The debate over the validity of evolutionary theory may be real enough when it comes to religious belief and cultural outlook. But it has nothing to do with science. No evidence seriously contradicts the idea that the plant and animal species found on Earth today are descended from common ancestors that existed long ago. Indeed, the evidence for natural selection is infinitely stronger than it was when Charles Darwin proposed it 150 years ago, mainly because later discoveries in the field of genetics supplied the biological mechanisms to explain the patterns that Darwin and his contemporaries were observing.

But scientists do disagree over the pace and time-span of human evolution. Gregory Cochran and Henry Harpending begin "The 10,000 Year Explosion" with a remark from the paleontologist Stephen J. Gould, who said that "there's been no biological change in humans for 40,000 or 50,000 years." They also cite the evolutionist Ernst Mayr, who agrees that "man's evolution towards manness suddenly came to a halt" in the same epoch. Such claims capture the consensus in anthropology, too, which dates the emergence of "behaviorally modern humans" -- beings who acted much more like us than like their predecessors -- to about 45,000 years ago.