The Evolution of Social Categories

A widely accepted view holds that human infants’ knowledge of the world develops not from a single, general-purpose ability to reason about objects and events but instead from several “core” systems of knowledge, each specialized for representing and reasoning about entities of different kinds. One functionally specialized system concerns knowledge about animate creatures. If knowledge about animate beings – particularly conspecifics – constitutes a core system of cognition in human infants, it may be possible to explain its evolution by 1) identifying a core system of social knowledge in nonhuman primates and other animals, 2) demonstrating that this knowledge constitutes a functionally specialized system and 3) demonstrating that knowledge of other individuals’ identities, category membership, and motives is adaptive, contributing to the reproductive success of individuals. Here we test these predictions using data from wild baboons. Results indicate that baboons classify each other along a number of dimensions simultaneously: as individuals, members of matrilineal kin groups, holders of specific dominance ranks, and participants in more transient social relationships. Their formation of social categories is based on certain expectations and assumptions of causality. Baboon social knowledge, moreover, is adaptive because it allows individuals to form relationships that reduce stress and increase reproductive success.