Is there a way to have ancient societies have some sort of a Eugenics progam? A Program that not only seperates people for the sake of social segregation but for actually creating seperate "humans"?
While the Idea sounds too modern, I am sure that ancient people had awareness of things like height and strength... so what if they arranged marriages in such way to get the tallest and strongest people. (Of course, it will require a thinker that recognizes that tall breeds tall and short breeds short, but that is a fairly straightforward thing to think of) Can there be a an ancient way to gauge intelligence that is somewhat accurate? Children being tested with problems in classical mathematics as a primitive IQ-test ? A Class of thinkers produced by breeding the best thinkers.
I think that there are proto-Eugenic ideas in all caste based societies. Could one of them had taken it a lot further. If Ancient Sparta is anything to judge by, ancient community are capable of imposing a version of "Ideological Totalitarianism" on their subjects... we just need to have something like that survive longer and carry things out farther, with Eugenics as a part of their Ideology. Maybe a "great person" (in the form of a leader or a thinker) that will butterfly things in favor of such a society?
One prerequisite, though, would be a level of gender equality in TTL ancient societies that recognizes that women also have an influence on the progeny and women too, need to get out of their houses and compete to prove that they are fit to breed. Other one is that the society needs to keep a detailed geneology to make sure somebody is a "thoroughbred"