"Race", as races are defined today, is absolutely a social construct. How can you point at someone like Beyonce and say "oh yeah, she's black". The racial characteristics that we look at are so vaguely defined. It's like dividing numbers into groups of ten. You have the single digits, the tens, the twenties, etc. But no one would argue that 11 is equal to 12, let alone 19. The lines are arbitrary. 
Racial descent? Sure, some people have various features that originated in certain geographic areas. Nose and eye shape, skin, eye, and hair color, all these things have geographic origins. But who gives a fuck? I don't care where someone's great great great great great grandparents was born.