Why Barack Obama isn’t black.

When asked about his race on the census form, Barack Obama, the child of a white Kansan and black African, did not take the option of checking both “white” and “black” or “some other race.” Instead, he checked “black, African American or Negro.” By doing that, Obama probably did what was expected of him, but he also confirmed an enduring legacy of American racism.

According to the Census Bureau, a little over 12 percent of Americans are “black, African American or Negro.” According to geneticist Mark Shriver, “the level of European ancestry in African-Americans averages about 20 percent.” Many notable “blacks” have been 50 percent or more “white.” These have included many notable Americans who were publicly identified as “black,” “colored,” or as “negroes,” including Frederick Douglass, NAACP president Walter White (who was one-sixty fourth black), union leader A. Phillip Randolph, and Harvard professor Henry Louis Gates.

The obvious question—perhaps not to an American, but certainly to a visitor from another planet—is why if someone’s ancestry is predominantly white, they are not identified as “white” rather than “black.” It’s not because of the way they look. Walter White was widely “mistaken” as a white person. As a student at Colgate, Adam Clayton Powell was initially believed to be “white.” But once it became known that they had black ancestry, they became black. And American law backed up this conclusion. In the South, the idea that any black ancestry would qualify someone as black, negro, or colored was called the “one-drop rule.”

In New Orleans in 1982, Susie Guillory Phipps went to court to have herself and her parents and blond, blue-eyed siblings declared “white.” When the 48-year-old, pale, raven-haired Phipps, who had married a white man and had always been known as white, had obtained her birth certificate in order to get a passport, she discovered that she was designated “colored.” The reason, she found out, was that she was the great-great-great-great granddaughter of a slave, Margarita, who had had a child in 1770 by a white French planter. The state’s lawyers challenged her claim to be white on the grounds that she was three-thirty seconds black, and they won.