Friendship, reciprocation, and interchange in an individual-based model

Reciprocation and interchange of grooming and support may emerge as a consequence of the socio-spatial structure of the group through which individuals interact with certain partners more frequently than with others. This is shown in a computational model of grouping, fighting, and grooming, called Groofiworld. In this case, no specific mechanism of exchange is needed, such as described in calculated reciprocity or emotional bookkeeping. One of the drawbacks of this model, GroofiWorld, however, is that it lacks social bonding, a factor that may play an important role in real societies of primates. To investigate the effect of social bonding on exchange relations, in the present study, we add 'social bonding' to the model 'GrooFiWorld.' In the new model, called 'FriendsWorld,' social bonds or 'friends' are defined as the top 25 % grooming partners and individuals are given a tendency to follow their friends. Note that they do not intend to reciprocate or interchange social services with friends. Results show that this mechanism of 'follow-your-friends,' not only increases social interactions among top grooming partners, but also strengthens the patterns of reciprocation and interchange. Our findings suggest that, in real primates, reciprocation and interchange may emerge as a side-effect of the social-spatial structure of the group and subsequently be strengthened by social bonding as represented in FriendsWorld. We give predictions that distinguish between the mechanism of 'follow-your-friends' and emotional bookkeeping.