Preverbal infants expect members of social groups to act alike.

The short ontogenetic time courses of conformity and stereotyping, both evident in the preschool years, point to the possibility that a central component of human social cognition is an early developing expectation that social group members will engage in common behaviors. Across a series of experiments, we show that by 7 months of age preverbal infants differentiate between actions by individuals that are and are not consistent with the actions of their social group members. Infants responded to group-inconsistent actions only in a social context: they failed to distinguish the same behavioral differences when presented with collections of nonsocial agents or inanimate objects. These results suggest that infants expect social group membership and behavior to covary, before extensive intergroup experience or linguistic input. This expectation is consistent with the socially motivated imitation and stereotyping evident in toddlers and preschoolers, and may play a role in the early emergence of one or both of these aspects of social behavior and cognition.