In fact, such lineages are not unusual. African ancestry is very common among Southern whites, though the bloodlines usually originated with slaveholding white men and enslaved black women.
The most prominent such case is that of Thomas Jefferson and his slave Sally Hemings. Over the last two decades, DNA tests have substantiated the long-held suspicion that Jefferson fathered Hemings' six children. Hemings was three-fourths white by ancestry, and although her children with Jefferson were born into slavery, they were legally "white" under Virginia law at the time.
Such legal classifications were not uncommon in the antebellum South, where there was a high degree of social mobility and few people possessed documentation of their ancestry. Despite the strictures of slavery, free people of mixed race could possess up to one-eighth or one-quarter African ancestry, depending on the state, and be considered legally "white." Others who didn't meet the legal definition were absorbed into the white mainstream because of their appearance or close association with whites.
Virginia had some of the least strict legal definitions of race until the late 1870s, when white Democrats regained political power in the former Confederate states. Over the next 20 years, those states passed Jim Crow laws to enforce segregation in public facilities, as well as constitutional provisions that disenfranchised most blacks by requiring literacy tests, longer residency requirements, and poll taxes.
Later, an informal "one-drop rule" came to define any person with "one drop of black blood" as black. Although the rule held sway in many Southern states long beforehand, it was not adopted as law until the early 20th century, with the rise of eugenics, ideas of racial purity, and scientific racism. Tennessee was the first state to codify the rule in 1910, and several other laws soon followed, including Virginia's Racial Integrity Act of 1924, which defined as "black" anyone with any black ancestry.
Predictably, extensive access to DNA testing and genealogical research in recent years has revealed mixed-race heritage in the families of the old planter aristocracy, as well as evidence of slave-owner ancestry in many black families, including that of first lady Michelle Obama.
If the genealogists could go far enough back, perhaps they would find that all those who settled on this continent were distant cousins. Such findings should put an end to the racism that has scarred our national character for centuries and - until recently - prevented the election of our first African American president.
William Kashatus is a historian and writer. He can be reached at firstname.lastname@example.org.