[Paleopsych] NYT: Gene That Determines Skin Color Is Discovered, Scientists Report

[Premise Checker]

Gene That Determines Skin Color Is Discovered, Scientists Report
http://www.nytimes.com/2005/12/16/science/16gene.html?pagewanted=print
[It's significant that the usual warnings against racism were not made by the 
reporter.]

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.