> thousands of genes that are unlikely to shift significantly over the course of around 50,000 years.
Large evolutionary changes can happen rather rapidly with the right sustained pressures, certainly within a 50,000 year window.
Check out this plot of brain size over time[1]
If we can have such a dramatic increase in brain volume over a 500k year window, then we can absolutely have nontrivial changes to intelligence in a 50k year window.
> Intelligence ... are also a result of culture
IQ differences between races
may be a result of prenatal nutrition, but I struggle to believe that they're a result of culture.
The reason I doubt this is transracial adoption studies where the child is adopted out at birth to well-off white parents and tested at a very young age. So I can plausibly see how bad prenatal nutrition could have reduced this kids' IQ but attributing it to culture stretches credulity a bit, in my opinion.
(I could be wrong about that though, as the kids weren't that young, so it's plausible that there's some cultural influence from early school friends, but I still think that it strains credulity).
[1] http://aquatic-human-ancestor.org/anatomy/images/brain-size-...