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The Science and the Investigators
Intro Race and Science The Tests Learning from DNA
Learning from DNA

The results of DNA testing, admixture and lineage testing alike, are in themselves relatively difficult to make sense of. Without an understanding of their cultural, genealogical and historical contexts, it is hard to make sense of what the percentages and genetic markers might mean.

Lineage based tests are not direct paternity or maternity tests -- as we've seen, they can only provide a sense of shared ancestry, and a limited sense at that, since they can only tell you about a couple of branches of your family tree. For example, if you were to chart your family tree over six generations, you would see you have 32 male ancestors and 32 female ancestors. Your mtDNA would have come from only one of those 32 women; if you're a man your Y-chromosome would have come from only one of those 32 men. To find out about more ancestors, you would need to ask other, more distantly related members of your family to test their mtDNA or NRY, and in order to make that effective you would need to begin from a clear understanding of your family's genealogy.

Dr. Henry Louis Gates Jr. discusses genetics and history with Dr. Linda Heywood and Dr. John Thornton of Boston University
Pushing back further into history with either admixture or lineage testing requires even more homework. While finding matches for one's Y- or mitochondrial DNA in present-day residents of a particular geographical region does indeed mean you've located distant cousins, it does not necessarily mean that your own ancestors lived in that region. As several of the participants in AFRICAN AMERICAN LIVES discovered, a knowledge of world history -- and in particular for African Americans, a knowledge of both the history of Africa and the detailed history of the slave trade -- is essential in interpreting the results of these tests.

For some participants in the program, mtDNA haplotype matches appeared among a number of groups spread out across the African continent -- from Cameroon to South Africa. This puzzle was explained by historians of Africa and the slave trade, Dr. Linda Heywood and Dr. John Thornton, both professors at Boston University. Beginning about 2000 BC and continuing on until around 500 BC, members of the Bantu ethnic group migrated from what is now southern Cameroon to southern Africa, and as they moved, they brought a new kind of genetic mixture to the southern African population -- which is why you can find people in Cameroon with the same haplotypes as people in South Africa.

Map of Africa, with matches from Dr. Peter Forster's DNA database to one of AFRICAN AMERICAN LIVES' guests highlighted
A map of Africa, with geographical matches from Dr. Peter Forster's DNA database to one of AFRICAN AMERICAN LIVES' guests highlighted as red points.
One of the series' guests worked with two bits of lineage information that, in and of themselves, were not conclusive: haplotype matches in present-day Liberia and paper records relating to a female ancestor who arrived in Mississippi in the early 1800s. Working backwards, the scholars deduced that her ancestor was likely a slave who was brought to Mississippi on a well-traveled route from South Carolina; to get to South Carolina, she was probably shipped from the region of Africa known today as Liberia. Using both genetic and historical evidence, they were able to fill in the missing parts of the story, and provide insight into how the geographical and genetic path, beginning in Africa and passing through the Americas, led to this person.

As we'll see on the following page, AFRICAN AMERICAN LIVES Host Dr. Gates encountered a number of confusing results in his own DNA testing process, which required the talents of historians Dr. Heywood and Dr. Thornton to decipher. To find out more about Dr. Gates' experience interpreting DNA test results, continue on to the next section of the site.

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