Using human genomes to illuminate the mysteries of early human history

September 21, 2011

ITHACA, N.Y. -- Cornell University researchers are utilizing the complete genome sequences of people alive today to shed light on events at the dawn of human history, such as the times of divergence of early human populations and of the "out of Africa" migration of the ancestors of modern Europeans, Asians, and other non-African groups.

Researchers studied the genomes of people from East Asian, European, and western and southern African descent and discovered that the San, an indigenous group of hunter gatherers from southern Africa, diverged from other human populations earlier than previously thought -- about 130,000 years ago. In comparison, the ancestors of modern Eurasian populations migrated from Africa only about 50,000 years ago. The study is published in the Sept. 18 issue of Nature Genetics.

Previous studies of human demography have primarily relied on mitochondrial DNA from the maternal line or Y-chromosomal DNA passed from fathers to their sons. The Cornell study uses the full genome of each individual, providing a richer, more complete picture of human evolution.

"The use of genome-wide data gives you much more confidence that you are getting the right answer," said Adam Siepel, Cornell associate professor of biological statistics and computational biology, and senior author of the paper. "With mitochondrial DNA, you are only looking at one family tree, with one pathway from each individual to its ancestors. We are sampling from all possible pathways."

"What's unusual about our methods is that, not only do they use complete genome sequences, but they consider several populations at once," said Ilan Gronau, the paper's lead author and a postdoctoral associate in Siepel's lab. "This is the first paper to put all of these pieces together."

Previous studies estimated that modern humans arose roughly 200,000 years ago in eastern or southern Africa; and that the indigenous hunting-and-gathering central and southern African San people -- one of the most genetically divergent human populations -- diverged from other Africans about 100,000 years ago.

But this study shows that the San people split from other African populations about 130,000 years ago (somewhere between 108,000 and 157,000 years ago). The estimate of an "out of Africa" migration of about 50,000 years ago is consistent with recent findings using other methods, the researchers said.
-end-
The study is available online at: http://www.nature.com/ng/journal/vaop/ncurrent/abs/ng.937.html

Contact Joe Schwartz for information about Cornell's TV and radio studios.

Cornell University

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