Rosenberg's team also found that the number of distinct genetic variants declined as the distance from Africa increased. "This suggests that a genetic history reflects a history in which populations migrated out of Africa, and along the way only a portion of the genetic diversity available migrated to the next location," he said.
There is still a great deal of genetic diversity in each population, Rosenberg pointed out.
In the study, Rosenberg's team looked at more than 500,000 DNA markers. The markers came from 485 volunteers in the Human Genome Diversity Project. Rosenberg's team looks at genetic variations in 29 different groups from Africa, Europe, the Middle East, Southeast Asia, the Pacific Ocean islands, and the Americas.
The implication of what Rosenberg's group found is that scientists now have a finer understanding of human evolutionary history.
"We can infer how our ancestors migrated across continents and became successful at living in a very diverse range of environments," Rosenberg said. "In addition, the genes are [a] database [that] can be used to search for disease genes in the human genome."
In the second Nature report, Carlos Bustamante, an assistant professor of biological statistics and computational biology at Cornell University, looked at DNA from European Americans and African Americans.
The researchers looked at 10,000 genes in 15 African Americans and 20 European Americans, all of whom were healthy.
"Across all the individuals, we found almost 40,000 DNA sites that varied. The African-American sample [had] more variations than the European-American sample, which is consistent with previous work showing higher levels of overall genetic diversity in African-Americans," Bustamante said.
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