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 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.