I was thinking yesterday that "race" doesn't mean what most people think it means, anyway.
Because even the "Isolated" populations weren't totally isolated. Australia got Polynesians in off the pacific in dugout canoes, as did South America, and vice versa, so genetic isolation was never quite total. And in a thousand years? In fifty generations a lot happens.
And if you go back four thousand years - pyramids are being built along the Nile, and I'd bet that most of the people alive then who have ANY descendants alive today, are the direct ancestors of EVERYBODY alive today. Everybody is everybody's cousin.
If we really, really had the knowledge to know which branch to look in at every generation, and you were living in America, you could sit down with your neighbor from across the street who immigrated from Tibet last year, and your neighbor from the house next to yours who immigrated from Kenya the year before that, and your friend from church whose grandparents were australian aborigines, and your fishing buddy who's allowed to fish on federal land because he's got a Choctaw tribe member ID, and the five of you could write down names, linking each generation to the last, until you could all come to at least one of the same names. You wouldn't have to fill more than one sheet of notebook paper with names to go back four thousand years. And you could do it again and again, coming down to the name of virtually anyone who was alive four thousand years ago, providing they left any progeny behind at all. Just two hundred generations.
And this is what "race" is. Everybody is connected. Some of the connections are stronger, through more lines of ancestry, and some of them more tenuous, through only a few threads. But everybody is everybody's cousin. There is no such thing as a "pure race" and never has been.