Michael Tomasello is one of the very few people to have done systematic research on the cognitive capacities of both nonhuman primates and human children. Tomasello argues that the roots of the human capacity for symbol-based culture, and the kind of psychological development that takes place within it, are based in a cluster of uniquely human cognitive capacities that emerge early in human ontogeny: sharing attention with other persons; understanding and imitating intentions. In his discussions of language, symbolic representation, and cognitive development, Tomasello explains how these capacities work over evolutionary and historical time to create the kind of cultural artifacts and settings within which each new generation of children develops. He also proposes a novel hypothesis, based on processes of social cognition and cultural evolution, about what makes the cognitive representations of humans different from those of other primates.