Consolation as possible expression of sympathetic concern among chimpanzees.

Chimpanzees are known to spontaneously provide contact comfort to recent victims of aggression, a behavior known as consolation. Similar behavior in human children is attributed to empathic or sympathetic concern. In line with this empathy hypothesis, chimpanzee consolation has been shown to reduce the recipient's state of arousal, hence to likely alleviate distress. Other predictions from the empathy hypothesis have rarely been tested, however, owing to small sample sizes in previous studies. An exceptionally large database of spontaneous consolation in two outdoor-housed groups of chimpanzees lends further support to the empathy hypothesis in that consolation occurred disproportionally between individuals that are socially close (i.e., kin and affiliation partners) and was more typical of females than males, which differences are also known of human empathy. These effects were demonstrated using generalized linear mixed models, which control multiple variables at once. An exception to the above pattern was formed by the highest-ranking males, which frequently offered consolation to victims of aggression, probably as part of their general policing function in chimpanzee society. Consolation occurred more frequently in the absence of reconciliation between former opponents, suggesting that actors are sensitive to the contact need of victims of aggression, which may be greater if the aggressor ignores them. That consolation is an integrated part of close mutual relationships is supported by the tendency for it being reciprocated.