DNA Testing: In Our Blood

Feb. 6, 2006 issue - Brian Hamman had always wondered: what was up with his great-grandfather Lester? Hamman, an avid genealogist, could trace his patrilineal line back to 19th-century rural Indiana, but there was a glitch in the family records. Great-Grandpa Lester, the documents showed, was born before his parents were married. So was Lester really a Hamman? Was Brian? Three years ago DNA tests confirmed the lineage and a simple family mystery was solved: Lester's parents had hooked up before they walked down the aisle on July 25, 1898. Lester was indeed a Hamman, and so is Brian. "I'm delighted," he says.

For Debra Anne Royer, DNA unlocked a deeper mystery. Adopted at birth, Royer knew nothing about her biological parents. But certain physical traits—wide nose, dark skin—led people to guess that she was Iranian or even Cambodian. "I always wondered," she says. Two hundred dollars and a swab of her cheek gave her an answer: Royer's maternal ancestors were most likely Native American. The knowledge, she says, "makes you feel more of a person."

And then there's Prof. Henry Louis (Skip) Gates Jr., head of Harvard University's African-American Studies department. Gates always knew he wasn't 100 percent African-American. According to family legend, Gates's only white ancestor was a slave owner named Samuel Brady, who had sex with Gates's great-great-grandmother Jane on his farm in Maryland in the 1800s. But recent DNA analyses turned Gates's world upside down. There was no trace of Brady on Gates's genome. Further testing revealed that Gates, in fact, carries as much Western European blood as he does African—and that one of his white ancestors was probably an Irish servant who met Gates's sixth or seventh great-grandfather sometime before 1700. "I'm thinking I'm a Brady and maybe I'm from Nigeria, and here I am descended from some white woman," says Gates. "It's incredible."

Our blood holds the secrets to who we are, and, increasingly, individuals, families and research scientists are using genetic testing to tell us what we don't already know. Human genomes are 99.9 percent identical; we are far more similar than diverse. But that tiny 0.1 percent difference holds clues to our ancestries, the roots of all human migration and even our propensity for disease. Tens of thousands of Americans have swabbed their cheeks and mailed in their DNA to companies nationwide for testing. 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, which has 52,000 customers. "Now the interest is huge." So huge that celebrities like Whoopi Goldberg and Quincy Jones are signing on. This week Gates and other high-profile black Americans will tell their stories on PBS's new series "African American Lives."

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. Last month one group of scientists found that 40 percent of the world's Ashkenazi Jews descend 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."

Human history lives in our genes. 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, spelling mistakes or 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 the places they lived in the world. Scrape the inside of your cheek a few times, and for $100 and up, a testing company will put your DNA under its microscope, map your markers into your own genetic pattern called a haplotype, then tell you which "haplogroup," or major branch of the human tree, you hail from.

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