Evolution has long shaped human behavior. Yet just recently have we learned that evolution based on natural selection is not the continuous process Darwin assumed. It is instead a two-part process of change and stability called punctuated equilibrium, with natural selection operating mainly on the frontiers of change. Taking account of biology's latest understanding of evolution, it becomes clear that culture evolves by a similar process. This is important because over the past 30,000 years most human evolution and the behavioral changes that go with it have occurred in our cultures-not in...