[haihaibye]

Why does everyone find much stronger genetic effects than parental in adoption studies?

“Little intergenerational correlation in education was observed in the absence of genetic similarity between parent and child—that is, among adoptees.”

https://gwern.net/docs/genetics/heritable/adoption/2021-lude...

“By examining parent-offspring resemblance in a sample of offspring that are among the oldest of any adoption study of IQ to date, we have effectively tested for the presence of parenting effects that would have persisted for more than a decade after the conclusion of the typical rearing period. No such persistence is found to occur in our unique sample.”

https://gwern.net/docs/iq/2021-willoughby.pdf

In an adoptive sample of Korean Americans parental income was unrelated to offspring income.

https://gwern.net/docs/genetics/heritable/adoption/2007-sace...

[vannevar]

Did you actually read your own references? From the abstract of the study of adopted Korean Americans:

"I find large effects on adoptees' education, income, and health from assignment to parents with more education and from assignment to smaller families. Parental education and family size are significantly more correlated with adoptee outcomes than are parental income or neighborhood characteristics."

[random78965]

I'm not sure, that's not my area of expertise! I think it's pretty well-replicated that IQ is more predicted by genetics than any other factor; however, my understanding is that variation in IQ within an ethnic population is much greater than variation between populations. If a population mean is significantly different from others (which appears to be the case with Ashkenazi Jews and Asians), I'd expect the effect to be primarily environmental, not genetic.

I don't know enough about the inheritance of intelligence to be sure of this at all, though.