> If these family-level environmental inputs had substantial effects on adult IQ, we'd see it in the behavioral genetics research. But we don't.
Actually there is a direct correlation between adult IQ and stress [1], it isn't genetic though.
> The adult IQs of adopted children have very little correlation with those of the adoptive parents who raised them or those of their adopted, non-biological siblings.
To quote [2]: "Studies of mixed-race children and black children adopted by white parents suggest, however, that racial differences in test performance are largely if not entirely environmental in origin."
In any case the question is open if "IQ testing" is actually a decent measure of intelligence, especially with children that suffer from a variety of stuff somewhere on the ADHD/autism spectrum (e.g. selective mutism, anxiety issues), or if it can be used as a metric at all due to disparities in testing incidence between population segments - often enough, it's teachers who recommend IQ and ADHD tests, and there have been a number of suggestions that racial and other discrimination can negatively affect children there.
Actually there is a direct correlation between adult IQ and stress [1], it isn't genetic though.
> The adult IQs of adopted children have very little correlation with those of the adoptive parents who raised them or those of their adopted, non-biological siblings.
To quote [2]: "Studies of mixed-race children and black children adopted by white parents suggest, however, that racial differences in test performance are largely if not entirely environmental in origin."
In any case the question is open if "IQ testing" is actually a decent measure of intelligence, especially with children that suffer from a variety of stuff somewhere on the ADHD/autism spectrum (e.g. selective mutism, anxiety issues), or if it can be used as a metric at all due to disparities in testing incidence between population segments - often enough, it's teachers who recommend IQ and ADHD tests, and there have been a number of suggestions that racial and other discrimination can negatively affect children there.
[1] https://www.pbs.org/newshour/economy/making-sense/analysis-h...
[2] https://www.brookings.edu/articles/the-black-white-test-scor...