Do chimpanzees reciprocate received favours?

Reciprocal interactions observed in animals may persist because individuals keep careful account of services exchanged with each group member. To test whether chimpanzees, Pan troglodytes, possess the cognitive skills required for this type of contingency-based reciprocity, we gave chimpanzees the choice of cooperating with a conspecific who had helped them previously or one who had not helped them in two different experimental tasks. In the first experiment, one of the partners preferentially recruited the subjects to cooperate in a mutualistic task, while the other potential partner never chose to cooperate with the subject, but rather chose a different partner. In the second experiment, one of the partners altruistically helped the subjects to reach food, while the other partner never helped the subject, but rather took the food himself. In both experiments there was some evidence that the chimpanzees increased the amount they cooperated with or helped the partner who had been more helpful towards them compared to their baseline behaviour towards the same individual ( or in a control condition). However, in both experiments this effect was relatively weak and subjects did not preferentially favour the individual who had favoured them over the one who had not in either experiment. Although taken together, these experiments provide some support for the hypothesis that chimpanzees are capable of contingent reciprocity, they also suggest that models of immediate reciprocation and detailed accounts of recent exchanges ( e. g. Tit for Tat) may not play a large role in guiding the social decisions of chimpanzees. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.