Irrational fear probably has genetic component. But Ethno-types are defined by humans, not by nature.
Look somewhere between those two statements. The concept here is the
application of that built-in tendency for "irrational fear" (or hatred)
to "ethno-types". And that does not require the "ethno-types" to be anything more than a figment of the imagination.
Caucasions have been killing other caucasions... Its what we do; racism or not. If we were all the same race, we'd invent new distinctions so that we could keep hate alive.
OK, but why is it always against other humans? Why not against cows, or big rocks, or flowers?
We're all familiar with the phrase "us against them". "Them" doesn't need to be another race, but it does usually need to be another set of humans. If you're both in an ancient Greek civilization, then it could be the people of another city several miles away, or it could be the slaves against the slave-owners. If you're both Mongolian nomads, it could be another tribe whose migration path crosses a certain river at the same place where yours does at roughly the same time of year. For that matter, in mythology, look at how often monsters are not just scary animals, but either anthropomorphized in some way or hybrids, or just more powerful humans (human-looking, generally human-acting gods or giants or such). It seems that the real choice is not "us" or "them" but needs a third option to be complete: "almost us". And the third one, "almost us", is even worse than "them". If it's truly not much like us, such as most animals and plants and pottery, then nobody cares much one way or the other.
So what makes "almost us" the worst possible category? There's no established answer so far. You could suppose that it's just an inevitable result of being social and prioritizing social matters above most else in life, because your worst social enemies are bound to be human and you're probably going to think of social enemies as the worst part of your world. But the real animosity seems to usually be applied outside the social group, so I think it needs a different explanation. My idea is that it dates back to resource competition, not necessarily just between groups within the species, but even between this species and others when there still were other homonids to compete with. In that context, it makes sense to react negatively to critters that are almost like you but not quite, because they're competition. But without other homonid species around for that evolved instinct to be triggered by, it latches onto the closest thing available: other members of the same species that are still outside the "us" group, making them "not quite us".
