‘Human evolution didn’t slow down; we just missed the signal’: Large-scale DNA study finds natural selection led to increased red hair and decreased male pattern baldness

Over the past 10,000 years, natural selection has contributed to the evolution of nearly 500 genes in the DNA of West Eurasians, influencing their appearance and susceptibility to various diseases, a new study finds.

Natural selection in this group increased the frequency of light skin color, red hair, resistance to HIV and leprosy (also known as leprosy), and decreased the frequency of androgenetic alopecia and susceptibility to rheumatoid arthritis, a new study of 16,000 genomes finds. This finding contradicts the long-held view that there are limits to recent human evolution.

“Human evolution didn’t slow down; we simply missed a signal,” Ali Akbari, the study’s lead author and a staff scientist at Harvard University, told Live Science in an email.

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Evolutionary change can occur through a variety of mechanisms, including mutations. natural selection. Traits that favor survival are passed on to offspring. Gene flow. Genetic material mixes between populations. The other is genetic drift, where the frequency of genes within a population changes due to random chance.

In a study published in the journal Nature on Wednesday (April 15), Akbari and colleagues developed a new statistical method to identify 18,000 years of natural selection in thousands of ancient and modern genomes of people living in Western Eurasia, a region that includes Europe and parts of Western Asia such as Turkey.

“Previous research was based on the scars that natural selection left on modern genomes, leading to the view that directional selection is rare,” Akbari said. But with large datasets like the ones the researchers have amassed, and techniques that can separate signals of natural selection from other evolutionary processes, “we can now detect small, consistent changes over time,” he explained.

The researchers found evidence of natural selection in 479 genetic variants in the Western Eurasian genome dataset, 60% of which matched known traits in modern humans. Some of the strongly positively selected genetic variants are responsible for the expression of traits such as light skin color, red hair, resistance to HIV and leprosy infection, and type B blood type. They also discovered genes associated with a lower chance of androgenetic alopecia and a lower risk of rheumatoid arthritis.

The results suggest that all of these mutations were instrumental in the evolution of modern West Eurasians, but the DNA does not help explain exactly why these traits were helpful. The increased frequency of light skin pigmentation probably reflects selection for increased synthesis of vitamin D in areas with less sunlight, the researchers wrote in the study. However, it is difficult to explain the increase in red hair. Red hair itself may not be beneficial, and the genes for the trait may also be associated with more important adaptations.

The researchers found that some traits were positively or negatively selected at different times. Over thousands of years, the frequency of tuberculosis susceptibility genes increased, but then decreased about 3,500 years ago. Similarly, genes associated with multiple sclerosis susceptibility increased until about 2,000 years ago, but then decreased in frequency.

“This likely reflects environmental changes and selective pressures over time, such as the introduction of new pathogens,” Akbari said.

The researchers have made their data and method, called AGES (Ancient Genomic Selection), freely available so that other scientists can expand on this work. Akbari said the research team now plans to study other populations outside Western Eurasia to better understand how the world’s humans evolved. They have already posted a preprint of a study that looked at East Eurasia among people with East Asian ancestry. The current study found a similar pattern, Akbari said.

“What may vary by region is not whether selection has occurred, but how changes in the local environment and culture, including factors such as diet, pathogens and climate, have shaped it,” Akbari said. “Extending this approach more broadly will help us understand how different historical pressures have influenced human biology in different environments.”

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