Supplementary material from "The perception of prosocial agents by chimpanzees and humans "

The human propensity for prosocial behaviour has no equal, not even in our closest living relatives, the chimpanzees. However, it remains unclear whether this difference is grounded in the sheer perception and cognitive evaluation of prosociality. We investigated how two hominid species, chimpanzees and humans, perceive third-party social interactions with prosocial, neutral and antisocial agents. Using a touchscreen paradigm, human and chimpanzee participants freely selected between two actors after viewing their interactions, ranging from pro- to antisocial. Contrary to current thinking, we found no evidence for species differences in their choices for agents, regardless of whether interactions were between conspecifics or not. Both humans and chimpanzees demonstrated comparable sensitivity to prosociality, challenging existing views of a profound chimpanzee-human difference in prosociality. Instead, our results indicate that the perception of social interactions is similar across hominids, but that humans have evolutionarily diverged in how they act upon such perceptions.