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The whole world could soon be seeing red.
Instead of being the punchline, redheads will have the last laugh, as a new study reports that humans have been constantly evolving to have flame-colored hair.
The finding has challenged previously held ideas about how much natural selection has influenced our DNA over hundreds of thousands of years.
Scientists once thought directional selection — a type of natural selection that favors one extreme phenotype over others — was rare in humans.
A study published last week in the journal Nature featured new DNA analysis of some 10,000 ancient human remains across Europe and parts of Asia, in addition to 5,820 previously published ancient sequences and 6,438 modern ones.
The researchers found that natural selection has played a much larger role in determining which traits survived or declined since the Ice Age, identifying 479 genetic variations that were greatly impacted — many more than the 20 previous instances of directional selection.
Evidence of this kind of natural selection had been lacking for some 300,000 years, since modern humans began splintering off from Africa and relocating around the world.
Researchers believe that natural selection sped up which genes — and therefore, traits — thrived or disappeared because of changing environments and lifestyles, such as the adjustment from hunter-gatherer to farmer.
More than 60% of the traits that were affected are present today. They include physical traits and links to disease risks.
Some of these include fair skin, red hair, risk of celiac or Crohn’s disease, immunity to HIV infection, lower chance of male baldness and lower risk of alcoholism and rheumatoid arthritis.
Other harmful health traits that were influenced include a lower risk of bipolar disorder and schizophrenia, as well as lower body fat percentage and waist-to-hip ratio.
While the researchers found that some genetic changes made sense, others were less obvious throughout history, such as gluten intolerance increasing alongside the farming of wheat.
Overall, the findings provide a clearer picture of genetic adaptation and human history.
They could help researchers better understand genetic factors in health and disease and offer the chance to develop new treatments.
“This work allows us to assign place and time to forces that shaped us,” senior study author and Harvard geneticist David Reich said.
Reich and his team plan to repeat their research in other areas, such as East Asia and East Africa, to identify more genetic variations that could help with disease prevention.
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