Donald Johanson's 1974 discovery in Ethiopia of "Lucy," the fossil of a three-and-a-half-feet-tall primate, helped scientists to redraw the family tree of our hominid ancestry. In this sequel to "Lucy: The Beginnings of Humankind," the paleoanthropologist records his excavation in 1986 at Olduvai Gorge in Tanzania, of the first known skeleton of Homo habilis, believed by many to be the first Homo species. From this fossil and other evidence, Johanson concludes that the evolutionary transition to humankind was more sudden and dramatic than was previously assumed. Far from being "killer apes," our early ancestors, he speculates, were clever scavengers who used their brains to adapt to dry seasons on the savanna. Gracefully written with Shreeve and riddled with the controversies that divide field researchers, this report offers a roll-up-your-sleeves glimpse of how paleontologists find bones and then use them to piece together a picture of human origins.