Chimpanzees do not take advantage of very low cost opportunities to deliver food to unrelated group members

Abstract

We conducted experiments on two populations of chimpanzees, Pan troglodytes, to determine whether they would take advantage of opportunities to provide food rewards to familiar group members at little cost to themselves. In both of the experiments described here, chimpanzees were able to deliver identical rewards to themselves and to other members of their social groups. We compared the chimpanzees' behaviour when they were paired with another chimpanzee and when they were alone. If chimpanzees are motivated to provide benefits to others, they are expected to consistently deliver rewards to others and to distinguish between the partner-present and partnerabsent conditions. Results from both experiments indicate that our subjects were largely indifferent to the benefits they could provide to others. They were less likely to provide rewards to potential recipients as the experiment progressed, and all but one of the 18 subjects were as likely to deliver rewards to an empty enclosure as to an enclosure housing another chimpanzee. These results, in conjunction with similar results obtained in previous experiments, suggest that chimpanzees are not motivated by prosocial sentiments to provide food rewards to other group members. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptHumans participate in a range of activities that benefit others. These behaviours range from simple acts of courtesy (holding the door for shoppers laden with packages) to modest forms of charity (sending money to victims of hurricane Katrina) and extraordinary feats of heroism (firefighters taking great risks to rescue victims of the 9/11 bombings). These activities are all prosocial because they benefit others, and some are altruistic because donors incur costs and receive no direct benefit themselves when they provide benefits to others. In many cases, the actors are unknown to the beneficiaries, thus eliminating the possibility of future reciprocity. In this paper, we consider whether chimpanzees take advantage of very low cost opportunities to behave prosocially towards conspecifics.In an effort to gain insight about the origin and evolution of other-regarding preferences in humans, we conducted a series of experiments on chimpanzees. We focus on chimpanzees for a number of reasons. First, chimpanzees are our closest living relatives (Glazko & Nei 2003). The absence of other-regarding preferences in chimpanzees would suggest that these preferences (and possibly reputational concerns) are derived properties of humans that evolved after Homo and Pan diverged. Conversely, the presence of other-regarding preferences in chimpanzees would indicate that the foundation for prosocial behaviour existed before the human and ape lineages diverged and was elaborated within the human lineage.Second, chimpanzees may share some of the cognitive capacities and moral sentiments that underlie prosocial behaviour in humans. Chimpanzees sometimes console victims of aggression (de Waal & van Roosmalen 1979), which...

Chimpanzees return favors at a personal cost

“…The findings of the current study demonstrate experimentally that under some circumstances chimpanzees are also motivated to deliver benefits to conspecifics. In the absence of any prior interaction (NA conditions), chimpanzee subjects' behavior was consistent with previous studies finding no prosociality in chimpanzees in similar prosocial choice paradigms (32)(33)(34). Indeed, when choosing the prosocial option was materially costly, subjects' prosocial choices in the NA condition were close to zero (Fig.…”

“…Furthermore, several studies have shown that when presented with one option delivering food to both themselves and a conspecific and another option only delivering food to themselves, chimpanzees choose completely randomly between these alternatives, which has been interpreted as suggesting that chimpanzees are indifferent to the welfare of conspecifics even when being prosocial is entirely noncostly (32)(33)(34). Although some studies show somewhat more mixed (but not easily interpretable) results concerning cost-free prosocial choices in chimpanzees (35,36), the picture is very clear when it comes to materially costly prosociality: to date there is no reliable experimental evidence that chimpanzees are willing to deliver resources to conspecifics when doing so entails a cost for themselves.…”

Evolutionary foundations of human prosocial sentiments

“…However, analyses of recipients' begging gestures in two experiments cast doubt on this possibility (60). Recipients that made begging gestures consistently directed them to the option that contained food for themselves, but begging had no consistent impact on proposers' responses.…”

“…However, when Jensen et al (58) tested chimpanzees with a payoff distribution that did not provide any rewards for the actor, they found that overall response rates dropped substantially, and proposers still did not distinguish between the test and nonsocial control conditions. In the experiments conducted by Vonk et al (60), proposers could deliver food rewards to themselves and others with separate actions. Proposers almost always obtained their own rewards first.…”

“…The chimpanzees were as likely to choose the 1/1 option in the test condition as in the nonsocial control condition. Vonk et al (60) conducted two experiments in which actors could deliver food rewards to themselves and others with independent but identical actions. In both of these studies, the actors were as likely to deliver rewards in the nonsocial control condition as in the social test condition.…”