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 âdispels a biological concept of race,â 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.
âWe knew quite a lot about why people have pale skin if they had European ancestry,â said Nicholas G. Crawford, a postdoctoral researcher at the University of Pennsylvania and a co-author of the new study. âBut there was very little known about why people have dark skin.â
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.