DNA Testing: In Our Blood

The research led Skorecki's team to Africa, where they tested members of the Lemba tribe, a group that believed they were descended from the Biblical land of Judea. Some of their DNA matched the Cohan signature. "We share a common paternal ancestry," says Skorecki. In 2001, Father Bill Sanchez, a Roman Catholic priest in Albuquerque, N.M., discovered he closely matched the Cohan signature, too. Sanchez's Jewish roots go back to Spain (his mother's heritage is Native American). Today he keeps pictures of his Christian and Jewish ancestors on his wall; in November he traveled to Israel. Now his niece Jessica Gonzales, 24, wants to go. Raised Catholic, she wants to learn more about her family roots. "I've been reading a lot about Judaism," she says.

DNA can now link regular people to high-profile ancestors—from Genghis Khan to the Iceman to the Irish warlord Niall of the Nine Hostages. Genghis-as-Great-Grandpa might be cool cocktail chatter, but since we don't have his DNA, proving direct descent is virtually impossible. Testing family roots through the Y chromosome and mitochondrial DNA has serious limitations, too: it tells you only about your direct paternal or maternal lineage, not the ancestor footprints hidden in the rest of your genome. Go back 10 generations, and that's 1,024 ancestors, says Stanford bioethicist Hank Greely. "Your Y might be from Japan, your mitochondrial DNA from Mexico and all other 1,022 ancestors from Sweden." Greely worries that customers may not fully understand what they're getting. One company, DNAPrint Genomics, does test markers outside of the Y and mitochondrial DNA, then maps them to four regions of the world (West Africa, Europe, East Asia and the Americas)—that's where Gates got his 50/50 ancestry. But the percentages are only estimates, not certainties. Some scientists are more than a little bit uncomfortable with the test. "I think the science of genetics is too important to become an entertainment," says Stanford geneticist Marcus Feldman, who also worries about the potential for racial stereotyping. With DNA tests, people may begin to link behaviors or characteristics with race, an idea that has been reviled in recent history. "I'm worried the more this is done, the more of that there's going to be."

The mutations in our DNA not only point to long-lost ancestors and homelands, they may also be markers for genetic disease. It's known as the founder effect: populations with marked susceptibilities to certain illnesses tend to be descended from a small group of ancestors who bred only within their own community. Sticking together meant a higher chance of inheriting a disease. The Amish, for example, are more likely to carry a genetic mutation for a condition called polydactyly, which causes extra fingers or toes. Ashkenazi Jews have an unusually high risk of certain cancers, as well as Gaucher and Tay-Sachs diseases. Men and women who inherit the mutation that causes Tay-Sachs are unaffected, but if they mate, they have a one-in-four chance of having an afflicted child. That's why Jewish parents-to-be are offered a panel of genetic tests before conceiving.

In rare instances, genetic mutations can offer medical benefits. Sickle-cell anemia is one of these double-edged swords. Patients who inherit a gene for the hereditary blood disease, which is common among people of African descent and causes red blood cells to lose oxygen, are also more likely to survive malaria. And the gene is highly prevalent in malaria-infested areas of Africa. Why? Scientists believe the gene has been naturally selected for its protective effect. Genealogical-testing companies aren't in the business of medical testing, but if you happen to discover an African ancestry you didn't know you had, should you be tested for sickle-cell? Possibly. In the brave new world of DNA testing, it would be a circuitous route to take. The express highway: submitting your genome for medical, not genealogical, analysis. In the future, this could be as routine as a physical. Already, the marketplace is eager to help. Most genealogical-testing companies stay as far from disease testing as possible, but other entrepreneurs are diving in. For $200 and up, a company called HealthCheckUSA will test your DNA (provided by cheek swab) for eight genetic illnesses, including celiac disease (an intestinal disorder) and hemochromatosis (an overload of iron). "People call us on a daily basis and let us know we helped save their life," says company president Holt Vaughan.

The more we learn about our families, the more we learn about our beginnings. Using DNA markers and mathematical time-clock calculations, researchers have identified our ancestral Adam and Eve. Scientists say that by using Y and mitochondrial DNA, they can date the earliest female to 150,000 to 250,000 years ago and the earliest male to 60,000 to 100,000 years ago. Until DNA testing, scientists debated whether humans originated in Africa or in a number of different places around the globe. These recent findings support the theory that humans descended from a small group of people who lived in Africa tens of thousands of years ago.

But when did groups of travelers leave that continent? Whom did they encounter and mingle with along the way? (At Arizona, Hammer is investigating the question of whether Homo sapiens and, say, Neanderthals mated and bore children.) Do major historical events, such as Alexander the Great's conquest of Central Asia, leave a genetic trail? These are questions National Geographic's Spencer Wells hopes to answer. The Genographic Project, launched last year, is inviting the public to test its own DNA, and already 110,000 individuals have purchased swabbing kits for $99.95. But the project's overarching goal is to collect DNA from indigenous populations worldwide whose DNA could hold clues to our origins and global migration—and to do it fast, before whole populations die out and leave their ancestral homelands. Early testing has already started in Southern Africa, where collaborator Dr. Himla Soodyall has collected blood samples from a small group of the San tribe. Genetically the San have among the oldest roots on earth and, it is believed, they provide a direct chromosomal link to ancestral Adam and Eve. Fi Mntungwa, 28, was one of the first to donate. "We were told about genes and a huge project that is looking into the origins of people across the world. It was very interesting," says Mntungwa. "I want to revive our ancient culture."

Last fall, Wells packed up 500 blood-collection tubes, needles, alcohol wipes and cheek swabs and headed off to Chad, one of the project's first testing sites, where he took 300 DNA samples from towns and villages around the country. Thirty-five to 40 came from members of the isolated Laal community, whose population, at fewer than 750, is declining. Wells fears that this community will die out within the next 10 to 30 years, taking with it valuable DNA and cultural traditions and an ancient language—information that could provide critical insights into the first people to live in Central Africa more than 40,000 years ago. "We can use DNA to figure out some of these great mysteries, to make sense of the past," says Wells.

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