HALF A CENTURY ago, as archaeologists worked in the wooded Pavlov Hills of the Czech Republic, they made a remarkable discovery. During the excavation of the Upper Paleolithic site known as Dolní Věstonice, they found a pair of shoulder blades from a mammoth. The bones had been placed so as to form the two sides of a pitched roof, one of them leaning against the other. Beneath them was a human skeleton, and in the earth that covered it and on the bones themselves were traces of red ocher. The body had been painted red before it was laid to rest. If nothing more had been found in this grave, it would have added little to what was already known about Ice Age peoples and their customs. During the Upper Paleolithic, corresponding to the final years of the Ice Age, about sixty thousand years ago, people already had the same anatomy as modern human beings. In Eurasia, most of them lived not in caves but in the dark coniferous forests and wide-open steppes that lay beyond the reach of the gla...