An intensive exploration of our current knowledge of the ecological influences on human evolution. Evolution is the result of interactions between a biological population and its entire environment. The multidisciplinary approach of modern paleoanthropology attempts to assemble a complex picture of those interactions, looking not just at bones but at all the varied evidence a fossil site provides. Boaz (Quarry: Closing in on the Missing Link, 1993) pays particular attention to the indications of environmental change, the engine driving all evolutionary processes. He focuses on eight specific turning points in the evolution of the primates and offers theories as to their causes. Gorillas, the largest of the anthropoid apes, split off from the common line of evolution fairly early, adapting to a highland forest life. Chimpanzee and Australopithecus lineages went their separate ways later, driven by different environments on opposite sides of the African Rift Valley, followed by the growth of the Sahara Desert. The East African savanna, which favored upright walking, was the ecological crucible in which Australopithecus developed into several species, one of which was ancestral to humanity. A shifting pattern of moist and dry eras allowed the genus Homo (originally a tropical animal) to expand out of Africa into Asia, Europe, and America. Boaz examines these events with careful attention not only to extant fossils but to the environmental factors: availability of foodstuffs, competition of other species (rodents outcompeted early primates in America), and, above all, the changes in climate. A final chapter looks into the future, exploring possible effects of environmental degradation brought about by overpopulation. Boaz warns that we and our descendants will be no freer of the effects of our environment than our remote ancestors. Boaz's thought-provoking subject makes up for his sometimes clumsy prose style; worth a look by anyone interested in our origins and probable future.