A large study looked at ancient DNA from about 16,000 people who lived over the past 10,000 years in West Eurasia, and found that natural selection has influenced human genes much more than scientists once believed.
By comparing DNA from ancient remains and over 6,000 people today, researchers found strong evidence that human evolution is still ongoing.
They discovered 479 gene changes that were favored by natural selection. These include genes linked to red hair, lighter skin, higher risk of coeliac disease, and genes that reduce the chances of diabetes, baldness, and rheumatoid arthritis. Notably, these traits have become more common over time.
Earlier, scientists had found only about 21 such examples, like the ability of adults to digest milk. Because of this, they thought natural selection had not played a big role in recent human history.
But this new study, using a much larger amount of DNA and advanced methods, shows that many genes have increased or decreased due to evolution. This process sped up after humans moved from hunting and gathering to farming.
The researchers noted that some changes are easy to understand. For example, lighter skin and red hair may have helped people produce more vitamin D in areas with little sunlight, especially when their diet lacked it.
"Perhaps having red hair was beneficial 4,000 years ago, or perhaps it came along for the ride with a more important trait," the researchers said. Previous research has shown that people with red hair and fair skin can produce vitamin D more efficiently, for instance, which may have conferred survival benefits in northern climates.
Meanwhile, other findings are more confusing, such as a gene that increases the risk of coeliac disease appeared about 4,000 years ago and became more common, even though it can cause health problems. Another gene that increases the risk of tuberculosis became more common for a time and then decreased again. It's possible that some risky genes helped people fight infections during certain periods.
The study also found that genes linked to storing more body fat became less common over time. This may be because storing fat was useful when food was scarce, but became less helpful once farming made food more available.
"With these new techniques and a large amount of ancient genomic data, we can now watch how selection shaped biology in real time," said first author Dr Ali Akbari, Harvard University.
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