Over the past 2 million years, the human lineage evolved from a group of bipedal, apelike beings to makers of stone tools, controllers of fire and producers of cave art. Humans went on to flourish in language and arts, becoming constructors of towns, cities, nations and empires, and ultimately becoming a core force in the global ecosystem. How did this happen? Were these advances solely the results of competition for resources, or did they grow from something more complex and distinctive?