Chimpanzees act cooperatively in the wild, but whether they afford benefits to others, and whether their tendency to act prosocially varies across communities, is unclear. Here, we show that chimpanzees from neighboring communities provide valuable resources to group members at personal cost, and that the magnitude of their prosocial behavior is group specific. Provided with a resource-donation experiment allowing free (partner) choice, we observed an increase in prosocial acts across the study period in most of the chimpanzees. When group members could profit (test condition), chimpanzees provided resources more frequently and for longer durations than when their acts produced inaccessible resources (control condition). Strikingly, chimpanzees’ prosocial behavior was group specific, with more socially tolerant groups acting more prosocially. We conclude that chimpanzees may purposely behave prosocially toward group members, and that the notion of group-specific sociality in nonhuman animals should crucially inform discussions on the evolution of prosocial behavior.
Humans regularly confer benefits on others, even at a cost to themselves (1, 2). The extent to which humans act prosocially has been suggested to be at the root of humans’ unique social abilities, arguably unparalleled in the animal kingdom (2–5). In an attempt to explore the evolutionary trajectory of this prosocial behavior, chimpanzees, as one of humans’ closest living relatives, have been studied extensively in prosocial paradigms, both in the wild and under controlled settings in captivity. To date, however, the evidence concerning chimpanzee prosociality remains equivocal.
Prosocial behavior has been defined as “any behavior voluntarily performed by one individual to benefit another” (6–8). On the one hand, evidence exists that wild chimpanzees spontaneously engage in prosocial behavior, for instance, in the form of food sharing, third-party consolation after fights, and infant adoption (9, 10). These observations have been corroborated by experimental paradigms in which chimpanzees readily helped experimenters obtain an out-of-reach object (11) and transferred useful objects to conspecifics without receiving anything in return (12, 13), although the extent to which instrumental helping in apes can be deemed “prosocial” is currently a hot topic of debate [see (14–16)]. On the other hand, evidence from so-called prosocial choice tests [see (8)] has culminated in the conclusion that “chimpanzees are indifferent to the welfare of others” (17). In these studies, in the experimental condition, one individual of a preselected dyad is presented with a choice between delivering a preferred food item only to themselves and to themselves and their partner, in contrast to a control condition, in which the surplus food item would be delivered to…