This work builds a bridge between evolutionary theory and cultural psychology. The author is one of very few people to have done systematic research on the cognitive capacities of both nonhuman primates and human children. This work identifies what the differences are, and suggests where they might have come from. Tomasello argues that the roots of the human capacity for symbol-based culture, and the kind of psychological development that takes p[lace within it, are based in a cluster of unique human cognitive capacities that emerge early in human ontogeny. These include capacities fort sharing attention with other persons, for understanding that others have intentions of their own; and for imitating, not just what someone else does, but what someone else has intended to do. In this discussions of language, symbolic representation, and cognitive-development, the author describes with authority and ingenuity the ratchet effect of the capacities working 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 process of social cognition and cultural evolution, about what makes the cognitive representations of humans different from those of other primates.