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Genetic Study Shows Skin Color Is Only Skin Deep

Genes for both light and dark pigmentation have been in the human gene pool for at least 900,000 years

(Alessia Ranciaro and Simon Thompson)
smithsonian.com

While many have turned to science to falsely support the notion of a biological construct of race, modern research has demonstrated genetics has little to do with it. Now, as Ed Yong at The Atlantic reports, a large-scale study of skin pigmentation demonstrates that humans with both light and dark skin pigmentation have co-existed for hundreds of thousands of years.

A long-standing assumption about the evolution skin color was that Homo sapiens started out in Africa with darkly pigmented skin, full of melanin to protect from the intense ultraviolet radiation from the sun. As humans migrated out of Africa, it was believed that mutations led to lighter skin that can supposedly regulate vitamin D production in lower sunlight levels. But the new study, published in the journal Science, shows that the evolution of skin color is much more complex. 

A team of researchers led by Sarah Tishkoff at the University of Pennsylvania and her postdoctoral fellow Nicholas Crawford measured the skin pigmentation of over 2,000 genetically and ethnically diverse people across Tanzania, Ethiopia and Botswana. They analyzed the genome of nearly 1,600 of those people, which allowed them to identify eight key areas in the DNA associated with skin pigmentation.

As Colin Barras at New Scientist reports, each of these sites had genetic variants associated with paler skin and ones associated with darker skin. Seven genetic variants associated with lighter skin developed at least 270,000 years ago and four more than 900,000 years ago. Considering our species, Homo sapiens, did not evolve until around 200,00 to 300,000 years ago, the discovery suggests that the genes responsible for lighter skin tones were present into the genetic material of our hominin ancestors—hundreds of thousands of years before the first humans walked the Earth.

The study suggests that genes of light and dark skin are more fluid than we once thought. Three of the genes associated with the darkest skin are likely to have evolved from genes for lighter skin tones, Barras reports, meaning that people with the darkest skin tones, like herdsmen who live in the Sahara, may have developed that deep pigmentation in the evolutionarily recent past.

“People have thought it was just light skin that has been evolving,” Tishkoff tells Barras. “I think dark skin continues to evolve as well.”

The new research "adds unexpected complexity" to the story behind skin color, writes Carl Zimmer at The New York Times. "The dark-skinned people of southern India, Australia and New Guinea, for example, did not independently evolve their color simply because evolution favored it. They inherited the ancestral dark variants Dr. Tishkoff’s team found in Africans," he writes.

The study also shows a variant of a gene associated with light skin common to Europeans and people form the Middle East called SLC24A5 developed relatively recently, just 29,000 years ago. It has only become widespread in the last several thousand years, even flowing back into Africa during waves of Middle Eastern migration.

The study confirms that societal constructions of race are not useful when it comes to genetics. “One of the traits that most people would associate with race—skin color—is a terrible classifier,” Tishkoff tells Yong, pointing out that there is variation even within dark skin. “The study really discredits the idea of a biological construct of race. There are no discrete boundaries between groups that are consistent with biological markers.”

White supremacists often subvert genetic studies to support their own ideas about race. Yong spoke with Jedidiah Carlson, a researcher at the University of Michigan, not associated with this study, who tracks this misappropriation of genetics research. “Because visually distinguishable traits common in present-day Europeans, such as light skin color, are also assumed to have arisen within European populations, white supremacists treat these traits as a proxy for superior intelligence,” he tells Yong.

But as this study shows, the genes for light skin have been there since the beginning. “If you were to shave a chimp, it has light pigmentation,” Tishkoff says in a press release. “So it makes sense that skin color in the ancestors of modern humans could have been relatively light. It is likely that when we lost the hair covering our bodies and moved from forests to the open savannah, we needed darker skin. Mutations influencing both light and dark skin have continued to evolve in humans, even within the past few thousand years.”

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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