Where We Come From
Recent advances in genetics are starting to illuminate the wanderings of early humans
Gene-based anthropology also struggles with the specter of racism. Australia has banned researchers from publishing work involving Aboriginal DNA, and India bars the export of its citizens' genetic matter. Geneticists are dismayed by these attitudes; if there's one thing the genes show, they say, it is that there is no such thing as race. The external differences that most people would use in defining race--skin color, eye shape, height--are genetically inconsequential, minor variations that evolved in response to the environment, the genetic equivalent of a sunburn. For instance, a change in just one gene accounts for Northern Europeans' fair skin, which may have developed to better absorb sunlight and synthesize vitamin D. "We are all brothers," says Stanford's Underhill, "and we're all different."
Custom medicine. The differences may be minor, but they matter a lot to medical researchers. African-Americans are more apt to get sickle-cell anemia; some people with Eastern European roots have a gene that confers resistance to AIDS; women with Scottish ancestry are predisposed to one form of breast cancer. So researchers are using molecular anthropology to seek the origins of disease and then using that knowledge to create customized treatments. They're looking increasingly at nuclear DNA--the DNA of genes and inherited traits--which mingles with every generation. "Go back five generations," says Yale's Kidd. "You have 32 ancestors. At each nuclear locus you may have a gene from a different set of two of those ancestors." Thus nuclear DNA paints a much fuller picture of the past than mitochondrial and Y, which represent only two ancestors in any generation. Kidd is now studying nuclear DNA in 33 populations around the world, seeking a better understanding of schizophrenia, Tourette's syndrome, and alcoholism. Science is far from being able to simply scan the human genome to find the causes of complex diseases like these. But the day will come, and soon, when it will be possible to pinpoint the genetic roots of disease without the geographic history. "Who cares where patients come from?" asks Aravinda Chakravarti, head of the institute of genetic medicine at Johns Hopkins University. "We'll be looking at what kind of diabetes is there, not whether they came from Timbuktu or Thailand or Towson."
But for some people, knowing where they came from matters a lot. Alice Petrovilli, a 71-year-old Aleut living in Anchorage, says she was eager to participate in a University of Kansas study on Aleut origins, even though other Aleut elders refused. "I think it's important. People always acted like because we were so far away we were a substandard species. It proves we were out here for a long, long time." Her DNA helps establish the Aleuts as people who migrated through Alaska and arrived in the Aleutian Islands 4,000 to 6,000 years ago and are genetically related to the Chukchi of northeast Russia.
Pearl Duncan is also interested in where her genes have been. The 51-year-old Jamaica-born writer had exhaustively researched her family history through genealogical records and traced several nicknames to Ghanaian dialects. But the trail ended there, lost in the Middle Passage when her slave ancestors were brought from Africa to the New World. So she tested her father's Y against DNA she gathered from members of Ghanaian churches in New York, where she lives, and found a match. "I really traced a cultural voice that is missing from the African-American narrative," says Duncan, who is writing a book about her search. She is incorporating her Ghanaian history with that of John Smellie, her Scottish ancestor 12 generations back.
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