Black roots are deeply and improbably tangled, inextricably intertwined with the history of slavery and the genes of the very Euro-Americans who enslaved our ancestors. In my personal case, geneticists floored me by revealing that not only did my father’s line go back to Ireland (we had thought this), but my mother’s did as well, which is very rare. (Only 1 percent of us descend from a white woman who slept with a black slave or former slave.) Not only that, but my own admixture shows that I am 49.4 percent European and 50.6 percent African, even though no one would ever mistake me for a “mulatto.”

The story of the paternity of Melvinia Shields’ children is all too common in the annals of American family trees. Among the guests in African American Lives, Quincy Jones (who is a direct descendant of King Edward I), Maya Angelou, Tom Joyner and Morgan Freeman all learned the names of the white male who impregnated their black female slave ancestor—unlike Mrs. Obama whose white ancestor remains anonymous. My paternal great-great-grandmother, Jane Gates, took the identity of the father of her children with her to her grave in 1888. But with DNA tests, we are closing in on this Irishman’s identity, almost a century and a quarter later.

What all this means is that in defiance of the law and social convention, and just what some “believe,” an enormous amount of “race mixing” has long been occurring in the United States. We as a society have been in deep denial about our heritage of interracial sexuality for just as long. Some of this sexual contact was voluntary, we now know: For example, Morgan Freeman is descended from white Alfred and black Celie Carr, who not only stayed together after slavery ended but lived together openly and are buried together in Mississippi. But most of it was coerced or violent or a species of rape, a reflection or a result of a profound imbalance of power. Because of a confluence of factors—the illegality of miscegenation, the prevalence of sexual abuse and rape at the root of these relationships, infidelity, guilt, shame and disgrace at an unwed pregnancy—both black people and white people had a certain vested interest in keeping these relationships in the dark, as it were.

The first lady’s family tree—and the social and sexual complexity it reflects—is quite typical of the family trees of a majority of African Americans. And we all have to be happy for Mrs. Obama that her ancestors—long lost—have now been found. There is a certain inexpressible joy in knowing from whom you have descended, knowing where and from whom and through whom you come from, no matter what their complexion or hair texture. Michelle Obama’s family tree enables all Americans to marvel at—and begin to accept—the very complexity of race relations in the history of this country, a complexity registered in our collective DNA, a complexity writ large on the very face of black, or mulatto, America.

Henry Louis Gates Jr. is the Alphonse Fletcher University Professor and the director of the W.E.B. Du Bois Institute for African and African American Research at Harvard University. He is the founder and the editor-in-chief of The Root.