Fossils in the Blood
Scientists Find Ancient DNA in Living Africans
April 4, 2000
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.
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 clergy. "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."
But then, no one ever needed DNA analysis to oppress the San. That's why Xixai Gakekgosi, a politically active villager, doesn't fear racist ramifications from the new research. It can hardly make matters worse, he says. "People already see us as outsiders and look down on us."
In nearby Quaa village, some women spot a mophane worm in a tree, and a boy clambers up into the branches to knock it down. Like the sweet, yellow-orange motsontsojane berries, this worm is one of the many delicacies relished by the !Kung hunter-gatherers. Avoiding the sharp, black spines that jut out from its blue and yellow body, a woman tosses the worm, fat and long as a breakfast sausage, onto hot coals. While it cooks, an elder named Tcgoma Xontae plays a handmade lyre called a quru and sings in a high, beautiful voice.
But if the scene appears idyllic, the life of the San is not. "My parents could control the forest and go out to hunt," says Xontae. "But now someone else controls our life." Indeed, for all practical purposes, the Botswana government has barred the San from hunting. Most have been removed from the Central Kalahari Game Reserve. The few licenses that are granted limit the hunting season and the number of animals the San can kill.
It's merely the latest chapter in an ancient history of oppression. The Bantu-speaking Africans, farmers who expanded throughout most of sub-Saharan Africa from the area near the present-day border between Nigeria and Cameroon, pushed the Khoisan off their land, sometimes enslaved them, and deemed them inferior. White Christian settlers slaughtered thousands of these indigenous people and had serious debates about whether the Gospels applied to them. (The Khoikhoi, called Hottentots by the Dutch settlers, herd cattle, while the San, to whom they are closely related, live by hunting and gathering.)
In the 1970s, the army of the old apartheid South Africa used the San as scouts in its war against Namibia and Angola. Pawns in a war that wasn't theirs, those scouts and their families -- about 4,000 people altogether -- now live in a tent city in South Africa, hundreds of miles from their homeland. And in Botswana, which has some of the world's richest diamond deposits, mining interests inevitably prevail in land disputes.
The San are quite possibly the most studied indigenous people on earth, yet myths about them abound. The San are reputed to be wholly innocent and peaceable -- "the Harmless People," as the title of one influential book put it -- but, as the anthropologist Richard Lee documented, murder does happen, and the San sometimes execute the perpetrators.
But nothing has been as damaging as the myth that the San are backward and primitive, which is profoundly entrenched in southern Africa. One widespread misconception is that they do not wash. A recent report on the educational problems facing the San -- they have astronomical dropout rates -- reported that one boarding school headmaster wouldn't give San children mattresses or even blankets, on the rationale that their unwashed bodies would dirty the bedding. It is possible that their isolation -- first geographic, then cultural -- is what preserved the ancestral genetic patterns.
Forced to abandon their traditional way of life but barred by prejudice from joining modern life, the San now subsist in a kind of limbo. In this region of Botswana, they live mainly on government food handouts. While they used to store what they gathered for future use, now they try to sell it -- and the cash often buys alcohol and tobacco.
"We don't have a life, says Xuma Kgao. "There is nothing we can do for ourselves. Our hands and feet have been cut off."
Joining the discussion on the origin of humanity, a young mother named Nxae Nxu rules out the possibility that people evolved from animals. "The first two people were San, and we were always like this," she says. So why do the races look so different? "That's a tough one," she says, laughing. "After God created these first two people, they had children, and generation after generation they started to change a bit."
And that, pretty much, is what the geneticists also think. They examined DNA from the Y chromosome, which is passed only from father to son, and from the mitochondria, tiny cellular proto-organisms that are passed down the maternal line. Using various mathematical models to estimate how frequently mutations are made, the researchers estimated the age of the different genetic variants, called polymorphisms.
At least two teams, working independently and looking at different parts of the Y chromosome, found that the oldest variants are most common in the Khoisan. Jenkins and Soodyall also analyzed the mitochondrial DNA. Virtually all of the !Kung have the most ancient mitochondrial fragments, which date to about 120,000 years ago, roughly the time humans are thought to have evolved into their modern form. The genetic findings accord with at least one line of fossil evidence, and various likely mathematical models yield similar results. Yet just as fossil evidence has often been reassessed, this genetic analysis could be off the mark. As one !Kung man said about the research, "I don't know my relationship to the first people, because I wasn't alive then."
One of the myths about the San is that their genes are what enable them to survive in the harsh Kalahari climate, where the nights are frigid, the days scorching, and water is scarce. But while they may have evolved some advantageous traits, the notion that they owe their survival mainly to unique physical characteristics is false, says Phillip Tobias, a South African anthropologist who has studied the Khoisan. He notes that the San traditionally filled ostrich shells with water and buried them for use in dry times, that they drank the juices out of the stomach of freshly hunted animals, and that they smeared their skin with animal fat to keep from dehydrating. Such "cultural tricks," he says, were more important than any genetic mutations in helping them to survive.
Now the San face the harsh climate of a culture stacked against them. Again their survival depends not on their genes, but on the ability to adapt culturally. But this time, their way of life depends not only on the San themselves, but on whether southern Africa's majority populations can overcome one of humanity's oldest and possibly inherent characteristics: prejudice.
Research intern: Elinore Longobardi
More articles by Mark Schoofs.
More articles by Mark Schoofs.
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