from the Detroit News.... -------------------------------------------------------------------------------- By William Hathaway / The Hartford Courant December 17, 2005 The skin color of Europeans might have turned white after their ancestors migrated from Africa because of a single mutation among the 3 billion genetic "letters" that make up the human genome, scientists reported this week. The mutation explains part of the lingering mystery of how human skin colors evolved during the last 50,000 years as modern humans migrated across the world after leaving Africa, according to research published Friday in the journal Science. "This really calls into question our ideas about race," said Mark Shriver, professor of anthropology and genetics at Pennsylvania State University and an author of the paper. Cancer researchers discovered the mutation in zebra fish while investigating a gene they suspected might play a role in malignant melanoma, a skin cancer. Researchers found that a mutation of a gene called SLC24A5 seemed to explain why golden zebra fish had lighter pigmentation in their stripes than other zebra fish. In humans as well as fish, variations in skin color are caused by melanin, or specifically the size and number of pigmentation granules called melanosomes within cells. People of European descent -- and the golden zebra fish -- have few, smaller and lighter granules within skin cells. While scores of genes have been identified in development of skin pigmentation, there is still confusion about which ones are most important in humans. So scientists at the Pennsylvania State College of Medicine in Hershey wondered whether the mutation of a single specific gene might account for lighter pigmentation in humans as well as in the zebra fish. "When you run into something incredibly interesting, you have an obligation to do the best science you can do," said Dr. Keith Cheng, a cancer researcher at the Penn State Cancer Institute and senior author of the Science paper. Cheng and his colleagues found they could produce a darker-striped zebra fish by simply switching the mutated gene in a developing golden zebra fish embryo with an unmutated human version of the SLC24A5 gene. The reason the stripes turned dark is in that almost all vertebrates, including humans, the normal version of the gene tends to create dark pigmentation. When geneticists from Penn State compared the human variations of the gene contained in DNA data bases, they found that West Africans and East Asians have the same SLC24A5 gene as dark-striped zebra fish. But Europeans and the golden zebra fish have similar mutations of that gene. "By default, we are all dark-skinned," said Kenneth K. Kidd of Yale's genetics department. "This type of research is a kind of footprint that can describe how modern humans spread out of African origins and occupied the rest of the world." The findings, however, only account for differences in skin color of Europeans. Differences in shades of skin color among Africans and East Asians, who also can have light skin, must be the work of other genes, the researchers said. But Shriver and Kidd say the work is an example of how a tiny molecular change can create a major difference in something as fundamental as skin color. Most scientists believe that mutations that created white skin took hold quickly among small groups of people who migrated to northern Europe with longer winter nights. Light skin absorbs more Vitamin D, which is needed to strengthen bones, Kidd said. But black skin is advantageous in hotter climates because it has more resistance to harsh ultraviolet rays of the sun. Genetic differences between races tend to be tiny, Kidd said. Because modern humans originated in Africa, genetic variation among people of African descent tend to be the greatest of all ethnic groups. That means that a person of African descent and a European can be related more closely genetically than two people of African descent, he said. For example, Ethiopians with dark skin are related more closely genetically to Europeans than to West Africans, he said. "That's what we mean when we say that race in a broad sense is not a useful concept," Kidd said. "I can't draw a line between where one race begins and the next one starts." Understanding subtle genetic differences between ethnic and other population groups might be important because they might explain different susceptibility to disease or resistance to some drugs, Kidd said.