Pam Atlas, meet Occam's Razor
I happen to know you're not personally acquainted with it yet, ever since liquifying my frontal lobes on this screed. (don't worry, "nofollow"ed)
Well, theoretically, things *could* have gone down the way you postulate, I suppose. However, when you look at the picture of Barack Obama's maternal grandfather over at Peg Britton's post at KansasPrairie.net, a different hypothesis, one that does not "multiply entities unnecessarily" comes to mind.
Even Mr. thalarctos, the poster child for prosopagnosia, can see the resemblance clear as day. As we say in Alabama, Obama "takes after" his grandfather, or he "favors" him.
And once again, it highlights the arbitrariness of the social construct "race"--when two men of such different origins look so alike, it points out how many possible features are ignored, just for the purpose of focusing on skin color.
(Not even to mention, Malcolm X was no "liberal", but there's so much else batshit craziness there, it hardly even seems worth mentioning.)