Chimpanzees are indifferent to the welfare of unrelated group members

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Abstract
Humans are an unusually prosocial species—we vote, give blood, recycle, give tithes and punish violators of social norms. Experimental evidence indicates that people willingly incur costs to help strangers in anonymous one-shot interactions1,2, and that altruistic behaviour is motivated, at least in part, by empathy and concern for the welfare of others (hereafter referred to as other-regarding preferences)1,2,3. In contrast, cooperative behaviour in non-human primates is mainly limited to kin and reciprocating partners, and is virtually never extended to unfamiliar individuals4. Here we present experimental tests of the existence of other-regarding preferences in non-human primates, and show that chimpanzees (Pan troglodytes) do not take advantage of opportunities to deliver benefits to familiar individuals at no material cost to themselves, suggesting that chimpanzee behaviour is not motivated by other-regarding preferences. Chimpanzees are among the primates most likely to demonstrate prosocial behaviours. They participate in a variety of collective activities, including territorial patrols, coalitionary aggression, cooperative hunting, food sharing and joint mate guarding5,6,7,8,9,10,11,12. Consolation of victims of aggression13 and anecdotal accounts of solicitous treatment of injured individuals suggest that chimpanzees may feel empathy14,15. Chimpanzees sometimes reject exchanges in which they receive less valuable rewards than others, which may be one element of a ‘sense of fairness’, but there is no evidence that they are averse to interactions in which they benefit more than others16,17,18.