In my Williams College address I said the following thing:
Modern Greeks boast themselves the descendants—the kin—of Homer, Pericles, and Aristotle. In fact Greece was massively invaded by Slavs in the Middle Ages, and modern Greeks have a large Slavic component in their ancestry. If you point this out to a Greek patriot, he’ll sock you on the jaw.
I don't know whether geneticist Greg Cochran was reading my piece—I'd be flattered to think he was—or whether it's just coincidence, but Greg has some brief observations on this topic over at West Hunter, with an interesting comment thread.