David Reich Vindicates Cochran & Harpending’s ‘10,000 Year Explosion’

Since the late Stephen Jay Gould helped cement the conventional wisdom about human evolution into place, it has been widely assumed by non-experts that Darwinian adaptation stopped tens of thousands of years in the past, with only cultural evolution happening since then. {snip}

Gregory Cochran and Henry Harpending’s 2010 book The 10,000 Year Explosion: How Civilization Accelerated Human Evolution argued instead that more recent inventions like agriculture roughly 10,000 years ago and the peopling of new worlds like the New World would lead to both larger populations (and thus more favorable mutations because of larger sample sizes) and new selection pressures. Hence, human evolution has likely sped up over the last 10,000 or so years.

Today, Harvard superstar geneticist David Reich and team posted an important paper validating the Cochran-Harpending perspective:

{snip}

We present a method for detecting evidence of natural selection in ancient DNA time-series data that leverages an opportunity not utilized in previous scans: testing for a consistent trend in allele frequency change over time. By applying this to 8433 West Eurasians who lived over the past 14,000 years and 6510 contemporary people,

This study is basically of whites, broadly defined (and of their ancestors before the current white race emerged from three ancient races: European hunter-gatherers, fertile crescent farmers, and steppe invaders). West Eurasians are what used to be called Caucasians (e.g., Europeans, Levantines, Iranians, Egyptians, etc.)

{snip}

we find an order of magnitude more genome-wide significant signals than previous studies: 347 independent loci with >99% probability of selection.

Previous work showed that classic hard sweeps driving advantageous mutations to fixation have been rare over the broad span of human evolution, but in the last ten millennia, many hundreds of alleles have been affected by strong directional selection. Discoveries include an increase from ~0% to ~20% in 4000 years for the major risk factor for celiac disease at HLA-DQB1; a rise from ~0% to ~8% in 6000 years of blood type B; and fluctuating selection at the TYK2 tuberculosis risk allele rising from ~2% to ~9% from ~5500 to ~3000 years ago before dropping to ~3%.

We identify instances of coordinated selection on alleles affecting the same trait, with the polygenic score today predictive of body fat percentage decreasing by around a standard deviation over ten millennia, consistent with the Thrifty Gene hypothesis that a genetic predisposition to store energy during food scarcity became disadvantageous after farming.

This was a 1962 hypothesis by James Neel to explain the existence of diabetes despite it’s obvious downsides.

We also identify selection for combinations of alleles that are today associated with lighter skin color, lower risk for schizophrenia and bipolar disease, slower health decline, and

Finally, the hottest of hot potatoes:

increased measures related to cognitive performance (scores on intelligence tests, household income, and years of schooling).

{snip}