Africans are more genetically diverse than the inhabitants of the rest of the world combined, according to a sweeping study that carried researchers into remote regions to sample the bloodlines of more than 100 distinct populations.
The report, published yesterday 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. . . .
The first anatomically modern humans originated in Africa about 200,000 years ago, and all humans today are their direct descendants. The study points to an area along the Namibia-South Africa border, the homeland of the San people, as the starting point for a southwest-to-northeast migratory route that carried people through Africa and across the Red Sea into Eurasia.
Tishkoff said the new findings will help medical researchers tailor drug treatments for different groups of Africans rather than treating them as homogenous.
"This is an absolute landmark. It's incredible," said Alison Brooks, a professor of anthropology and international affairs at George Washington University. "It's the most comprehensive document ever published describing the very complex issue of African genetic variation." . . . Although the study's main focus was on Africa, Tishkoff and her colleagues studied DNA markers from around the planet, identifying 14 "ancestral clusters" for all of humanity. Nine of those clusters are in Africa. "You're seeing more diversity in one continent than across the globe," Tishkoff said.
Her team looked at 98 African Americans from North Carolina, Baltimore, Chicago and Pittsburgh. The researchers determined that, on average, 71 percent of their genes could be traced to the far-flung African linguistic group Niger-Kordofanian, 8 percent to other African groups and 13 percent to Europe, with a smattering of genetic markers pointing to other places on the globe.
But the percentages vary widely from individual to individual. In a conference call with reporters, Tishkoff said the 13 percent figure for European genetic markers may be a slight underestimate; other studies have found numbers closer to 20 percent.
The study may be close to the best evidence that humanity will ever get of its genetic roots. As time passes, human migration in a modernizing African will make connecting individuals to their ancestral homes more difficult and hence muddy the data that benefits for centuries of geographically stable and isolated populations.