Many scientists have contended that humans have evolved very little over the past 10,000 years. A few hundred generations was just a blink of the evolutionary eye, it seemed. Besides, our cultural evolution — our technology and agriculture — must have overwhelmed our biological evolution by now.
A vast study, published in the journal Nature, suggests the opposite. Examining DNA from 15,836 ancient human remains, scientists found 479 genetic variants that appeared to have been favoured by natural selection in just the past 10,000 years. The researchers also concluded that thousands of additional genetic variants have probably experienced natural selection. Before the new study, scientists had identified only a few dozen.
“There are so many of them that it’s hard to wrap one’s mind around them,” said David Reich, a geneticist at Harvard Medical School and an author of the study. He and his colleagues found that a mutation that is a major risk factor for celiac disease, for example, appeared just 4,000 years ago, meaning the condition may be younger than the Egyptian pyramids.
The mutation became ever more common. Today, an estimated 80 million people worldwide have celiac disease, in which the immune system attacks gluten and damages the intestines. The steady rise of the mutation came about through natural selection, the scientists argue. For some reason, people with the mutation had more descendants than people without it — even though it put them at risk of an autoimmune disorder.
Other findings are even more puzzling. The researchers found that genetic variants that raise the odds of a smoking habit have been getting steadily rarer in Europe for the past 10,000 years. Something is working against those variants — but it cannot be the harm from smoking. Europeans have been smoking tobacco for only about 460 years.
The scientists cannot see from their research so far what forces might be making these variants more or less common. “My short answer is, I don’t know,” said Ali Akbari, a senior staff scientist at Harvard and an author of the study.
The study is making a stir among evolutionary biologists. Experts generally agreed that at least some of the genetic variants would turn out to have been influenced by natural selection. “The scale of what Reich’s research team has accomplished with more than 15,000 genomes of ancient people is just astounding,” said John Hawks, a paleoanthropologist at the University of Wisconsin.
In the early 2000s, Reich and other researchers pioneered a new way to reconstruct human evolution by extracting DNA from ancient bones. In 2015, they found 12 variants that had been subject to natural selection, including one that helps adults digest milk. Subsequent studies raised the total to only 21.
Reich’s team went on to amass thousands of new samples, while Akbari developed new methods to analyse them. He was shocked to find so many new variants evolving in the past 10,000 years. “It took about two years to convince myself this was real,” Akbari said.
The New York Times