Movie S2. Experiment 2 Video Abstract from Bonobos voluntarily hand food to others but not toys or tools

A key feature of human prosociality is <i>direct transfers</i>, the most active form of sharing in which donors voluntarily hand over resources <i>in their possession</i>. Direct transfers buffer hunter-gatherers against foraging shortfalls. The emergence and elaboration of this behaviour thus likely played a key role in human evolution, by promoting cooperative interdependence and ensuring that humans' growing energetic needs (e.g. for increasing brain size) were more reliably met. According to the <i>strong prosociality hypothesis</i>, among great apes only humans exhibit sufficiently strong prosocial motivations to directly transfer food. The <i>versatile prosociality hypothesis</i> suggests instead that while other apes may make transfers in constrained settings, only humans share flexibly across food and non-food contexts. In controlled experiments, chimpanzees typically transfer objects but not food, supporting both hypotheses. Here we show in two experiments that bonobos directly transfer food but not non-food items. These findings show that, in some contexts, bonobos exhibit a human-like motivation for direct food transfer. However, humans share across a far wider range of contexts, lending support to the versatile prosociality hypothesis. Our species' unusual prosocial flexibility is likely built on a prosocial foundation we share through common descent with the other apes.