We are also interested in the evolution of prosocial behavior in human and nonhuman primates. We are investigating how young children and nonhuman primates behave when they have an opportunity to assist another individual, and how their behavior changes when opportunities to help themselves by being prosocial, such as the potential for reciprocity, are included. This research has added to a growing body of information indicating that nonhuman primates excel at both cooperation and reciprocity, but in many cases appear to be motivated by self-oriented rather than other-oriented concerns.
We have demonstrated that chimpanzees are indifferent toward rewarding conspecifics, even at no real cost to themselves. Moreover, this is not the result of a focus on their own outcomes, as the pattern persists even when they can reward themselves first, followed by their partner. Finally, the introduction of reciprocity did not change their behavior; they continued to show no prosocial preference. However, in an inequity study in which partners received high value rewards, grapes, that were sometimes the same as what their partner received and other times were a better reward than their partner's, subjects were more likely to refuse when their grape was a superior reward to their partner's. This indicates that they at least notice when their partner receives a less good reward, although it does not address their underlying motivations. More recent evidence indicates that capuchin monkeys are prosocial in similar tasks, indicating a need to examine this in more detail. We are currently investigating prosocial paradigms in capuchins in an effort to determine which factors play a role in their decisions.