Donald Johanson and Blake Edgar discuss human prehistory — from the appearance of bipedal walking to the origin of language — in a volume lavishly illustrated with original (and often life-size) photographs of fossils and artifacts. The first part of the book concentrates on the interpretation of the paleoanthropological evidence, considering such topics as migration, diversity, anatomy, society, bipedalism, tools, customs, and "imponderables" (such as clothing and the problem of consciousness).