It is perfectly reasonable for critics to ask, every so often, if there is any work showing that genes make a contribution to intellectual differences between genetic groups. I assume it can be accepted that genes make a difference within a genetic group, and the animus arises only when genetic groups are being compared.
One approach is to begin by mentioning the major findings of the last century of research, which set the context of the debate. Although reasonable, the reading involved may seem unreasonable to those who want immediate answers. A brief summary would be that, despite many interventions over seven decades, African Americans remain roughly one standard deviation behind European Americans. Whatever the reason for the ability gap, it has not proved malleable.
Another approach is to discuss a selection of recent papers. This ought to be welcome, but unfortunately for those who want to skip the reading, it is necessary to go back to some old debates.
For example, although differences in intelligence between racial groups could be caused by different genetics, they might also be caused by trivial aspects of race like skin colour, which then triggers non-trivial bad treatment by other races. This bad treatment, the argument goes, could cause intellectual under-performance, either by denying educational access and quality, occupational opportunity, sufficient encouragement and mentoring, or leads to some other broad, unfair impositions. So, if a research finding is to be believed, it must distinguish between deep intrinsic causes and superficial social ones.
Furthermore, if some ancestral backgrounds really create higher intelligence in offspring, then those who have less of that advantageous genetic material should have progressively lower intellectual ability; that is to say, there must be a linear dose-response relationship. Purely European children must be brighter than those with a little less European in their genetic mix; and they must be brighter in turn than those with even less European blood. No excuses allowed.
Global Ancestry and Cognitive Ability.
Jordan Lasker, Bryan J. Pesta, John G. R. Fuerst and Emil O. W. Kirkegaard
Psych 2019, 1(1), 431-459; https://doi.org/10.3390/psych1010034
30 August 2019
This is a very detailed paper, which makes use of a natural experiment. Since Europeans, African Americans, and the children of European/African American parents have varying amount of European ancestry, it ought to be possible to check whether that genetic mix predicts intelligence, and whether is does so better than superficial characteristics like skin colour.
The paper is set out in a series of logical steps, each countering objections commonly raised against the hereditarian hypothesis.
The present work uses a population-representative Philadelphia-based sample, the Philadelphia Neurodevelopmental Cohort (PNC), otherwise known as the Trajectories of Complex Phenotypes study (TCP). Due to the location, the results are directly comparable to those of Scarr et al.. Our analysis has numerous advantages compared to earlier admixture studies.
First, participants all came from the same location, so geographic confounding is not an issue.
Second, we assessed measurement invariance (MI) for the cognitive test battery using multi-group confirmatory factor analysis (MGCFA;).
Third, the heritabilities of the g factor and subtest scores have already been estimated for this sample. Specifically, Mollon et al. reported heritabilities for g of 0.61 (standard error (S.E.) = 0.14) and 0.72 (S.E. = 0.07) for the non-Hispanic African and European-Americans in this sample respectively.
Fourth, we included estimates of skin, hair, and eye color to evaluate phenotypic discrimination (i.e., colorism) models of the observed differences.
Fifth, we validated polygenic scores (PGS) associated with cognitive ability for both the African- and European-American samples and we examined to what extent cognitive ability- and education-related PGS (eduPGS), could account for group differences.
Sixth, we tested for Jensen effects in relation to ancestry, heritability, and eduPGS.
Seventh, we examined whether MI was tenable across the full range of European ancestry using local structural equation modeling (LSEM).
Measurement invariance means that the tests are testing the same things in all populations. This is done by carrying out confirmatory factor analyses in both populations. The study already has calculations of the heritability of intelligence in different racial groups. The fourth point is a great addition: they have predictions of what people looked like in racial terms, so one can test if people have been treated differently because of skin-colour and hair-type superficial characteristics. If intelligence is affected by racism, then these superficial appearances will be useful predictors of the size of the deleterious effect on intelligence. Fifth, on the basis of DNA taken from most of the subjects, polygenic risk scores have been calculated, which show the genetic estimates for intelligence for each person. The sixth and seventh points are further tests for whether the genetic explanation is tenable for the test scores in these different racial groups.
There is a great deal in this paper, so I will pick out the main features only, and the technical details are all there in the text, many of them dealing with possible methodological objections.
The total sample includes data from 9421 genotyped participants assessed primarily from 2010 to 2013. Demographically, the sample was 51.7% female, 55.8% European-American, 32.9% African-American, and 11.4% Other, with a mean age of 14.2 (standard deviation (SD) = 3.7) years of age. Participants were recruited from the Philadelphia area. Persons with severe cognitive or medical impairments were excluded from the final sample. The subjects were English-speaking people aged 8–21 years at the time of testing.
Participants were administered the Penn Computerized Neuro-cognitive Battery. This battery was built to be highly-reliable, psychometrically-robust, and to incorporate tasks linked to specific brain systems. The battery consists of 14 tests grouped into five broad behavioral domains: Executive Control, Episodic Memory, Complex Cognition, Social Cognition, and Sensori-motor Speed.
The tests in the battery are as follows: Penn Conditional Exclusion Test (meant to assess Mental Flexibility), Penn Continuous Performance Test (Attention), Letter N-Back Task (Working Memory), Penn Word Memory Task (Verbal Memory), Penn Face Memory Task (Face Memory), Visual Object Learning Test (Spatial Memory), Penn Verbal Reasoning Test (Language Reasoning), Penn Matrix Reasoning Test (Nonverbal Reasoning), Penn Line Orientation Test (Spatial Ability), Penn Emotion Identification Test (Emotion Identification), Penn Emotion Differentiation Test (Emotion Differentiation), Motor Praxis Test (Sensorimotor Speed), Finger Tapping (Sensori-motor Speed), and the Penn Age Differentiation Test (Age Differentiation). The sample also completed the Wide Range Achievement Test, which is a highly-reliable broad ability measure.
Of the included participants, there were 5183 European-Americans, 3155 African-Americans, and 242 biracial African-European-Americans.