I don’t think anyone denies that intelligence is partially heritable. The problem is that many laypeople misunderstand exactly what heritability means. This disparity between the public and scientists is the central point of the piece.

There’s general heritability, which is estimated from twin studies, and for intelligence that’s .50, but that doesn’t mean that in all instances the genetic contribution to intelligence is 50 percent. Heritability is specific to a population and environment. In certain environments the contribution increases. The biggest effect is socioeconomic status. In families with low socioeconomic status, the genetic contribution to intelligence is “near zero” according to Turkheimer.

From the 2012 APA literature review:

Turkheimer, Haley, Waldron, D’Onofrio, and Gottesman (2003) conducted an analysis of socioeconomic status (SES) by heritability interactions in the National Collaborative Perinatal Project (NCPP). The NCPP is particularly well-suited for this purpose because it comprised a representative sample of twins, many of them raised in poverty. A well-validated measure of SES with good psychometric properties is available in the NCPP dataset (Myrianthopoulos & French, 1968).

Structural equation modeling demonstrated large statistically significant interactions for Full Scale and Performance IQ (PIQ) but not for Verbal IQ (VIQ), although the effects for VIQ were in the same direction. For families at the lowest levels of SES, shared environment accounted for almost all of the variation in IQ, with genes accounting for practically none. As SES increased, the contribution of shared environment diminished and the contribution of genes increased, crossing in lower middle-class families. Finally, in the most socioeconomically advantaged families (who were not wealthy), practically all of the variation in IQ was accounted for by genes, and almost none was accounted for by shared environment.

Using heritability to estimate the contribution to differences between groups is even more problematic. Population geneticist Richard Lewontin offered a simple analogy. If you take one group of seeds and you planted them all in the same soil, heritability in this case would be 1.00 because 100 percent of the variation in that specific population would be attributable to genetic differences in the individual seeds (because their environment is exactly the same).

Now say you take two groups of seeds and plant one in good soil and one in nutrient deficient soil. In both populations heritability will be 1.00 while the difference between will be entirely environmental.

You can’t reasonably say that black people and white people occupy the same exact environment, whether we’re talking schools, communities, health, natural environment, etc., so it’s obviously dodgy to make comparisons and assume it’s 50/50 or even 90/10.

When you say race is a better predictor than other aspects of schooling, you can’t just assume that’s genetic either, obviously. You can’t rule out the various social aspects of race. There are different outcomes on the SAT when you control for income, but that can also be explained by disparities in wealth. Black households have on average 14 percent of the wealth of white households vs. about 70 percent of the income. Wealth is a much more influential factor because it embodies all sorts of accumulated advantage. We’re still only about a generation and a half removed from Jim Crow, and full legal equality was attained at a time when social mobility was reduced for all races.

Lastly, I’d like to add that we need to exercise caution when it comes to social science research, which is in the middle of a replicability crisis—one that is particularly pronounced in the field of psychology. It’s sensible to try to base social policy on empirical research, but we have to be careful because the stakes are so high.