Define race. Not sure what you mean by unnatural anyway. It has no scientific currency any more, that's for sure.
Dividing the world into stuff which seems similar to you and stuff which seems different can be considered part of psychological schemata development if you're a Piaget fan although even he didn't go as far as to say the capability to build schema beyond 'Oww, that hurt/feels good' is innate. The development of in/outgroups, favouratism, etc. the waters are still really muddied and there's some evidence for it being regulated by oxytocin levels but, in general, I would suggest racism and in-group bias is a learned, social behaviour (which may possibly be exaccerbated by levels hormones like oxytocin), not innate. Don't think it's controversial to say that humans have very few innate behaviours.
I dunno, it's been a long time since I studied psych but that was my impression of where the science is at.