April 30, 2009
Study Reveals Source of Human Evolution, African Genetics
An international team of researchers has reported the largest-ever study of genetics in Africa that helps pinpoint where human evolution began.
The 10-year study combined efforts from African, American, and European researchers who studied 121 African populations, four African American populations and 60 non-African populations to uncover more than four million genotypes.
Teams were looking for patterns of variation at 1327 DNA markers. They discovered that about 71 percent of the African American population has genetic traces back to origins in West Africa. They also have between 13 percent and 15 percent European ancestry and a smaller amount of other African origins.
"This is the largest study to date of African genetic diversity in the nuclear genome," said Sarah Tishkoff, a geneticist with joint appointments in the School of Arts and Sciences and the School of Medicine at the University of Pennsylvania.
"This long term collaboration"¦has resulted in novel insights about levels and patterns of genetic diversity in Africa, a region that has been underrepresented in human genetic studies."
Researchers have placed the origins of human evolution to be in southern Africa, near the South Africa-Namibian border. They compiled a map of ancient human migrations to show that modern humans likely left the continent near the middle of the Red Sea in East Africa.
Analysts also uncovered evidence for ancient common ancestry of geographically diverse hunter-gatherer populations in Africa, including Pygmies from central Africa and click-speaking populations from southern and eastern Africa, suggesting the possibility that the original pygmy language may have contained clicks.
"Given the fact that modern humans arose in Africa, they have had time to accumulate dramatic changes" in their genes, Tishkoff told the Associated Press.
She added that there is no single African population that represents the modern diversity on the continent. This suggests that many ethnically diverse African populations should be included in studies of human genetic variation, disease susceptibility, and drug response.
"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 Tishkoff.
Scott Williams, Associate Professor of Molecular Physiology & Biophysics at Vanderbilt University, told the AP that the study "provides a critical piece in the puzzle" for determining genes that may predispose certain populations to a particular illness, such as prostate cancer, hypertension or diabetes.
"Everybody's history is part of African history because everybody came out of Africa," said Muntaser Ibrahim of the department of molecular biology at the University of Khartoum, Sudan.
"Now we have spectacular insight into the history of the African population ... the oldest history of mankind.
Christopher Ehret of the department of history at the University of California, Los Angeles, compared genetic information to the migration of different languages.
He found that about 2,000 language groups exist in Africa, but they are not always correlated to a specific genetic variation. Movement of a language usually involves arrival of new people, Ehret told the AP. The genetic variations typically transfer along with the movement.
The study, published in the journal Science, was supported by the National Cancer Institute, the National Institutes of Health, the Advanced Computing Center for Research and Education at Vanderbilt University, the L.S.B. Leakey and Wenner Gren Foundation, the National Science Foundation, the David and Lucile Packard and Burroughs Wellcome foundations.
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