Frithjof Capra used to say that there is an awareness at the lowest levels of biological existence, e.g. cells, and I think a lot of sexual selection is sort of a guidance in this way, happening at a lower level than what the human brain is consciously aware of. Life already sees the possibility of some kind of novel arrangement and tries to make it happen. This is why on occasion you'll get women who have a visceral sexual attraction for you that they can't control. As Schopenhauer put it, sexual attraction is actually the will of the unborn to be born. In the real world it seems to care little for racial differences. Albeit, sometimes the outcomes are botched; nature is cruel and not all the combinations are good. On average though the botched will tend to perish absent the system we have today which favors dysgenics.

Also I think it is rather silly to worry about race mixing when we live in a multinational Empire that white people themselves were responsible for bringing about where all the peoples of the world are being mixed together. Race mixing is going to happen in this context. If we ever get to a less mobile and more isolated world again, then probably races will get more homogeneous again. Until then, good luck.

Sorry if I rambled, I have a headache and I'm not at my best, maybe it's from the big geomagnetic solar storm of the past few days.