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Nornagest comments on Why Are Individual IQ Differences OK? - Less Wrong
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Comments (526)
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.)
The usual biochemistry that makes neurons go, as far as I know, is not unique to humans and has been stable for quite a long time.
But I think we're getting a bit confused and start to chase our own tails. Let's circle back and see what the original disagreement was.
You said that "intelligence is metabolically expensive, and it seems likely that it shows some fairly steep diminishing returns in a subsistence farming environment". I countered by doubting that there's any metabolic difference (cost) between an IQ130 and an IQ70 human -- implying that while the returns are diminishing, the cost doesn't change in the range we're talking about. And after that it looks like the core of the discussion is whether somewhat higher intelligence (say, moving the average from 100 to 130) carries enough of a metabolic cost to make the evolution prevent that move.
My position is that the metabolic cost for IQ moves of a couple of standard deviations is sufficiently close to zero.
I would keep in mind that IQ differentials involving increased cranial capacity are more likely to have metabolic costs than ones that don't. It also seems to me that most of the pressure against higher IQs is going to be cognitive rather than metabolic.
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...
Ok.
But China is also pretty smart, and as far as I know it doesn't have a North-South IQ gradient: http://akarlin.com/2012/08/analysis-of-chinas-pisa-2009-results/
According to Wikipedia, the genetics of the Han Chinese is... complicated.
But even if high-IQ genes were ancestral in northen Hans and then were transferred to southern Hans due to migrations, if warm climates selects negatively for intelligence I think we should expect that in the last 2,000 years those high-IQ genes would not have thrived in South China.
That doesn't show the absence of a gradient, because they're reporting, if I'm understanding the description right, a PISA-aggregate of 12 provinces; the only other scores are places you'd expect to be outliers and unaffected by any evolution (Shanghai, Hong Kong, etc). There is a map, but:
Yeah... Plus, note the striking East-West gradient. So this map is serving more as a measure of economic development and Internet access than a random sample demonstrating lack of gradient.
I'm not surprised. The Han have been expanding relentlessly for a long time.
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)