okay- (sorry)- basically the last point i was trying to make is:
If culture is the only difference, then why would a black person who grew up in a totally white setting/culture, etc., and never known any black culture/setting NEVER be considered white? and a white person who grew up in a totally black culture/setting would never be considered black? I understand that they wouldn't be, but that kinda says that there is more to it than just culture- that the physical aspects (or genetic) do have some relevance, even if it is simply bc society has ascribed that significance to it.

I dunno- am i answering my own question? comments, anyone??