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Nornagest comments on Why Are Individual IQ Differences OK? - Less Wrong
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Comments (526)
The Ashkenazi Jews are still a small population, though. And intelligence may be an reproductive advantage in their niche, but that's only one niche. If you don't like the example of the Holocaust, consider the Khmer Rouge going after anyone who seemed intelligent.
The Khmer Rouge were dramatic, but I'd bet money that simpler forces have played a greater role in the evolution of intelligence since the Neolithic. As you say upthread, intelligence is metabolically expensive, and it seems likely that it shows some fairly steep diminishing returns in a subsistence farming environment -- particularly since its gains there are distributed over large populations. If a mutation gives you a chance of dying in a childhood famine and a much smaller chance of coming up with an agricultural innovation that might save your kids (and the rest of your village, but your mutation doesn't care) from dying of childhood famine, it's no advantage from a gene-centered point of view.
(On the other hand, if being good at Torah study is sexy in your subculture, then sexual selection might make up the difference.)
That's true comparing chimps to humans. I am not sure that's true comparing an IQ70 human to an IQ130 human.
Why wouldn't it be? Some of that increase might come from gains in efficiency, but precisely because brains are metabolically expensive, I'd expect most of the low-hanging efficiency gains in mammalian brains to be mined out already. Brute-force gains are limited by more than just energy, but I'd expect most architectural improvements to come with energy tradeoffs, too. When you get right down to it, something's got to do the computing.
Is there any evidence for it?
Is there any evidence against it? Not to play reference class tennis here, but given the choice between magic efficiency gains and continuing a curve that we can project out from the lower primates, the latter seems like the more reasonable null.
It seems like a relatively straightforward empirical question whether BMR correlates with IQ. I have no idea if it does, but maybe somebody who knows more neuroscience will chime in?
I would definitely expect metabolic cost to vary with brain size or neuron count or something, but AFAIK that varies relatively little between humans (compared to humans vs other primates). It's much less clear that better software or architecture is also more expensive.
No, not really. You can point to increased number of neurons, increased brain energy consumption, etc. for humans compared to primates very easily. I don't think you can point to the same thing for IQ130 humans compared to IQ70 humans. I don't have any hard data, but it doesn't seem to me that all the extra-smart people have unusually large heads and eat more than usual.
I don't buy the argument that the evolution must have optimized for intelligence already. The ability to e.g. hold a complicated structure in your mind wasn't particularly valuable for a pack of proto-humans in the African savannah.
Not optimized for intelligence, optimized for neural efficiency. Wikipedia tells me that most mammals devote single-digit percentages of BMR to brainpower, but for anatomically modern humans it's closer to 25%. Maybe more in childhood; Wikipedia doesn't say but the brain-to-body-mass ratio there is higher. When you've got an overambitious monkey burning a quarter of its calories keeping its freaky big monkey brain happy, there are very good reasons for evolution to explore all the corners that it can easily cut, as long as they don't exist in a state of ridiculous abundance. And since we know of at least one population bottleneck in the Paleolithic, I'm pretty sure food scarcity was a thing at that stage.
Neural efficiency at doing what? Our contemporary idea of intelligence involves doing things that evolution did not optimize for. And again -- look at very smart people, look at very dumb people. Is the difference due to neural efficiency?
Sure, but evolution works slowly. Big brains are very new in evolutionary time, it's not like evolution had hundreds of millions of years to polish them.
On the neuron level, all the usual biochemistry that makes neurons go. On the architecture level, any structure that helped paleolithic humans do their thing, and none that didn't. Our thinking seems pretty general and flexible, for example, which means that a lot of the reflexive, special-purpose stuff we see in other mammals would have gotten pruned away at some stage of development.
No. That is, in part, my point. If I'm right about this, we should expect the efficient phenotypes to have reached fixation long ago.
(Strictly speaking, I'd probably expect some of the difference, especially on the low end, to be due to de novo mutations, some of which might have deleterious effects in this domain. But that's a corner case and I think we can ignore it for the purposes of this discussion.)
Did you look for any?
Quoted from here, the paper is here (they should have quoted the correlation of 0.38, which is what you get when you weight by sample size).
It's obvious that mental tasks do consume glucose. Jensen mentions metabolic correlations here, but not which direction they go in. This paper suggests that IQ and cerebral glucose metabolic rate are inversely correlated, and that after learning a new task more intelligent individuals showed larger decreases, but it looks like it has a very low n and I'd want to draw conclusions from review papers rather than individual investigations. I would not be surprised if the brain efficiency hypothesis dominates, and that higher IQ individuals get more bang for the buck instead of burning more to get more. I also hear more about cooling costs than calorie costs with regards to brain metabolism, but that may be because cooling costs fits with the observed data of smarter people evolving in colder places with higher latitudes.
Like Singapore?
Singapore is a small country which deliberately attracts elites and tries to practice eugenics; so I don't think that's a very good example at all to use against a statistical generalization...
What gwen said. Also the majority of Singapore is ethnic Chinese, whose ancestors came from higher latitudes.
Or, having access to paper and pen, it may actually be less valuable now than it was for a pack of proto humans. (The environment was pretty complicated even back then - competing tribes, complex network of alliances within a tribe, the habits of different animals, etc etc. But you couldn't put it down, you had to keep it all in your mind)
If there was no metabolic difference between building an IQ70 brain and an IQ130 brain, why would there be any effects from micronutrient deficiency?
Remember, expensive isn't limited to adult basal metabolic rates, there are other ways to be expensive; for example, a better brain could suck up tons of iron, iodine, and protein in childhood, requiring lots of meat and fat and seafood, and if a fetus or child's metabolic needs are not met, whups, there goes some myelination (fat), some non-cretinism (iodine), some energy and lassitude (iron and protein)...
Also cranial capacity is in fact correlated to iq
Well, hypothetically, if we have a chip fab, and it has a "micronutrient deficiency", it can produce noisier circuits that don't consume less power, or which would even consume more power.
It would seem that there are some basic requirements which need to be met to build the brain correctly, requirements that are proportional to the brain volume, with no gains from exceeding those requirements. One could further hypothesise that those requirements are met in almost all "IQ130" brains.
Sure. Chip fabs probably even have 'micronutrient deficencies' in a very similar way - if you can't get enough of the exact right exotic element or mineral for say doping semiconductors, the engineers can probably work around it but won't get as power-efficient or fast a chip. (Now I'm imaging correlating chip fab 'brain damage' to global commodity prices...)
I don't think deficiency in dopants can ever arise, though, as they're used in incredibly tiny amounts.
For micro-nutrient deficiencies the issue is often not so much with obtaining the micronutrient as with the lack of craving for it. We can smell iodine, but we don't crave it when deficient, so we didn't have seaweed and the like as a high value spice which everyone craves.
But they need to be extremely pure and in the right form to be used. (If just having the raw material was enough, no one would ever die of thirst drinking salt-water and plants would never lack for nitrogen.)
Maybe we can smell very large quantities of iodine, but can one really smell deficiency-relevant amounts in seaweed?
Yeah, but so is silicon (and even more so in terms of purity), and there's million times the silicon. I think industry is sort of similar to the ancestral animal that is eating a diet where it obtains enough micronutrients alongside macronutrients. But if we were to try to build a self replicating factory on the moon... we'd probably just ship anything like this from the earth.
The RDA is 300 micrograms per day, 0.3mg, and if I have a 3% solution of iodine, that's 10mg of that solution. 1 drop of water is 50mg , and I think you could easily smell 1/5th of a drop (or a drop 58% the size of a regular water drop), but probably not if its mixed up in food. Still it is close enough that given an absence of such adaptation I wouldn't expect any other complex adaptations to lack of iodine. edit: plus we can detect seaweed without smelling iodine itself.
Oh, you mean that smell is one of the easiest adaptations for dealing with a lack of iodine, and since we don't have a smell adaptation, we don't have any more complex adaptations? Sure, I agree with that. Tweaking smell sensitivity seems to be pretty easy. Humans aren't dogs, but we can still smell some things at very low thresholds. For example, t-butyl mercaptan can be smelled at 0.3 parts per billion, it seems. (Although now that I think about it, what on earth was the selection pressure for that? Maybe some smell thresholds are just random.)
Seaweed has an awful lot of stuff in it; we could be smelling any of the components without smelling a particular component. You can easily smell tobacco, but can one smell important parts like nicotine?