The coordination of attention and action in great apes and humans.

Great apes can discern what others are attending to and even direct others' attention to themselves in flexible ways. But they seemingly do not coordinate their attention with one another recursively-understanding that the other is monitoring their attention just as they are monitoring hers-in acts of joint attention, at least not in the same way as young human children. Similarly, great apes collaborate with partners in many flexible ways, but they seemingly do not coordinate with others to form mutually obligating joint goals and commitments, nor regulate the collaboration via acts of intentional communication, at least not in the same way as young human children. The hypothesis defended here is that it is precisely in their capacities to coordinate attention and action with others-that is, in their capacities for shared intentionality-that humans are most clearly distinguished from other great apes. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.