Human children, but not great apes, become socially closer by sharing an experience in common ground

To create social closeness, humans engage in a variety of social activities centered around shared experiences. Even simply watching the same video side by side creates social closeness in adults and children. However, perhaps surprisingly, a similar psychological mechanism was recently shown in great apes. Here we asked whether the process by which this social closeness is created is the same for children and great apes. Each participant entered a room to see an experimenter (E1) watching a video. In one condition, E1 looked to the participant at the start of the video to establish common ground that they were watching the video together. In another condition, E1 did not look to the participant in this way so that the participant knew they were watching the same video, but the participant did not know whether E1 was aware of this as well, so there was no common ground (E1 looked to the participant later in the procedure). Children, but not great apes, approached the experimenter faster after the common ground condition, suggesting that although both humans and great apes create social closeness by co-attending to something in close proximity, creating social closeness by sharing experiences in common ground may be a uniquely human social-cognitive process.