Explanatory gaps in test score gaps
Why environmental explanations for racial differences in intelligence fail to amount to very much.
Explanatory gaps in test score gaps
Gregory Conner has written a very good and detailed examination of intelligence differences between white and black Americans, showing that a purely environmental cause is unlikely to be true. Despite that, it is the standard and widely accepted view, in public at least.
It is worth reading.
In the hope of getting it an even wider readership, here is a very simplified summary of his arguments.
1: The intractable Black-white test score gap
Despite six decades of aggressive (and expensive) policy measures in the US to address the gap, a very substantial Black-White test score gap of 15 IQ points stubbornly remains, which is one standard deviation, and very big in practical terms. The evidence for this intractable gap is very strong.
2: Comparisons of average cognitive ability between nations
The international data on intelligence shows a uniform, worldwide underperformance of all predominantly African populations when compared to predominantly European or East Asian populations, despite different histories of slavery and colonialism. Only 6% of sub-Saharan African youths have the basic academic skills necessary to be internationally competitive in the modern global economy, compared to 72% in Europe, 76% in North America, and 71% in East Asia and the Pacific.
3: Spearman’s Hypothesis
The environment-only theory implies that the test score gap will be larger for intelligence test questions which are more susceptible to environmental influences. In fact, the gap is larger for intelligence test questions more strongly linked to genetic influences and smaller for test questions more strongly linked to environmental influences. For example, digits forwards is weakly related to general intelligence, while the harder digits-backwards task is more related to intelligence, and shows more race differences. It is not a cultural difference, since digits are used in both tests, it is a difference in intrinsic mental demands.
4: The low power of shared environment in explaining cognitive ability
The environment-only theory says that it is bad environments which lead to poor test scores in different races. How much of the difference within any group can be explained by bad environments? In fact, not all that much unless they are very, very bad environments. Since shared environments don’t explain much of the difference between people, the environmental differences between blacks and whites will need to be extraordinarily large to explain the size of the intelligence gap, and those profound differences are no longer found in the US.
Also, the gaps should be biggest when siblings are living together in the same (disadvantaged) family, and reduce when adults go on to build their own better environments, but in fact they hold steady throughout the entire life span.
5: Admixture
This one is very simple, and also very powerful. If intelligence gaps are due to how other groups treat you, then your social identity (the race you classify yourself as) will be more powerful than your genetics. In fact, it is the other way round. The “added together mixture of your genetic races” will be the stronger predictor of your life outcomes. For example, “an individual who has 60% African and 40% European ancestry will have a 60%-40% expected weighting of the cognitive-ability related genetic variants from these two populations. This leads naturally to a simple linear relationship between individuals’ ancestry proportions and their expected cognitive abilities.
“Admixture regression analysis has been used over the last two decades by genetic epidemiologists to study race and ethnicity related differences in alcohol dependence, height, asthma risk, cardiovascular disease, sleep depth, cigarette smoking behavior, metabolomics, cancer, and diabetes.” It also works for intelligence.
6: Brain size differences across biogeographic ancestries
The evidence finds substantial differences, with on average larger brains among individuals with higher proportions of European versus African ancestry.
Individuals with African ancestry have average cranial volume 6% below those with European ancestry, whereas individuals with East Asian ancestry have average cranial volume 1.3% higher.
7: New findings on the recent evolution of intelligence-related genetic variation
Recent genetic research shows that genes associated with higher intelligence (polygenic risk scores) have increased substantially in the European population over the last ten thousand years. Parallel evolution in other regions could have similar effects after the African dispersal of humans to multiple continents, but the impact on average intelligence of any evolution in other continents is unlikely to be exactly the same worldwide. In fact, the intelligence-related average polygenic risk score for academic achievement of people who identify as Black is significantly lower than that of people who identify as White. This finding is suggestive, but must be considered tentative, since not enough Black individuals have been studied. Alarmingly, access to the available data on race differences is being restricted, and publication of results hampered.
In conclusion, the “environment only” explanation is very weak. The “genetics and environment” explanation is stronger. It explains things seamlessly using fact-finding methods from different tests and different countries, which supports a cohesive theoretical structure. The “environment only” theory relies on a patchwork of explanations to counter each separate line of empirical evidence against it. This is important: even if each of the seven counter-arguments sound plausible, Occam’s Razor leads us to give more weight to the simpler argument: that there is a genetic component to racial differences in intelligence. Privately, the majority of researchers believe there is a genetic component of at least 20%; and half of them think the component is as high as 50%.
Why don’t people admit this in public? Probably because they fear the findings would increase racial hostility against Blacks, which might be the case. Individual differences in ability are generally seen in a kinder light, but group differences might not be accepted so compassionately.
In sum, the public position is to promulgate a Noble Lie, without allowing an open discussion of the costs of such dishonesty.
It would also be interesting to see a list of the strongest reasons why some think the gap may not be significantly genetic. I think the list would probably be shorter, but it would still be good to know.