The article in the original post referenced a book called Black People and Their Place in World History, by historian Leroy Vaughn. I looked up some articles on the subject after seeing a video of Prince talking about it. He said he learned about the black presidents from a video by activist Dick Gregory. I couldn't testify to the veracity of any of it, but it sounds likely. We're all mixed race. And it seems silly to call Obama black when he himself calls says he's mixed race. His True Believers have been conditioned to shout down all opposition with cries of racism, and that gets tedious, as does their claim that he's the "first black president."