Chimpanzee (Pan troglodytes) consolation: third-party identity as a window on possible function

Consolation, that is, postconflict affiliative contact by a bystander toward a recipient of aggression, has acquired an important role in the debate about empathy in great apes because it has been proposed that the reassuring behavior aimed at distressed parties reflects empathetic arousal. However, the function of this behavior is not fully understood. The present study tests specific predictions about the identity of bystanders on the basis of a database of 1102 agonistic interactions and their corresponding postconflict periods in two outdoor-housed groups of captive chimpanzees (Pan troglodytes). We found that recipients of aggression were more likely to be contacted by their own "friends" than by "friends" of the aggressor and that frequent targets of aggression were not more likely to offer consolation than were nontargets of aggression. These findings support the stress reduction hypothesis rather than two proposed alternatives, that is, the opponent relationship repair hypothesis and the self-protection hypothesis. Our results provide further support for relationship quality as a fundamental underlying factor explaining variation in the occurrence of consolation.