JT and LH: Initially the results were uneven. We combined DNA results with other data, such as family history in America and shipping records, to try to get over ambiguities in the results. Many users of the services found that they had potential ancestors in more than one area in Africa, and at times these contradictions could be limited or resolved by these methods. But for only a few could the results be considered really definitive.

Linda [Heywood]'s result was one of the more secure ones, because of the peculiarities of her ancestral group. Her mitochondrial DNA test showed that she matched people today who are called Fulbe, in the Futa Jallon part of Guinea Bissau. We know historically that the Fulbe of Futa Jallon, along with those of Futa Tooro, undertook long migrations in the 16th through 19th centuries from the coast of West Africa (Senegal and Guinea) all the way to modern-day Chad and Cameroon.

Linda had a number of matches in the Fulbe homeland, but also with people not identified as Fulbe but clearly living on their migration path. Since she was dealing with female ancestors, through the mitochondrial DNA these problems could be understood by thinking of marriages by Fulbe women to non-Fulbe men, whose descendants would not claim Fulbe origin.

In Linda's case, and some others like hers, yes. But for others, more data will certainly help. There have still not been many Africans tested, and many of those who have been tested do not come from the core regions of the slave trade. For example, Cameroon is heavily sampled, thanks to a variety of projects often not related to the study of the slave trade, whereas Angola is very poorly sampled. Yet Cameroon supplied very few people to North America, and Angola supplied over one-quarter of the African-American ancestral population.

TR: What areas of African history are you exploring at this time?

JT and LH: We both have continuing projects that investigate the history of the African regions that supplied the slave trade. Linda is working on a biography of Queen Njinga, the 17th-century Angolan queen who fought the Portuguese, and Africans in Brazil. John is working on the history of the Kingdom of Kongo as well as other parts in Atlantic Africa and some of the American regions where these Africans went.

Joel Dreyfuss is managing editor of The Root.

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