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Underlying the DNA tests is the idea, accepted by most scientists, that modern humans evolved in Africa some 100,000 years ago and then spread out across the globe, picking up genetic mutations along the way. Researchers have been trying to determine when and where various mutations occurred. Genetic genealogists track these mutations and compare them with a database of DNA markers culled from thousands of people with deep roots in specific regions of the world, such as the Aborigines in Australia or the Basques in Spain. If an individual's mutations match those of an indigenous group, a link may be established.
For some, DNA tests help confirm an ancestry that was suspected but never proved. William Sanchez, a Catholic priest in Albuquerque, N.M., always knew that he had a Spanish heritage but says he also felt a spiritual connection "to Israel and the chosen people." Although he was raised Catholic, his mother followed many Jewish traditions, such as covering mirrors in the house when someone died. But it wasn't until Sanchez took a test from Family Tree DNA in Houston that he learned he had inherited genetic markers for the Cohanim, Jewish high priests said to be descended from Moses' brother Aaron.
First identified by Michael Hammer at the University of Arizona, markers for the Cohanim show up in more than 80% of people who report that lineage but in less than 1% of the rest of the population. After getting his results, Sanchez learned from relatives that he descended from "converso-Jews," who pretended to convert to Catholicism during the Spanish Inquisition in order to avoid persecution. On learning of his Jewish origins, Sanchez says, "I felt happy, because it proved an ancient ancestry."
Genetic testing has a special attraction for African Americans because most have no other way to trace their lineage; the slave trade did a thorough job of severing their African roots. Washington-based African Ancestry aims to re-establish these links by telling its customers whether their DNA matches that of any of hundreds of ethnic groups in Africa, from the Hausa in northern Nigeria to the Ashantis in Ghana. For Juanita Thompson, a real estate agent in Arlington, Va., the test had special significance because her mother had been adopted as an infant and her birth family was unknown. "There was always a void," says Thompson, 61. "Having this DNA test gave me a connection to my mother's side of the family. I feel good about finding another piece to the puzzle of who I am."
As satisfying as it was for Thompson to be told that her mother's family descended from the Yorubas in Ghana, it is exactly this kind of precision that has critics fuming. "I think it is a disgraceful thing to try to tell an African American that you can match them to any group in Africa now," says Bruce Jackson, a geneticist at the University of Massachusetts at Lowell and co-director of the African-American DNA Roots Project, a nonprofit research group that is digging into the genetic history of American blacks. Jackson says making such classifications is premature because not enough people have been tested to establish distinct markers for each group. "Every ethnic group in Africa is a mix that we don't understand yet," says Jackson.