Turkheimer's Projects: Genetics and Human Agency | Origin of Race Differences in Intelligence is Not a Scientific Question

Race Differences in IQ: The Limitations of Empirical Evidence

This is the first of a series of blog posts about race and intelligence. My opinions on this topic are, I think, the least popular arguments I have ever made, and I have made a few unpopular ones over the years. My assertion, basically, is this: discussions of differences in IQ among racial groups are not actually about empirical data. My argument is unpopular, I think, because both sides of the issue are committed to the idea that they are being scientific about it. The hereditarians want to be seen as scientific so they aren’t seen as racists; the anti-hereditarians want to be scientific so they aren’t seen as frightened by socially difficult scientific findings.

We recently published a criticism of Sam Harris’s interview with Charles Murray, published on Harris’ Waking Up podcast. It produced a predictable outcry, with replies published here and here and here. We are working on a response to our critics that will be published soon. I am not especially interested in getting into a back and forth on all of this, exactly because much of the objection to what we wrote focused on the part that I personally think is least important: the so-called empirical evidence on the issue.

It was Arthur Jensen who first attempted to extract claims of genetically-based differences in the IQs of racial groups from the obviously racist context in which they had previously existed. Jensen’s writing on the subject adopted a measured scientific tone, denounced racism directed at individuals, referred extensively to data, and was extremely well-informed about the science of human intelligence. Jensen’s work on race differences produced pushback of all kinds, but the predominant strand accepted his contention that the question of race differences was a scientific hypothesis deserving of careful empirical consideration. The classic work of this kind, still the only take on the subject that appears genuinely to avoid reaching a conclusion ne way or the other, was written by my mentor John Loehlin.

More recently, discussions of the racial hypothesis have been more adversarial in tone, but they remain focused on the empirical evidence. My colleague and co-author Dick Nisbett has been a stalwart opponent of Jensenism in his book, in an article in American Psychologist on which I was a co-author, and in a series of replies to papers co-authored by Jensen and J. Philippe Rushton. Those of us who are opposed to the hereditarian hypothesis should be deeply in gratitude to Nisbett for carrying this torch. In fact, no one owes more to Nisbett on this front than me, because this is a case I have never felt particularly motivated to take on. When all is said and done I find the whole empirical argument unconvincing, starting with the studies that presumably make the case for genetically-based differences, and then for the other studies, or re-interpretations of the same studies, that presumably show that the group differences are environmental. The whole discussion has the tone of an unpleasant dinner table argument, and despite my strong allegiance to one side I can’t say that I think anything has progressed significantly in the last thirty years. I want to start by considering why the discussion is so frustrating.

The first two reasons are common in life and social science. The first is that everyone is stubborn. One thing I actually have in common with Charles Murray is that (as he notes about himself in the podcast) I haven’t changed my mind about much on this topic over a thirty-year career. The second reason involves the nature of the studies that are invoked. When one is discusses questions about the origins of human differences, most of the scientific designs that might be most informative aren’t available. You can’t breed people, you can’t mess with their DNA, you can’t raise them under controlled conditions. So the discussion is necessarily based on quasi-experimental science that is by definition fundamentally flawed. In research of this kind the grounds for objection are almost always greater than the valid scientific signal, making it endlessly possible to trade insults about the low quality of the evidence produced by the other side. Many if not most social scientific arguments are tiresome in exactly this way. (The hereditarians are always saying that any day now there will be new genomic data that will settle the question once and for all. They are wrong. More on that in subsequent posts.)

The third reason why this argument never gets anywhere is the most important: there is no valid scientific basis for answering the question in the first place. Think for a moment what the discussion would be like if it was about heritability of individual differences in IQ rather than group differences. There are still a few people out there who don’t believe that genes have anything to do with individual differences in intelligence. If one were to write a review paper making the case for heritability, one would naturally produce tables of the heritability coefficients produced by different studies; probably you would conduct a meta-analysis of them. And although I have spent a lot of time wondering about exactly what those heritability percentages mean, there is nevertheless a well established methodology—quantitative genetics—that has worked out exactly how they should be estimated, and what kind of empirical data are required for the purpose. One way to say this is that the discussion wouldn’t actually have to be about heritability coefficients at all, it could be about the empirical data on which the coefficients are based. Someone arguing for the heritability of individual differences in IQ could say, “I predict that the MZ correlation will be higher than the DZ correlation, and that the IQs of adopted children will correlate with the IQs of their biological parents.” There is a theory—a difficult theory, but a broadly accepted one—linking data to computation to interpretation. That is why the whole long argument about individual level heritability—its existence, not its interpretation—has pretty much gone away. Like I once said, it is why the nature-nurture debate is over.

Now have a look at the Rushton and Jensen paper making the case for the partial genetic determination of racial differences, or listen to Murray and Harris, or read any of the replies to our piece in Vox. Where are the percentages? Where is the equivalent of the ACE model? Where are the structural equation models with parameters quantifying the “partly genetic and partly environmental” hypothesis the hereditarians keep repeating? For all the hereditarians’ idle intuitions about differences being part genetic and part environmental, where is the empirical or quantitative theory that describes how this apportioning is supposed to work? There is no such thing as a “group heritability coefficient,” no way to put any meat on the speculative bones about partial genetic determination. In the absence of an actual empirical theory, the discussion is all about your intuitions against my intuitions. “Well, it sure seems to me that if the black-white difference was environmental, it would have been reduced at least a little by now!” “Yeah, but it has been reduced by five IQ points, and what about the children born to white German mothers and African-American soldiers?” “Well, OK, but what about Scarr’s trans-racial adoption study?” “Yeah, that’s not how I interpret the trans-racial adoption study!” And so on ad infinitum.

I should be clear that I am not making a “both sides do it” argument. It is the hereditarians who are trying to reach a strong and potentially destructive conclusion, and the burden is absolutely on them to demonstrate that they have a well-grounded empirical and quantitative theory to work with. So, if you are out there and think that group differences t are at least partially genetic, please explain exactly what you mean, in empirical terms. Do you mean that some portion of the IQ gap will never go away, no matter what we do environmentally? Do you mean we will discover genes with hard-wired biological consequences for IQ, and their frequencies will differ across groups? Are polygenic risk scores going to do it somehow? But don’t let me mischaracterize your position: explain it yourself.

My concern is that anti-hereditarians play into race scientist’s hands when we agree to engage with them as though there existed a legitimate research paradigm proceeding toward a rational conclusion. At least in the social sciences, legitimate empirical research paradigms rarely come to all or none conclusions, so it becomes natural for people to conclude, with Murray and Harris, that the whole long argument is bound to settle eventually on the idea that group differences are a little environmental, a little genetic. But in fact, that is not where we are headed. I predict that in a relatively short period of time, contemporary race science will seem just as transparently unscientific and empirically untrue as the race science of the early 20th Century now appears from our modern perspective.

Declaring something to be a science doesn’t make it so. The hereditarians want all the good things that come from being thought of as scientists. They want academic respect, they want protection from charges of racism, they want clear separation from the very recent history of “race science” that led directly to the Holocaust and Jim Crow. They have to earn it, by doing the hard work of developing the quantitative and empirical theories that transform intuitions about stereotypes into real science.

Enough for now. I have a lot more to say on the subject, and I hope to keep this going for a while. Over the next several posts I will continue to explore the theoretical reasons why speculation about innate differences among racial groups do not qualify as science.

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