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Sunday, October 23, 2005

The Latest Reconstruction of Human Migration Patterns from DNA Evidence

Discovery News reports:

Oct. 21, 2005— Modern humans left Africa in waves and colonized the Mideast first and then Europe, according to a new study that traced early human migration patterns through variations in DNA.

The study, which supports the "Out of Africa" theory that humans first emerged in Africa before migrating to other parts of the world, determined that South America was the last settled region.

"In (the) dataset (we studied), genetic diversity is highest in Africa and then decreases in the following order with diversity being the lowest in the Americas: Mideast, Europe, Asia, Oceania (the Pacific Islands), America. This indicates what the order of the human expansion might have been," said Sohini Ramachandran, lead author of the study, which is published in the current Proceedings of the National Academy of Sciences.

Based on this evidence the sequence of human settlement proceeded from Africa to the Middle East, then to Europe, then Asia, then Oceania, finally the Americas with North American being settled before South America.

The basic measurement is the degree of genetic variation within a population.

"Basically the idea is that we begin with a mother colony and then a small group of individuals leaves the mother colony and migrates away to form a new population," Ramachandran said. "This population grows in size and then a small group of migrants leaves this new population and forms another population some distance away."

Since each subset involved fewer representatives from the initial mother colony, DNA diversity decreased over time, with South Americans showing the lowest level of genetic diversity.

There were some interesting exceptions:

The only exceptions were the Maya, whose interbreeding with Europeans over the years actually has changed their genetic makeup, and three other populations: the Kalash, the Mbuti Pygmies, and the San.

The Kalash live in the mountains of Pakistan and believe they are descended from Alexander the Great. While the current study cannot confirm this claim, it does suggest the Kalash are genetically different from other Pakistanis.

The Mbuti Pygmies and the San both are hunter-gatherer populations in Africa. Ramachandran suggested that these populations could represent "our closest link to ancient modern humans genetically."

No real surprises here. The pattern suggested by this study agrees generally with the emerging consensus in the field and is accepted by most scholars. The only really questionable result was the suggestion that Europe was settled earlier than Asia, and that is certainly plausible.

Read the whole thing here.

For a slideshow presentation of an alternative interpretation of DNA evidence, one that has Asia being settled before Europe, see here. [pretty cool]

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