Anthropologists, historians and linguists now have at their disposal a completely new volume of research with which to test theories of human migration, cultural evolution and population history in Africa. A massive genetics study published yesterday cataloged more than 4 million DNA variations collected over a 10-year period to give the clearest picture yet of the most genetically diverse group of people on Earth.
The study also sheds some light on the ancestry of African Americans—decedents of slaves brought to the Americas—whose genealogy has been difficult to trace.
“Our goal has been to do research that will benefit Africans, both by learning more about their population history and by setting the stage for future genetic studies, including studies of genetic and environmental risk factors for disease and drug response," said study leader Sarah Tiskhoff, a geneticist at the University of Pennsylvania.
It remains a mystery, for example, why some individuals or populations are more resistant than others to diseases like HIV and malaria, or more prone to high-blood pressure, prostate cancer and diabetes.
Researchers from three continents studied 121 African populations, African American populations from Chicago, Baltimore, Pittsburgh and North Carolina, and 60 non-African populations for patterns of variation at 1327 DNA markers from the nuclear genome.
They traced the genetic structure of Africans to 14 ancestral population clusters that correlated with modern ethnicity and shared culture or language.
They also determined that the ancestral origin of humans some 200,000 years ago was probably located in southern Africa, near the South Africa-Namibian border. From there, ancient populations migrated toward the northeast, exiting the continent from a point near the middle of the Red Sea.
Analysis showed the four populations of African Americans studied originated predominantly (71 percent) from Niger-Kordofanian language groups in western Africa. But, they say, the continental ancestors of African Americans were themselves genetically mixed with diverse groups from that region.
“Most African Americans are likely to have mixed ancestry from different regions of western Africa,” the report says. That “will make tracing ancestry of African Americans to specific ethnic groups in Africa challenging, unless considerably more markers are used.”
The research team demonstrated African and African-American populations show the highest levels of genetic diversity of any group, while some African populations contain genetic structures not found anywhere else in the world.
Because there is no single African population that represents the diversity on the continent, Tishkoff says many ethnically diverse African populations should be included in studies of human genetic variation, disease susceptibility, and drug response.
“The Genetic Structure and History of Africans and African Americans” is published in the April 30 issue of the journal Science Express.
The study was funded by the National Cancer Institute, the National Science Foundation, the Advanced Computing Center for Research and Education at Vanderbilt University, the L.S.B. Leakey and Wenner Gren Foundation, the David and Lucile Packard and a Burroughs Wellcome Foundation Career Award given to Tishkoff.
—By Leslie Fink/NSF.