Posted at 15:53h in Uncategorized by Eric Turkheimer 7 Comments
Reactions to my post yesterday about Human Diversity mostly involved my invocation of the idea of genetic determinism, henceforth GD.
Please define “genetic determinism”.
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I know that GD is sometimes used as an all-purpose tool to attack any assertion of a role for genetics in human behavior, but that isn’t my point. In fact I think the hereditarian argument requires GD, isn’t interesting without GD, and that there are good examples of actual GD. The point is that asserting GD requires additional evidence over and above what is actually available for the vast majority of the human differences we are talking about here.
As usual, let’s start with marital status. Marital status is heritable, and there are real-world consequences of that heritability. If you are studying (as I have) the effects of divorce on children in the family, you can’t just compare kids in divorced and non-divorced families, because the environmental pathways are confounded with genetic ones. But suppose a friend of yours is getting divorced. You probably wouldn’t say, well of course, that’s because you have genes that caused you to get divorced. Why not, exactly? Marital status, we have agreed, is heritable in twins, and if no one has gotten around to the GWAS of marital status yet it is only because it hasn’t seemed worth it. The genetics of divorce is not scientifically different from the genetics of personality or intelligence or mental illness.
Divorce is heritable, but it is not GD. What I mean by this is that we have utterly no idea about the how or why or when of the particular genes that happen to be involved in the correlation between marital status and genotype. Would our friend’s genes have led to divorce in a world with better access to mental health care, or if he had had a kid, or if he didn’t drink, or…. on and on and on. The list of things that might– almost certainly do– modify the “causal” (the word barely applies) pathway between a bit of DNA and divorce is so vast, so uncontrolled, that we know that we can’t say anything more than, “genotype and phenotype are modestly correlated.”
This universal, causally indeterminate heritability leaves the hereditarian in a dilemma. You could say, no, the heritability is all I need. Divorce is heritable, and that means one way or another you have to think about genes when you think about divorce. That’s fine, but it is true for everything, and it leads to an empty GE interactionism– both genes and environment contribute to the genesis of behavior– that is never going to get Murray where he wants to go. If you want to write a scary book about how the problem of divorce in America is the result of our genetic makeup, it won’t do to just point to the first law of behavior genetics. You need to say there is something specific about our genes that is making us get divorced in a specific way, and you can’t do that.
Groups, like I say, are just collections of individuals, and the exact same argument applies to the explanation of group differences. Divorce rates are higher in the US than they are in Korea. Marital status is heritable in both places, and there are identifiable genetic differences between Koreans and Americans. Is the difference in divorce rates the result of genetics? Presumably not, and once again the situation isn’t really any different for divorce than it might be for personality or IQ. And the hereditarians have the same choice: if they want they can say, everything is heritable, all groups differ to some extent genetically, and therefore all behavioral differences must have something to do with (or “be partially determined by” or “have a component of” or whatever weaselly phrase they want to trot out) genetics. But once again that won’t get them anywhere, because it applies to everything. It’s just a generic assertion that genes are involved in all human development.
Contrast that to Huntington’s Disease, which is GD. If our friend comes down with HD, it is perfectly sensible to say that they got the disease because they have the gene. If there is a country somewhere with a higher rate of HD than the US it is because of genetic differences between the two countries.
I would sum up Murray’s argument as the assertion that group differences in personality and IQ, among other things, are more like HD and less like marital status than has previously been acknowledged. What’s the evidentiary basis of that assertion? What kind of additional evidence do you need? This is what is never spelled out in hereditarian arguments. I think there are two main possibilities.
The first, which I have discussed before, is knowledge of mechanism. People sometimes respond to this idea as though I am just making up an impossibly high criterion for GD, but that isn’t the point. The problem with asserting GD for marital status is that we have no knowledge of the scope and potential moderators of the relationship between genotype and phenotype. Would person X be prone to divorce in all conditions? We don’t know and have no particular hope of finding out. For HD, we more or less understand how the gene causes the behavioral disability, and that allows us to rule out all sorts of uncontrolled possibilities that might moderate the relationship. In the same way, we don’t have to worry about moderators of HD across groups. The gene causes HD in Japan in more or less the same way it does here.
I know it seems pretty unlikely that we will achieve that kind of understanding for marital status, or in my opinion for intelligence or personality, so I want to sketch out another possibility that may apply more to psychology. Suppose for a moment that it turns out that the Plomins and the Murrays are correct, and the 2-3% of the IQ variance we can currently account for (within families) with a PGS eventually increases to 40%, about where it is for height. Families come to routinely use it to select embryos, producing an amazing crop of hyper-intelligent children. Moreover, it turns out that the PGS works in pretty much the same way everywhere, rich and poor, male and female, Asia, Africa and North America. I think we would pretty soon starting treating the PGS as GD, even if we didn’t understand the mechanism. It would be like the effect of poverty on cognitive ability, or smoking and lung cancer. A big effect size, plus a meaningful theoretical, if not exactly mechanistic, basis. It would have genomic construct validity. Interesting idea to pursue.
I emphasize that this is not where we are, and I don’t think we are ever going to get there. But it explains why the Plomins and Murrays are always leaning on the inexorable progress of science to base their arguments on some imagined genomic future that is sure to arrive before 2030. The structure of the argument is like this: Soon we are going to have personal flying cars, and society had better start building appropriate traffic control structures, or everything is going to be a mess when it happens! Except instead of some harmless science fiction fantasy, they are anticipating a genomic dystopia in which poverty has turned out to be a biological given and racism has turned out to be empirically verified.
A final note is that this conversation has been going on for a long time. The vast majority of Human Diversity could have been written by Arthur Jensen in 1990. And as a result, I have been saying these things for a long time myself. The following is from 1998, using “weak” and “strong” biological explanation in place of garden variety heritability and GD:
Proponents of biological explanation do not generally defend the claim that one can or ought to reduce complex behavior to biological terms. Instead, they report the results of experiments that purport to demonstrate that behavior has turned out to be biologically based. However, to the extent these experimental results are necessary consequences of the physical instantiation of psychological processes, they provide only the weakest support, analogous to the support a behaviorist could claim on the basis of an experiment showing that behavior is “influenced” by schedules of reinforcement. This confounding of the philosophical and empirical underpinnings of biological explanation has provided biologism’ s adherents with a nearly impregnable defense: They claim biological .explanation as a strong empirical result on the basis of experiments that depend solely on the necessary instantiation of behavior in the body and brain.