The Legacy of Slavery in African American DNA

This week at Pacific Standard,  I discuss a recent study that examines the influence of slavery and its discriminatory aftermath in the genetic diversity in over 4,000 African American genomes. One of the most striking results of the study is probably the most obvious: On average, about 15% of the DNA of African Americans is of European origin – and, according the researchers’ best statistical model, that European DNA largely dates back to before the Civil War. That was a time when interracial sexual relations overwhelmingly took the form of whites raping black slaves. After the Civil War, according to the model, admixture between blacks and whites dropped off sharply.

Like I said, it’s not particularly surprising, but the breadth of the genetic legacy of slavery is striking.

The study makes some other intriguing suggestions about African American genetic history, especially regarding the enormous demographic shift of the Great Migration (~1915-1970), when 6 million African Americans left the South and settled in other parts of the country. The big takeaway from this study is that African American genetic history is one of coercion: coerced migration and coerced sex over a relatively short period of time, which left strong signals in the genetic diversity of present day African Americans.

Aside from the historical aspect, studies like this matter if African Americans are going to participate in the ongoing development of personalized genomic medicine. Because the genetic structure of the African American population differs from that of whites, African Americans have different genetic risk factors for disease – and even different risk variants for the same diseases. Studies like this lay the groundwork for an inclusive practice of genomic medicine.

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