December 16, 2005
Gene That Determines Skin Color Is Discovered, Scientists
Report
By NICHOLAS WADE
A gene that is responsible for the pale skin of Europeans and the
dark skin of Africans has been discovered by scientists at
Pennsylvania State University.
The gene comes in two versions, one of which is found in 99 percent
of Europeans and the other in 93 to 100 percent of Africans, the
researchers report in today's issue of Science.
The gene is unusual because with most human genes, different
versions are generally shared, though one version may be more
common in one race than another. One exception is the Duffy null
allele, a version of a gene that prevents malaria, that is found
almost exclusively in one race, sub-Saharan Africans.
The new gene falls into the same category as the Duffy gene, and it
may shed light on the evolutionary pressures to which Europeans
were subjected as their ancestors, who were presumably dark
skinned, moved into the northern latitudes some 40,000 years
ago.
Humans acquired dark skins in Africa about 1.5 million years ago to
shield their newly hairless bodies from the sun. Its ultra-violet
rays destroy folic acid, a shortage of which leads to birth
defects.
But when the modern humans who left Africa began to live in
northern latitudes, they needed more sunlight to penetrate the
skin, to permit the chemical reaction that produces vitamin
D.
The new gene was first identified not in humans but in a mutant
zebra fish, a small striped fish common in aquariums. The mutant
fish are known as golden, because their stripes, usually black, are
much paler and their bodies more yellow.
Dr. Keith C. Cheng, an author of the report, and his colleagues
showed that the golden version of the fish gene altered production
of melanosomes, the tiny black particles of pigments that give skin
its color.
The researchers then found that in humans, who have their own form
of the gene, the version common in Africans allowed larger
melanosomes, which tend to clump together, whereas the version in
Europeans produced smaller and more dispersed melanosomes.
Asians have the same version of the gene as Africans, so they
presumably acquired their light skin through the action of some
other gene that affects skin color, said Dr. Cheng.
Mark D. Shriver, another author of the article, said his laboratory
was trying to assess when the European version of the gene became
so common, as well its geographical origin.
The intense selective pressure that drove the version to become
universal in Europeans may have included sexual selection.
"In Africa people are much darker than they need to be for UV
protection, so to me that screams sexual selection," Dr. Shriver
said. Black skin, in other words, may have been favored by men and
women in sexual partners, just as pale skin may have been preferred
in sexual partners among Europeans and Asians.
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Would consider changing your skin
colour? What colour would you change to, if you want?
Why?