(1) IQ is very polygenetic - a big IQ gene might be 0.1 IQ, and there aren't a lot even that large, if I recall the large genome wide association studies done on this. As GWAS studies get larger we find more, but they're all super small effects.
(2) Having an extra 0.1 IQ point is easy to lose in the noise of other effects on having offspring.
So even if we assumed IQ was perfectly correlated with more surviving offspring in modern societies, it might take an extremely long time (even longer than a whole planet and a thousand years) to make a detectable difference.
https://www.gwern.net/Drug-heuristics
Here’s a brief snippet
> the intervention may be simple, give major enhancements, but result in a net loss of reproductive fitness The famous Ashkenazi theory of intelligence comes to mind. According to this theory, the Ashkenazi were forced into occupations demanding intelligence, and micro-selected for high intelligence. Except the high IQ genes were not previously prevalent among either Jews or gentiles because - like sickle-cell anemia - when they became too prevalent, they result in horrible diseases like Tay-Sachs. In 2007, a unique mutation in a Scottish family was found to increase verbal IQ in afflicted family members vs non by something like 25 points; this would be great for them - except for how that mutation starts causing blindness in one’s 20s or later. (In general, it’s much easier to find mutations or other genetic changes breaking intelligence than helping in cases of retardation26 and autism27.)
Based on all the GWASes and additional studies which have been done since 2007 and a continued absence of confirmed examples of IQ-boosting variants with negative pleiotropic effects, I now would explain the lack of optimization of intelligence as being an example of 'too complex for evolution because too many little changes to do simultaneously', that is, mutation load: essentially, there are too many little effects (which sum up to make us far stupider than we have to be), which have been created & maintained by too many demographic bottlenecks and genetic drift and other effects, too much background selection, and too much selection on other traits (plus some level of dysgenics), for the various harmful variants to have been meaningfully selected against over the past 50kya. And that's why we could boost intelligence a lot with few harmful and many beneficial side effects.
(Note I am not advocating for gene editing)
Also I don't think we have reached a local maximum, human society kind of fucks with natural selection so I imagine there is room for improvement.
I didn't do good at school but i had many friends! I never felt i was less intelligent than my friends which make me question the IQ score thing.
My Dad has high IQ (135) and he's a mathematician.
So how did i inhert low IQ? My mom's score is average at best, 102.
I've sold 3 companies, i am married and I've managed to be quite wealthy.
You don't need to posses high intelligence to survive and reproduce in this world that's why it's not selected for.
We don't walk out of womb and given a puzzle to solve where if we fail, we are instantly killed.