Please don't misapprehend this in any way as rooted in hatred or bigotry.
It's almost impossible to ask these sincere questions anywhere but in some academic setting. Even then it's fraught with peril. I'm curious about this from a purely scientific standpoint.

Yes, I'm familiar with "Scientific Racism". Beyond that (hopefully), if it's possible to extract emotion and the evidently psychopathic from the discussion, do any theories of primate speciation investigate possible influence of race/ethnicity on sexual selection? Again... no judgment here whatsoever. Neither good or bad. Any such value is not in the question.

I'm not trained in natural science beyond high school level (obviously). I'm admitting to gross ignorance right up front, so spare me the insult if you're inclined.

I (think I) understand that Caucasian is to Negro(id) is to Mongolian as House Wren is to House Wren is to House Wren. A human is to a chimpanzee as a House Wren is to a Cobb's wren... Sort of. That's where I start to get confused. The two wrens are of different species. But given sufficient environmental pressure they are likely to mate and hybridize.** So does the instinct that mitigates against them doing so exist in any even small measure within human ethnic groups? Is it possible that any similar instinct accrues within human populations that have been sufficiently isolated, isolated enough that they have acquired recognizable characteristics, height, skin color, hair color, facial features, suggestive of eventual (millions of years hence) divergence as another species.

I've often wondered, for instance, how different species of wren, sometimes with surprisingly subtle differentiation in plumage and habits, resist cross species breeding unless forced together by circumstance.. wherein they often display the capacity to breed. In animals that are evidently capable of producing offspring resist the opportunity to do so, how does that resistance correlate to their survival/reward instincts? See where I'm going? What's the point of it? Specialization. Adaptation to environment.

So do i have this wrong? Would any group of humans with sufficient time (many millions of years) in complete isolation from other human populations achieve a state of distinct speciation that eliminated the capacity to interbreed with other human "species"?

If so is it possible that even within the very limited process toward that evolution among distinct ethic groups around the world some faint impulse to sexually select from within your group has already accrued? Even if it's a faint impulse might it account for any biological origin of racism?

For the first millions of years of our species existence on this planet a particular adaptation to local environment may have contributed to such impulses. But the environmental imperatives humans face in the last couple of millenia are so clearly reversing any further ethnic distinction that I'd like to think that what I'm describing might in a small part contribute to an understanding of our natures and help to overcome such parts of our instinct that are no longer appropriate to our evolution as a species. Maybe racism can be understood as a vestige of some hard-wiring that we will (if we survive long enough) eventually discard.

** of course the human and ape can no longer interbreed. And the human species has had insufficient time and isolation within the species to diverge as other species, like specific species of wren, have done to suit their environment. But I get to that question eventually.