An information explosion? Ingenious mnemonics? A ""twilight"" state of mind? These are among the necessity-inventive causes that Pfeiffer (The Emergence of Man, The Emergence of Society) ascribes to the sudden appearance of cave art in the Upper Paleolithic, 30,000 years ago, and its flowering in the pre-agricultural millenium ending 10,000 years ago. He has followed an international set of scholars into Lascaux, Trois FrÃ¨res, Altamira, and scores of less-familiar French and Spanish sites to report theories and findings in the widely controversial area of cave art and interpretation. Throughout, he distinguishes between accessible art--panoramic scenes of horses, bison, and oxen in central cave areas, for example--and secret art, revealed only after tortuous passages and descents. The secret art--e.g., a half-man, half-feline clay head, along with signs of children's footprints--suggests to Pfeiffer rites of passage in which important lore was transmitted to a new generation. As to why-then and why-there, Pfeiffer iterates themes from earlier books on prehistory: the pressures of population and a more settled lifestyle, changes in climate and food sources, the emergence of a two-tier level of society of knowers and doers. To arrive at that point, he reviews earlier stages of human development. (Readers jaded by hearth-burning-bright romanticism about Homo erectus et al. will find little new in the retelling.) On cave art, Pfeiffer introduces other interpretations--hunting magic and fertility symbols--and concludes that much more work has to be done to shore up any theory. His own eye for detail serves best on the hands-and-knees level of exploring the caves and experiencing the art. But what compels is the art, generously illustrated, and Pfeiffer's seasoned skills at providing survey and update.