Africans have more genetic variation than anyone else on Earth, according to a new study that helps narrow the location where humans first evolved, probably near the South Africa-Namibia border. The largest study of African genetics ever undertaken also found that nearly three-fourths of African-Americans can trace their ancestry to West Africa. The new analysis published Thursday in the online edition of the journal Science. "Given the fact that modern humans arose in Africa, they have had time to accumulate dramatic changes" in their genes, explained lead researcher Sarah Tishkoff, a geneticist at the University of Pennsylvania. People have been adapting to very diverse environmental niches in Africa, she explained in a briefing. Over 10 years, Tishkoff and an international team of researchers trekked across Africa collecting samples to compare the genes of various peoples. Often working in primitive conditions, the researchers sometimes had to resort to using a car battery to power their equipment, Tishkoff explained.