This book develops a novel account of the speed and extent of human evolutionary divergence from the great ape stock. It does not explain human uniqueness by positing a critical adaptive breakthrough (episodic memory; advanced theory of mind; planning and causal reasoning; language). Rather, it identifies a series of positive feedback loops between initially minor advances in social tolerance, ecological flexibility, cooperative foraging, social learning, and links the results of these feedback loops to the archaeological and anthropological record. The analysis is organised round a new model of the evolution of social learning — the evolved apprentice model — and its coevolutionary interaction with cooperation in foraging and reproduction. Social learning expands through the increasing organisation and enrichment of juvenile learning environments, not just through changes in the intrinsic architecture of human minds. Initially, and for millions of years, these organised social learning environments made it possible for humans to reliably transmit a few core skills, but without supporting the reliable and intergenerationally stable transmission of incremental improvements to those skills. Ultimately, though, enriched and somewhat larger social environments made cumulative cultural evolution possible. Cumulative cultural evolution — Tomasello`s Ratchet — depended on some adaptations for social learning, richly structured learning environments, and demographic critical mass. Critical mass matters, for small and scattered groups can easily lose complex skills through unlucky accident. Humans are so different from great apes in part because they have constructed such novel developmental and selective niches.