Look at this page:

twins

These little girls are sisters! They have the same forebears. What race are they? Is the light one supposed to like Bach while the dark one likes rap? Are they supposed to have different accents? Is it okay if they both have rhythm?

This unusual pair shows that much of what we call 'white' or 'black' is simply custom which is imposed on people.

(I remember a book I read on a black gang member in San Diego. Fellow gang members objected to his girlfriend because 'She doesn't talk like a black person.' As if there is only one way for a black person to talk = their way.)