This chapter argues for two crucial ideas. First, over deep history and at different times and places, humans have experienced very different physical, biological, economic and social environments. Even as foragers, our ancestors experienced different worlds, but over the last 10,000 years change has become more frequent and intense. As a consequence, human adaptive response to the many environments with which we have coped cannot solely or primarily be based on innate, genetically programmed capacities. Social learning is the engine of human adaptability. Second, while defenders of the social intelligence hypothesis are right to emphasise the cognitive challenges posed by human social environments, they have typically over-rated the importance of deception and manipulation, and under-rated the cognitive challenge of coordination. Humans evolved as technically skilled, ecologically informed, cooperative foragers, and that was a cognitively demanding lifeway, especially given the dynamism of human environments.