Just when we think the arguments can’t sink much lower, some kids have a party in the crypt and the dead walk again. Dominic Cummings wants to select designer babies with higher IQs. Andrew Sabisky repeats the canard that African Americans have lower IQs than whites. There’s been no direct comment from Boris Johnson, but he’s on the record as believing stuff about IQ: “it is surely relevant to a conversation about equality that as many as 16% of our species have an IQ below 85 … while 2% have an IQ above 130 … And the harder you shake the pack, the easier it will be for some cornflakes to get to the top”.
IQ tests are supposed to be a proxy for Spearman’s ‘g‘, an underlying factor denoting general intelligence and intellectual potential. There are two common complaints about that. The first is that it’s not obvious that anything called general intelligence actually exists. The second is that even if it does, it’s not clear that g is the underlying factor that IQ tests measure. It’s much more plausible to suggest that IQ tests reflect the skills that people gain through education. The suggestion that people in some racial groups have lower IQ looks very different if we understand it to mean that some groups are disadvantaged in education, educational testing and educational attainment. We wouldn’t expect a different result.
The other side of the IQ debate is, of course, the assertion that g, and IQ, both reflect people’s genetic endowment. To establish genetic influence, the believers have relied extensively on twin studies. There are three big problems with that. First, twins are generally reared together; they have a common background as well as a common genetic inheritance. Second, the data are rigged: twins are often accepted as monozygotic on the say-so of their parents rather than a genetic test, and twins where one is disabled (although such twins still have common genetic factors) are routinely discounted from the studies. And that rigging points to the third problem: the cultists are determined to prove their case, regardless of what the evidence actually shows. Of course, they say, social factors must be inherited. Of course that will be manifest in twin studies. Of course, if genetic evidence isn’t there, it must be lurking in there somewhere. This is very bad science; a scientist is supposed to set out to disprove a proposition, not to prove it. Twin studies could prove something; they could show, if there are differences in monozygotic twins (such as the known differences in sexuality), that the difference cannot be genetically determined. But that is not what the scientists are looking for.
From twin studies we have estimates of ‘heritability’. Many believers claim that this is a measure of genetic influence; it isn’t. Technically, heritability refers not to genes, but to a combination of genotype and phenotype. In practice, that combines genetic and environmental influences; it is supposed to disregard familial influences such as culture and language, but in practice that can only be done by weeding those out of a study. In human terms, heritability means only that something runs in the family. And that, despite repeated assertions to the contrary, is not the same thing as genetic influence.
Scientists have not been able to link genes, either individually or in combination, with intelligence – or indeed, with any other social trait. The problem has been discussed in Nature under the heading of ‘missing heritability’. Differences in physical traits such as height are hardly explained by genetic endowments. That shouldn’t be surprising, because the progressive gain in height over the past few generations has clearly been environmental, and the environmental difference is so large that it far outweighs the limited, if more extreme, genetic influences. There is a more recent summary of the state of play here. Like many people in the field, the writer still seems to be convinced that there is something there to be found. If there is, it’s well hidden. The fact remains that after 150 years of trying, no-one has been able to prove that factors like intelligence are inherited. Indeed, one of the assertions made by specialists in this field is that there is a ‘regression to the mean’. So their case is held to be proved if children are cleverer than their parents (that’s ‘breeding’), proved if one generation is like another, and proved if children are not as clever. This is pseudo-science.
The problem that people like me have in engaging with this kind of topic is that believers in genetic influences often assert that their expertise exempts them from critical scrutiny by non-specialists. Eysenck, whenever he was faced with criticism for the rubbish he published about IQ and inheritance, would deride the critic for not devoting his or her self to the study of the psychology of intelligence. Of course none of the critics would have done that, because no-one wants to waste their life refining the measurement of meaningless claptrap. You might as well devote your attention to astrology, or ley lines, or the mystic significance of the great pyramid. And you don’t, as Dr Johnson said, need to be a carpenter to know that a table wobbles. It takes more than scientific method to make a study scientific.