>Attention conservation notice: A 1400-word addendum to the previous post, because the correspondence reveals that the inevitable mis-understandings have, being inevitable, taken place. Any interest it contains is derivative of that post; so you're doubly warned.
Q: Some of our readers seem to be taking you to be denying that there is any genetic influence on human mental faculties at all. A, how do you respond?
A: I respond, Q, with a desire that these people read more carefully. Obviously, human beings have evolved to have the kind of intelligence we presently enjoy (if that is the word). This means that these traits must be under some degree of genetic control, and that there must, at least once, have been genetic variation among our ancestors. Traits which have been under strong selection pressure do not continue to show much variation, however, or at least not much that is fitness-relevant. Whatever genes influence (say) decision-making under uncertainty have not been under as much selection pressure as those for color vision, still less that for cytochrome c, so I would expect somewhat more variation, but, honestly, not a lot. Of course, mental abilities were not the only traits subjected to selection, and one can easily imagine a situation where there was divergent selection on hominids, which lead to two species surviving into modern times, one with our sort of mind and another which was just dumber, say at what we take to be the level of the australopithecines.
Q: Didn't you just steal that example from Stephen Jay Gould?
A: Yes, but, like you, I can't find the passage right now. As I remember him saying, the point is that human mental equality is a fact, but it's a contingent evolutionary fact.
Q: But wouldn't any genetic variation here undermine your argument?
A: Not at all. In the first place, this idea that there is a single thing called "intelligence" which tells us how well the mind works is on all fours with the idea that there is some single over-all "immunity" which tells us how well the body fights off infection. That's not how the immune system works, and it's not how the mind works either. On biological grounds, I would expect any ability we might actually care about to be influenced by many genes (and please remember what "X is a gene for Y in context Z" actually means), and in fact I'd expect many such genetic variations to be pleiotropic and epistatic.
Q: But don't you often call people "smart" and "stupid" — it seems to me that this weblog gives plenty of examples, more of the latter than the former...
A: So what? Those are general, and vague, ordinary-language terms, with the usual sort of mixture of description and evaluation. It's like calling someone "athletic" or "healthy" or, for that matter, "wicked". It suffices as a short-hand for daily life, but if you need to do serious thought, you need a much more refined set of concepts (such as jealousy, envy, spite, arrogance, cruelty, gluttony, avarice, etc.).
Q: And in the second place, which I sense is coming?
A: In the second place, what biological development gives us are learning mechanisms — "instincts to acquire arts", to use a nice phrase from Darwin by way of Pinker. They make it easy for us to acquire certain habits from certain kinds of environmental interaction, and (consequently) harder to acquire other habits, or those same habits from different sorts of environments. This is what you'd expect if you put together what we know about learning theory with what we know about morphogenesis, and, to repeat a link, has in any case been well-explained by Gary Marcus, at greater and lesser length — among others.
Q: Do you ever get tired of beating that dead horse?
A: It's not dead yet; that horse will keep kicking until the last person who thinks there's something to The Bell Curve is hanged in the entrails of the last Durkheimian.
Q: I really did not need that image, thank you very much. So you're perfectly happy to agree that there is genetic variation in the human population which affects the facility with which various cognitive skills are learned, and so mental ability?
A: Sure. In a more cautious mood, instead of saying "there is" I'd say "there could be, for all we know at present, which seems to be squat". But, sure.
Q: And yet, miraculously, this genetic variation is somehow not under natural selection?
A: Did I say anything of the kind? I can think off the top of my head of a really obvious example of recent human evolution, and gene-culture co-evolution at that, namely the four independent evolutions of adult lactose tolerance. For that matter, over the last, oh, 515 years basically the whole human population has been put under intense selection pressure for immune systems which easily develop resistance to smallpox. My guess is that this sort of thing overwhelms any selection pressure for, say, facility of learning symbolic arithmetic (in which symbol system, by what pedagogical method?), unless there are truly weird pleiotropic genes in play.
Q: But it's possible?
A: Sure. I'll go further. Suppose that our new alien overlords showed up tomorrow, and after demonstrating that resistance is futile, decide to institute a selective breeding program. They tie everyone's tubes just before puberty, and then at age 25 everyone is given a test in which they must prove certain theorems about non-Abelian Yang-Mills field theories; those who pass are allowed to breed, those who fail are permanently sterilized. If this persisted for, say, a thousand years, I am quite confident that a randomly selected human being from 3007 will be much more likely to be able to prove those theorems than a randomly selected member of the present population.
Q: In this scenario, whatever you call it —
A: How about "Classical Lumps and Their Quantum Descendants"?
Q: I'm going to pretend you didn't say that. So, how would that come about?
A: How should I know? On the basis of the Baldwin effect, and the other sorts of coupling between individual- and population-level adaptation, I'd expect it to happen somehow. It could be that people will evolve to have geometric intuitions about non-commutative Lie groups. Or they might get really good at memorizing proof-length bits of text, if that kind of thing would get past the alien overlords. Or — and somehow this sounds more plausible to me — they might just find studying really interesting and enjoyable.
Q: And why does that last sound more plausible?
Q: OK, so leaving behind the alien overlords and their weird thing for Yang-Mills —
A: Can I help it if they are interested in the same parts of high-energy theory as I used to be?
Q: — leaving them, as I was saying, behind, could there be traits under selection in the present?
Q: Any more interesting suspects?
A: The prospects for influenza resistance look bright.
Q: You know what I meant.
A: You're asking me to pull speculations out of the air.
Q: It's a weblog, isn't it?
A: People are going to think I'm advancing a genetic explanation for the Flynn Effect, when it's much too strong for it to be due to any remotely plausible degree of selection.
Q: Haven't you just issued a disclaimer which should keep anyone not determined to misunderstand from thinking that?
A: Fine. If IQ really correlates with the ability to flourish in an industrial society (and I'm quite prepared to believe that), then it is, as I said last time, a measurement of the ability to navigate paper-pushing bureaucracies — to learn to manipulate arbitrary abstract explicit rules, and to do so on command. Presuming that people who don't manage to pull off at least some minimum level of this make very unattractive mating partners, and so have below-average reproductive success, then those of us in developed countries have spent the last one or two centuries breeding for docility, in both senses of the word.
Q: You're saying that —
A: We have met our alien overlords, and they are us.
Posted by crshalizi at June 24, 2007 12:18 | permanent link