If wonder if Neanderthals discussed an idea akin to the great replacement and if most of them thought/argued that was a conspiracy theory.
about 42K years ago the Earth poles flipped and as a result there was a 1K years period of high UV which, especially without change in visible light to trigger pupil response, would have caused a lot of early cataracts and other issues to the large light colored Neanderthals' eyes with them not having any idea what is happening to them while African originated Cro-Magnon with smaller darker eyes used to stronger African Sun would have fared much better in Europe in that period.
Sometimes supposedly inferior genes work better in a specific environment as is the case with sickle cell anaemia where mutation resulting in under-performing haemoglobin confers some resistance to malaria.
Genes survived either because some populations were aided by geography, as in they weren't challenged by foreign populations or because the individuals were smarter.
The modern humans are trying to reverse how nature worked until the recent past but I'm not sure it will work. Competition will always win.
What do you mean by inferior genes? Not being adapted to the climate? Being predisposed to some diseases? Having a low IQ? Not enough physical strength?
Sexual selection is probably not even a significant factor because you mostly always find an idiot to team up with.
So much so that education of women is considered a solution to overpopulation in underdeveloped countries.
For example, exposing a particular population to a specific challenge will select for particular traits which might cause slower population growth. For example, alcoholism might be the side effect some genetics that enable survival in certain situations that might seem irrelevant until they occur.
And modern humans let culture/politics be deciding factors for reproduction. This is causing particular selection pressures that are not understood and can not be evaluated until far in the future.
You mean a conspiracy theory about why. Though the article does not dispute that demographic changes are taking place, or even that they are the result of deliberate changes of immigration policy, it does go to great lengths to avoid mentioning them. This is not by accident - there is a lively debate on its talk page about including (more) demographic statistics*, to which the editors are highly resistant.
For example, there is not a single graph found in the entire article similar to that at the beginning of https://en.wikipedia.org/wiki/Immigration_to_France
Like refusing to mention JFK is dead on JFK assassination conspiracy articles.
*https://en.wikipedia.org/wiki/Talk:Great_Replacement#Lack_of... among others
The whole idea of "our people" being replaced by "those other people" assumes there are "our people" and "those other people" and skin color (or more broadly ethnicity of their ancestors) is the way you recognize which is which.
It assumes that culture is unchanging and tied to skin color. It assumes that birth rates are unchaining in time and tied to skin color. It assumes that demographics of birth rate are relevant in less than hundreds of years - during which culture can completely change (see US or Russia or China in 1821, 1921 and 2021).
The whole idea is based on stupid, racist thinking.
Edit: Actually, I've just noticed this question shifts us from "it's not happening" to "it's happening but it doesn't matter". Is that your claim now, and you're conceding that it is happening? Or would "it's not happening but if it did it wouldn't matter" be closer to your opinion?
*'Genetic' to separate it from the culture and customs that are also passed down through ancestry.