2007). Competitive status solitary punishers can sustain human cooperation. signaling in peer-to-peer file sharing networks. Evolutionary Proceedings of Royal Society of London Series B, 276, 323–329. Psychology, 5, 363–382. O’Gorman, R., Sheldon, K. M., & Wilson, D. S. (2008). For Majolo, B., Ames, K., Brumpton, R., Garratt, R., Hall, K., & the good of the group? Exploring group-level evolution- Wilson, N. (2006). Human friendship favours coopera- ary adaptations using multilevel selection theory. Group tion in the Iterated Prisoner’s Dilemma. Behaviour, 143, Dynamics: Theory, Research, and Practice, 12(1), 17–26. 1383–1395. Ohtsubo, Y., & Watanabe, E. (2009). Do sincere apologies Marlowe, F. W., & Berbesque, J. C. (2008). More “altruis- need to be costly? Test of a costly signaling model of apol- tic” punishment in larger societies. Proceedings: Biological ogy. Evolution and Human Behavior, 30, 114–123. Sciences, 275, 587–590. Ohtsuki, H., & Iwasa, Y. (2004). How should we define good- Mealey, L. (1995). The sociobiology of sociopathy: An inte- ness? Reputation dynamics in indirect reciprocity. Journal grated evolutionary model. Behavioral and Brain Sciences of Theoretical Biology, 231, 107–120. 18, 523–599. Ohtsuki, H., & Iwasa, Y. (2007). Global analyses of evolution- Mesoudi, A. (2009). The cultural dynamics of copycat suicide. ary dynamics and exhaustive search for social norms that PLoS ONE, 4(9), e7252. doi:10.1371/journal.pone.0007252 maintain cooperation by reputation. Journal of Theoretical Mifune, N., Hashimoto, H., & Yamagishi, T. (2010). Altruism Biology, 244, 518–531. toward in-group members as a reputation mechanism. Ostrom, E. (1990). Governing the commons: The evolution of Evolution and Human Behavior, 31, 109 –117. institutions for collective action. Cambridge, UK: Cambridge Miller, G. (2007). Sexual selection for moral virtues. Quarterly University Press. Review of Biology, 82, 97–125. Panchanathan, K., & Boyd, R. (2004). Indirect reciprocity can Milinski, M., Semman, D., Bakker, T. C. M., & Krambeck, stabilize cooperation without the second-order free rider H.-J. (2001). Cooperation through indirect reciproc- problem. Nature, 432, 499–502. ity: Image scoring or standing strategy? Proceedings of Royal Penner, L., Dovidio, J., Piliavin, J., & Schroeder, D. (2005). Society of London Series B, 268, 2495–2501. Prosocial behavior: Multilevel perspectives. Annual Review Milinski, M., Semmann, D., & Krambeck, H.-J. (2002). of Psychology, 56, 365–392. Reputation helps solve the “tragedy of the commons.” Petrinovich, L., O’Neill, P., &Jorgensen, M. (1993). An empiri- Nature, 415, 424–426. cal study of moral intuitions: Toward and evolutionary

58 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 58 12/12/2014 4:36:59 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

ethics. Journal of Personality and Social Psychology, 64, Smith, E. A. (2004). Why do good hunters have higher repro- 467–478. ductive success? Human Nature, 15, 343–364. Queller, D. C. (2011). Expanded social fitness and Hamilton’s Smith, E. A., & Bliege Bird, R. (2000). Turtle hunting and rule for kin, kith, and kind. PNAS, 108, 10792–10799. tombstone opening: Public generosity as costly signaling. Raihani, N. J., & Bshary, R. (2011). The evolution of pun- Evolution and Human Behavior, 21, 245–262. ishment in n-player public goods games: A volunteer’s Sober, E., & Wilson, D. S. (1998). Unto others: The evolution and dilemma. Evolution, 65, 2725–2728. psychology of unselfish behavior. Cambridge, MA: Harvard Reeve, H. K. (2000). Multi-level selection and human coopera- University Press. tion. Evolution and Human Behavior, 21, 65–72. Sommerfeld, R. D., Krambeck, H.-J., Semmann, D., & Reeve, H. K., & Hölldobler, B. (2007) The emergence of a Milinski, M. (2007). Gossip as a alternative for direct superorganism through intergroup competition. PNAS, observation in games of indirect reciprocity. PNAS, 104, 104, 9736–9740. 17435–17440. Richerson, P. J., & Boyd, R. (2005). Not by genes alone: How cul- Sosis, R. (2004). The adaptive value of religious ritual. American ture transformed human evolution. Chicago, IL: University Scientist, 92, 166–172. of Chicago Press. Sparks, A. (2011). How do subtle cues of social presence influ- Ridley, M. (2003). The agile gene. Toronto: HarperCollins. ence cooperation? Poster presented at the 23rd Annual Rigdon, M., Ishii, K., Watabe, M., & Kitayama, S. (2009). Meeting of the Human Behavior & Evolution Society. June Minimal social cues in the dictator game. Journal of 2011. Montpellier, France. Economic Psychology, 30, 358 –367. Stevens, J., & Hauser, M. (2004) Why be nice? Psychological Roberts, G. (1998). Competitive altruism: From reciprocity to constraints on the evolution of cooperation. Trends in the handicap principle. Proceedings: Biological Sciences, 265, Cognitive Science, 8, 60–65. 427–431. Stewart-Williams, S. (2007). Altruism among kin vs. non- Roberts, G. (2005). Cooperation through interdependence. kin: Effects of cost of help and reciprocal exchange. Animal Behaviour, 70, 901–908. Evolution and Human Behavior, 28, 193–198. Roberts, G. (2008). Evolution of direct and indirect reciproc- Sylwester, K., & Roberts, G. (2010). Cooperators ben- ity. Proceedings: Biological Sciences, 275, 173–179. efit through reputation-based partner choice in economic Roberts, G., & Renwick, J. S. (2003). The development of coop- games. Biology Letters, 6, 659–662. erative relationships: An experiment. Proceedings: Biological Takahashi, C., Yamagishi, T., Tanida, S., Kiyonari, T., & Sciences, 270, 2279–2283. Kanazawa, S. (2006). Attractiveness and cooperation in Roberts, G., & Sherratt, T. N. (1998). Development of cooper- social exchange. Evolutionary Psychology, 4, 315–329. ative relationships through increasing investment. Nature, Tinbergen, N. (1968). On war and peace in animals and man. 394, 175–179. Science, 160, 1411–1418. Sachs, J. L., Mueller, U. G., Wilcox, T. P., & Bull, J. J. (2004). Todd, P. M. (2001). Fast and frugal heuristics for environmen- The evolution of cooperation. The Quarterly Review of tally bounded minds. In G. Gigerenzer & R. Selten (Eds.), Biology, 79, 135–160. Bounded rationality: The adaptive toolbox (pp. 51–70). Searcy, W. A., & Nowicki, S. (2005). The evolution of animal Cambridge, MA: MIT Press. communication: Reliability and deception in signaling sys- Tooby, J., & Cosmides, L. (1990). On the uniqueness of tems. Princeton, NJ: Princeton University Press. human nature and the uniqueness of the individual: The Seinen, I., & Schram, A. (2006). Social status and group role of genetics and adaptation. Journal of Personality, norms: Indirect reciprocity in a helping experiment. 58(1), 17– 67. European Economic Review, 50, 581–602. Tooby, J., & Cosmides, L. (1996). Friendship and the Banker’s Semmann, D., Krambeck, H.-J., & Milinski, M. (2004). Paradox: Other pathways to the evolution of adaptations for Strategic investment in reputation. Behavioral Ecology and altruism. Proceedings of the British Academy, 88, 119–143. Sociobiology, 56, 248–252. Trivers, R. (1971). The evolution of reciprocal altruism. Seymour, R. M., & Sozou, P. D. (2009). Duration of court- Quarterly Review of Biology, 46, 35 –57. ship effort as a costly signal. Journal of Theoretical Biology, Trut, L. N. (1999). Early canid domestication: The farm-fox 256, 1–13. experiment. American Scientist, 87, 160–167. Shen, S.-F., Reeve, H. K., & Herrnkind, W. (2010). The Brave Van den Bergh, B., & Dewitte, S. (2006). The robustness of Leader game and the timing of altruism among non-kin. the “Raise-the-Stakes” strategy: Coping with exploitation The American Naturalist, 176(2), 242–248. in noisy Prisoner’s Dilemma Games. Evolution and Human Sherratt, T. N., & Roberts, G. (1999). The evolution of quanti- Behavior, 27, 19–28. tatively responsive cooperative trade. Journal of Theoretical Van Vugt, M. (2006). The evolutionary origins of leadership Biology, 200, 419–426. and followership. Personality and Social Psychology Review, Sih, A., Bell, A., & Johnson, J. C. (2004). Behavioral syn- 10, 354–372. dromes: An ecological and evolutionary overview. Trends Van Vugt, M. (2009). Averting the tragedy of the com- in Ecology & Evolution, 19, 372–378. mons: Using social psychological science to protect the Simon, H. A. (1990). A mechanism for social selection and suc- environment. Current Directions in Psychological Science, cessful altruism. Science, 250, 1665–1668. 18, 169–173. Simon, H. A. (1993). Altruism and economics. The American Van Vugt & Ahuja (2010). Naturally selected: The evolutionary Economic Review, 83, 156 –161. science of leadership. New York: Harper. Simpson, B., & Willer, R. (2008). Altruism and indirect reci- Van Vugt, M., De Cremer, D., & Janssen, D. (2007). Gender procity: The interaction of person and situation in prosocial differences in competition and cooperation: The male war- behavior. Social Psychology Quarterly, 71, 37–52. rior hypothesis. Psychological Science, 18, 19–23.

Barclay, Van Vugt 59

Schroeder251014OUS_PC.indb 59 12/12/2014 4:36:59 PM OUP UNCORRECTED PROOF – FIRSTPROOFS, Fri Dec 12 2014, NEWGEN

Van Vugt, M., & Hardy, C. (2010). Cooperation for reputa- West, S. A., Griffin, A. S., & Gardner, A. (2007). Social seman- tion: Wasteful contributions as costly signals in public tics: altruism, cooperation, mutualism, strong reciprocity goods. Group Processes and Intergroup Relations, 1–11. and group selection. Journal of Evolutionary Biology, 20, Van Vugt, M., & Iredale, W. (2012). Men behaving 415– 432. nicely: Public goods as peacock tails. British Journal of West, S. A., Murray, M. G., Machado, C. A., Griffin, A. S., & Psychology doi: 10.1111/j.2044-8295.2011.02093 Herre, E. A. (2001). Testing Hamilton’s rule with competi- Van Vugt, M., & Schaller, M. (2008). Evolutionary per- tion between relatives. Nature, 409, 510–513. spectives on group dynamics: An introduction. Group West, S. A., Pen, I., & Griffin, A. (2002). Cooperation and Dynamics, 12, 1–6. competition between relatives. Science, 296, 72–75. Van Vugt, M., & Van Lange, P. (2006). Psychological Williams, G. C. (1966) Adaptation and natural selection. adaptations for prosocial behaviour: The altruism Princeton, NJ: Princeton University Press. puzzle. In M. Schaller, D. Kenrick, & J. Simpson Wilson, D. S. (1979). Structured demes and trait-group selec- (Eds.), Evolution and Social Psychology (pp. 237–261). tion. The American Naturalist, 113, 606–610. New York: Psychology Press. Wilson, D. S. (1990). Weak altruism, strong group selection. Vickery, W. L., Giraldeau, L.-A., Templeton, J. J., Kramer, D. Oikos, 59, 135–140. L., & Chapman, C. A. (1991). Producers, scroungers, and Wilson, D. S. (1998). Hunting, sharing, and multilevel group foraging. The American Naturalist, 137, 847–863. selection: The tolerated-theft model revisited. Current de Waal, F. B. M. (2000). Attitudinal reciprocity in food shar- Anthropology, 39, 73 –97. ing among brown capuchin monkeys. Animal Behaviour, Wilson, D. S. (2002). Darwin’s cathedral: Evolution, reli- 60, 253–261. gion, and the nature of society. Chicago, IL: University of de Waal, F. B. M., & Suchak, M. (2010). Prosocial pri- Chicago Press. mates: selfish and unselfish motivations. Philosophical Wilson, D. S. (2004). What is wrong with absolute fitness? Transactions of the Royal Society of London Series B, 365, Trends in Ecology and Evolution, 19, 245–248. 2711–2722. Wilson, D. S., Van Vugt, M., & O’Gorman, R. (2008). Wedekind, C., & Braithwaite, V. A. (2002). The long-term Multilevel selection theory and major evolutionary transi- benefits of human generosity in indirect reciprocity. tions. Current Directions in Psychological Science, 17, 6–9. Current Biology, 12, 1012–1015. Wilson, W. (1971). Reciprocation and other techniques for Wedekind, C., & Milinski, M. (2000). Cooperation through inducing cooperation in the Prisoner’s Dilemma game. image scoring in humans. Science, 288, 850–852. Journal of Conflict Resolution, 15, 167–196. West, S. A., El Mouden, C., & Gardner, A. (2011). Sixteen mis- Yamagishi, T. (1986). The provision of a sanctioning system as conceptions about the evolution of cooperation in humans. a public good. Journal of Personality and Social Psychology, Evolution and Human Behaviour, 32, 231–262. 51, 110–116. West, S. A., Gardner, A., Shuker, D. M., Reynolds, T., Zahavi, A., & Zahavi, A. (1997). The handicap princi- Burton-Chellow, M., Sykes, E. M., Guinnee, M. A., & ple: A missing piece of Darwin’s puzzle. New York Oxford Griffin, A. S. (2006). Cooperation and the scale of compe- University Press. tition in humans. Current Biology, 16, 1103–1106.

60 the Evolutionary Psychology of Human Pro-sociality

Schroeder251014OUS_PC.indb 60 12/12/2014 4:36:59 PM