Ties-in with a new 6-part series on BBC 2. Roberts traces the epic routes traversed by our human ancestors as they set out from Africa and populated the entire world. From the Ethiopian desert to the Amazon basin, she tries to understand the challenges they faced: mountains, deserts, oceans, changing climates, giant beasts, volcanoes, and, perhaps most dangerous of all, other humans. Neanderthals and Homo erectus were present in Europe and Asia, so why did only Homo sapiens survive?