Sunday, September 25, 2016

Many genes from out-of-Africa wave

Carl Zimmer reports in the NY Times:
Modern humans evolved in Africa roughly 200,000 years ago. But how did our species go on to populate the rest of the globe?

The question, one of the biggest in studies of human evolution, has intrigued scientists for decades. In a series of extraordinary genetic analyses published on Wednesday, researchers believe they have found an answer.

In the journal Nature, three separate teams of geneticists survey DNA collected from cultures around the globe, many for the first time, and conclude that all non-Africans today trace their ancestry to a single population emerging from Africa between 50,000 and 80,000 years ago.

“I think all three studies are basically saying the same thing,” said Joshua M. Akey of the University of Washington, who wrote a commentary accompanying the new work. “We know there were multiple dispersals out of Africa, but we can trace our ancestry back to a single one.” ...

In the 1980s, a group of paleoanthropologists and geneticists began championing a hypothesis that modern humans emerged only once from Africa, roughly 50,000 years ago. Skeletons and tools discovered at archaeological sites clearly indicated that modern humans lived after that time in Europe, Asia and Australia. ...
I posted before that the Out-of-Africa theory had been falsified, but now I am not so sure.
“The vast majority of their ancestry — if not all of it — is coming from the same out-of-Africa wave as Europeans and Asians,” said Dr. Willerslev.

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

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

Dr. 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.
As I understand it, the Out-of-Africa theory said that Africans completely displaced others 50k years ago. The previous theory said that humans had multiregional ancestors.

Now we know that Europeans and Asians definitely had ancestors from Neanderthal and other populations that were quite distinct from that out-of-Africa wave.

So maybe the out-of-Africa theory is 98% correct, in terms of nucleotide count. Maybe the multiregional theory is also mostly correct.

I do not trust Zimmer as long as he says things like "Modern humans evolved in Africa roughly 200,000 years ago." No, that theory has also been disproved, as human evolution has been accelerating in the last 10k years. There were no modern humans 200k years ago.

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