More IQ kerfuffle

Mark Kleiman complains about:

People who dogmatically deny either that some sort of generalized cognitive ability is measurable, and that IQ testing is a decent though imperfect proxy for that measurement, or that different human population groups with different genetic heritages might have different distributions of cognitive ability

And links to an utterly marvelous piece by Cosma Shalizi about the current state of ignorance regarding the meaningful heritability of IQ. (Among other things, Shalizi explains why the statistical question of heritability, which is about how much information knowing people’s genetic heritage adds to your knowledge about their IQ score’s, is pretty useless for answering questions about what contributions DNA makes to the fact the ostensibly smart parents tend to have ostensibly smart children.)

I’m not at all sure how strongly you have to hold the opinion Kleiman complains about to be considered “dogmatic” — in other parts of the article, Shalizi politely demolishes the notion that IQ measures something either innate, immutable or objective. She cites studies of early-childhood intervention and repeat measurements of IQ in people with different levels of schooling to show how whatever innate cognitive abilities people have can be either sharpened or dulled by environment. And then, of course, there’s the Flynn Effect, that pesky 3-point-per-decade rise in IQ scores (which, if it were genetically based, Shalizi points out, would turn the entire world into a sort of reverse Lake Wobegon where the average IQ of people who at some point have children would be significantly higher than the average IQ of the population as a whole, even though the two populations are essentially indistinguishable).

Shalizi also does a nice job unraveling some of the details of twin studies (in some of them, identical twins living in the same town and going to the same school, presumably in the same classroom, could still be counted as “raised apart” for purposes of discounting cultural and other environmental influences).

The riff on the inextricable connection between culture and genetics is funny, and Kleiman probably should have thought its implications through more carefully before pronouncing that the appearance of hybrid vigor in IQ is “the smoking-gun finding that population genetics matters”.

And while we’re on the interaction between genes and environment, you have to wonder just how much the remaining apparently-genetic correlation between the cognitive abilities of identical twins raised apart says about the homogeneity of our culture. We treat taller, prettier and more graceful people better, shorter, uglier and clumsier people worse. It would be surprising indeed if identical individuals introduced into the same cultural milieu didn’t evoke very similar responses from the people around them, with the obvious effects on development. (If anything, this suggests that correlations between identical twins raised together should be somewhat suppressed, simply because each acts as a confounder for the other.)


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