Kevin Drum is right to say that studies of separately adopted twins have long been considered the gold standard in research on the heritability of IQ. But I’ve never understood why. Each twin in a pair spends nine crucial months in precisely the same environment, and an environment whose quality varies strongly with social class.
Just to be clear: I’m not an IQ denier, a viewpoint with as about as much scientific cred as global warming denial. Of course there are quantitatively measurable differences among humans (and in the distributions among population groups, even imprecise ones such as “race”) in cognitive capacity and personality traits. And of course some of those differences relate to the genetic constitution of individuals and groups. (And of course the overall human gene pool, including the parts of it with large cognitive/behavioral impacts, has been determined by Darwinian processes, but that’s the topic of a different denial.)
But the political question, as opposed to the scientific question, is how much of the disadvantage suffered by poor people generally and by particular ethnic groups specifically in the United States is due to immutable personal characteristics, and how much to potentially mutable social conditions. If poor people are poor mostly because they’re stupid due to genetic deficiencies, and if black people are disproportionately poor because they’re disproportionately subject to those genetic deficiencies, then it would seem that poverty and racial disadvantage are, as Aristotle might have said, “by nature” rather than “by convention.” I know the defenders of The Bell Curve deny that Herrnstein and Murry meant to say that, but I know too that the book was a best-seller because people who wanted to read it as saying that could and did.
(I say “it would seem” that genetic determinism justifies inequality, because even that argument depends on the belief that it’s fully just to distribute rewards according to social contributions, no matter how unequal the result, and on the further belief that Ken Lay and Ann Coulter make larger social contributions than do schoolteachers and social workers.)
Insofar, however, as those “innate” human characteristics are the product of social conditions — insofar, for example, as poor prenatal environments help transmit disadvantage from generation to generation — then the disparities we see are partly the product of social choice rather than of unvarying natural law, and the question arises whether we ought to make different social choices (which of course requires, among other things, changing the behavior of today’s disadvantaged groups in the interest of their descendants, for example by discouraging smoking among poor pregnant women).
Now I would be for greater equality of income and of social and political power even if I thought that we lived in a pure meritocracy and also that intergroup differences in cognitive skills were the product of genetic variation. (Similarly, I’d be against discrimination on the basis of sexual orientation even if I thought that male homosexuality was mostly chosen rather than innate.) But lots of voters will make the link I reject, so it matters what they think about the underlying scientific question, even though only a few percent of the population actually knows enough on the question to be entitled to an opinion.
Just as it would be an offense against the reality principle to shape one’s opinions about human psychology to one’s preferred political outcomes, it would be naive to ignore the political implications of scientific controversy. The more human inequality is taken to be natural rather than conventional , the better for the haves in their age-long struggle to continue to oppress the have-nots with a clear conscience.