Video 2 - Eye tracking fragment of Study 1 from Visually attending to a video together facilitates great ape social closeness

Humans create social closeness with one another through a variety of shared social activities in which they align their emotions or mental states towards an external stimulus such as dancing to music together, playing board games together or even engaging in minimal shared experiences such as watching a movie together. Although these specific behaviours would seem to be uniquely human, it is unclear whether the underlying psychology is unique to the species, or if other species might possess some form of this psychological mechanism as well. Here we show that great apes who have visually attended to a video together with a human (Study 1) and a conspecific (Study 2) subsequently approach that individual faster or spend more time in their proximity than when they had attended to something different. Our results suggest that one of the most basic mechanisms of human social bonding—feeling closer to those with whom we act or attend together—is present in both humans and great apes and thus has deeper evolutionary roots than previously suspected.