Not even by DNA testing can you prove that your ancestors were here during slavery. I suppose if a particular family has maintained rigorous family records, that'd help but I can't imagine how such a task would be undertaken. Imagine the MONEY it would cost first of all. Now that I'm methodically thinking about it, it's even more of a bad idea than I thought it was previously *LOL*
And what of those blacks who are also descended from slave owners? That'd be an interesting formula for reparations. Or what of those blacks that owned slaves? There were a few. Or what of the noble Indians who owned slaves?