Race isn't something that is well defined in general, and the lines get even blurrier when looking at biology. Biologically, it's not something I've seen much of and the bit I have is all related to bones, and that has a strong tie to anthropology. So there's Negroid, Mongoloid and Caucasoid. Most of the time, in biology populations are referred to, not races. It's why the example I gave was about African Americans (and was pretty specific then to those who were dependents from those who were in America already, as a population they would be different than those who immigrated to the US more recently).