Non-heritable effects (including epigenetic) are estimated to contribute to less than 30% of population intelligence variance.

If you were familiar with the data, you wouldn't make statements like that, because heritability is a population statistic, not a constant. It varies significantly between populations, to the point where you can't make claims about it without controlling for the population you're studying.

For instance, we could say that the heritability of intelligence among the children of suburban Chicago families in a particular income bracket is 70%, but not that the heritability of intelligence in general is 70%.

If you were familiar with the data, you wouldn't make statements like that, because heritability of intelligence is largely the same across all population studied so far, and universally high. There are exceptions, e.g. Scarr-Rowe effect is most likely real, but it only seems to work on very low end of SES range, which is virtually unseen in today's America, even at the lowest end of what counts as poverty.

Via what mechanism are we testing? Did we send some kids through a good upbringing and some to a bad one in a randomized controlled way, or did we just take a survey and assume intelligence was passed down through genealogy instead of upbringing?

Through foster children, and measuring whether their IQs are ultimately more correlated with their foster family or genetic family.

> Via what mechanism are we testing? Did we send some kids through a good upbringing and some to a bad one in a randomized controlled way, or did we just take a survey and assume intelligence was passed down through genealogy instead of upbringing?

The most informative studies in this area are usually of twins-separated-at-birth, but the datasets aren't very large.

Scarr's original twin study was done in Philadelphia. Seems strange to discount the Scarr-Rowe effect as not existing in the US at all when it was originally found there in the first place.

Scarr’s original study was done over 50 years ago on kids who grew up in pre-Civil Rights America. That level of deprivation is, as I’ve said, virtually unseen in today’s America. Recent studies usually fail to replicate it on more recent experimental data.

We know it holds up to scrutiny, because the epigenetics excuse, constructed without the information supply needed to support it, doesn't hold up to scrutiny.