I’ve been thinking, off and on, about sudden changes in the cognitive abilities of populations: groups low suddenly scoring much higher or lower on a time scale too short to be explained by selection: say, three generations or less. This is, of course, not the same as some immigrant group learning English. Their scores change when that happens, but I don’t really think their intellectual potential changes one way or the other. I can point to populations that became a lot more educated, but that’s not the same as getting smarter. Lots of admixture with a smarter or dumber population might cause changes over that time frame, but again that’s not what I’m talking about.
The general assumption in the US is that such change is bound to happen (only increases, of course). In fact, that is often expressed with great emotion, strongly suggesting that a world in which this didn’t happen wouldn’t be worth living in. Thing is, I don’t see clear examples of such change, or at least not much – not enough to effectively equalize populations, let alone put bottom rail on top. Gaps persist, despite vast efforts. And if the behavioral geneticists are to be believed, that’s not too surprising. Most of the social factors that are generally thought to boost intelligence – don’t. They show up as between-family differences, and they have very little effect on adult IQ.
I can think of two perfectly feasible strategies that would cause significant one-generation increases in intelligence, in certain populations. Iodine supplementation, in places where it’s short, has a big payoff. It’s also dirt cheap. I don’t know if anyone has looked hard at it, but there used to be goiterous areas around the Great Lakes, before iodized salt, and I’ll bet that scholastic achievement improved significantly after the introduction of iodized salt. The other practical, low-tech strategy would be stopping cousin marriage. The next generation would be in much better shape, since the children of first cousins take a substantial IQ hit - maybe six points or so. And, of course, those children suffer from considerably higher levels of mortality and morbidity. Iraq has lots of cousin marriage, but (and I hadn’t known this) has a fair amount of iodine deficiency as well. This makes clear why the US picked Iraq as the ideal country to install a Jeffersonian democracy: if we could do it there, we could do it anywhere!
One useful heuristic: since enlightened opinion is increasingly swinging in favor of cousin marriage, you know it has to be some kind of ball-busting, civilization-undermining mistake. Liberals and libertarians share this inverse-weathervane property.