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A large-scale DNA study published in Nature has found evidence of natural selection acting on hundreds of genetic variants in Western Eurasian populations over the past 18,000 years — with findings pointing to increases in fair skin, red hair, and resistance to HIV and leprosy, alongside decreases in male-pattern baldness and susceptibility to rheumatoid arthritis.
The study, led by Harvard University researcher Ali Akbari, analyzed 16,000 genomes drawn from ancient and modern populations spanning Europe to Türkiye.
Using a newly developed statistical method, the team identified signals of natural selection in 479 gene variants – 60% of which correspond to known traits in present-day humans.
"Human selection has not slowed down – we just could not detect the signal," Akbari said.
Earlier research relying solely on modern genomes had suggested that directional selection was rare in humans.
Akbari and his team argue that larger datasets and refined methods capable of separating selection signals from other genetic processes, such as gene flow between populations and random genetic drift, now make it possible to detect small but consistent shifts over time.
"Previous studies based on present-day genomes gave the impression that directional selection was rare," Akbari said. "But with massive datasets and new methods that distinguish the selection signal from other processes, we can now detect those small yet steady changes over time."
Among the variants showing strong positive selection were those associated with fair skin pigmentation, red hair, resistance to HIV and leprosy (Hansen's disease), and blood type B.
Variants associated with a lower likelihood of male-pattern baldness and a reduced risk of rheumatoid arthritis were also identified.
Researchers note that the data does not explain why each trait conferred an advantage. The increase in lighter skin pigmentation is thought to be linked to vitamin D synthesis in regions with low sunlight.
The rise in red hair remains less clear — researchers suggest the trait may be carried alongside other genes tied to a more direct adaptation rather than conferring a direct benefit on its own.
The study also found that selection is not static. Genes associated with tuberculosis susceptibility increased over several thousand years before declining around 3,500 years ago.
Susceptibility markers for multiple sclerosis (MS) followed a similar pattern, rising then falling around 2,000 years ago.
Akbari attributes these fluctuations to shifting environmental pressures — including the emergence of new pathogens. The team has made the AGES (Ancient Genome Selection) dataset publicly available to researchers.
The team is currently extending its analysis to East Eurasian populations and expects to find similar patterns of natural selection operating worldwide.
According to Akbari, what varies across regions is not whether selection occurs, but how local environmental factors – including diet, climate, and infectious disease – drive the process.
Akbari said expanding the approach globally would help clarify how different historical pressures have shaped human biology across different environments.
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