Mechanisms influencing friendship in chimpanzees (Pan troglodytes): Kinship, familiarity or personality trait similarity?

Abstract

Traditionally the term ‘friendship’ in chimpanzee (Pan troglodytes) research has been avoided. Yet descriptions of close affiliative bonds similar to those described in human friendships have been well documented. The present study aimed to prove the existence of chimpanzee friendship, by considering whether there are similar mechanisms to those which have been implicated in the formation of human friendships, kinship and the residual effects of two kin recognition mechanisms; familiarity and phenotype matching. Eleven chimpanzees (6 males and 5 females) from Edinburgh Zoo were studied to investigate the influence of kinship, proximity and personality trait similarity on duration and number of affiliative behaviours. Results indicated that kinship between mother and offspring, and measures of proximity within arm’s length, were good indicators of time spent in affiliative interactions. Personality trait similarity had no effect on affiliative interactions. We concluded that chimpanzees show friendships, and similar kinship and kin recognition mechanisms operate in their formation and maintenance as those in human friendships. The existence of friendship in chimpanzee societies provides an insight into chimpanzee social complexity, that previous research may have overlooked.