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

by David Reich

We truly have no idea right now what the nature or direction of genetically encoded differences among populations will be. An example is the extreme overrepresentation of people of West African ancestry among elite sprinters. All the male finalists in the Olympic hundred-meter race since 1980, even those from Europe and the Americas, had recent West African ancestry.46 The genetic hypothesis most often invoked to explain this is that there has been an upward shift in the average sprinting ability of people of West African ancestry due to natural selection. A small increase in the average might not sound like much, but it can make a big difference at the extremes of high ability—for example, a 0.8-standard-deviation increase in the average sprinting ability in West Africans would be expected to lead to a hundredfold enrichment in the proportion of people above the 99.9999999th percentile point in Europeans. But an alternative explanation that would predict the same magnitude of effect is that there is simply more variation in sprinting ability in people of West African ancestry—with more people of both very high and very low abilities.47 A wider spread of abilities around the same mean and a hundredfold enrichment in West Africans in the proportion of people above the 99.9999999th percentile point seen in Europeans is in fact exactly what is expected given the approximately 33 percent higher genetic diversity in West Africans than in Europeans.48 Whether or not this explain...