Parents pass on their genes and their culture to their offspring, so when a group has certain traits, it can be difficult to tell which is more responsible.
One way to get around this is through cross-adoption studies. If children from culture A are adopted into culture B, we can just look at what happens in their lives and see which group they end up most resembling on the measurement or trait we care about. Note that practically nobody says culture is irrelevant, but there are a lot of people who are highly motivated to believe that genes have no role in determining group differences.
One problem with this approach is that you have to account for the fact that children are not placed up for adoption at random. People usually give children away because they are in no position to take care of them. So you might expect, all else equal, adoptees to have worse life outcomes. Adopted children in the United States do in fact have IQs that are below the mean compared to the general population. See table 3 of this metanalysis, despite the misleading framing in the abstract. They also do worse than peers in academic achievement and show behavioral problems. This is despite the fact that adoptees have on average good home environments, since adoptive parents had to meet standards to be allowed to adopt in the first place.
East Asians, people of Korean, Chinese, and Japanese descent, score high on IQ tests and measures of scholastic achievement. This is true when we’re looking at cross-national data, and also when East Asians move to Western countries and are compared to natives. Can cross-adoption studies provide insight into whether this is at least in part due to inherent ability?
Thankfully for science, we do have some papers taking this approach. And they consistently show East Asian adoptees doing better on cognitive measures and educational attainment than reference populations in the West.
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Stop talking about race and IQ...I swear I read that somewhere? Good piece, though.