Mon, Sep 26, 2016 - Page 7 News List

How we got here:
DNA points to a single
migration from Africa

Separate studies of diverse groups of humans all found that modern humans originated from one exodus from Africa

By Carl Zimmer  /  NY Times News Service

Intrigued, Willerslev decided to contact living Aborigines to see if they would participate in a new genetic study. He joined David Lambert, a geneticist at Griffith University in Australia, who was already meeting with Aboriginal communities about participating in this kind of research.

In collaboration with scientists at the University of Oxford, the researchers also obtained DNA from people in Papua New Guinea. All told, the team was able to sequence 83 genomes from Aboriginal Australians and 25 from people in Papua New Guinea, all with far greater accuracy than in Willerslev’s 2011 study.

Meanwhile, Mait Metspalu of the Estonian Biocentre was leading a team of 98 scientists on another genome gathering project. They picked out 148 populations to sample, mostly in Europe and Asia, with a few genomes from Africa and Australia. They sequenced 483 genomes at high resolution.

David Reich, a geneticist at Harvard Medical School, and his colleagues assembled a third database of genomes from all six inhabited continents. The Simons Genome Diversity Project, sponsored by the Simons Foundation and the US National Science Foundation, contains 300 high-quality genomes from 142 populations.

Examining their data separately, all three groups came to the same conclusion: People everywhere descend from a single migration of early humans from Africa. The estimates from the studies point to an exodus somewhere between 80,000 and 50,000 years ago.

Despite earlier research, the teams led by Willerslev and Reich found no genetic evidence that there was an earlier migration giving rise to people in Australia and Papua New Guinea.

“The vast majority of their ancestry — if not all of it — is coming from the same out-of-Africa wave as Europeans and Asians,” Willerslev said.

Reich and his colleagues then investigated whether people in Australia and Papua New Guinea descended from an early wave of humans from Africa. They could find no evidence supporting that idea in the genomes.

The people of Australia and Papua New Guinea descended from the same expansion of Africans that produced Europeans and Asians, Reich’s team concluded.

Working with a separate set of genomes, Willerslev and his colleagues came to much the same conclusion.

“The vast majority of their ancestry — if not all of it — is coming from the same out-of-Africa wave as Europeans and Asians,” Willerslev said.

However, on that question, Metspalu and his colleagues ended up with a somewhat different result.

In Papua New Guinea, 98 percent of each person’s DNA can be traced to that single migration from Africa, Metspalu and his colleagues found. However, the other 2 percent seemed to be much older.

Metspalu concluded that all people in Papua New Guinea carry a trace of DNA from an earlier wave of Africans who left the continent as long as 140,000 years ago, and then vanished.

If they did exist, these early human pioneers were able to survive for tens of thousands of years, said Luca Pagani, a coauthor with Metspalu at the University of Cambridge and the Estonian Biocentre.

However, when the last wave came out of Africa, descendants of the first wave disappeared.

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