Emil O W Kirkegaard

2) If a trait like IQ is omnigenic, then it's difficult to see what kinds of 'biological' interventions could be developed. If what you mean is eugenics, they'd need to work out how every gene in the body interacts with environment to affect IQ, so no.

Twin studies alone aren't conclusive but they're corroborated by GCTA and increasingly GWAS. I don't see how the idea that, say, embryo selection can't increase IQ is compatible with non-trivial narrow sense heritability.

Of course, these heritability estimates are still not causal & provide no major biological or mechanistic insight. Since heritability is contextual embryo selection will likely not work in disadvantageous environments. That's why crop breeding takes place in uniformly good fields

I agree heritability estimates are not causal & are contextual. But to say embryo selection will not work in a disadvantageous env is assuming env explains variance. Wouldn't negligible shared env cast doubt on this? Presumably twin studies capture variance from some poor envs.

@KirkegaardEmil Do you have any thoughts on this discussion? Am I totally misguided here? I am finding it hard to fathom (perhaps because it is discouraging) that we can learn nothing applicable from behavioral genetics research.

It's a common angle you will get from, say, Turkheimer and generally people who approach these things from a philosophical angle instead of practical-empirical. Environmentality (1 - H²) is a kind of crude index of the malleability of a trait, sure.

You can make predictions of likely efficacy of interventions based on variance analysis. If it targets environmental variation already known to not affect the trait, of course, intervention won't work (e.g. parenting reading to enhance adult offspring intelligence).