Thursday, October 12, 2017

Genes for Skin Color Rebut Dated Notions of Race, Researchers Say

Photo
A gallery of busts from the 19th century showing human diversity on display in the Museum of Mankind in Paris. Scientists have found that the genetic variations that determine skin color are widely shared. Credit Romuald Meigneux/SIPA, via Associated Press
For centuries, skin color has held powerful social meaning — a defining characteristic of race, and a starting point for racism.
“If you ask somebody on the street, ‘What are the main differences between races?,’ they’re going to say skin color,” said Sarah A. Tishkoff, a geneticist at the University of Pennsylvania.
On Thursday, Dr. Tishkoff and her colleagues showed this to be a profound error. In the journal Science, the researchers published the first large-scale study of the genetics of skin color in Africans.
The researchers pinpointed eight genetic variants in four narrow regions of the human genome that strongly influence pigmentation — some making skin darker, and others making it lighter.
These genes are shared across the globe, it turns out; one of them, for example, lightens skin in both Europeans and hunter-gatherers in Botswana. The gene variants were present in humanity’s distant ancestors, even before our species evolved in Africa 300,000 years ago.
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The widespread distribution of these genes and their persistence over millenniums show that the old color lines are essentially meaningless, the scientists said. The research “dispels a biological concept of race,” Dr. Tishkoff said.
Humans develop color much as other mammals do. Special cells in the skin contain pouches, called melanosomes, packed with pigment molecules. The more pigment, the darker the skin.
Skin color also varies with the kind of pigments: Melanosomes may contain mixtures of a brown-black called eumelanin and a yellow-red called pheomelanin.
To find the genes that help produce pigments, scientists began by studying people of European ancestry and found that mutations to a gene called SLC24A5 caused cells to make less pigment, leading to paler skin. Unsurprisingly, almost all Europeans have this variant.
“We knew quite a lot about why people have pale skin if they had European ancestry,” said Nicholas G. Crawford, a postdoctoral researcher at the University of Pennsylvania and a co-author of the new study. “But there was very little known about why people have dark skin.”
Since the early 2000s, Dr. Tishkoff has studied genes in Africa, discovering variants important to everything from resistance to malaria to height.
African populations vary tremendously in skin color, and Dr. Tishkoff reasoned that powerful genetic variants must be responsible.
Studying 1,570 people in Ethiopia, Tanzania and Botswana, she and her colleagues discovered a set of genetic variants that account for 29 percent of the variation in skin color. (The remaining variation seems tied to genes yet to be discovered.)
One variant, MFSD12, was particularly mysterious: No one knew what it did anywhere in the body. To investigate its function, the researchers altered the gene in reddish lab mice. Giving them the variant found in darker-skinned Africans turned the mice gray.
NYT

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