Prosociality in a despotic society

Humans possess remarkable prosocial tendencies beyond the confinement of kinship, which may be instrumental in promoting cooperative interactions and sociality at large. Yet, prosociality is an evolutionary conundrum as it does not provide immediate benefits to the actor. The ‘domestication’ and ‘cooperative-breeding’ hypotheses postulated that enhanced social tolerance and inter-individual dependence could nonetheless facilitate the evolution of prosociality. However, inconsistent results due to varying experimental paradigms, and restricted focus of research on tolerant and cooperatively breeding species, have impeded our understanding so far. Albeit counterintuitively, despotic societies with relatively low social tolerance levels represent an excellent opportunity to investigate prosociality due to their kin favoritism and potential interdependence among individuals in terms of social support. Japanese macaques ( Macaca fuscata ) live in strictly hierarchical matrilineal societies, where kin members have strong social bonds. Additionally, support from non-kins can be crucial to form coalitions and rank up in the hierarchy. Using a group-service paradigm, we tested prosociality in a semi-free-ranging group of Japanese macaques. In contrast to currently existing evidence, we found that individuals (n=25) can act prosocially and at comparably high rates as cooperative breeding- or self-domesticated species. The macaques benefitted not only their kin members but other individuals to whom they showed relatively high social tolerance. We emphasize the roles of complex socio-ecological conditions in facilitating individual prosocial tendencies. Furthermore, these results call for a novel evolutionary framework regarding prosociality that focuses on different forms of interdependence and expands beyond cooperative breeding- and (self-)domesticated species. Significance statement What made humans so incredibly prosocial? Examining the evolutionary trajectory of prosocial acts led comparative psychologists to explore various taxa. Empirical evidence so far suggests that enhanced social tolerance and interdependence among individuals facilitate prosociality. Conventionally, despotism is characterized by low group-level tolerance, yet kin favoritism, nepotism, and high interdependence (in support and coalition formation) are also fundamental properties of despotic societies. Under such complex socio-ecological conditions, individual prosocial acts could thus be vital. We found, for the first time, high levels of prosociality in the very despotic Japanese macaques. Individuals benefitted both kin-relatives and others to whom they showed relatively high dyadic social tolerance. This study signifies that prosociality can be favored even in a highly despotic society.