After digging into the literature on race and genetics, Ta-Nehisi interviews geneticist Neil Risch about race, IQ and other genetics issues. There’s a lot of good stuff TNC has unearthed – among them these papers: “The Importance of Race and Ethnic Background in Biomedical Research” and “Assessing Genetic Contributions to Phenotypic Differences Among ‘Racial’ and ‘Ethnic’ Groups“. Have at them. Here’s the final question and answer:
Your paper on assessing genetic contributions to phenotype, seemed skeptical that we would ever tease out a group-wide genetic component when looking at things like cognitive skills or personality disposition. Am I reading that right? Are “intelligence” and “disposition” just too complicated?
Joanna Mountain and I tried to explain this in our Nature Genetics paper on group differences. It is very challenging to assign causes to group differences. As far as genetics goes, if you have identified a particular gene which clearly influences a trait, and the frequency of that gene differs between populations, that would be pretty good evidence. But traits like “intelligence” or other behaviors (at least in the normal range), to the extent they are genetic, are “polygenic.” That means no single genes have large effects — there are many genes involved, each with a very small effect. Such gene effects are difficult if not impossible to find. The problem in assessing group differences is the confounding between genetic and social/cultural factors. If you had individuals who are genetically one thing but socially another, you might be able to tease it apart, but that is generally not the case.
In our paper, we tried to show that a trait can appear to have high “genetic heritability” in any particular population, but the explanation for a group difference for that trait could be either entirely genetic or entirely environmental or some combination in between.
So, in my view, at this point, any comment about the etiology of group differences, for “intelligence” or anything else, in the absence of specific identified genes (or environmental factors, for that matter), is speculation.
I note that Risch says that “traits like ‘intelligence’ or other behaviors (at least in the normal range), to the extent they are genetic, are ‘polygenic.'” That has to be true. The answer to this question is likely to be extremely complicated – rather like the impact of genetics and environment in the persistent phenomenon of homosexuality. But what if the normal range is where we shouldn’t look for insight. The major ongoing Chinese experiment to find the genetics of intelligence is focusing on extremely high IQ individuals – to see how their DNA is different than the rest of us. Razib praises TNC’s interview. But he thinks that the race, IQ and genetics question “will semi-resolve within the next 10 years”:
Let’s focus on the black-white case in the American context. On intelligence tests the average black American scores a bit less than 1 standard deviation below the average white American. As I’ve observed before the average black American is ~20% European, but there is variation around this value. Because the admixture is relatively recent (median ~150 years before the present) there is a wide range across the population of ancestry. In fact, the admixture is recent enough that siblings may even differ in the amount of European ancestry on a genomic level. An additional issue which is of relevance is that the correlation between ancestry and physical appearance in mixed populations is modest. By this, I mean that there are many individuals who are more European in ancestry in the African American population who have darker skins and more African features than those who have less European ancestry. Obviously on average more European ancestry predicts a more European appearance, but this is true only on average. There are many exceptions to this trend.
At this point many of you should have anticipated where I’m going. If the gap between blacks and whites on psychometric tests is totally driven by genetic differences between Africans and Europeans, then the gap should be obvious between pools of individuals of varying levels of European ancestry within the African American population. It seems unlikely that it would be that simple (i.e., all driven by genes without any sensitivity to environmental inputs or context). Therefore I suspect some design where you compare siblings would be more informative.
I cannot predict scientific findings. But I hope we make empirical progress, with less political drama. The main threat to that, of course, is the political stigmatization of such research. Which is why Jason Richwine’s sweeping political inferences from decent empirical work was actually self-defeating.