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CHAPTER T e Evolution of Morality: Which 23 Aspects of Human Moral Concerns Are Shared With Nonhuman Primates?

Mark Sheskin and Laurie Santos

Abstract Morality is a critical part of human society. This chapter explores the origins of human morality by examining whether nonhuman primate species share aspects of fi ve domains thought to be important in human moral behavior—concerns involving harm, fairness, hierarchy, ingroup allegiance, and purity. Behaviors in the harm domain have received the most attention from researchers, and converging lines of evidence suggest that some primates express harm concerns. The domain of fairness has become a recent focus of primate research, with active debate about whether closely related primates share human-like concerns. Moral behaviors regarding ingroup allegiance, authority, and purity have received the least attention in nonhuman species, though recent work suggests that research with primates might productively pursue the ingroup allegiance and authority domains. Future primate research will continue to elucidate the nature of human morality, and should include an increased focus on the previously neglected domains of ingroup and hierarchy. Key Words: morality, nonhuman primates, fairness, cognitive origins

Introduction As humans, we often experience social interactions It was feeding time and, as usual, Felix was the fi rst in as complicated as the one just described. Despite line. As the head of his group, he got to eat before all their complexity, we quickly and easily make sense others. He stepped up to the bounty and began leisurely of such scenarios—understanding who did what to eating more than he needed, never looking back to the whom in a way that lets us both interpret these events others in his group who watched him from behind, and make predictions about what will occur next. As waiting silently. Suddenly, there was a crash out of view. humans, our comprehension of complex social sce- Felix paused for a second and headed off to look at what narios goes beyond the mere s urface properties of the commotion was. Most of the others soon followed the events we witness. When reading the above sce- Felix, but Ric, the lowest-ranking member of the group, nario, for example, we spontaneously interpret the stayed behind. As soon as Felix was out of view, Ric agents’ behaviors not merely in terms of what each quickly ran up to the food and grabbed as much as he agent did—how they behaved—but also in terms of could, shoving it into his mouth quickly. When Felix what the agents intended, thought, and experienced. fi nished looking in the direction of the crash, he turned We quickly recognize that Felix intended to keep the back, and saw Ric feeding. Felix retaliated immediately. food all to himself, that Ric was hungry and trying to He screamed loudly, grabbed the food from Ric’s hands, deceive Felix, and that Felix was outraged when he and reached for his throat. Ric ran off crying, as the realized what happened and wanted to punish Ric. others watched the entire altercation in silence. In this way, humans naturally interpret social events

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in ways that go beyond the mere behavior witnessed, a social environment almost as complicated as our inferring the mental states that are causally respon- own, do they also bring to bear the same cognitive sible for the agents’ actions. machinery to process these events? However, humans take a step even beyond these Primate researchers have made considerable head- mentalistic causal inferences when we interpret social way in exploring at least some of these questions. events. Just as we spontaneously interpret agents’ Over the past few decades, much empirical work has behaviors in mentalistic terms, we also spontane- examined the question of whether primates also inter- ously evaluate those behaviors, deeming them good or pret their complex social world in the same mental- bad, acceptable or unacceptable, fair or unfair, moral istic way as humans, namely, by representing agents or immoral, and so on. When we witness a scenario in terms of their unseen mental states (e.g., Rosati, like the one described, we naturally form evaluations Santos, & Hare, 2009; Tomasello, Hare, & Call, of the actors’ behaviors, thinking for example that 2003a, 2003b; Tomasello, Carpenter, Call, Behne, it’s unfair for Felix to keep the food to himself, dis- & Moll, 2005). Although there is still considerable honest for Ric to take food from his group mate when controversy about the extent to which primates repre- he’s not looking, or wrong for group mates not to sent others’ behavior mentalistically (Hare, Addessi, step in during a physical altercation. Such moral Call, Tomasello, & Visalberghi, 2003; Penn & evaluations share several features with our mental- Povineli, 2007; Povinelli & Vonk, 2003; Tomasello istic interpretations of others’ behavior. First, moral et al., 2003a; 2003b; Tomasello et al., 2005), a con- evaluations require us to go beyond a simple behav- siderable body of work has demonstrated that many ioral interpretation of the events we have witnessed. primates behave in ways that are consistent with an Indeed, even scenarios that are simple at the behav- understanding of others’ perceptions (Flombaum ioral level can involve nuanced moral evaluations. & Santos, 2005; Hare, Call, Agnetta, & Tomasello, We might evaluate Felix’s behaviors in the preceding 2000) knowledge (Hare, Call, & Tomasello, 2001; scenario diff erently if we knew more about the his- Kaminski, Call, & Tomasello, 2008; Santos, Nissen, tory of interactions between him and Ric, the way & Ferrugia, 2006), and intentions (Call, Hare, that Felix fi rst came to his high status, and so on. Carpenter, & Tomasello, 2004; Phillips, Barnes, In addition, like our omnipresent mentalizing, our Mahajan, Yamaguchi, & Santos, 2009) tendency to evaluate actions in moral terms is ubiq- Less work, however, has investigated another uitous. People universally make moral evaluations aspect of primate social cognition—whether pri- of others’ behavior. Moreover, we apply our evalu- mates also share human-like moral considerations ations not just to the actions of others, but also to when watching and acting in social activities. Do our own behaviors. Such self-evaluations mean that primates, like humans, evaluate others’ actions as people often evaluate whether their own behaviors moral or immoral? Do they represent actions as fair are right or wrong, which much of the time seems to or unfair? Do primates decide how to behave based motivate them to behave in ways that are good and on notions of right and wrong? Primate researchers avoid actions that would be evaluated as wrong. Our have been able to gain new insight into these ques- human tendency to spontaneously evaluate actions tions in just the last few years. In this chapter, we and act on the basis of such evaluations—our human review this recent empirical work in an attempt to moral cognition—is a fundamental aspect of human address which features of human moral cognition social life, one that plays out universally in our spe- might be shared with nonhuman primates. We fi rst cies and dictates much of our social interactions. outline the kinds of domains in which moral cogni- Of course, humans are not the only species forced to tion has been examined in our own species and then navigate complicated social situations. Like humans, turn to what is known about how primates reason in nonhuman primates (hereafter, primates) face a com- these domains. Although there are still many ques- plex array of social events. Consider, for example, the tions to be addressed, recent empirical work pro- events described in the opening scenario. Although vides new insight about the kinds of foundational you would be forgiven for assuming that this story moral capacities that are and are not shared broadly involved human agents, the scenario described actu- within our evolutionary order. ally involved a group of capuchin monkeys living in our colony at Yale University. Capuchin monkeys, Carving Out the Domains like other primates, consistently deal with individu- of Moral Cognition als who willfully try to deceive, unfairly attempt to Before launching into a review of the foundation harass, and so on. Given that other primates face of moral cognition in primates, we must fi rst discuss

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two caveats about our approach. T e fi rst caveat al., 2009). First, these fi ve domains capture the moral involves the question of how to carve up human intuitions not just of participants from Western moral cognition to investigate the possibility that educated backgrounds (who tend to focus mostly similar capacities exist in other species. Given that on harm and fairness violations), but also the kinds there are centuries of philosophical inquiry into the of intuitions commonly observed in non-Western nature of human morality, fi nding a simple defi ni- cultures, in which people tend to focus more on tion of human moral cognition that could apply to issues related to ingroup allegiance, authority, and primates is undoubtedly going to be tricky. However, purity (Haidt & Graham, 2007; Haidt & Joseph, a number of psychologists have successfully argued 2007). In this way, Haidt’s foundational domains that human moral concerns—even when viewed capture the universal aspects of human moral con- cross-culturally—tend to fall into a relatively small cerns, exactly the ones we might want to focus on number of specifi c domains (Haidt & Joseph, 2004, when taking an evolutionary approach to similar 2007; Hauser, 2006; Shweder, Much, Mahapatra & concerns in primates. Second, Haidt and colleagues Park, 1997). developed these fi ve foundational domains with an Although there is superfi cial societal variation in eye for the diff erent kinds of evolutionary selection the nature of people’s moral concerns, people uni- pressures that may have led to human moral intu- versally tend to consider the same types of behav- itions (see Haidt and Joseph, 2007, for a review). iors when they evaluate others’ actions as “good” or For example, Haidt and colleagues hypothesize that “evil.” Haidt and his colleagues (Graham & Haidt, harm concerns emerged as a result of selection pres- 2010; Graham, Haidt, & Nosek, 2009; Haidt, sures to protect vulnerable yet closely related kin, 2008; Haidt & Graham, 2007; Haidt & Joseph, while concerns about purity emerged based on pres- 2004, 2007; Haidt & Kesebir, 2009) have divided sures to avoid microbes and other pathogens. In this these types of human moral concerns into a set way, Haidt’s organization of human moral concerns of fi ve “foundational” domains of morality. T ese is based on the idea that our moral intuitions evolved domains include: harm (concern for the welfare of in response to selection pressures in exactly the same others), fairness (concern for equitable outcomes), way we might expect if some aspects of these con- ingroup allegiance (concern for the welfare of the cerns were shared in other primate species. group), authority (concern for maintenance of group T e second caveat, however, concerns how we hierarchy), and purity (concerns for the sacred- can determine whether primates share a human- ness of certain objects and actions). T e content like moral concern in these domains. For a verbal of each of the fi ve domains can be illustrated with species like humans, determining a subject’s moral example items from Haidt’s “Moral Foundations concerns can often be addressed simply by asking: Sacredness Scale” (Graham & Haidt, 2010), which human participants can be asked whether they con- asks how much money you would require to agree sider the actions verbally presented in a scenario to do various unsavory things. T e harm domain to be “right” or “wrong.” T e situation is much includes actions such as kicking a dog in the head trickier when you’re dealing with nonverbal subjects and taunting an overweight person. T e fairness like primates. Given that primates cannot verbally domain includes actions such as cheating in a game express whether they consider any actions to be of cards with strangers and agreeing to secretly hire good or bad, what evidence can we use to deter- only same-race applicants for a job. Violations of mine whether they share human-like moral consid- ingroup allegiance include actions such as break- erations? Although this question is sure to generate ing off communication with all family members for much debate among philosophers and animal cogni- a year and changing citizenship to another coun- tion researchers, in this review we have chosen to use try. Examples of immoral actions in the author- two kinds of evidence to argue for similarity across ity domain include throwing a rotten tomato at a humans and primates. T e fi rst piece of evidence we disliked political leader and slapping your father as discuss concerns whether primates behave in ways part of a rehearsed comedy skit. Finally, violations that are consistent with possessing a given moral in the purity domain include getting a two-inch tail concern. When humans think an action is wrong, surgically added for three years and getting a blood they tend to avoid doing it. Similarly, when people transfusion from a child molester. think actions are permissible or obligatory, they Haidt’s fi ve domains of moral consideration have tend to engage in them. In this way, we can use evi- provided a promising approach to studying moral c dence about whether primates behave in ways that ognition in humans for several reasons (Graham et are consistent with certain moral considerations as

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evidence for possessing such concerns. For example, regarding hierarchy or ingroup. T at is, although do primates engage in actions that violate author- some primates act diff erentially toward others based ity or fairness considerations? Or do they instead on hierarchy and ingroup status, there is little evi- make choices in ways that are consistent with obey- dence that they positively or negatively evaluate oth- ing these considerations? By examining whether ers for violations of the hierarchy or ingroup. Finally, primates themselves behave in ways that are consis- little primate work has explored concerns that fall tent with diff erent considerations, we can see—at within the purity domain, although our intuition is the very least—whether they behave as though they that purity concerns are a domain of human moral represented that such a moral norm was in place. concern that might be unique to our species.1 A second form of evidence concerns whether pri- mates evaluate the actions of others who do and do Evolution of Harm/Care Behaviors not behave in ways that are consistent with diff er- and Concerns ent moral considerations. When humans watch an Behaviors in the harm domain focus on the individual performing an action that they think is physical welfare of others. Put in the most general wrong, they tend to evaluate that individual nega- terms, moral concerns in the domain of harm stipu- tively. Such negative evaluations in humans can take late that it is moral (and sometimes obligatory) to diff erent forms, including punishment, shunning, a increase others’ physical welfare and often immoral refusal to interact with the individual in the future, to decrease or harm it. Prototypical cases of harm and so forth. As such, we review whether primates violations are hypothesized to involve bodily injury, show evidence of evaluating others’ actions when but other cases of welfare removal also fall under those others violate moral considerations. Do pri- this defi nition. Moral concerns in the harm domain mates refuse to interact with those that violate harm also seem to recruit a standard set of emotions (e.g., constraints or ignore ingroup allegiances? Do they compassion) as well as characteristic motivations punish such individuals when given the opportu- for increasing others’ welfare (kindness, prosocial nity? T roughout the review, we also pay attention preferences, etc.). Several researchers have hypothe- to whether primates’ evaluations depend on who is sized that intuitions about harm represent the most being aff ected by the moral violation. Do primates developmentally basic moral evaluations (Haidt react negatively only when they themselves are neg- & Joseph, 2007; Hauser, 2006; Mikhail, personal atively aff ected by the moral violation (e.g., cases communication), and there is evidence that such in which their own place in their hierarchy is not intuitions come on line in our own species in the respected, when they are harmed personally, etc.), fi rst few months of life (Hamlin, Wynn & Bloom, or do they also show similar evaluations when they 2007). are not involved in the violation, such as when only T e harm domain is a foundational area of moral a third party is negatively aff ected (i.e., someone else cognition that has been extensively studied in a is treated unfairly, a third party individual is harmed, wide range of species. T is is not surprising, given etc.). If primates’ moral evaluations operate like the hypothesized origin of harm concerns—namely, those of humans, then primates should negatively a motivation to help kin (see Haidt & Joseph, evaluate immoral agents based on transgressions 2007). Indeed, many organisms increase their fi t- against a wide range of targets (and certainly not ness indirectly by acting in ways that help closely just transgressions against the evaluator). related kin, either by behaving in ways that increase Focusing on these two kinds of evidence, we next kin’s welfare (e.g., feeding children) or decrease the examine whether primates seem to possess moral risk of harm to kin (e.g., alarm calling to prevent considerations within each of Haidt’s fi ve domains. predation; see Hamilton, 1963). A more interest- Behaviors in the harm domain have received the ing case of harm considerations, however—and most attention from researchers, and converging one that maps most directly onto human moral lines of evidence suggest that some primates express concerns—involves attitudes and behaviors that are harm concerns as well. T e domain of fairness has directed toward the welfare of nonkin. Human harm also become a recent focus of primate research, with concerns move beyond closely related family mem- some debate regarding whether closely related pri- bers. Actions as varied as off ering directions to lost mates share human-like fairness concerns. On the tourists to donating blood anonymously suggest other hand, although some nonhumans have social that humans are motivated to increase welfare and hierarchies and participate in intergroup confl icts, decrease harm toward unrelated (and sometimes there is little study of primate moral concerns unknown) individuals.

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Do primates show similar concerns when dealing way. Instead, proposers across many cultures tend to with nonrelatives? Early research with primates iden- give at least some money to the recipient (Henrich tifi ed some situations in which individuals respond et al., 2006), suggesting that humans seem to have negatively toward the distress of other individuals. preferences to behave prosocially, sometimes benefi t- In one famous study, rhesus monkeys refrained from ting others’ welfare at an immediate personal cost.2 pulling a chain that delivered food when the chain Primate researchers have developed a set of non- was linked to an unrelated conspecifi c experienc- verbal economic games that are conceptually simi- ing a painful electric shock (Masserman, Wechkin lar to the human Dictator game, but are simplifi ed & Terris, 1964). T is early study provided some of in several ways (Burkart, Fehr, Eff erson, & van the fi rst evidence that primates may avoid actions Schaik, 2007; Jensen, Call, & Tomasello, 2007a; that cause unrelated individuals to experience pain. Jensen, Call, & Tomasello, 2007b; Jensen, Hare, Unfortunately, however, this early work was also Call, & Tomasello, 2006; Lakshminarayanan & consistent with a number of other more defl ation- Santos, 2008; Silk et al., 2005; Vonk et al., 2008; ary alternatives. For example, witnessing the dis- de Waal, Leimgruber, & Greenberg, 2008). First, tress of others can often provide a good indicator in primate studies, the proposer is usually off ered a of danger, and so individuals may fi nd others’ pain dichotomous choice between two diff erent resource aversive simply because of this association. Put more distributions, making the cognitive demands of this basically, the motivation to avoid aversive signals in task simpler than that of the human Dictator game. one’s environment is diff erent from the motivation In addition, the primate choice task is often set up to increase the welfare of other social agents; only in such a way that there is no direct cost to act- the latter motivation falls under the moral domain ing prosocially: although the receiver’s reward dif- of harm avoidance. fers between the two options, the proposer typically obtains the same reward no matter which option is Economic Games in Humans and given to the recipient. T us, acting prosocially in Nonhuman Animals the nonhuman Dictator game is easier than in the To get around the kinds of interpretational human Dictator game in the sense that it does not problems that plagued conspecifi c distress studies, demand that primates accept a cost to themselves to researchers developed new methods to examine non- increase the welfare of another individual. human harm concerns. Such new methods typically Despite the attempts to “stack the deck” in favor mimic the scenarios in which humans are motivated of fi nding prosocial tendencies in primates, the to increase others’ welfare and test whether primates results using economic games have been mixed. Silk are willing to do the same. T e most prolifi c of these et al. (2005), for example, presented chimpanzees new methods, primate economic games, are based with a choice between pulling a handle that deliv- on the kinds of economics games typically used to ered one piece of food to the proposer and one piece test human moral intuitions. In human versions of to the receiver (a 1/1 option) and pulling a handle these games, participants are asked to allocate dif- that delivered one piece of food to the proposer and ferent kinds of resources between themselves and nothing to the receiver (a 1/0 option). Chimpanzees other individuals. Such tasks can, therefore, provide showed no preference for pulling the handle that a window into the situations under which partici- provided the receiver with food, choosing the 1/0 pants are and are not willing to increase others’ wel- option as often as they chose the 1/1 option. Jensen fare (i.e., give them more or less money). and colleagues (2006) replicated this eff ect, and con- One of the most famous of such human eco- fi rmed that chimpanzees understand the diff erences nomic games is known as the Dictator game, a in payoff to the receiver position. T ey confi rmed resource allocation task that takes place between that chimpanzees understood the receiver payoff by two players, a proposer and a receiver (Henrich including a condition in which the proposer had et al., 2005; Kahneman, Knetsch, & T aler, 1986). access to the receiver position, and fi nding that in T e proposer is given control over the division of an this condition proposers chose the option that sent endowment of money (e.g., $10) that must be split food to the receiver position. When another chim- between the two players. In cases in which the play- panzee had access to the receiver position, they rep- ers do not know each other and play only once, a licated the results from Silk et al. (2005), fi nding rational and self-interested proposer should keep all that chimpanzees acted with indiff erence to increas- the money and give none to the receiver. However, ing the welfare of the receiver in both a 1/0 vs. 1/1 humans tend not to behave in such a self-interested condition and a 0/0 vs. 0/1 condition. In a further

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extension, Yamamoto and Tanaka (2010) found tamarins are not more likely to provide a 1/1 out- that chimpanzees’ selfi sh focus is resistant not only come over a 1/0 outcome when a receiver is pres- to concerns of kin (in this case mother-off spring ent (Cronin, Schroeder, Rothwell, Silk, & Snowdon, pairs) but also to the potential cooperation-induc- 2009, see also Stevens, 2010). ing structure of reciprocation (in which chimpan- In sum, nonhuman performance on simple zees took turns playing the proposer and receiver economic games provides evidence of prosocial- roles). ity in some species, but the failure of chimpanzees One initially plausible explanation for chimpan- (among our closest evolutionary relatives) to behave zee’s selfi sh behavior in these tasks is that they are prosocially indicates that the evolutionary his- so distracted by their own rewards that they fail to tory that leads humans to behave prosocially in a notice how their behaviors infl uence the welfare of donation task may not be as simple as we originally the receiver. To test this possibility, Vonk and col- thought. Before attempting to dissect the pattern leagues (2008) provided chimpanzees with separate any further, however, it will be useful to look at pri- choices to deliver food to themselves and a receiver. mates’ performance on another measure of proso- Subjects were armed with a stick that could dislodge cial preferences. food set to roll toward the subject position and food set to roll toward the receiver position. T us, the Instrumental Helping Tasks in Humans chimpanzees could dislodge and receive their own and Primates reward and then, no longer distracted, provide a Humans also demonstrate a motivation to reward to the receiver. Although chimpanzees reli- increase others’ welfare, helping others achieve a ably dislodged their own reward, they were not variety of goals; helping a friend move their couch or more likely to dislodge the receiver reward when handing someone an out-of-reach pen are situations a receiver was present as opposed to absent. T is in which people are willing to incur a slight cost result suggests that, in the previous tasks, chimpan- to help someone achieve a goal and thus increase zee lack of concern for others was not due merely to another’s welfare. Do primates also show a willing- distraction with their own reward. ness to increase others’ welfare through instrumen- Although chimpanzees, one of our closest evolu- tal helping? Several studies have examined this issue, tionary relatives, do not show human-like prosocial observing that primates, like humans, are willing concerns in a dictator-style economic game, some to act in ways that instrumentally help others. In more distantly related primates do (Burkart et al., contrast to their indiff erent performance on other 2007; de Waal et al., 2008; Lakshminarayanan & economic games (Jensen et al., 2007a; Silk et al., Santos, 2008; Takimoto, Kuroshima, & Fujita, 2005; Vonk et al., 2008; Yamamoto & Tanaka, 2009;). Burkart and colleagues (2007) found that 2010), Warneken and Tomasello (2006) found common marmosets, a New World monkey species, that chimpanzees were willing to go out of their were more likely to pull a 0/1 option than a 0/0 way to help humans and conspecifi cs achieve goals. option when a receiver was present than when the Chimpanzees, for instance, are willing to help a reward was delivered to an empty chamber. Similar person reach an out-of-reach object and also help results have been reported in another New World a conspecifi c enter a room to obtain food. Indeed, monkey, the brown capuchin (de Waal et al., 2008; chimpanzee subjects acted in ways that increased Lakshminarayanan & Santos, 2008; Takimoto others’ welfare even when it required them to take et al., 2009). Takimoto and colleagues (2009), for a slight cost, climbing into a raised raceway to example, found that capuchins were willing to pro- retrieve the object (Warneken, Hare, Melis, Hanus, vide conspecifi cs with high payoff s, especially when & Tomasello, 2007). Although chimpanzees failed recipients were visible and low ranking. Capuchin to help in some types of tasks (removing physical prosociality in these tasks is remarkably robust; obstacles and completing a failed action through Lakshminarayanan and Santos (2008) found that either imitated or novel means), chimpanzees capuchin proposers provide another monkey with showed helping behavior in a number of situa- a reward that is greater than its own reward, will- tions. Such results suggest that this species possesses ingly delivering a high-value treat (marshmal- prosocial motivations that would fall under the low) to a receiver even when they themselves got a defi nition of human-like harm concerns (Warneken low-value treat (cucumber). However, not all New et al., 2007). World primates show prosocial preferences on this Extending this line of work to other primate spe- task. Cronin and colleagues found that cotton-top cies, Barnes, Hill, Langer, Martinez, and Santos,

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(2008) found that capuchins were minimally inter- harm violation, namely, the act of physically hurt- ested in helping a human retrieve an out-of-reach ing someone (see Haidt & Joseph, 2007). Indeed, object, although this eff ect was not observed as human infants understand such harm violations robustly as in chimpanzees. When helping was dif- when they are only three months of age (Hamlin fi cult (the capuchin had to reach outside the cage et al., 2007; Hamlin et al., in press). In addition, to manipulate the object), capuchins showed almost developmental psychologists have developed a set of no helping behavior. When helping was less costly, nonverbal methods (e.g., looking measures: Hamlin capuchins attended to a person’s goals and exhibited et al., in press; choice measures: Hamlin et al., 2007) higher rates of helping. T us, in contrast to per- to test these intuitions that could be applied to non- formance in economic games, in which capuchins verbal primates. show prosocial preferences and chimpanzees do not, Another profi table next step in this area of research instrumental helping tasks are more likely to elicit might involve investigating how primates evalu- welfare concerns from chimpanzees than they are ate individuals that violate norms against harm. from capuchins. Most of the work addressing primates’ concerns has focused on exploring whether primates behave in Accounting for Species Diff erences ways that are consistent with prosocial norms. Few in Harm and Care Behaviors researchers have explored whether primates react Taken as a whole, the results of these experiments negatively to those who act harmfully toward oth- indicate that primates show some prosocial motiva- ers. Recently, Subiaul, Vonk, Okamoto-Barth, and tions—and, therefore, behave in ways that are con- Barth (2008) found that chimpanzees will prefer- sistent with some harm-related moral concerns—but entially beg for food from a human that has been tend not to express such behaviors as consistently as seen giving (rather than refusing to give) treats to humans. One plausible explanation for the lack of either a human or another chimpanzee. Similarly, prosocial behavior in some experimental contexts Russell, Call, and Dunbar (2008) also found that is that aspects of the context in which researchers chimpanzees preferred humans seen being gener- have tested these capacities hinder the expression of ous rather than stingy, while fi nding that bonobos, prosocial concerns. One issue, for example, concerns gorillas, and orangutans did not form preferences in the ecological validity of the tests typically used to this situation. Although these results hint that some study these considerations—namely, food donation primates may evaluate others’ harmful actions, more tasks (see also chapter 20 of this volume). In their work is clearly needed on this issue. In particular, natural behavior, primates rarely directly share with additional methods would be useful for investigat- or donate food to other individuals in the way they ing primate responses to third-party harm evalua- are required to do in donation tasks. As such, dona- tions. For example, would an individual behave tion tasks may represent a situation that primates diff erently on a prosocial food donation task after are unlikely to encounter in the wild. Indeed, the fi rst witnessing the prospective recipient doing a species with the most robust evidence for prosocial harmful act toward another individual? If given a preferences on donation tasks—the brown capuchin choice to donate food to one of two individuals, monkey—is also the one best known for its toler- would an individual who obeyed harm norms be ated food sharing (de Waal, 2006). An additional preferred over one who did not? By exploring these issue concerns the researchers’ ability to account for questions, researchers may gain new insight into not the subjects’ expectations of the experimenters. In just how primates behave when dealing with poten- tasks that elicit helping behavior, certain popula- tially harmful situations but also how they evaluate tions may have stronger expectations that helping others who do and do not act in the same ways. behavior may earn a treat. Under this view, what Such new tasks may also allow researchers to get appears to be species diff erences in prosocial behav- around some of the task demands that plague other ior may actually be population-level diff erences in studies in this line of work. performance that arise due to diff erences in rearing and reinforcement histories. Evolution of Fairness/Reciprocity Researchers will likely profi t from developing Behaviors and Concerns new tasks, ones that better mimic the kinds of situ- Behaviors in the fairness domain focus on equity ations in which primates might naturally express among social partners. Haidt and colleagues hypoth- their own harm concerns. One such situation would esize that fairness concerns evolved in part to culti- involve testing primates on a more prototypical vate and maintain mutually benefi cial partnerships

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with other cooperators by establishing a norm of was allowed to select one of two diff erent reward equitable treatment (Haidt & Joseph, 2007). T e distributions for themselves and the receiver. prototypical fairness violations, then, occur in cases However, like the human ultimatum game, the pro- in which a social partner is cheated by not receiving poser was able to obtain his payoff s only if the receiver an equal share. Under this defi nition, fairness con- chimpanzee “accepted” the off er—in this case by cerns can include cases in which the unfairness has completing a pull required to bring the rewards a direct negative eff ect on the self (what research- into reach. In contrast to human performance, ers have referred to as “disadvantageous inequity”), Jensen and colleagues found that chimpanzees rarely cases in which the self benefi ts from the unfair split rejected low off ers. Instead, chimpanzees behaved (“advantageous inequity”), and cases in which the like rational payoff maximizers. Proposer chimpan- self is not involved (which we will refer to as “third- zees chose the distribution that provided themselves party inequity”). In any case of unfairness between selfi shly with more food, and receiver chimpanzees two individuals, one is experiencing disadvanta- only rejected in cases in which they were off ered a geous inequity and the other is experiencing advan- payoff of zero. T is result suggests that chimpanzees tageous inequity (and an uninvolved observer may are unwilling to reject off ers that are unfair, at least notice and evaluate the third-party inequity). in cases when such rejections are costly. Recent research has also examined whether pri- Human Behavior in Fairness Tasks mates exhibit negative reactions when they receive T ere are many real-world examples to suggest disadvantageous treatment relative to a conspe- that humans act on the basis of fairness consider- cifi c. In an infl uential early study, Brosnan and de ations. Just as in the case of harm considerations, Waal (2003) allowed capuchin monkeys to trade however, researchers have investigated people’s fair- tokens in exchange for cucumber slices. Despite ness norms empirically using a number of economic being a low-value treat, the monkeys were almost games that tap into the tendency to avoid inequity. always willing to trade for and eat the low-value One of the most famous methods involves an eco- treat when no other interactions were taking place. nomic scenario known as the Ultimatum game. Rejections of the low-value treat rose to almost 50 T is game is identical to the Dictator game, except percent, however, when the subject fi rst saw another that the second player (the receiver) has the oppor- monkey receive a high-value grape treat. When tunity to reject the fi rst player’s (the proposer’s) divi- another monkey received a grape without needing sion of the payoff . If the receiver chooses to reject, to trade a token, the rejection rates rose to about both players get nothing. As in the Dictator game, 80 percent. Similar results were reported for at least people tend not to play this game in ways that maxi- some populations of chimpanzees tested on an iden- mize self-interest, which would involve the receiver tical task (Brosnan, Schiff , & de Waal, 2005). T ese accepting any nonzero off er. Instead, people tend results were initially interpreted as evidence that to play based on considerations of fairness. Henrich some primates are willing to reject unfair off ers, and et al. (2006), for example, tested participants across thus that these species evaluate unfair payoff s by many diff erent cultures and found that over half the choosing not to trade with unfair experimenters. players were willing to reject some nonzero amounts T e rich interpretation of Brosnan and colleagues’ off ered to them. T us, people incur costs to avoid fi ndings has been challenged by several researchers. certain unfair situations. Dubreuil, Gentile, & Visalberghi (2006) argued that primates may reject low-valued foods on this Nonhuman Behavior in Fairness Tasks task merely because they are frustrated at not get- Do primates share the fairness concerns of humans? ting a high-value reward. To test this, they examined T e question of whether primates care about fairness whether capuchin monkeys would show similar has recently become a focus of research in primate rejection eff ects when preferred food was present but cognition. As in the case of studying harm con- out of reach. T ey found that capuchins exhibit the cerns, researchers have begun examining this issue same behaviors when the preferred food was given by developing primate versions of human economic to another monkey as they do when the preferred games that tap into inequity aversion. Jensen and food is simply out of reach. On the basis of these colleagues (2007a), for example, developed a ver- data, Dubreuil and colleagues (2006) argued that sion of the ultimatum game for chimpanzees. In Brosnan and colleagues’ fi ndings were due to simple this experiment, a chimpanzee proposer and receiver frustration eff ects rather than “true” fairness con- were tested in adjacent enclosures. T e proposer cerns. Using a similar logic, Silberberg, Crescimbene,

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Addessi, Anderson, and Visalberghi (2009) per- Re-evaluating Primate’s Performance in formed a direct test of the frustration account of Fairness Studies capuchin rejections. T eir subjects did not get the In sum, there is much less conclusive evidence high-value treat during previous trials and, there- regarding primate fairness concerns as compared to fore, they could not be frustrated at getting the low- the evidence that primates possess concerns in the value treat during test trials. Silberberg et al. (2009) harm domain. To the extent that primates have any found that capuchins accepted nearly every off ered concerns about being personally cheated, they seem trade and showed no diff erences based on observa- to lack a general fairness concern that would respond tions of high- or low-value treats being delivered to to others being cheated. Even when focusing on dis- another monkey. Silverberg thus argued that previ- advantageous inequity aversion, there are sugges- ous research interpreted as evidence of fairness con- tions that the observed eff ects may result more from cerns in primates were the result of unaccounted general frustration than from a concern for equity. for frustration eff ects. Other researchers have also It is, however, worth considering whether the reinterpreted Brosnan and colleagues’ fi ndings by general-frustration eff ect described earlier might be arguing that these results refl ect only how primates relevant for the evolution of fairness concerns. Put react when their expectations are violated. Chen and diff erently, a frustration eff ect could in fact be a criti- Santos, for example, have argued that capuchins may cal part of the fairness response in humans. Humans, react negatively in Brosnan and colleagues’ studies of course, tend to exercise fairness concerns quite merely because they got less of a reward than they specifi cally, only when dealing with distributions originally expected (see Chen and Santos, 2006, for involving other social agents. Nonetheless, one a more detailed discussion of these issues). Finally, could imagine how a simple frustration-based mech- Bräuer, Call, and Tomasello (2006) attempted to anism—one that responded negatively to any payoff replicate Brosnan and colleagues’ (2005) chim- that was lower than one expected—could perform panzee version of the study with another group of in much the same way as a true fairness consider- chimpanzees. T eir study observed a confl icting ation—it too would allow an organism to respond pattern of performance; chimpanzees in Bräuer negatively when it received a smaller-than-expected and colleagues’ study became more involved when reward in interactions with other social agents. In experimenters delivered better rewards to other this way, a simple mechanism that allows primates to chimpanzees, becoming more motivated to beg for treat all instances of smaller-than-expected rewards food when better food was present. Taken together, as “unfair” exchanges might be an evolutionarily these confl icting results suggest that fairness con- advantageous one, if the benefi ts of displaying cerns observed in primates are, at best, extremely negative reactions to unfairness in social situations fragile: they may or may not be elicited, depending outweigh the costs of displaying those reactions in on minor variations in experimental design. nonsocial settings. In this analysis, the original fair- Given the diffi culty in establishing fairness con- ness concern, from an evolutionary perspective, may cerns in cases of disadvantageous inequity, it is result from a more general frustration eff ect, exactly not surprising that there are no reports of pri- the kind of eff ect that many of the preceding experi- mates reacting negatively to cases of advantageous ments were designed to factor out. In this way, we inequity, in which the subject himself benefi ts argue that researchers may want to reinterpret some from the unequal distribution of payoff s. Indeed, of the so-called frustration eff ects in the primate fair- Brosnan (2006) anecdotally noted that monkeys ness experiments (Dubreuil et al., 2006; Silberberg who were unfairly paid the higher reward in the et al., 2009) and think more critically about whether original Brosnan and de Waal (2003) study never a general-frustration mechanism might be more rel- spontaneously shared their own reward with the evant to fairness concerns than previously thought. subject who received less. (In fact, they sometimes stole the subject monkey’s rejected cucumber!). In Evolution of Ingroup/Loyalty Behaviors this way, primates’ fairness concerns seem to emerge and Concerns only in cases of disadvantageous inequity; there is no Moral concerns in the third domain—that of evidence that primates show any fairness concerns in ingroup allegiance—focus on productive coopera- cases of advantageous inequity. Similarly, little work tion within the group and appropriate reactions to has explored whether primates also attend to fairness challenges by other groups (Haidt & Joseph, 2007). considerations in third party cases, cases in which Some standard moral violations in the ingroup they themselves are not directly involved. domain would include breaking off contact with

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your family or changing citizenship (Graham & confl ict. In an extreme case, chimpanzee popu- Haidt, 2010). Although harm and fairness concepts lations are known to take part in outgroup raids, are considered important in all human cultures, the entering neighboring communities to hunt down moral signifi cance of ingroup concerns varies a bit and kill members of other groups. across cultures, often taking on more importance Only recently have researchers begun to explore among non-Western than Western people (see Haidt what primates actually know about their own social and Joseph, 2007). Nevertheless, as we review in the groups, and whether they represent ingroup and out- next section, all human cultures appear to represent group members in ways that are similar to humans. social groupings and favor ingroup members when Pokorny and de Waal (2009) examined whether interacting with others in their social world. capuchin monkeys could be trained to categorize members of ingroups and outgroups using a touch- Human Ingroup Loyalty screen task. T ey presented monkeys with an “odd- A long research tradition in social psychology has ball task” in which arrays of ingroup or outgroup focused on the ease with which humans form social monkey faces appeared on a touch screen. In this groups and act in ways that favor their own over other task, subjects must select the individual who is not a groups (see reviews in Fiske, 1998; Sidanius, 1993; member of the same group as the others. Capuchins Tajfel & Turner, 1979). Much of the early work in easily succeeded on this task, demonstrating that, this area observed that humans are naturally predis- with training, capuchins could learn to discriminate posed to see the world in terms of social groups, faces of ingroup and outgroup members. Mahajan spontaneously segregating themselves into groups et al. (2011) explored whether monkeys show a sim- based on the most minimal of grouping dimen- ilar level of discrimination in the absence of train- sions. In a classic experiment, Tajfel (1970) had par- ing. T ey presented free-ranging rhesus macaques ticipants indicate their liking for various paintings with faces of ingroup and outgroup members and and then told each participant that they belonged explored which faces captured the monkeys’ atten- to a group of people who, on average, preferred tion. T e monkeys spontaneously discriminated the paintings of Klee or of Kandinsky. When par- ingroup from outgroup faces, looking longer at ticipants subsequently played an economics game the outgroup member with increased vigilance. In in which they could maximize payoff s to members addition, the monkeys’ categorizations were likely of their own group at the expense of maximizing not driven merely by familiarity; Mahajan and col- payoff s to everyone, participants showed a clear leagues observed that monkeys showed more vigi- ingroup bias, selectively increasing the welfare of lance toward recent transfers out of the group (who their own group members. T is preference for one’s are very familiar yet still outgroup) than recent ingroup is a bias known to emerge relatively early in transfers into the group (who are relatively unfamil- human development. By only a few months of age, iar yet newly ingroup). T ese results demonstrate human infants have already developed preferences that monkeys spontaneously categorize conspecifi cs for individuals of their own race and native lan- as members of ingroups and outgroups, even in the guage (Bar-Haim, Ziv, Lamy & Hodes, 2006; Kelly absence of training. Moreover, these fi ndings sug- et al., 2005; Kinzler, Dupoux & Spelke, 2007). gest that macaques may naturally devote more vigi- lance toward outgroup than ingroup individuals. Nonhuman ingroup favoritism T e work just described suggests that some pri- Social groups also play an important part in the mates spontaneously recognize ingroup members, lives of many primates. Nearly all primates form but do primates have a preference for ingroup mem- social groups (Pusey et al., 1987). Primate groups bers, as would be consistent with some kinds of are typically based on kin lines, but most primate ingroup moral considerations? To explore this issue, groups also contain some unrelated individuals who Mahajan et al. (2011) developed a looking-time also engage with each other as part of long-term test of monkeys’ attitudes toward diff erent social social interactions. As in humans, primates often groups. T e logic of their attitude measure was simi- behave more nicely toward ingroup members than lar to that of the famous implicit association test toward outgroup individuals. Most primate groups (IAT), which is often used to assess category asso- are characterized by high levels of intergroup aggres- ciations in humans (Greenwald & Banaji, 1995; sion. For some species, such intergroup hostility can Greenwald, McGhee & Schwartz, 1998): subjects translate to harmful behaviors directed at outgroup should habituate more quickly to sets of images that members, such as physical aggression and vocal have consistent valence than to sets of images that

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have inconsistent valence. In this way, Mahajan and considerations in primates. First, there appear to colleagues could explore whether monkeys associ- be several important ways in which primate inter- ated ingroup members with positively valenced group cognition may diverge from that of humans. stimuli and outgroup members with negatively For humans, group identity, even when trivially valenced stimuli. T ey presented free-ranging determined, can be a critical part of self-construal. macaques with sequences of pictures that alternated Given the limitations on nonhuman self-perception between monkey faces (either ingroup or outgroup and identity formation, such elements would likely members) and positive/negative objects. When the be missing from any nonhuman ingroup cognition. picture sequences alternated between ingroup faces Second, human groups have several unique mecha- and positive images or outgroup faces and negative nisms for promoting group affi liation that primate images, monkeys habituated quickly. In contrast, groups lack, such as linguistic labels for diff erent when presented with inconsistent sequences of social groups. Finally, human ingroup concerns go ingroup faces and negative images or outgroup faces beyond personal preferences to act positively toward and positive images, monkeys failed to habituate, the ingroup—humans also evaluate others based on suggesting that these sets of images do not have the their own actions toward ingroup and outgroup same valence for monkeys. In this way, Mahajan et members. For example, third-party punishers are al.’s results suggest that monkeys naturally perceive much more aggressive toward norm violators that ingroup members positively and outgroup members harm an ingroup (rather than an outgroup) mem- negatively, suggesting that monkeys share a human- ber (Bernhard, Fischbacher & Fehr, 2006). Would like favoritism toward ingroup members and dislike nonhuman primates positively evaluate individuals toward outgroup members. who promote their ingroup and negatively evaluate Do primates’ diff erential attitudes toward ingroup those who violate ingroup solidarity? Again, answers and outgroup members translate into moral intu- to these questions will allow us to better understand itions about how these diff erent groups should the extent to which primates’ ingroup preferences be treated? Do primates have preferences toward actually map onto the kinds of moral concerns that selectively increasing the welfare of ingroup mem- humans experience when dealing with the domain bers? Do they negatively evaluate those who do not of ingroup allegiance. show favoritism toward the group? Little work has addressed these issues directly, but one hint comes Evolution of Authority/Respect Behaviors from a recent experimental economic study by de and Concerns Waal and colleagues (2008). Frans de Waal and col- Moral concerns in the fourth domain—the leagues presented capuchin monkeys with an exper- domain of authority—focus on negotiating the imental economic task in which proposers could hierarchy within one’s group, so that confl ict can donate food to other recipient monkeys. When the be avoided, by subordinates showing deference recipient was an ingroup member, capuchin mon- to superiors (Haidt & Joseph, 2007). T us, harm keys reliably chose to donate the prosocial option against political leaders or elder family members are (see Lakshminarayanan and Santos, 2005 for simi- in violation of the authority domain (Graham & lar results in this species). However, de Waal and Haidt, 2010). Whereas the ingroup domain focused colleagues observed a diff erent pattern of perfor- on favoritism toward one’s own group over others mance when the recipient was an outgroup monkey. (an attitude that would be important during, for When proposers had the option to deliver a piece example, intergroup confl ict), the hierarchy domain of food to a monkey from a diff erent group, their focuses on respecting the divisions within a group. performance fell to chance; proposers were indif- T ere is much evidence that primates attend to ferent to outgroup monkeys’ welfare. T ese results authority issues, at least in their natural behavior. provide an important hint that capuchins’ prosocial Many primate groups exhibit dominance hierar- motivations may be specifi c to ingroup members, chies, a stable hierarchical pattern of dominance that consistent with the view that an individual’s group dictates many aspects of an individual primate’s daily may aff ect the extent to which they are seen as part behaviors. High-ranking individuals enjoy a number of the moral circle. of privileges in primate groups—they often have fi rst T e preceding results are consistent with the idea access to food, mating, and grooming opportuni- that the human ingroup moral domain could be ties, as well as other valued resources (e.g., Saunders shared with other primates. Unfortunately, however, & Hausfater, 1988). In this way, primates’ natural there are still many questions regarding ingroup social behavior appears to follow authority-related

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constraints—lower-ranking primates tend to toe the primates obey authority norms, such as deferring to line, allowing preferential resource access to individ- the knowledge or skills of a high-ranking individual. uals who outrank them. One hint, however, comes from a study of primate T ere is also a growing body of research suggest- social preferences. Deaner and colleagues (Deaner, ing that primates carefully represent and attend to Khera, & Platt, 2005) presented macaque monkeys the order of individuals within their own hierarchy. with a choice between obtaining diff erent amounts Using an observational approach, Silk (1999) found of juice and the opportunity to look at diff erent that male bonnet macaques selectively recruited alli- images of other monkeys. Monkeys were willing to ance members that outranked not only themselves give up juice rewards to see images of high-ranking but also their opponent, suggesting that recruiting individuals, but had to be paid in juice to stare at macaques have some knowledge of their own and images of low-ranking monkeys. T is result suggests others’ relative positions in the hierarchy. Similarly, that monkeys value the opportunity to interact with Slocombe & Zuberbühler (2007) found that chim- high-ranking individuals, even when such interac- panzees produce more pronounced screams when tions involve merely observing images of individu- an individual of higher rank than their aggressor als in authority. Another hint comes from a recent is present than when only lower-ranked individu- study by Horner and colleagues (Horner, Proctor, als are present. Such decisions require third-party Bonnie, Whiten, & de Waal, 2010). In this study, knowledge of rank relationships between others, researchers allowed chimpanzees to socially learn rather than merely fi rst-party knowledge of one’s how to obtain food by placing tokens in one of two own rank relationship to others. To test this possi- containers. Observer chimpanzees saw two diff erent bility using an experimental approach, Cheney and demonstrators: a high-ranking individual who was colleagues (Cheney, Seyfarth, & Silk, 1995) exam- trained to use one container and a low-ranking indi- ined, using playback methods, whether baboons vidual trained to use the other. When later given the form expectations about an individual’s position chance to put tokens in the containers themselves, in the dominance hierarchy. T ey capitalized on a the observers were more likely to copy the high- natural feature of vocal communication between ranking individual than the low-ranking individual. dominant and subordinate female baboons: domi- T is result provides a hint that chimpanzees may nant female baboons tend to address subordi- selectively follow the behaviors of individuals in nate females with grunts, but subordinate females authority. Unfortunately, this result remains silent tend to respond with a diff erent vocalization, the regarding the moral implications of this behavior. fear bark. Cheney and colleagues recorded indi- Would, for example, chimpanzees punish others viduals making these vocalizations and then played who chose to copy the low-ranking individual? baboon subjects sequences that were either expected In summary, then, there are many hints that (dominant individual grunted to a subordinate) or primates are likely to have moral concerns relevant unexpected (dominant individual fear barked to a to the domain of authority, but little work has subordinate) based on the hierarchy. T ey observed addressed this possibility directly. Nevertheless, the that baboons responded more strongly to the unex- empirical stage is set for just such an investigation— pected rather than expected sequences, demonstrat- researchers now have methods in place to examine ing the female baboons represent the relative ranks who primates choose to interact with, how they of other members of their group. In another study, choose to distribute rewards, and so on. We predict Kitchen, Cheney, and Seyfarth (2005) found that that using these techniques to examine primates’ male baboons responded more strongly to playbacks intuitions in the authority domain will be fruit- that simulated vocal contests between individuals ful. Indeed, the available literature suggests that the ranked far apart as opposed to close to each other in domain of hierarchy concerns is likely to be one in the group hierarchy, suggesting that they recognized which primates may show strong moral concerns. which individuals should and should not be engag- ing in dominance contests. Taken together, this work Evolution of Purity/Sanctity Behaviors and suggested that primates may represent the order of Concerns other individuals in their hierarchy and expect such Behaviors in the fi fth and fi nal domain, the individuals to interact in prescribed ways. purity domain, focus on avoiding contaminants. Although there is much evidence to suggest that T e original targets of such behaviors were avoid- primates recognize the rank ordering of individu- ing ingestion of physical contaminants, but the als in their group, there is less direct evidence that emotional reaction associated with violations in this

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domain—our disgust reaction—has since expanded impure actions, such as eating contaminated food? to include more symbolic contaminants, such as T e answers to these questions would seem to be contact with unsavory individuals or behavioral no, but little empirical work has directly addressed practices (Haidt & Joseph, 2007). T us, surgically this issue. adding a tail or getting blood from a child molester Before ending our review of work in the purity elicit disgust and also constitute violations of our domain, it’s worth noting that the absence of disgust purity norms (Graham & Haidt, 2010). in primates may have broader implications for the Rozin, Haidt, and Fincher (2009) hypothesized evolution of moral cognition. In humans, the moral that natural selection may have shaped our origi- emotion of disgust can be leveraged to strengthen nal purity response—which at fi rst was specifi c to moral reactions that extend far beyond purity and physical contamination—in ways that allowed it into other domains. A growing body of work in to incorporate symbolic purity violations. Rozin human moral cognition has led to the view that elic- and colleagues propose that the original physiolog- iting disgust can be used to strengthen people’s reac- ical distaste reaction was initially elicited directly tions to other non-purity-based moral violations. For by certain tastes (e.g., bitterness) that indicated example, Moretti and di Pellegrino (2010) found food that should be avoided. Once such a distaste that experimentally induced disgust increased rejec- reaction existed, it could be harnessed by a later- tions of unfair off ers during an ultimatum game. developing disgust-evaluation system that could Importantly, the negative emotion of sadness did be used to evaluate more cognitively elaborated not have this eff ect. T us, disgust (and not just inputs (e.g., to avoid even putting certain types negative emotion) seems to increase disadvanta- of food in the mouth). Finally, they argue that geous inequity aversion—a fairness-based moral the system may have been further leveraged by consideration. T is result is mirrored by studies a later-developing moral-evaluation system, one that show disgust-related physiological reactions to that required other contaminating actions or peo- unfairness, specifi cally activation of similar muscles ple (especially those that remind us of our animal in the face (Chapman, Kim, Susskind, & Anderson, nature) to be avoided. 2009). If disgust serves to increase reactions across Primates, like many nonhuman animals, have all fi ve domains of morality, then the lack of dis- the physiological distaste response that Rozin and gust in nonhumans may partially account for many colleagues hypothesize led to more complex purity of the species diff erences in moral behaviors in the norms. More impressively, many animals have the other four domains as well. ability to learn distaste for novel foods. Garcia, Hankins, and Rusiniak (1974) report on a wide Conclusions range of experiments on learned food aversion that In this chapter, we have explored the evolution include multiple species and methods for causing ill- of moral concerns in fi ve domains, focusing on ness, including the famous example of rats avoiding the extent to which these concerns are present in foods they were introduced to shortly before being primates. Clear evidence exists for primate harm induced to feel nausea from radiation. T is distaste concerns, though harm concerns do not show up reaction does not, however, seem to be elaborated as consistently in primates as they do in humans. into a disgust reaction. Indeed, Rozin and colleagues T e evidence for primate fairness concerns is less have proposed that distaste is shared across animals, conclusive, though we argue in favor of some degree but true disgust may be unique to humans. of fairness concerns, perhaps based on a more gen- Given that disgust reactions may be unique to eral frustration response. T ere is far less evidence humans, it is reasonable to assume that moral con- regarding primates’ concerns in the moral domains siderations in the purity domain may also be limited of ingroup or authority, though many primates to humans. T is leads to the prediction that pri- behave in ways that appear to be consistent with mates should not show moral considerations related such concerns. Finally, we believe there is little rea- to issues of purity. To our knowledge, little work son to suspect that primates will engage in moral has explored this issue directly. Would primates, like evaluations similar to those of human in the purity humans, prefer not to interact with stimuli previ- domain. ously associated with a low-ranking individual, or T us, there are a few clear conclusions from our something associated with a conspecifi c who has review regarding primate moral cognition. First, committed an immoral act? Do they, like humans, some of our moral concerns (e.g., against harm) are negatively evaluate individuals who engage in present, to some degree, in primates. Second, many

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of the cognitions that underlie our moral concerns out because of the violation. To better understand (e.g., preference for our ingroup) are also present in the nature of primates’ considerations, researchers primates. Similar to the state of morality research with would profi t from exploring cases of advantageous humans, there is a critical lack of primate research in norm violations, when the violation benefi ts the the moral domains of ingroup and hierarchy. T ird, subject, and cases of third-party violations, when the there appear to be several features of human cogni- subject is not involved. It is possible that primates tion that allow our species to reason about moral lack moral concerns in cases in which they them- considerations in ways that are not shared with other selves are not negatively aff ected. On the other hand, species. We have already discussed the role of an it could be that researchers simply do not yet have elaborated disgust response, but other obvious can- evidence of such unselfi sh considerations. didates are human language and the cognitive abili- Another current weakness in the literature on pri- ties it entails (Spelke, 2003; Tse, 2008) and human mate moral considerations stems from the dispro- culture and learning within cultures (Chater, Vlaev portionate focus on certain domains. As reviewed & Grinberg, 2008; Henrich et al., 2010). Without here, nearly all the work on primate moral cognition disgust, language, and culture, primates may lack the to date has focused on harm and fairness violations. capacity to introduce novel moral norms via the pro- Such a biased focus makes some sense, given that the cess of moralization (Rozin, 1999). same bias appears to have played out in research on T e goal of this chapter was to provide a current human moral cognition, where most work has also snapshot of what is known in the area of primate focused on harm and fairness domains (see Haidt moral cognition using a framework based on human & Joseph, 2007). However, in the case of primates, moral cognition work. Although our review revealed the bias toward studying only the harm and fairness numerous open questions and areas in need of empir- domains winds up being especially unfortunate, ical work, it also reviewed a variety of new methodical because primates’ natural behavior suggests they techniques that can readily be applied to address these may have well-formulated norms in the domains open issues. T us, we look forward to the upcoming of ingroup and authority. Future work, therefore, years of empirical work in this area. Such new work should focus far more on these domains, exploring will provide further insight into the nature of pri- whether primates do, in fact, make moral evalua- mates’ moral considerations and new hints into the tions when they see violations in these areas. evolutionary origins of our own moral capacities. Endnotes . Incidentally, work on human moral cognition has also dis- Future Directions proportionately focused on the harm and fairness domains (see T roughout the chapter, we focused on two kinds Haidt & Joseph, 2007). of evidence for primate moral considerations—fi rst, . T e Dictator game can also be thought of as a measure of fairness considerations, specifi cally as a test of how and when whether primates themselves behaved in ways that participants decide to give others a fair split. However, given that obeyed diff erent moral norms, and second, whether this test has mostly been discussed in terms of prosocial prefer- they evaluated others who failed to obey these ences in the primate fi eld, we’ve presented this work as part of the norms. To date, researchers have mostly focused on harm domain (i.e., as a measure of how and when primates are the former kind of evidence. In the harm domain, willing to increases others’ welfare). for example, researchers have devoted considerable References eff ort to examining whether primates act in ways Bar-Haim, Y., Ziv, T., Lamy, D., & Hodes, R. M. (2006). Nature that increase others’ welfare, but little work has and nurture in own-race face processing. Psychological Science: investigated how primates feel about other individu- A Journal of the American Psychological Society / APS, 17, als when they violate these norms. Turning to the 159–163. question of primates’ evaluations in this domain Barnes, J. L., Hill, T., Langer, M., Martinez, M., & Santos, L. R. (2008). Helping behaviour and regard for others in capuchin may provide some insight into the confusing pattern monkeys (cebus apella). Biology Letters, 4, 638–640. of fi ndings regarding how diff erent primate species Bernhard, H., Fischbacher, U., & Fehr, E. (2006). Parochial evaluate the welfare of others. In the domain of fair- altruism in humans. Nature, 442, 912–915. ness, some work has begun to explore how primates Bräuer, J., Call, J., & Tomasello, M. (2006). Are apes really react to others when they violate fairness norms inequity averse? Proceedings of the Royal Society of London, Biology, 273, 3123–3128. (e.g., Brosnan and de Waal, 2003), but nearly all of Brosnan, S. F. (2006). Nonhuman species’ reactions to inequity this work to date has focused on cases of disadvan- and their implications for fairness. Social Justice Research, 19, tageous norm violation, in which the subject loses 153–185.

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