It’s just another TV ad, but it speaks volumes. Titled “Anthem,” the latest commercial from Ancestry.com offers a video montage of an African woman attired like a female warrior from the pre-colonial kingdom of Dahomey, a white brewer inspecting his vats, a band of Native Americans on a forced march through the snow, an Appalachian moonshiner getting arrested by the feds, a Puritan girl fleeing down a cobblestone hill, a 17th-century ship setting forth from a rocky coast, the same female warrior defiantly standing before the throne of a hostile ruler, and the face of a lovely young woman who could well be descended from all these people, followed by the slogan: “Unlock your past. Inspire your future.”

From the perspective of genetic science, these ads are pure snake oil. Dozens of companies now offer ancestry testing, each using a different database of DNA samples from broadly defined geographical regions, and there is no scientifically agreed-upon method for validating the results. In addition, each company tests only a small part of the genetic material you submit, and often the test is limited to only one side of your family. Finally, the regional DNA samples used in the test are from the people who live in the regions now, as opposed to during your ancestors’ time.

What’s more, it’s hard to see how an ancestry