Self-interest precludes prosocial juice provisioning in a free choice group experiment in bonobos.

Previous studies on prosociality in bonobos have reported contrasting results, which might partly be explained by differences in experimental contexts. In this study, we implement a free choice group experiment in which bonobos can provide fruit juice to their group members at a low cost for themselves. Four out of five bonobos passed a training phase and understood the setup and provisioned fruit juice in a total of 17 dyads. We show that even in this egalitarian group with a shallow hierarchy, the majority of pushing was done by the alpha female, who monopolized the setup and provided most juice to two adult females, her closest social partners. Nonetheless, the bonobos in this study pushed less frequently than the chimpanzees in the original juice-paradigm study, suggesting that bonobos might be less likely than chimpanzees to provide benefits to group members. Moreover, in half of the pushing acts, subjects obtained juice for themselves, suggesting that juice provisioning was partly driven by self-regarding behavior. Our study indicates that a more nuanced view on the prosocial food provisioning nature of bonobos is warranted but based on this case study, we suggest that the observed sex differences in providing food to friends corresponds with the socio-ecological sex difference in cooperative interactions in wild and zoo-housed bonobos.