British-American, German-American, Polish-American ... how do they know?
A person’s makeup is determined by combination of both mother and father and they each bring the combination of their ancestors. After a few generations in this country, the number of potential racial combinations would be so great that almost no one could state with any degree of certainty what their racial makeup was. That is what is so uniquely American. I think America was once referred to as the melting pot for that reason. (I suppose that if incest was practiced you could keep the bloodlines pure but you would then have either idiots or royalty.)
AngloFrancoCelto-American ;-)