Africans are more diverse genetically than the inhabitants of the rest of the world combined, according to a sweeping study that carried researchers into remote valleys and mountaintops to sample the bloodlines of more than 100 distinct populations.



The report, published today in the journal Science Express, suggests that, because of historical migrations and genetic mixing across the continent, it will be hard for African Americans to trace their ancestry in fine detail. African American genealogies are increasingly popular and commercialized, but the authors of the new study cast doubt on how precise such searches can be given the complexity of the genetic makeup of Africans.



"It may be very challenging to trace back ancestry to particular tribes or ethnic groups," said Sarah Tishkoff, a University of Pennsylvania geneticist who led the international research team.



The first anatomically modern human beings originated in Africa about 200,000 years ago, and all human beings today are their direct descendants. The study points to an area along the Namibian-South African border, the homeland of the San people, as the starting point for a...