Rodney Sam:

I was actually very insulted to my face at an Afrocentric bookstore when the seller said in front of my children mind you, "too bad your grandma was raped." Of all the gaul and without any conversation between us. Yes, this is the commonly accepted belief and it happened sadly enough but not to everyone. It appears as though one of my lines was started by a white woman who gave birth to a biracial son, as we've discussed here. Another line was started in terms of admixture with a relationship similar to the placage you speak of. I urge you get your admixtures done. I've found my results fascinating and just wrote a long post about them on our DNA Forum.