We know that prehistoric humans made fire and shaped tools, but in this book the author argues that our ancestors shaped us - the human face, our racial differences and our problematic relationship with nature are all self-made. The author suggests that the price our tropical ancestors paid for their expansion out of an African Eden was an irreversible dependence on their own technology. It was in the process of developing man-made economies and adapting to man-made habitats that humans diversified.