Culture as an Agent of Biological Change

Evolve_articleBenjamin Phelan in Seed:

John Hawks started out as a “fossil guy” studying under Milford Wolpoff, a paleoanthropologist who is the leading proponent of the faintly heretical multiregional theory of human evolution. Coming to genetics from such a background has perhaps given Hawks the stomach to wield unfashionable hypotheses. In December of last year, he, Harpending, and others published a paper whose central finding, that evolution in humans is observable and accelerating, would have been nonsensical to many geneticists 20 years ago. Up to 10 percent of the human genome appears to be evolving at the maximum rate, more quickly than ever before in human history.

“Seven percent is a minimum,” Hawks says. “It’s an amazing number,” and one that is difficult to square with the prevailing view of natural selection’s power. Because most mutations have a neutral effect on their carriers, making them neither fitter nor less fit, neither more fertile nor sterile, only slightly different, those changes are invisible to natural selection. They spread or don’t spread through a population by chance, in a process called genetic drift, which is often thought of as the agent of more change than natural selection. But the changes that Hawks detected, if he is correct, are too consistent from person to person, from nationality to nationality, to have been caused by genetic drift alone.

By looking at the data from HapMap, a massive survey of the genetic differences between selected populations from around the world, Hawks identified gene variants, or alleles, that were present in many people’s DNA, but not in everyone’s. These alleles seemed to be moving, over time, through populations in a way that matched mathematical predictions of what natural selection should look like on the genomic level. And though Hawks doesn’t know why possession of the new alleles should be advantageous, he doesn’t need to know. The signature that natural selection inscribes on the genome is legible even when the import of the message is unclear.