I think the underlying mechanism is simply natural selection, just like you can breed dogs, tulips or bacteria for traits, humans can be "breed" into intelectual performance. None of religions/cultures do it, with exception of Ashkenazi.
> I think the underlying mechanism is simply natural selection
Genetic natural selection takes thousands of years, or at an absolute minimum multiple generations. Social selection occurs far more rapidly, often within a single generation. A person born in the 1950s that is genetically predisposed to manual labor may do well for the first few decades of their life, but as society changes and starts valuing white collar work more, they will do far worse. Their genetics didn't change, but society did.
Those that favor nature over nurture vastly under-estimate the time-scales which it takes natural selection to occur as compared to social selection.
I think you underestimate how powerful this mechanism can be. Take 20 years for one generation, ie. 100 years is 5 generations. We're talking about roughly time from 800 CE, that is 60 generations. Imagine taking smartest people to reproduce, then taking smartest from their kids and so on - 60 times. You will see an effect. You can optimize on anything, ie. "time you can dive underwater" you will see the difference compared to other people after 60 generations, see https://www.sciencemag.org/news/2018/04/indonesian-divers-ha...
