Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past

by David Reich

The evidence for this is that the density of mutations separating San genomes from non-San genomes is uniformly high, implying few shared ancestors between San and non-San in the last hundred thousand years. “Pygmy” groups from Central African forests harbor ancestry that is arguably just as distinctive. The extremely ancient isolation of some pairs of human populations from each other conflicts with the idea that a single mutation essential to distinctively modern human behavior occurred shortly before the Upper Paleolithic and Later Stone Age. A key change essential to modern human behavior in this time frame would be expected to be at high frequency in some human populations today—those that descend from the population in which the mutation occurred—and absent or very rare in others. But this seems hard to reconcile with the fact that all people today are capable of mastering conceptual language and innovating their culture in a way that is a hallmark of modern humans.