I suspect experiments with almost-genetically identical twin tests might advance our understanding about almost all genes except sex chromosomes.
Sex chromosomes are independent coin flips with huge effect sizes. That’s amazing! Natural provided us with experiments everywhere! Most alleles are confounded (e.g.. correlated with socioeconomic status for no causal reason) and have very small effect sizes.
Example: Imagine an allele which is common in east asians, uncommon in europeans, and makes people 1.1 mm taller. Even though the allele causally makes people taller, the average height of the people with the allele (mostly asian) would be less than the average height of the people without the allele (mostly European). The +1.1 mm in causal height gain would be drowned out by the ≈-50 mm in Simpson’s paradox. Your almost-twin experiment gives signal where observational regression gives error.
That’s not needed for sex differences. Poor people tend to have poor children. Caucasian people tend to have Caucasian children. Male people do not tend to have male children. It’s pretty easy to extract signal about sex differences.
I suspect experiments with almost-genetically identical twin tests might advance our understanding about almost all genes except sex chromosomes.
Sex chromosomes are independent coin flips with huge effect sizes. That’s amazing! Natural provided us with experiments everywhere! Most alleles are confounded (e.g.. correlated with socioeconomic status for no causal reason) and have very small effect sizes.
Example: Imagine an allele which is common in east asians, uncommon in europeans, and makes people 1.1 mm taller. Even though the allele causally makes people taller, the average height of the people with the allele (mostly asian) would be less than the average height of the people without the allele (mostly European). The +1.1 mm in causal height gain would be drowned out by the ≈-50 mm in Simpson’s paradox. Your almost-twin experiment gives signal where observational regression gives error.
That’s not needed for sex differences. Poor people tend to have poor children. Caucasian people tend to have Caucasian children. Male people do not tend to have male children. It’s pretty easy to extract signal about sex differences.
(far from my area of expertise)