I think that it is more the taboo of things than nature. people were forcibly separated for a long time and interracial sex was taboo for a long time so the taboo is exciting. A lot of white guys go after black or asian girls too... most of my friends are fucking non whit girls hard while dating their girlfriends - just as the girlfriends are getting fucked hard by non white guys! If it were natural selection all the nerdy guys and girls would be hooking up as intelligence determines survival, us normal people would never get laid. Either way its all about fun! What do the girls fell about it?? What attracts them to their partners???