New York Times Book Review,
March 2, 2003Link
Review of The Journey of Man: A Genetic Odyssey, by Spencer Wells.
(Princeton University Press, 2003)
You probably haven't heard of the Yagnob, but Spencer Wells has. In fact, he traveled to war-torn Tajikistan to meet these Central Asian people, driving an old Soviet van over mountain passes and along dirt roads of the remote Zerafshan Valley. The Yagnob were not so hard to find 1,500 years ago. They were masters of the Silk Route, and their language was the lingua franca of trading merchants from Persia to China. But the Yagnob have dwindled, and by the time Wells reached the Zerafshan Valley, he could find only a single village where Yagnobi was still spoken.
Wells is a geneticist, and he had come all this way to get samples of Yagnob blood. The blood of the Yagnob tells a story -- one that can also be read in the blood of the Yanomami, the Yemeni and you. It is the saga of humanity over the past 60,000 years. ''Our genes carry the seams and spot-welds that reveal the story,'' Wells explains. He and other geneticists have identified genealogical markers in human DNA that record the spread of humans around the world.
It has taken decades to make sense of these markers, because our genomes are mostly a scrambled sample of the DNA of our parents. But men pass along virtually intact a chromosome known as the Y. On rare occasions it picks up small mutations. A father will pass a mutant Y down to all his sons, who will pass it down to theirs, and so on. The mutation marks them all as his descendants. And because these mutations hit the Y chromosome at a roughly steady rate, they can also act like a molecular clock that shows when that common ancestor lived.
Working at Stanford and Oxford universities, Wells has helped identify these Y chromosome markers. In ''The Journey of Man,'' he translates them into the epic of our species. He explains how all men alive on earth today can trace their ancestry to a single African man who lived around 60,000 years ago. This genetic Adam belonged to a new breed of humans that evolved in Africa, with a brain far more sophisticated than that of their ancestors. It's probably no coincidence that these new humans were soon expanding their range, spreading throughout Africa and then out of the continent altogether. In Asia and Europe, they outcompeted the other human species they encountered -- Neanderthals and Homo erectus -- until they were the only two-legged ape left on the planet.
Wells offers fascinating evidence that the first wave out of Africa may have been a coast-hugging people who depended on the sea for food. They traveled east through India and Southeast Asia until they reached Australia around 50,000 years ago. A second wave migrated out of Africa later, moving inland. Wells speculates they were adept at hunting animals of the grasslands, and followed their game to the Central Asian steppes. From there, one branch of hunters steered west to Europe. (The Yagnob share genetic markers with the British and the Basque, markers that other people in Tajikistan lack.) Another branch of the steppe people populated East Asia. Around 20,000 years ago, a few hundred of these East Asians crossed the Bering Straits to settle North America. But later the coastal people also made their way up to the New World.
The Y chromosome not only documents where people went but how their lives changed. Agriculture appears to have been brought to Europe by Middle Eastern people who settled in the Mediterranean. Northern Europeans -- who had been on the continent for 20,000 years -- also took up farming, and eventually the new source of food allowed both peoples to multiply.
Wells traces our distant history with a mix of clarity and charm that's rare among scientists. He makes the complexities of population genetics wonderfully clear with smart metaphors. And he navigates gracefully from his home waters of genetics into paleontology and climatology and back again. I was disappointed, though, to watch him steer clear of one important subject: the transformation of our genomic heritage into a commercial product.
Geneticists are busy these days searching genomes for the variations that make people vulnerable or resistant to diseases. They hope their discoveries will lead to new kinds of drugs, and perhaps even a new kind of ''personalized medicine,'' in which doctors can tailor treatment to their patient's individual genomes. But geneticists must analyze thousands of genomes to isolate the effect of any individual gene. Databases from far-flung peoples are particularly precious. In some parts of the world people have evolved natural defenses against diseases like malaria and AIDS. On remote islands settled by a few founders, people may suffer high rates of certain genetic diseases. But only by understanding the history that produced genomes is it possible to decode their medical secrets. It shouldn't be a big surprise, then, that Wells is a consultant at Genomics Collaborative, a Massachusetts outfit that manages a medical collection of DNA and tissue samples from 120,000 people around the world.
But genomic prospecting has also triggered angry backlashes. Critics ask why companies should make fortunes from the genes of others -- particularly poor groups of people who are facing cultural extinction. In recent years, for example, an Australian enterprise came to the Pacific island of Tonga and proposed paying the government for the right to set up a genetic database. Church leaders and political activists protested. First they came for our sandalwood, opponents complained; now they are coming for our genes. The project is now dead in the water.
There are important arguments on both sides of this debate, but Wells doesn't do them justice. ''Scientists have a responsibility to explain the relevance of their work to the people they hope to study,'' he writes, ''in order for their participation to become what it really is -- a collaborative research effort.'' What sort of a collaboration is this, really? Do the Yagnob get a financial stake in the secrets in their blood, the way Western scientists do? Wells doesn't tell us. That's a shame, because elsewhere in the book he shows that he isn't afraid to confront sticky issues, like the racist legacy of eugenics.
It's possible that Wells decided the messy implications of modern genetics might distract his readers from the epic that he and his colleagues have uncovered. But just the opposite is true. The battle over our genomes is a stark illustration of how relevant the wanderings of cave men 50,000 years ago remain today.
Copyright 2003 The New York Times. Reprinted with permission.