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Archbishop Tutu Gets Sequenced--And Finds a Surprise in His Ancestry

The richness of the African gene pool is demonstrated by decoding DNA from the anti-apartheid activist and several Bushmen hunter-gatherers

Archbishop Desmond Tutu has lent his genome to science.

In a confluence of developing-world politics and high-tech science the South African cleric, whose voice stood out in the long fight against apartheid, voluntarily shed some blood so that a high-tech sequencing machine could decode every letter of his DNA.

"The interest of Archbishop Tutu in participating in this project is that he wants to see a medical benefit extended to the southern African population," says Stephan C. Schuster of The Pennsylvania State University, one of the leaders of the sequencing project, and a member of a team that previously sequenced the genome of a woolly mammoth.

This genetic information, Schuster comments, can be used in tailoring drugs and diagnostic tools to the southern African population, which has not been targeted in previous sequencing efforts and sometimes has different responses to drugs for HIV and other diseases. Moreover, he adds, it is hoped that a pharmaceutical and biotechnology industry will respond to accommodate the medical needs of the region. "We will see an enormous diversification in [the] drug market and a large number of niches opening up," he says.

The decoding of Tutu's genome appears in a February 18 publication of a paper in Nature, which also describes the entire genome of an elder from a Bushman hunter–gatherer tribe, in addition to three other Bushmen who had the protein-coding portion of their genomes sequenced. (Scientific American is part of Nature Publishing Group.)

A ceremony on February 17 in Windhoek, the capital of Namibia, took place with Tutu, two Bushmen and high-ranking government officials from there and South Africa, including the former country's prime minister.

Previous studies have shown that Africa, from where humans set out to populate the rest of the world tens of thousands of years ago, harbors populations with the most genetic diversity, and this sequencing projectsupplies additional evidence for this consensus. "If you take two Bushmen groups that might live in walking distance to one another, they might have dramatically different languages, and we found them to be as genetically different as a European to a Chinese," Schuster notes.

Of the three billion unique DNA letters, or nucleotides, in the human genome, the new sequencing turned up 1.3 million novel variants—differences in single letters of DNA—that had not been seen before in other whole genomes that had been sequenced. Prior to this study, about nine million variants had been discovered.

Genetically, Tutu serves as a poster child for southern African genetics, with a lineage primarily from the Sotho-Tswana and Nguni language groups—and a surprise ancestor discovered from the sequencing results. "With a single person, we pretty much covered the largest possible breadth of diversity," Schuster says. "At the same time, there was this amazing outcome in which we could also show Archbishop Tutu coming from the Bushmen, which was something he didn't know and was pleased to learn."

The original sequencing of the human genome a decade ago is now being widely extended. "Overall, I think the paper is a good example of how genome sequencing is rapidly becoming a ubiquitous tool," comments Jonathan Pritchard, a geneticst from the University of Chicago, who cited a study reported last week about sequencing the genome of a human who lived 4,000 years ago on the western coast of Greenland.

Sarah Tishkoff, a University of Pennsylvania researcher who has done genetic testing on selected genetic variants in many parts of Africa, praised the work. "I'm excited [by a paper] that marks the first time a whole genome sequence has been characterized for a minority population within Africa," she says, contrasting it with previous African genome-wide sequencing projects, which until now had been confined only to the genome of a west African, who represented one of at least 14 ancestral populations on the continent. "It's been well known that the Khoisan or Bushmen have some of the oldest genetic lineages in the world. That's not new, we've known that. But if we can characterize more about their genetic variation we can learn something more about the evolutionary history of modern humans and, in particular, the population history of these click-speaking Khoisan group[s]."

Tishkoff remarks that future research could probe in more detail how this variation gives rise to particular genetic traits. The paper documents certain known traits, such as the absence in Bushmen of a European genetic variant for digesting milk. But Tishkoff adds that the researchers in upcoming studies could, for instance, admister to one of the Bushmen a lactose tolerance test. "Maybe he [the Bushman] can drink milk but has a different variant associated with the trait," she says, a finding that Tishkoff has confirmed through her own research in populations in other parts of Africa. The researchers who sequenced Tutu and the Bushmen now plan to create assays based on the 1.3 novel SNPs that will enable them to explore further genetic variation among populations throughout southern Africa.

Other than scientific celebrities, such as Craig Venter, most whole-genome sequencing has been conducted anonymously. And the issue of the potential for exploitations of indigenous peoples in population studies has often provoked ardent debate. The research team that probed the Bushmen's genes questioned each subject carefully about whether he wished to be identified by name in the paper. "It was important for them to be named," says Vanessa Hayes, a co-author on the paper from the University of New South Wales in Australia. "They felt that it would be uplifting for a group of individuals who are often perceived as underdogs." (The four hunter–gatherers decided that they would be prefer to be called Bushmen, a name that is sometimes considered derogatory.) None of the companies or researchers who participated plan to take out patents based on the data.

Schuster remarked that this latest work adds to an emerging picture of humanity's genetic vigor. "We should all be thankful that we find this large amount of genetic diversity in the human population," he says. "It allows for a good prediction for our future. We will be a very robust and resilient population. Our population numbers are proof of that."

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