Smithsonian Magazine has a fascinating interview with Daniel Sharfstein about his book, “The Invisible Line: Three American Families and the Secret Journey from Black to White.” His book shows just how fluid the idea of race could be, even in the American South, which was pretty rigid about the concept, particularly during the 17th and 18th centuries. There’s lots of interesting discourse here, so you should check it out, but here are a couple of things worth quoting:

Q: You note that an early 18th-century governor of South Carolina granted the Gibsons, who clearly had African-American ancestry, permission to stay in his colony because “they are not Negroes nor Slaves.” How did the governor reach such a nebulous conclusion?

Sharfstein: It shows how fluid understandings of race can be. The Gibsons were descended from some of the first free people of color in Virginia, and like many people of color in the early 18th century they left Virginia and moved to North Carolina and then to South Carolina, where there was more available land and the conditions of the frontier made it friendlier to people of color. But when they arrived in South Carolina there was a lot of anxiety about the presence of this large mixed-race family. And it seems that the governor determined that they were skilled tradesmen, that they had owned land in North Carolina and in Virginia and—I think most important—that they owned slaves. So wealth and privilege trumped race. What really mattered is that the Gibsons were planters.

Q: One of your subjects, Stephen Wall, crossed from black to white to black to white again, in the early 20th century. How common was that crossing back and forth?

Sharfstein: My sense is that this happened fairly often. There were many stories of people who, for example, were white at work and black at home. There were plenty of examples of people who moved away from their families to become white and for one reason or another decided to come home. Stephen Wall is interesting in part because at work he was always known as African-American, but eventually, at home everyone thought he was Irish.

Q: As you look at the United States now, would you say the color line is disappearing, or even has disappeared?

Sharfstein: I think the idea that race is blood-borne and grounded in science still has a tremendous amount of power about how we think about ourselves. Even as we understand how much racial categories were really just a function of social pressures and political pressures and economic pressures, we still can easily think about race as a function of swabbing our cheek, looking at our DNA and seeing if we have some percentage of African DNA. I think that race has remained a potent dividing line and political tool, even in what we think of as a post-racial era. What my book really works to do is help us realize just how literally we are all related.