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11 Justice- and Fairness-Related Behaviors in Nonhuman Primates--Sarah F. Brosnan
Pages 191-210

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From page 191...
... One way to address this is comparatively, exploring behaviors related to justice and fairness in other species. In this chapter, I review work exploring responses to inequity, prosocial behavior, and other relevant behaviors in nonhuman primates in an effort to under stand both the potential evolutionary function of these behaviors and the social and ecological reasons for the individual differences in behavior.
From page 192...
... Most experimental studies involving nonhuman species measure subjects' responses to different distributions of food rewards and, hence, concern distributive justice or fairness. In humans, two common distribution mechanisms are egalitarianism, in which all individuals get the same outcome (e.g., equality)
From page 193...
... This comparative approach is informative in two complementary ways, through homology and convergence. Homologies occur when a behavior exists in multiple species because the behavior existed in a shared common ancestor.
From page 194...
... The first is to adapt game theory methods to explore decision making in other species. Game theory is a powerful approach that allows complex decision making to be modeled experimentally as a series of carefully controlled choices, which can be experimentally manipulated to rigorously explore the behavior of interest (Smith, 1987)
From page 195...
... USING GAME THEORY TO EXPLORE JUSTICE-RELATED BEHAVIOR The Ultimatum Game In 1982, Werner Guth presented the Ultimatum Game (UG) , designed to explore fairness in bargaining behavior in humans (Guth et al., 1982)
From page 196...
... , indicating that they may not have understood the task. A subsequent study showed that human responders rarely refused in a similar situation, possibly because of the difficulty of inhibitory responses
From page 197...
... . The procedure was repeated using children paired with another familiar individual from their daycare class to ensure that humans would respond similarly to chimpanzees in this procedure.
From page 198...
... or gives one a more preferred reward (Inequity condition)
From page 199...
... were more likely to refuse to complete the interaction (e.g., return the token or accept the subsequent food reward) in the Inequity condition compared with either the Equity condition or the Contrast condition, although there was variation within and between studies [discussed below in more detail (Brosnan et al., 2005; Bräuer et al., 2009; Silberberg et al., 2009)
From page 200...
... Exchange Other Task No Task Effort? Social Context?
From page 201...
... Macaque Yes Yes (Hopper Yes (Massen -- Yes (Massen Rank (Massen et et al., 2013)
From page 202...
... The orangutan's behavior also rules out the possibility that this is related to increased brain size or advanced cognitive capabilities, because orangutans have a brain-to-body ratio and cognitive skills similar to the other great apes. Thus far, negative response to inequity correlates positively with whether a species cooperates routinely with nonkin [reviewed in Brosnan (2011)
From page 203...
... The photos representing species that show a negative response to inequity in this task are outlined in green, and those that do not are outlined in red. The names of species that show extensive social cooperation, such as coalitions and alliances, are in green, those that do not are in red, and interdependent species (e.g., those that show biparental care)
From page 204...
... Results in the inequity studies described above imply that chimpanzees may recognize when they receive a better outcome than a partner even when they chose not to act to change the situation. In one study, subjects sometimes refused preferred rewards when their partners got less-preferred ones and did so at greater rates than when both received preferred rewards (Brosnan et al., 2010b)
From page 205...
... . Finally, long-tailed macaques also showed prosocial behavior, but in this study, dominants chose the prosocial option, whereas subordinates did not (Massen et al., 2010)
From page 206...
... A recent study explored which of two novel experimenters the monkeys preferred to interact with in a task in which the monkey returned a token to an experimenter to get a food reward. Subjects first gained experience with both experimenters, one of whom consistently provided the offered rewards and one of whom failed to provide the offered reward (or any reward)
From page 207...
... Moreover, observational work yields correlations, which cannot tell us causation without controlled studies that alter one variable at a time. Nonetheless, these situations may be the best window we have into primates' sense of fairness and justice because they are natural interactions, unconstrained by interactions with humans or experimental contingencies.
From page 208...
... Again, for practical experimental reasons, much work focuses on inequity of food rewards, but attention to inequity may have evolved in the social realm and only more recently adapted to physical outcomes, such as food. Future work will help to determine how responses to inequity vary depending upon the commodity in question.
From page 209...
... All of the studies described above focus on behavioral responses to differing outcomes, but subjects may notice an inequitable situation that they do not respond to, for instance, because they are unable to inhibit their desire for the reward, because of social pressure, or for other reasons not yet known. One way to address this question is to explore changes in individuals' affect across different conditions to identify responses that occur in the absence of an overt behavioral change.
From page 210...
... All of the experimental work to date has involved an egocentric approach to fairness and justice, yet observational studies of natural behavior indicate that primates will intervene in the interactions of others, in some cases impartially. Although challenging, it is possible to study fairness in the laboratory removed from egocentric reactions.


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