October 19, 2005

More Genetic Support for the Out of Africa Hypothesis

A new study by a team led by Sohini Ramachandran, an evolutionary biology doctoral candidate at Stanford University, and reportedly published yesterday in the Proceedings of the National Academy of Sciences supports the out of Africa hypothesis. I don't as yet have access to the Proceedings of the National Academy of Sciences. In fact, I'm even having trouble finding the abstract of the paper on the website of the Proceedings. However, National Geographic News outlined her team's research yesterday's online edition. The following is the central conclusion of the findings:

The team says their research kept pointing back to a single place of human origin—Africa.

"When we searched over 4,000 points around the world, we found that no point outside of Africa had as high a fit as any point inside of Africa," Rosenberg said. "So this seems to support an 'Out of Africa' historical model for human evolution."

Genetic diversity is highest, and thus oldest, in Africa. This fact has led many geneticists to point to the continent as the birthplace of humankind.

This research is much more detailed than the work of people like Alan Wilson and Rebecca Cann or Luigi Luca Cavalli-Sforza for example but comes to about the same conclusion. It also seems to come to a more firm conclusion. It will be interesting to see how anthropologists like Milford Wolpoff, who is a multiregionalist and sees modern man arising from “a process of change within a species" rather than in Africa and migrating to Asia, Europe and beyond. On Wolpoff's views check out this National Geographic article.

Another finding of the team had to do with the relative importance of genetic drift and natural selection.

The team concludes that perhaps 75 percent of humankind's modern genetic variation is the result of random genetic drift.

The researchers suggest that only 25 percent of our genetic diversity stems from the evolutionary process of natural selection—though such a number is still significant.

"Undoubtedly natural selection has played an important role in altering our genome during this migration out of Africa," Ramachandran said. "But it is kind of new to think that genetic drift might have been responsible for this much of human genetic variation."

This is very interesting stuff and I look forward to seeing the details.


Robert Boyd and Joan B. Silk, How Humans Evolved, Norton, 2003, pp 367-409

Luigi Luca Cavalli-Sforza, Genes, Peoples and Languages, North Point Press, 2000

Milford H. Wolpoff, Paleoanthropology, Alfred A. Knopf, 1980. pp. 217-249

Posted by Duane Smith at October 19, 2005 4:07 PM | Read more on Evolution |

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