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Are You My Cousin?

How DNA technology can help solve mysteries in your family tree.

Then he got an idea. Geneticists had recently proven that some African Americans were descendants of Thomas Jefferson or a close male relative of his, and that certain Jewish men were descendants of the priestly line of the biblical Aaron. If genetic testing could help other people discover their ancestry, Greenspan thought, “Why not me?”

He tracked down Michael Hammer, Ph.D., at the University of Arizona, one of the geneticists whose work had been in the news. All Greenspan wanted to do was pay to submit a sample of his DNA. But Hammer wasn’t interested. “Someone should start a company doing this kind of testing,” the doctor sighed. “I get calls from crazy genealogists like you all the time.”

And that, Greenspan says, “was a true eureka moment.” He sat down, wrote a business plan, and within months launched Family Tree DNA, the first company to offer the general public the opportunity to use genetic science in the pursuit of genealogy. And he enlisted, as his chief scientist, Michael Hammer.

To understand how all this works, it helps to know that almost all of the genetic material you inherit from your parents is thoroughly mixed together, and is thus unique to you. It can be used to link you to living relatives, but it can’t tell you much about your ancestors.

There are two intriguing exceptions, though—and, so far, they form the whole basis of genetic genealogy. One is something called mitochondrial DNA (mtDNA), which a mother passes on to all of her children. If you’re a woman, you have that. If you’re a man, you also have your father’s Y-chromosome, which is passed down, intact, from father to son to son. (For more details, see “Under the Microscope,” below.)

Because these two genetic elements remain virtually unchanged generation after generation, they create two clear, if narrow, trails you can follow back through time—the line of your mother’s mother’s mother and so on, and the line of your father’s father’s father and so on. Because these genes don’t come bearing microscopic labels that read “Senegalese” or “Mongolian” or “Dutch”—let alone “Grandma Gertrude” or “Great-grandpa Fred”—the only way to determine anything about your ancestry based upon your DNA is to find your genetic matches and then compare your paper (or digital) family tree with theirs. Because you and your matches share a common ancestor, their research could fill gaps in your own—and vice versa. Most genetic genealogy companies will put you in touch with your genetic matches, but the rest is up to you. “What I tell people,” says James Freed, Ph.D., an avid genealogist and retired professor of zoology who taught genetics, “is that you have to have a hypothesis about your family beforehand.”

Fortunately for me, I had one. In fact, I had more than just a hypothesis. I actually knew where my ancestors had come from in the 19th century. Still, when I first received my DNA test results, I found the data confusing. I liken it to walking into an antiques shop with the lights off: you know the place is full of fascinating stuff, but you have to wait a bit, until your eyes get adjusted to the darkness, to find out exactly what’s there.

The more obvious discoveries will reveal themselves first. For instance, in comparing myself with my matches, it quickly became apparent that I am of Jewish descent—something I had suspected at least since my bar mitzvah. I also wasn’t too surprised to learn that my matches’ ancestors were mostly, like mine, from eastern Europe. But eastern Europe is a big place; while I had believed that my maternal line originated in Lithuania, I found close matches in western Poland, Romania, the Czech Republic, and eastern Ukraine. Even more dispersed is the family on my father’s side: while my earliest known ancestor in that line came from Belarus, I found close matches in such distant locales as Germany, Latvia, Hungary, and Bosnia. Oh, and also Puerto Rico, where the family of a man I’m supposedly related to has been living for more than 300 years.

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