Nature Is Still Molding Human Genes, Study Finds

An anonymous reader quotes a report from the New York Times: 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, agriculture and the rest -- must have overwhelmed our biological evolution by now. A vast study, published on Wednesday 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 favored 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 variants. "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 new 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 can't be the harm from smoking. Europeans have been smoking tobacco for only about 460 years. The scientists can't 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 researchers also found that some variants, like the one linked to Type B blood, became much more common in Europe around 6,000 years ago, while others changed direction over time. For example, a TYK2 immune gene variant that may have once been beneficial later became harmful because it increased tuberculosis risk.

The study also found signs of natural selection in 44 out of 563 traits. Variants linked to Type 2 diabetes, wider waists, and higher body fat have become less common, possibly because farming and carbohydrate-heavy diets made once-useful fat-storing traits more harmful. Other findings, such as selection favoring genes linked to more years of schooling, are harder to interpret.

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