The Ties That Bind

Our blood holds the secrets to who we are. Human genomes are 99.9 percent identical; we are far more similar than diverse. But that tiny 0.1 percent difference reveals clues to our ancestries. In recent years, as companies have sprung up claiming to trace one's background through genetic testing, tens of thousands of people have swabbed their cheeks and mailed in their DNA to discover more about where they came from. Far-flung cousins are finding each other; family legends are being overturned. Six years ago the term "genetic genealogy" was meaningless, says Bennett Greenspan, head of Family Tree DNA, a testing firm with 52,000 customers. "Now the interest is huge."

As individuals track down their personal family narratives, population geneticists are seeking to tell the larger story of humankind. Our most recent common ancestors--a genetic "Adam" and "Eve"--have been traced back to Africa, and other intriguing forebears are being discovered all over the map. One group of scientists recently found that 40 percent of the world's Ashkenazi Jews are descended from just four women; another reported that one in five males in northwest Ireland may be a descendant of a legendary fifth-century warlord. The most ambitious effort by far is the National Geographic Society's $40 million Genographic Project, which aims to collect 100,000 DNA samples from indigenous populations around the world over the next five years. The goal: to trace human roots from the present day back to the origin of our species. To create, says project director Spencer Wells, "a virtual museum of human history."

How does genetic testing work? The DNA in each of our cells not only dictates the color of our eyes, it also contains the footprints of our ancestors. A child's genome is almost entirely a mix of genetic material created by the union of mother and father. Only two parts of the genome remain pure, untainted by the influence of a mate's DNA: the Y (passed down from father to son), and mitochondrial DNA (from mother to both sons and daughters). Occasionally, mutations arise in these regions, creating unique sequences of A's and G's and C's and T's that serve as genealogical signposts or markers--providing links backward in time, not just to paternal and maternal ancestors but to where they lived. Scrape the inside of your cheek, and for $100 and up, a testing company will map your DNA markers into your own genetic pattern called a haplotype, then tell you which "haplogroup," or major branch of the human tree, you hail from.

Armed with haplotypes, genealogists can now join Surname Projects on the Internet. These online communities allow people to compare genomes. Find a match, and you may be able to fill in branches on your family tree. Looking for relatives without your surname? You can search within individual testing companies or in public databases like the Sorenson Molecular Genealogy Foundation, funded by Mormon philanthropist John Sorenson, which has collected 60,000 DNA samples and ancestral charts. "Eventually, you'll be able to query the database and find relatives you don't even know you have," says Sorenson's chief scientific officer Scott Woodward.

The science can also uncover links to ancient cultures, even religious heritage. Dr. Karl Skorecki was told from childhood that he was one of the Cohanim, descended from Moses' brother Aaron, a high Jewish priest. Sitting in synagogue one day, he noticed that another Cohen who was called to the Torah looked nothing like him. "He was a Jewish male of North African ancestry, I am a Jewish male of European ancestry," Skorecki, of the Technion-Israel Institute of Technology, remembers thinking. "If he has that tradition and I have that tradition, perhaps there's a greater chance that we share similar markers on the Y chromosome." Would the oral history passed down from Cohen father to Cohen son also be inscribed in their DNA? After studying DNA samples, Skorecki, geneticist Michael Hammer of the University of Arizona and colleagues at University College London uncovered a genetic Cohanim signature.

The research led an international team of researchers to Africa, where scientists 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 Cohanim signature. "We share a common paternal ancestry," says Skorecki. In 2001, Father Bill Sanchez, a Roman Catholic priest in Albuquerque, New Mexico, discovered he closely matched the Cohanim 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.

The science does have its limits. Since researchers don't have any actual DNA from the likes of Genghis Khan, proving direct descent from certain historical figures 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 ancestral 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). But the percentages are estimates, not certainties. Some scientists worry that these tests will be used as entertainment, or that people will link behaviors or characteristics with race, an idea that has been reviled in recent history.

The most interesting results may come from investigations into human, rather than personal, ancestry. 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 identifiable female to 150,000 to 250,000 years ago and the earliest identifiable 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 with partner IBM, is inviting the public to test its own DNA, and already more than 100,000 individuals have purchased swabbing kits for $99.95. But the project's overarching goal is to collect samples from indigenous populations worldwide whose DNA could hold clues to our origins and global migration--and to do it fast, before these fragile populations die out or 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 may provide a direct chromosomal link to the 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.

Not everybody supports the Genographic Project. Indigenous populations have had their share of colonialist pillaging, and many, still distrustful of the dominant culture, are wary of handing over their blood and the information it contains. Debra Harry, director of the advocacy group Indigenous People's Council on Biocolonialism, has posted a petition on her Web site opposing the project, which she says has 1,000 signatures so far. But some members of the Seaconke Wampanoag tribe in Seekonk, Massachusetts, have already been tested. "We have our cultural story of creation, but there's another story that needs to get out, and it's right inside each and every one of us," says the tribe's chair, Michael Markley. Wells says he understands indigenous concerns, but he has found that once the details are explained, the excitement builds. "Everybody finds it fascinating that they're carrying this historical document inside their cells." Scientists are now piecing together the first volume of this history.

The Ties That Bind | News