Culture Didn't End Selection — It Became the Selective Environment

2026-08-15 · AI-generated insight

Degler credits Boas with one of the great intellectual substitutions of the twentieth century: culture instead of biology as the explanation for human group differences. The framing that conquered anthropology and spread outward was fundamentally an either/or — the more work culture does, the less biology matters, and human evolution effectively recedes into deep prehistory as a finished process.

The ancient DNA findings quietly invert this architecture. The study finds that classic selective sweeps were rare over the long span of human evolution — but that in just the past ten millennia, hundreds of alleles came under strong directional selection, shifting polygenic predictors of complex traits by a full standard deviation. The past ten millennia are, of course, precisely the era of agriculture, cities, dense settlement, epidemic disease — the era when culture became the dominant force in human life. The period Boasians would point to as evidence that culture had taken over from biology turns out to be the period of the most intense measurable selection.

The resolution is that Boas's substitution had the relationship backwards, or at least incomplete. Culture didn't replace selection; culture is a selective environment, arguably the most powerful one humans have ever faced. Grain diets, animal domestication, social stratification, and crowded living all changed what survived and reproduced. Biology and culture aren't competing explanations sharing a fixed pie of causal credit — they're coupled in a feedback loop, each accelerating the other.

There's a historical irony here too. Boas's move was politically motivated in the best sense — science against prejudice, as the note is filed. And the ancient DNA authors are visibly careful in the same tradition, stressing that trait predictions measured in industrialized societies may not map onto what was adaptive in the past. Both are managing the same danger: that findings about biology and human difference will be misread as rankings. The Boasian firewall was to deny biology recent relevance altogether. The new work suggests a different posture is needed — one that can acknowledge rapid, recent, ongoing human evolution without surrendering the anti-racist point, because what was selected was contingent on local, cultural circumstances, not a ladder anyone climbed.

Woven from these notes

Until the 1890s Boas used the term as his fellow anthropologists did: as another word for civilization or “high culture.” Franz Boas’s exposition of the concept of culture as an alternative to race in accounting for differences among human groups was a genuine seminal contribution. The idea not only conquered his own field of anthropolgy but spread as well to other social science disciplines. The diffusion was remarkably rapid. Again and again in the early years of the new century American social scientists outside of anthropology testified to the influence of his writings on their conception of human nature and the place of biology or race within it.

— 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