Fossils in the Blood

Scientists Find Ancient DNA in Living Africans

DOBE, BOTSWANA—In the shade of a tree, 140 kilometers from the nearest paved road in an endless plain of scrub brush and sand, Nxuka Nxu is discussing the origin of human beings. An elder of the !Kung San hunter-gatherer tribe, with a face as wrinkled as a raisin, she says emphatically, "We are the first people."

Many traditional cultures mythologize themselves as the progenitors of all humanity, but the !Kung San people, sometimes called the Bushmen of the Kalahari, have a better claim than most. Geneticists have found fragments of DNA in the Khoisan ethnic group, of which the !Kung are one tribe, that appear to date back to the very first human beings. Most other African ethnic groups lack these genetic traces, as do people from Asia, Europe, and the Americas. Indeed, a few of these ancient genetic fragments have been found only in the Khoisan.

These findings, which are still emerging, "help us understand our past," says Himla Soodyall, a South African geneticist who has conducted much of this work. In addition to bolstering the theory that modern humans arose in Africa and then migrated around the globe, these findings also weigh in on the newer debate of exactly where humans originated. They support the idea that the cradle of humanity is southern Africa, where the San live, and not eastern Africa, as was widely thought.

San elders with their grandson: scientists have found genetic fragments in this tribe that may date back to the origin of humans.
photo: Mark Schoofs
San elders with their grandson: scientists have found genetic fragments in this tribe that may date back to the origin of humans.

On this continent, where people are trying to kindle an African renaissance, this new genetic research "can reinstill pride in the richness of African history," says Soodyall.

Yet the research could also be twisted to bolster deep-seated prejudices against the San, probably the most abused and downtrodden ethnic group in southern Africa. One method used to determine the age of genetic fragments is to compare them to the genes of chimpanzees and other nonhuman primates. The ancient DNA segments in the Khoisan are more closely related to chimp DNA than are those of any other people. Given how the Khoisan have been dehumanized—scientists once postulated that they had fewer chromosomes—it is all too easy to imagine how this research could be misused. Here in the village, an elderly San man named Xuma Kgao ponders the idea that his people bear traces of the first humans. "God made us lucky in that way," he says. But, noting how his culture has been denigrated and destroyed, he adds, "It's not luck anymore. It's a drawback."

So, given the tragic history of the San, not to mention all the other ethnic and racial bigotry this continent has endured, perhaps the most astonishing fact is that the research appears not to have inflamed prejudice. In fact, when Soodyall and her colleague Trefor Jenkins presented their preliminary findings to a 1997 conference devoted to Khoisan identity, they were met with praise, not protest.

That's partly because the researchers vigorously resist bigoted interpretations of their findings. They note that the genetic traces that date back to the first humans are just that: traces, fragments picked out of the 3 billion letters that make up the human genetic code. In other parts of their DNA, the Khoisan have very recent mutations. "It's not as if they stopped evolving and were put away on a shelf," says Michael Hammer, a University of Arizona geneticist who has collaborated with Jenkins and Soodyall. "They preserve ancient lineages, but they are not an ancient group. They are as evolved as any other people."

The new South Africa might be the best place for such research, because freedom from the crushing oppression of apartheid has fostered a candid and mostly positive discussion about ethnic differences and identity. In his inauguration speech last year, South African president Thabo Mbeki vowed to "rediscover and claim the African heritage," noting that, "From South Africa to Ethiopia lie strewn ancient fossils, which, in their stillness, speak still of the African origins of humanity." What geneticists have essentially discovered is that DNA is also strewn with "fossils," mutations that have been preserved through generations.

In addition to shedding light on humanity's origins, "population genetics," as this branch of science is known, can also illuminate more recent episodes in history. For instance, Jenkins and Soodyall have studied the Lemba, a group of so-called Black Jews who claim to be a lost tribe of Israel, and found that many of them have genetic markers similar to those of Semitic people. Another team of geneticists has discovered that a few of the Lemba even have a marker common among the Jewish "Cohens," a hereditary lineage of priests. "There are so many stories written in the genes," says Soodyall. "My goal is to understand the history of each mutation."

For Jenkins, the goal is to "counter racism scientifically" and candidly. "You can't claim there are no differences" among ethnic groups, he notes, "because people will say, 'We can see we're not the same.' " What genetics does show is that the similarities among all humans far outweigh their differences.

Under apartheid, when every citizen was assigned an official racial identity, people used to ask Jenkins to help them gain a "race reclassification." He recalls, "I would say to the person, 'What race do you want to be classified as?' " Examining their blood, it was always easy to find genetic markers in blacks or "coloreds" that were also present in whites, allowing Jenkins to bolster their appeal to be racially reassigned. As Jenkins explains: "What people use to classify the races"—skin color, hair type, and nose shape—"represents only a very small proportion of the whole genome."

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