Gould's Timescale Assumption Meets the Data

2026-07-23 · AI-generated insight

Gould's argument is really an argument about time. Races are recent, therefore genetic differences must be minor—the visible traits are literally skin deep. The hidden premise is that a few tens of thousands of years is simply too short for selection to sculpt anything of consequence beneath the surface. Recency implies triviality.

The ancient DNA paper detonates precisely that premise. Its headline finding is not about race at all—it studies West Eurasians over time, not populations against each other—but it demolishes the pace assumption Gould relies on. Over just the past ten millennia, hundreds of alleles underwent strong directional selection, producing one-standard-deviation shifts in the genetic architecture of complex traits, including cognition and body fat. Selection turns out to be fast, pervasive, and capable of moving polygenic scores meaningfully within the very timescale Gould treats as negligible. If that much change can accumulate in a single population's recent history, "recent origin" is no longer a reassurance that differences must be small.

Winegard and Carl supply the missing half of the mechanism. Gould concedes populations settled radically different environments; Winegard and Carl add that oceans, deserts, and mountains throttled gene flow while divergent selection pressures pulled populations apart. Combine their mechanism with the ancient DNA paper's demonstrated rate, and Gould's inference collapses from both ends: the time is sufficient, and the isolating conditions were present.

What's striking is that none of this settles the empirical question Gould actually cared about—whether between-group differences in any given trait are in fact large or small. That remains open, and the ancient DNA study, confined to one region, cannot answer it. But it does relocate the debate. Gould won his argument on the strength of a theoretical claim about evolutionary tempo that the genomics of his era couldn't test. That claim was doing the heavy lifting, and it now appears to be false. The honest position is that recency guarantees nothing; the magnitude of any difference is an empirical matter to be measured, not deduced from the calendar.

Woven from these notes

Ancient DNA has transformed our understanding of population history, but its potential to reveal as much about human evolutionary biology has not been realized because of limited sample sizes and the difficulty of distinguishing sustained rises in allele frequency increasing fitness—directional selection—from shifts due to migrations, population structure, or non-adaptive purifying or stabilizing selection. Here we present a method for detecting directional selection in ancient DNA time-series data that tests for consistent trends in allele frequency change over time, and apply it to 15,836 West Eurasians (10,016 with new data). Previous work has shown that classic hard sweeps driving advantageous mutations to fixation have been rare over the broad span of human evolution8,9. By contrast, in the past ten millennia, we find that many hundreds of alleles have been affected by strong directional selection. We also document one-standard-deviation changes on the scale of modern variation in combinations of alleles that today predict complex traits. This includes decreases in predicted body fat and schizophrenia, and increases in measures of cognitive performance. These effects were measured in industrialized societies, and it remains unclear how these relate to phenotypes that were adaptive in the past. We estimate selection coefficients at 9.7 million variants, enabling study of how Darwinian forces couple to allelic effects and shape the genetic architecture of complex traits.

Ancient DNA reveals pervasive directional selection across West Eurasia 2026-07-20

obvious: As long as most scientists accepted the ancient division of races, they expected important genetic differences. But the recent origin of races… squares well with the minor genetic differences now measured. Human groups do vary strikingly in a few highly visible characters (skin color, hair form)—and this may fool us into thinking that overall differences must be great. But we now know that our usual metaphor of superficiality—skin deep—is literally

— Gould 2026-07-20

A more plausible conception of race, one that is consistent with how careful philosophers and geneticists use the term, recognises that: When humans began leaving Africa around 75,000 years ago, they dispersed across a much greater range of environments than they had previously inhabited. The humans that settled in different geographic regions subsequently came under different selection pressures (e.g. temperature, seasonality, altitude). Natural barriers such as oceans (e.g. the Atlantic), deserts (e.g. the Sahara) and mountain ranges (e.g. the Himalayas) impeded gene flow between different populations for substantial periods of time. When there is limited gene flow between populations that have come under different selection pressures, we would expect them to gradually diverge from one another over via the processes of genetic drift and natural selection.

— Bo Winegard, Noah Carl Superior: The Return of Race Science—A Review 2026-07-21