According to a new study, natural selection has led to the evolution of light skin tones, red hair, and resistance to HIV and leprosy in West Eurasians over the past 10,000 years.
It also decreased the frequency of male-pattern baldness and susceptibility to rheumatoid arthritis.
A team of researchers developed a new statistical method to identify natural selection in thousands of genomes from West Eurasians over a period of 18,000 years. West Eurasia consists of Europe and areas of western Asia, including Turkey.
“With these new techniques and a large amount of ancient genomic data, we can now watch how selection shaped biology in real time,” said Ali Akbari, the study’s first author and a scientist at Harvard University.
“Instead of searching for the scars natural selection leaves in present-day genomes using simple models and assumptions, we can let the data speak for itself.”
The researchers uncovered evidence of natural selection in 479 gene variants in the West Eurasian genome dataset. About 60% of the variants correspond with traits in modern-day people.
They found that genes for red hair, resistance to HIV and leprosy infections, B blood type, and a light skin tone were all becoming more common.
There were also genes related to a lower risk of rheumatoid arthritis, alcoholism, tobacco smoking, schizophrenia, and bipolar disorder, as well as a lower chance of male-pattern baldness. These traits may have been useful in the evolution of modern West Eurasian people, but it is unclear exactly why.
The increase in lighter skin tones may have arisen to help people absorb more vitamin D in regions with less sunlight. However, the rise in redheads was harder to explain.
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Possibly, having red hair itself was not beneficial, but the red hair may have been associated with a more important adaptation.
Other traits, both positive and negative, were selected at different times. Genes for tuberculosis susceptibility increased in frequency over thousands of years.
Then, they decreased around 3,500 years ago. Genes for susceptibility for multiple sclerosis saw a similar pattern, decreasing in frequency about 2,000 years ago.
“This likely reflects changes in environment or selective pressures over time; for example, the introduction of new pathogens,” said Akbari.
Overall, the results of the study could help scientists determine new genetic factors in health and disease, leading to improvements in preventing illness and developing medicines.
In the future, the team hopes to investigate the genomes of other groups outside West Eurasia to gain a better understanding of how humans evolved across the globe.
Akbari expects local environments, pathogens, and cultural habits like diet to affect how natural selection occurs in different regions.
The findings of the study were published in the journal Nature. The data, called AGES (Ancient Genome Selection), is available for free so that other scientists can review the work and make their own discoveries.
By Emily Chan
Emily Chan is a writer who covers lifestyle and news content. She graduated from Michigan State University with a degree in... More about Emily Chan
