The existence of a Black-White IQ gap in the US is not controversial at all. A 2001 meta-analysis with 6 million sample size found a gap of 1 standard deviation. This article will go through some lines of evidence of why the gap is significantly due to genetic reasons.
1. Within-group heritability
While it is true within-group heritability doesn’t determine between-group heritability (at least by itself), within-group heritability does help in determining it. There is in fact a statistical relationship between the two (which I will not go through in this post).
Next, consider the rising constraints model:
The broad-sense heritability of IQ is around 80% in adulthood and there are no Black-White differences in heritability. Thus, the Black-White difference in environmental factors that impact IQ must be 2.24 standard deviation, or in other words, the average black cognitive environment must be below the bottom 0.2% of white environments. This is unlikely, to say the least:
But then the challenge becomes generating a plausible list of dozens of nonredundant variables that all have a possible causal impact on intelligence after genetic influences have been controlled for. Given the lackluster results of randomized interventions to increase intelligence (e.g., Lipsey, Farran, & Hofer, 2015; U.S. Department of Health & Human Services, 2010) and the severe attenuation in effect sizes in correlational studies when genetic effects are controlled for (e.g., Bouchard, Lykken, Tellegen, & McGue, 1996), we believe that a lengthy list of variables that each have a small detrimental impact on African Americans’ intelligence levels would be extremely difficult to produce — Warne et al 2018
At this point, some will think of Lewontin’s thought experiment which consists of a magical X factor that affects all blacks. This theory was tested, and no such factor was found. See Rowe 1994, Rowe 1995. Furthermore, measurement invariance implies common sources of within- and between-group variation as shown in Lubke et al 2002.
2. Admixture analysis
The logic behind admixture analysis is simple, and it’s a widely used method to find out if phenotypic differences between populations are due to genetic differences. If a trait differs between populations due to genetic factors, then ancestry will correlate with it. It has been done for diabetes, height, sleep depth, and numerous other traits.
In terms of IQ, the vast majority of the studies arrive at a Hereditarian result:
Shuey 1966 meta-analyzed 16 studies. 13 of them supported that the gap is genetic, while 2 did not and 1 was unequivocal. These studies are obviously too old and dubious, but it should set the stage for what we expect.
Rowe 2002 found that mixed children score in-between Black and White children, and evidence against colorism.
Direct genetic estimates have also been used and the usual correlation was found.
The way we know confounding factors like racism are not at fault for this is because most of the variance between skin colour and IQ is between sibling pairs. This means that darker Blacks have lower IQs than lighter Blacks, but not that darker Blacks have lower IQs than their lighter sibling. This is contrary to what we would from a colorism model in which skin colour causes lower IQ through racism.
Furthermore, there is little evidence for the colorism model.
More generally, it is not clear that colorism is actually a potent force, at least in the USA. Consider research based on sibling designs, which can distinguish between discriminatory and intergenerational effects. A number of studies in the economics literature have utilized sibling control designs in this fashion [81,82,83,84,85,86]. Unfortunately, they differ somewhat in design (e.g., raw vs. SES-controlled results for between-family regressions), and do not report standardized effect measures, so we were unable to quantitatively meta-analyze them. However, generally speaking, when family characteristics are controlled for, residual associations between racial appearance and social outcomes are small. In the words of one researcher who studied a large dataset from Brazil: “[T]he estimated coefficients are small in magnitude, implying that individual discrimination is not the primary determinant of interracial disparities. Instead, racial differences are largely explained by the family and community that one is born into” [81]. Mill and Stein [83] make statements to the same effect based on an analysis of a large dataset from the USA. — Kirkegaard et al
3. Correspondence with the Wilson effect
The Wilson effect refers to heritability rising with age. If heritability rises with age, then we expect the gap to also rise with age if the gap is due to heritability. This is the case. There is almost a perfect correlation between the Wilson effect and the Black-White IQ gap. The likely conclusion is that the gap is heritable.
4. Subtest heritability and g
Different subtests have different heritability. Thus, if the gap were genetic, we would expect subtest heritability to correlate with the Black-White IQ gap. This was shown in Nichols 1970. The correlation was 0.67, suggesting the gap is largely genetic.
A similar correlation was found with inbreeding depression (a purely genetic phenomenon) by Rushton 1989.
Furthermore, consider Dragt 2010:
Recent psychometric meta-analyses have clearly shown that g loadings correlate highly with measures of heritability. te Nijenhuis and Grimen (2007) show that g loadings of subtests correlate perfectly with these subtests’ heritability coefficients. Moreover, te Nijenhuis and Franssen (2010) show that inbreeding depression correlates .85 with g loadings. This strongly suggests that g loadings and heritability coefficients may be interchangeable. This in turn suggests that the high correlation between g loadings and group differences could imply that mean group differences have a substantial genetic component.
and Metzen 2010:
The picture that emerged from all these studies is straightforward: Differences in IQ caused by these biological-environmental variables are virtually unrelated to general intelligence.
Since the gap is on g, and only genetic factors have been found to correlate with g, likely because the gap is genetic. Of course, a magical environmental factor that somehow affects g may exist but pseudoscience should not be entertained.
5. Structural Equation Modelling
This method has found between-group heritabilities ranging from 36% to 74%. See Rowe 1996. While it assumes that no X factor exists, this assumption holds as I showed.
6. Stability
While some allege the gap has narrowed, this is false. The adult gap has remained the same since it was first tested. Shuey 1966 conducted a meta-analysis and found a 1SD gap.
Dickens and Flynn 2006 found the same 1SD difference between adults.
It should go without saying that Blacks are now doing much better, by virtually all measures, than in the first half of the 20th century but the IQ gap hasn’t budged. The gap is thus unlikely to be significantly caused by environmental factors.
7. Expert opinion
While this is not empirical evidence per se, one should wonder about what the expert opinion on the cause of the gap is.
In 1987, 45% of intelligence experts believed the gap is due to genetic and environmental factors, 15% entirely due to the environment, 24% that there is not enough data, and 14% did not respond.
In 1994, 52 experts believed “both environment and genetic heredity are involved.” in the Black-White IQ gap.
In 2013–2014, intelligence experts on average attributed nearly half of the Black-White difference to genetic factors.
In 2017, 90% of experts believed that genes had at least some influence on cross-national differences in cognitive ability.
On potential non-arguments
Some people might invoke the “race is socially constructed” non-argument. They should read:
Our difficulty with this position is not that Gould (or others who make similar arguments) is wrong about the blurred lines between the races, or about how long the races have been separated, or ahout the number of genes that are racially distinctive. All his facts can be true, and yet people who call themselves Japanese or Xhosa or Caucasians or Maori can still differ intellectually for genetic reasons. We may call them “ethnic groups” instead of races if we wish-we too are more comfortable with ethnic, because of the blurred lines-but some ethnic groups nonetheless differ genetically for sure, otherwise they would not have d~ffering skin colors or hair textures or muscle mass. They also differ intellectually on the average. The question remaining is whether the intellectual differences overlap the genetic differences to any extent. — the Bell Curve, page 296
and
Human beings form a single interbreeding species and no serious geneticist or anthropologist today would subscribe to a view of genetically distinct ‘races’. There is no single genetic marker common to all white groups and absent in blacks, or vice versa; all human genes are found in both groups. Some writers (e.g. Gould, 1 986) have attempted to argue from this that there could not be genetic differences for IQ between blacks and whites. The argument seems curious, for it is clear enough that blacks and whites do, on average, differ in the distribution and frequency of certain genes, and the genetic hypothesis needs nothing more than an average difference in the distribution of the no doubt vast array of genes affecting IQ (Jones, 1996). — Mackintosh 1998
Another red herring is the Flynn effect.
The Flynn effect is qualitatively different from the Black-White IQ gap. Thus, it can’t tell us anything about it.
Some may have problems with heritability estimates, yet these have been extensively validated through various methods. There is no evidence for any significant gxe interactions and they are a prior unlikely.
Others may claim that the environmental effects can’t be distinguished from the genetic effects. This is false.
Throughout the history of GxE research, the question of whether or not GxE effects are separable from genetic and environmental main effects has been asked on many occasions. The answer is yes (though it is not necessarily intuitive); GxE effects are meaningfully and actually separable from genetic and environmental effects. Plomin and colleagues explained this elegantly in 1977, making the point that “interactionism,” which they define as the idea that “environmental and genetic threads in the fabric of behavior are so tightly interwoven that they are indistinguishable,” is simply false at the population level. To be clear, it is true that — for an individual — genetic effects cannot be expressed in the absence of an environmental context just as environmental effects necessarily manifest themselves in the context of an organism’s genome. However, at a population level, it is possible to distinguish genetic from environmental effects. — Duncan 2014
Conclusion
In conclusion, it’s obvious the gap has a significant genetic influence. The Hereditarian Hypothesis makes a lot of risky predictions, and it comes up on top. Meanwhile, the Environmentalist hypothesis bends itself at every new finding that goes against it. This is not how science works.
