Culture as the Engine of Selection, Not Its Opposite

2026-08-12 · AI-generated insight

Degler's account of Boas frames the twentieth century's great intellectual settlement: culture, not biology, explains differences among human groups. Boas won that fight so decisively that "culture over biology" became the default posture of American social science. The ancient DNA study on West Eurasia looks, at first glance, like a challenge to that settlement — hundreds of alleles under strong directional selection in just the past ten millennia, with measurable shifts in the genetic predictors of complex traits, including cognitive performance.

But the deeper reading dissolves the opposition Boas's framing depends on. The last ten thousand years is precisely the era of culture — agriculture, dense settlement, cities, epidemic disease, social stratification. If selection accelerated in that window, the most plausible driver is the cultural environments humans built for themselves. Culture didn't replace biological evolution; it became its most powerful selective force. Lactase persistence is the textbook case, but this study suggests the pattern runs far wider. Boas's weapon against hereditarianism turns out to be the very thing shaping heredity.

There's a second irony worth noting. The paper's own caveat — that trait effects were "measured in industrialized societies" and may not correspond to what was adaptive in the past — is a fundamentally Boasian point. What counts as "cognitive performance" or a disadvantageous body composition is defined against a particular cultural context; the phenotype has no context-free meaning. The geneticists needed Boas's insight to interpret their own data honestly.

So the synthesis isn't "Boas was wrong, biology matters after all." It's that the culture/biology dichotomy was always a polemical simplification, useful for demolishing the crude racial hereditarianism of the eugenics era but misleading as a model of how humans actually change. Gene–culture coevolution means Boas's relentless articulation of culture and the ancient DNA revolution are describing two halves of a single feedback loop — one that neither the Boasians nor their hereditarian opponents had the tools to see.

Woven from these notes

Boas’s influence upon American social scientists in matters of race can hardly be exaggerated. At the same time that racial segregation was being imposed by law in the states of the American South, and eugenics was emerging as a hereditarian solution to social problems. Boas was embarking upon a life-long assault on the idea that race was a primary source of the differences to be found in the mental or social capabilities of human groups. He accomplished his mission largely through his ceaseless, almost relentless articulation of the concept of culture.

— Carl Degler In Search of Human Nature: The Decline and Revival of Darwinism in American Social Thought 2026-07-20

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