Social networks and social complexity in female-bonded primates

Most primates are intensely social and spend a large amount of time servicing social relationships. The social brain hypothesis suggests that the evolution of the primate brain has been driven by the necessity of dealing with increased social complexity. In this study, we use social network analysis to analyse the relationship between primate group size, neocortex ratio and several social network metrics. We found that in female Old World monkey grooming networks, neocortex ratio is negatively correlated with clan size and with proportional clan membership when group size effects are controlled for. This indicates that - contrary to expectation - females of species with large neocortices generally belong to only a few, small grooming cliques despite living in closely bonded groups. The finding suggests that social complexity may derive from managing indirect social relationships, i.e. relationships in which a female is not directly involved, which may pose high cognitive demands on primates. We suggest that a large neocortex allows individuals to form intense social bonds with some group members while at the same time enabling them to manage and monitor less intense indirect relationships without frequent direct involvement with each individual of the social group. © The British Academy 2010.