Kelly L Ross, PH.D. provides the following description in his essay "Genetic Distance and Language Affinities"

Genetic Distance Between Autochthonous Human Populations

"Genetic drift" is the phenomenon by which small mutations in DNA (or RNA, and the proteins that are coded by them) add random variations over time to genetic material, resulting in differences between isolated groups of animals, whether of different species or of the same species that are not inter-breeding. Thus there is about a 5% difference in DNA between humans and our closest Primate relations, Chimpanzees. Between human populations, there is always much less than 0.1% difference. What these differences are and how much they vary can be used to construct a tree showing the relationships between human populations. The following tree is the result of such research, reported by Luigi Luca Cavalli-Sforza. The numbers across the top show the percentage difference in DNA, which is thus no more than 0.03% for all human beings. The most dramatic characteristic of the tree is the division between populations in sub-Saharan Africa and the rest of humanity. This is usually interpreted to mean that modern humans originated in Africa and that the population from which the rest of humanity descended left Africa somewhat less than 300,000 years ago, ultimately replacing earlier humans, like the Pithecanthropines (Homo erectus, like Peking Man, etc.), who had also evolved in Africa but left many thousands of years earlier.

Percent defference in DNA
Source: "Genes, peoples and languages," by Luigi Luca Cavalli-Sforza, Scientific American , (November, 1991)

Part of this research was the theory of "Eve," a single female in Africa, around 200,000 years ago, from whom every living human being is now descended. This does not mean that there were not other human females -- there were -- or that we are not descended from them too -- we are. The theory is based on the circumstance that some human genetic material is contained in the mitochondria, little organs in a cell outside the nucleus (where most genetic material is contained). Sperm cells do not pass on their mitochondria to a fertilzed egg and so all human mitochondrial DNA is inherited from the mother. If a woman has only sons (a highly desirable result in many traditional cultures), then her own mitochondrial DNA is actually lost. Over time, this seems to have happened to all lines of descent of mitochrondiral DNA, except one, the line from "Eve." Another interesting feature of the chart is the closeness of American Indians to modern population across Europe, the Middle East, and northern East Asia. Thus, curiously, Europeans are more closely related to American Indians than to Polynesians. Finally, it is noteworthy that skin color is not at all helpful is providing clues to genetic affinity. The darkest colored people on earth, in Africa, India, Melanesia, and Australia, are scattered between groups that are only distantly related. Dark skin color is certainly a function of living under the equatorial sun for many generations, but all human populations have the genetic wherewithal to make that adaptation.

The March 29, 1999, Newsweek reports (p. 72) that population geneticist Jody Hey and anthropologist Eugene Harris, of Rutgers University, reported in the Proceedings of the National Academy of Sciences that, using DNA techniques again, the African population split from the non-African about 189,000 years ago. The article presents this as well before the emergence of "modern" Homo sapiens and somewhat surprising, but it actually seems fairly consistent with the numbers presented above. If Home sapiens goes back 300,000 years and "Eve" is around 200,000 years ago, then it is not beyond the bounds of crediblity that we could get the basic split in the populations not too long after that. The margin of error is also probably pretty large.
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last updated 10 Jan 2008