I am striving to see the human animal in the right perspective."" So says paleoanthropologist Walker in the first person, although the text of this first-rate exposition was actually penned by Shipman, Walker's wife and colleague in Pennsylvania State University's anthropology department. The ""human animal"" in this case is the 1.5-million-year-old Nariokotome boy, unearthed by Walker near a sand river of the same name on the west side of Lake Turkana in Kenya. The discovery of an almost complete skeleton of Homo erectus, the hominid species presumed to have preceded us, was an extraordinary event. The painstaking analysis of the bones that followed involved collaborations with experts in nutrition, neuroscience, language, and behavior. From their findings and the distribution and dating of other erectus fossils, Walker concludes that populations of the species originated in Africa and were the first hominids to spread to other continents; that they were bipedal, social omnivores who could hunt and kill prey. Like us, their babies were born helpless, so that the head could fit through the narrowed pelvic opening needed for stable walking. This meant that infant care was essential and that the brain could continue to expand during the first year--if not much after that, apparently. The big surprise--based on studying the markings that the brain surface leaves on the inside of the skull--was that H. erectus lacked language: Nariokotome boy was a ""large, strong, tall youth of 15 . . . with the brain of a toddler."" Such a discovery raises a number of pressing questions--and may be challenged in the contentious field of paleoanthropology. Nevertheless, the care with which Walker and Shipman lay out the evidence and their theories may well win the day. And even if not, readers will be rewarded by a fine telling of the always fascinating story of where we came from.