The emergence of social cognition in three young chimpanzees.

We report a series of 10 studies on the social-cognitive abilities of three young chimpanzees. The studies were all ones previously conducted with human infants. The chimpanzees were 1-5 years of age, had been raised mostly by humans, and were tested mostly directly by a familiar human experimenter. First, in a longitudinal investigation with repeated measurements from a social-cognitive test battery, the three young chimpanzees were similar in many ways to human infants; the major difference was a total lack of attempts to share attention with others either in joint attentional interactions or through declarative gestures. Second, in imitation-based tests of the understanding of intentional action, the chimpanzees, like human infants, showed an understanding of failed attempts and accidents; but they did not pay attention to the behavioral style of the actor or the actor's reasons for choosing a particular behavioral means. Third, in tests of their understanding of visual perception, the chimpanzees followed the gaze direction of a human to an out-of-sight location behind a barrier and gestured more to a human who could see them than to one who could not; but they showed no understanding that perceivers can focus their attention on one thing, or one aspect of a thing, within their perceptual fields for a reason. Finally, in tests of joint intentions and joint attention, the chimpanzees showed no ability to either reverse roles with a partner in a collaborative interaction or to set up a joint attentional framework for understanding the communicative intentions behind a pointing gesture. Taken together, these findings support the idea that the early ontogeny of human social cognition comprises two distinct trajectories, each with its own evolutionary history: one for understanding the basics of goal-directed action and perception, common to all apes, and another for sharing psychological states with others in collaborative acts involving joint intentions and attention, unique to the human species.