i can also copy pasta this critique again from the interwebz of that study you linked
"But Murray still hasn’t managed to answer the academic community’s chief complaint: His theory does not adequately account for the role social environment plays in determining one’s lot in life.
As you may recall, in The Bell Curve Herrnstein and Murray used an extremely crude measure of social background, then contrasted its effects with those of a test of mental skills given to most of the sample in late adolescence. Murray claims his new study answers this criticism: "The Bell Curve’s method of controlling for SES [socioeconomic status] and the sibling method of controlling for everything in the family background yield interpretations of the independent role of IQ on income that are substantively indistinguishable," he writes. But the test Murray uses, the Armed Forces Qualification Test, is not an environment-free measure of intelligence, so it does not identify "the independent role of IQ." Scores on the afqt have been shown to vary significantly with the quantity and quality of education to which a young person has been exposed.
Moreover, comparing siblings, while helpful, does not come close to "controlling for everything in the family background." Environments can differ within families, too—because of differences in the sex, personality, or birth order of the children, for example. In any case, Murray’s conclusion—that improving the environments of unrelated children will do little to reduce inequality—is a non sequitur. Finding a correlation between intelligence and success within families says nothing about the extent to which inequality in a population is driven by differences between families. After all, incomes are much more equal among siblings than among unrelated individuals, which attests to the equality-enhancing effects of a common family environment. Variance in IQ explains at most one-fifth of the variance of incomes; so, most inequality is caused by other factors. It is by now well-established that, holding ability constant, more education raises earnings, and well-designed, early childhood interventions can improve later-life outcomes for disadvantaged youths in a cost-effective way. But Murray seems utterly unfazed by these results."
lol sounds like a much lambasted study by the looks of it