Recent Human Evolution in West Eurasia

Evolution didn’t stop when we settled down; it sped up

Photo by Alexander David on Unsplash

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A new Nature paper by Ali Akbari, David Reich, and colleagues explores recent evolution - that is, evolution in the last 14,000 years - in West Eurasians.

Comparing the genomes of ancient West Eurasians to those of modern ones, they found strong evidence that gene variants associated with intelligence were under positive selection, whereas gene variants associated with body fat, darker skin, and disorders like schizophrenia and bipolar were under negative selection.

The body-fat finding is particularly interesting; it fits with the idea that farming reduced the need to stockpile fat on the body, and thus that farming populations evolved to do less of it.

We show 12 instances where tests of polygenic selection—γ, γ_sign and r_s—are all significant, with the relevant statistics at the top of each panel. The mean PGS of West Eurasian individuals over 10,000 years is denoted by a solid black line, with the 95% CI in grey. The red line represents the linear mixed model regression, adjusted for population structure, with slope γ. The circles represent mean PGS in Western hunter–gatherers (green; n = 131), early European farmers (orange; n = 452) and steppe pastoralists (pink; n = 293); the error bars indicate 95% CIs. All P values are two-sided and evaluated against a Bonferroni-corrected threshold for multiple testing (P < 8.9 × 10⁻⁵). Source: Akbari et al. (2026).

Here’s the abstract:

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 evolution. 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.

You can access the paper here for free.

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