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

They found, for example, that any two Bushmen in their study who spoke different languages were more different genetically than a European compared to 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. He's an author of the study, which appears in Thursday's issue of the journal Nature.

The study also found 1.3 million tiny variations that hadn't been observed before in any human DNA. That should help scientists sort out whether particular genes promote certain diseases or influence a person's response to medications. Findings like that could have payoffs both within Africa and elsewhere, experts said.

The genetic diversity of Africa's population is no surprise to scientists. Modern humans evolved on that continent about 200,000 years ago and have lived there longer than anyplace else. So that's where they've had the most time to develop genetic differences. The varied environments of Africa have also encouraged genetic differences.

Africa was the ancient source of modern humans worldwide, so "we're looking really back into the wellspring of our genetic origins here," said Richard Gibbs, a study author from the Baylor College of Medicine in Houston.

The study focused on genomes, a person's complete collection of DNA. The researchers decoded genomes of a Kalahari Desert bushman and of Tutu, the 1984 Nobel Peace laureate and former head of the Anglican Church of Southern Africa. They also decoded partial genomes from three other Bushmen.

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

But when researchers looked at Tutu's genome, they found surprising evidence that his mother's ancestry includes at least one Bushman woman. It's not clear how many generations back that woman lived.

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

While the study found many previously unknown DNA variations in Tutu's genome and especially the Bushman DNA, it's important to remember that overall, the genomes of any two people are virtually identical. The differences tracked in the new 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.

The new work "is a great start" toward more genome-decoding studies in Africa, said Sarah Tishkoff of the University of Pennsylvania.

More studies are needed to get a fuller picture of the continent's diversity, said Tishkoff, who studies that topic.