Post-conflict third-party affiliation in chimpanzees: what's in it for the third party?

Abstract

Affiliative behavior after conflicts between conflict participants and other group members is common in many primate species. The proposed functions for such triadic interactions are numerous, mostly concerning the benefit for the former conflict opponents. We investigated post-conflict third-party affiliation (TPA) in captive chimpanzees (Pan troglodytes) with the aim of assessing what the affiliating third parties may gain from affiliation. Specifically, we tested whether third-party-initiated affiliation protects the third parties from further aggression by conflict opponents. We found support for this "self-protection hypothesis," in that third parties selectively directed affiliation to those opponents who more often gave further aggression to them, and affiliation effectively decreased their chance of receiving aggression from these opponents. However, a subset of affiliation, provided to conflict victims by their own kin, appeared to not be self-protective and the function of it remained open. We conclude that chimpanzee third-party-initiated affiliation is a more heterogeneous behavior than thus far assumed.