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Decoded DNA of some Africans shows genetic diversity

Scientists who decoded the DNA of some southern Africans have found striking new evidence of the genetic diversity on the continent, and uncovered a surprise about the ancestry of Archbishop Desmond Tutu.

Any two bushmen in their study who spoke different languages were more different genetically than a European compared with an Asian. That was true even if the bushmen lived within walking distance of each other.

"If we really want to understand human diversity, we need to go to [southern] Africa and we need to study those people," said Stephan Schuster of Pennsylvania State University, an author of the study, which appears in today's issue of nature, the International weekly journal of science.

The study found 1.3 million tiny variations that hadn't been observed before in any human DNA. The discovery should help sort out whether particular genes promote certain diseases or influence response to medications.

The genetic diversity in Africa is no surprise to scientists. All modern humans evolved there about 200,000 years ago and have lived there longer than anywhere else.

"We're looking really back into the wellspring of our genetic origins here," said study co-author Richard Gibbs of Baylor College of Medicine in Houston.

The study focused on genomes, a person's complete collection of DNA. The genomes of a Kalahari Desert bushman and of Tutu, the 1984 Nobel Peace laureate, were decoded. Also decoded were partial genomes from three other bushmen.

Tutu was included to represent Bantu ancestry, in contrast to bushmen. The Bantu have a tradition of farming while bushmen are hunter-gatherers who represent the oldest known lineage of modern humans.

In Tutu's genome, researchers found surprising evidence that his mother's ancestry includes at least one bushman woman. How many generations back is not clear.

Tutu told The Associated Press that discovering he is related to "these wise people" made him feel "privileged and blessed."

The genomes of any two people are virtually identical. The differences tracked in the study lie in individual "letters" of the 3 billion-letter genetic sequence.

"We are all very, very similar to one another," Schuster said.

Gibbs said the DNA differences discovered in the African subjects can't be used to support racist arguments. He noted that DNA diversity within a continent is greater than the differences between continents. The study found, in fact, that bushmen are as different from a previously studied Yoruba man in Nigeria as a European man is.

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