Eugenics and regression to the mean


Jason Collins


May 28, 2012

Richard Conniff’s Yale Alumni Magazine articleon Irving Fisher’s support of eugenics has some great stories (HT Arnold Kling), but one of the closing paragraphs caught my attention.

We know better now, of course. And yet eugenic ideas still linger just beneath the skin, in what seem to be more innocent forms. We tend to think, for instance, that if we went to Yale, or better yet, went to Yale and married another Yalie, our children will be smart enough to go to Yale, too. The concept of regression toward the mean—invented, ironically, by Francis Galton, the original eugenicist—says, basically: don’t count on it. But outsiders still sometimes share our eugenic delusions. Would-be parents routinely place ads in college newspapers and online offering to pay top dollar to gamete donors who are slender, attractive, of the desired ethnic group, with killer SAT scores—and an Ivy League education.

Regression to the mean often gets trotted out in discussion of eugenics or human evolution, but it is a misunderstanding of the concept. If we eliminated the bottom half of the population by measured IQ, the average IQ of that population will change as the underlying genotype will have changed. The next generation will not have as high IQ as the survivors, as we would have eliminated some people with high-IQ genotypes who had low phenotypic IQ due to luck or environment, and vice versa. However, that population and their descendants will have a higher mean than the original population. Gregory Clark amusingly pointed out the evolutionary implications of the regression to the mean argument in response to critiques (pdf) of his book A Farewell to Alms.

Adapting one of Bowles’s points McCloskey tries to land a knockout blow. Regression to the mean would in a few generations destroy any effects of ‘survival of the richest’ on behavior, by taking descendants back to the average characteristics of the population. Such selection could thus only influence behavior for any descendants of the economically successful for a few generations.

This is just a misunderstanding of the concept of regression to the mean. If McCloskey was right, farmyard animals would all be at their medieval sizes still, and instead of the wonderful modern extravagance of dog breeds, all dogs would have the characteristics of wolves and would make bad house pets. As a further reductio ad absurdum, humans would never have evolved from apes in the first place. Why haven’t creationists latched onto this wonderful insight, which, according to McCloskey, Galton, the great social Darwinist, fully appreciated (and yet clung to social Darwinism)?

The problem with eugenics is not that it could not change the average of traits in the population. The stronger arguments rest on human decency, freedom from interference, untended consequences and the tyranny of government.

Conniff’s example of seeking a high-IQ Yalie as a mate has another amusing problem. The process of selecting mates and the evolutionary result is known as sexual selection. As described in Geoffrey Miller’s The Mating Mind, sexual selection may have shaped our brains as those with higher intelligence were more reproductively successful.  Those who did not seek intelligent, attractive mates are no longer with us as their unintelligent, ugly children left no descendants. The process of seeking suitable mates described by Conniff , whatever the difficulty in observing the traits we care about, is not delusional. It is also a large reason why we are as we are.