Examines the implications of Orrorin tugenensis, a group of six million year-old fossils found in the Tugen Hills of Kenya, which may shed light on the origins of humankind. Suggests that if the bones do belong to upright-walking, hominid creatures, then our current theories about the evolution of human beings may have to be rewritten. Also looks at new ideas about the development of upright walking in humans, which propose that bipedalism developed in the trees, not the open savannah.