Dr. Tishkoff collects samples in Tanzania. Participants provided information about their ethnicity, language, parents, and grandparents. [Image courtesy of Sarah Tishkoff]
By analyzing genetic differences among more than 3,000 individuals from across Africa and in other parts of the world, researchers have shown how modern-day Africans evolved from 14 ancestral populations.
The findings, which appear in the 30 April Science Express, reveal immense genetic diversity across the continent. They also lay the groundwork for future studies that could lead to important medical advances in Africa as well as a better understanding of human evolutionary history and modern human origins in Africa.
The international research team, led by Sarah Tishkoff, a geneticist at the University of Maryland and the University of Pennsylvania, studied genetic variation among 121 African populations, four African American populations, and 60 non-African populations by collecting DNA from many volunteers and comparing the sequences at various genetic markers around the genome.
"This long-term collaboration, involving an international team of researchers and years of research expeditions to collect samples from populations living in remote regions of Africa, has resulted in novel insights about levels and patterns of genetic diversity in Africa, a region that has been underrepresented in human genetic studies," said Tishkoff.
"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."
The researchers found high levels of mixed ancestry in most populations, reflecting historic migration events across the continent. Generally, the picture from the genomic data matches well with what researchers have reconstructed based on cultural and linguistic patterns.
The results also show shared ancestry among geographically diverse hunter-gatherer populations, including pygmies and click-speaking San as well ask click-speaking groups in East Africa. The ancestry of African American is predominantly from the Niger-Kordofanian population of West Africa (71%) as well as from European (13%) and other African (about 8%) populations.
In addition to providing long-awaited information about the evolutionary history of Africans and African Americans, the study provides a foundation for many other lines of research.
For example, it may help genetic epidemiologists identify the most informative populations to study when looking for genetic risk factors for certain diseases. Or, it may help pharmacogenomics scientists maximize the representation of genetically diverse populations in their research.
Evolutionary geneticists could also use the data to investigate questions such as when and where modern humans evolved in Africa and the size of the population that migrated out of Africa.