Helping in young children and chimpanzees shows partiality towards friends

Friendship naturally leads to treating some people differently from the way we treat everyone else. One manifestation of such preferential treatment is in the domain of prosociality: we are more likely to extend favors towards our friends. Little is known about the developmental and evolutionary roots of such preferential prosociality. Here, we investigate whether young children and chimpanzees show partiality towards friends in helping contexts. Results show that young children at the age of three - when they first form preferential peer relationships - already bias their helping decisions in favor of their friends, both when they have to make a choice whether to help a friend or a neutral peer (Study 1) and when measuring their overall motivation to help (Study 2). In Study 3, by combining observational and experimental methods, we demonstrate similar though less robust motivations to provide help preferentially to friends in our closest living relatives, chimpanzees. Taken together, these studies suggest that partiality towards friends is grounded early in ontogeny and human evolution.