Many people who consider themselves “white” would be surprised to discover they have African ancestry — especially those in the South.

In an ironic twist, a new study has found that some of the states with the most racial tension are also the ones where the most white people have black ancestors. The findings published this month in the American Journal of Human Genetics found that whites in the South were far more likely to have black ancestry than any other part of the country.

Researchers examined 145,000 DNA samples provided to genetic testing company 23andme for ancestry analysis. They have now determined that at least six million Americans who called themselves white had at least 1 percent African ancestry.

South Carolina and Louisiana ranked highest on the list. Researchers found that one in 20 people who called themselves white in those states had at least 2 percent African ancestry. And in a lot of the South, about 10 percent of people who identified as white turned out to have African DNA as well.

What’s also worth noting is the genders of the specific people responsible for some Americans’ mixed ancestry. A whopping 19 percent of the ancestors of self-identified black people — were European male, while only 5 percent were European females. This racial mixing generally occurred in the early 1800s, when slavery was legal, further validating what historians know about white slave owners raping enslaved women who descended from Africa.

Just like white people in the South had the most African ancestry, so did black people living in the south; with those in Georgia and South Carolina topping the list. Conversely, black Americans with the lowest percentage of African ancestry were those in West Virginia and Oregon.