Co-author University of California at Berkeley sociology professor Troy Duster says many Americans are emotionally invested in finding an ancestral homeland, and this search for a homeland is particularly poignant for African-Americans, who hope to recapture a history stolen by slavery.

"It can give them false hope," Duster says in a statement.

More than two dozen companies sell genetic ancestry tests, which range in cost from $100 to $900, that use a swab of DNA from the inside of the mouth to trace either the mother's or father's ancestry.

Tracing only one bloodline can exclude most ancestors and cannot pinpoint where these ancestors lived, the researchers said.

"Each test examines less than 1 percent of the test-taker's DNA and sheds light on only one ancestor each generation," the study found.

The study, published in the journal Science, indicated the ancestry tests cannot pinpoint the place of origin or social affiliation of even one ancestor with exact certainty.