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.)
If there was no metabolic difference between building an IQ70 brain and an IQ130 brain, why would there be any effects from micronutrient deficiency?
it doesn’t seem to me that all the extra-smart people have unusually large heads and eat more than usual.
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)...
If there was no metabolic difference between building an IQ70 brain and an IQ130 brain, why would there be any effects from micronutrient deficiency?
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.
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.
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.
I don’t think deficiency in dopants can ever arise, though, as they’re used in incredibly tiny amounts.
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.)
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.
Maybe we can smell very large quantities of iodine, but can one really smell deficiency-relevant amounts in seaweed?
But they need to be extremely pure and in the right form to be used.
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.
Maybe we can smell very large quantities of iodine, but can one really smell deficiency-relevant amounts in seaweed?
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.
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.
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.)
edit: plus we can detect seaweed without smelling iodine itself.
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?
Yeah and also we used to have a much better sense of smell. Smell is also used for identification (it seems, in most mammals except humans) and for that the more compounds you detect at the lesser concentrations the better. With mercaptans I think it’d be related to bacterial toxins in rotting meat, which kill at absurdly low concentrations. We can’t detect poisons themselves but we can detect other stuff that goes along with it.
Seaweed has an awful lot of stuff in it
Yeah, that’s the point—those who live next to the coast (within what ever range you can have a preventable iodine deficiency—right next to the coast maybe nobody ever gets it, but some distance inland...) could evolve taste for seaweed based on some other compounds or their combination, to get iodine.
Yeah, that’s the point—those who live next to the coast (within what ever range you can have a preventable iodine deficiency—right next to the coast maybe nobody ever gets it, but some distance inland...) could evolve taste for seaweed based on some other compounds or their combination, to get iodine.
Would that fit food transportation patterns? I’ve never heard of seaweed being collected and shipped in large quantities. Most communities were generally pretty self-sufficient as far as food goes. If you don’t have optional access to seaweed, there’s not going to be anything evolution can exploit—you’ll just get entire communities of deficient people.
Which apparently did exist historically: https://en.wikipedia.org/wiki/Cretinism#History The consequences are pretty severe: starting from birth, retardation, small size, frequent infertility. And lots of variation within villages and between regions—which sounds like there would have been a lot of selection pressure for particular food preferences, within-village and between-village, but there doesn’t seem to’ve been any kind of adaptation.
What I mean is that a lot of people live quite close to the coast, where they could either go to the trouble of finding more kelp (as people do for salt) or not.
I think it’s just that there wasn’t enough generations and enough pressure. Adaptations like being able to drink milk do occur in a short timeframe, but those could have attained full adaptation in 1 mutation, while this may be the sort of adaptation where 1 mutation only yields a slight preference.
edit: or it may be that iodine deficiency is historically recent and sufficiently rare to result in any specific adaptations. I was basing it on Lithuania which has iodine deficient soil even fairly close to the coast, but that state of affairs may be geologically recent.
Something else with regards to IQ… regarding the variance of IQ (and potential for any breeding). There’s a correlation between the IQ of spouses, which implies that variance is larger than it would have been otherwise (high IQ genes combine more often than they would with random mating). I imagine that the level of correlation between IQ would be dependent on the social institutions and equality (as in a very gender unequal society, there’s no selection mechanism at play, or at least, no direct selection). This also serves as an existing breeding program within the general population (if you look at just the high IQ population and ignore what the rest are doing), with the advantage of not destroying genetic diversity. (Something like Aktion T4 has all the potential of losing those high IQ genes that can backfire when combined with ‘wrong’ genes or the copies of themselves—selective breeding can easily backfire (and does when selectively breeding animals) ).
edit: or it may be that iodine deficiency is historically recent and sufficiently rare to result in any specific adaptations. I was basing it on Lithuania which has iodine deficient soil even fairly close to the coast, but that state of affairs may be geologically recent.
What would cause iodine deficiencies to be recent? As far as I know, remedies using seaweed go back thousands of years; that was enough time for milk and altitude adaptations in some populations, and it seems to me that fixing iodine deficiency would be much more valuable if possible: being completely lactose-intolerant is not nearly as bad as being a shriveled retard who’s infertile.
By recent I meant last ~20 000 years. The lactose tolerance is an exceptionally simple adaptation: full adaptation in 1 step. Whereas I’d imagine available mutations for seaweed craving could only produce a slight preference for a wide class of foods with the first mutations.
Also it may be that there is such an adaptation, it’s just that it’s in a sub-population where it gone unnoticed. In either case we have an apparent fact that there’s no such adaptation, even though it would seem to be advantageous. Which perhaps can’t tell us much about why but can tell us not to expect more complex adaptations to that specific problem.
edit: also, isn’t iodine only necessary for the synthesis of thyroid hormones? In principle it ought to be possible to evolve not to need iodine in the first place, but that obviously won’t happen if iodine is common enough.
Also it may be that there is such an adaptation, it’s just that it’s in a sub-population where it gone unnoticed. In either case we have an apparent fact that there’s no such adaptation, even though it would seem to be advantageous. Which perhaps can’t tell us much about why but can tell us not to expect more complex adaptations to that specific problem.
I suspect such an adaptation would have been noticed. There’s a stupid number of studies in which the researcher takes urine/blood samples from women, measures iodine levels or a proxy for iodine level like TSH, and do a followup on the infants, and, mirabile dictu, the infants tend to have smaller heads or other problems in a fairly linear correlation with the mothers’ deficiencies. (Seriously, there’s like 1 a week of these in my Pubmed alerts for iodine, it’s quite a nuisance. Who funds this crap?) It’s common to record race or ethnicity as part of the covariates; if someone had found an interaction where, I dunno, Europeans were immune to iodine deficiency, I figure I would have heard about it because it would be so much more interesting and sexy a result than the usual one.
also, isn’t iodine only necessary for the synthesis of thyroid hormones? In principle it ought to be possible to evolve not to need iodine in the first place, but that obviously won’t happen if iodine is common enough.
I’m not sure. It may be that iodine is the only way to do the things it does in mammals—either because it’s a local optima or global. For example, you can theoretically have blood which doesn’t require iron for hemoglobin (which requires iron), as demonstrated by octopus blood using hemocyanin which relies on copper rather than iron, but no matter how little iron is available, it’s hard to see mammals ever evolving hemocyanin and abandoning hemoglobin. And more generally, now that the arsenic-bacteria seem to have been debunked, there doesn’t seem to be any replacement at all for phosphate in key roles like ATP; if Earth-life has no access to phosphate, it’s doomed.
(Of course, some other examples suggest the other way: humans lost the ability to synthesize vitamin C a while ago, and could probably recover it; but there’s never been enough selection pressure.)
But they wouldn’t be immune to deficiency, merely eating a diet that prevents the deficiency, through some sort of craving for seafood which is virtually impossible to discern from cultural. We do seem to have a preference for variety in food.
I’m not sure. It may be that iodine is the only way to do the things it does in mammals
My understanding is that it is used in signalling molecules used to control growth, but is not used in any key steps in main metabolism itself. Animals can survive on very little iodine, it seems—stunted and not growing right, but i’d imagine given enough time evolution would find a way to re-do that growth control using another molecules for hormones.
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 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.
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.
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.
Rushton and Ankney (2009) summarize the findings to date with regards to brain size and intelligence: based on 28 non-clinical published brain imaging samples (N= 1,389) a .40 correlation between IQ and brain size measured by MRI was found; based on 59 published samples (N= 63,405) a .20 correlation between IQ and head circumference was found. These findings are consistent with others.
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.
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...
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:
all perform well above average according to stats from a Chinese online IQ testing website.
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.
According to Wikipedia, the genetics of the Han Chinese is… complicated.
I’m not surprised. The Han have been expanding relentlessly for a long time.
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.
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)
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.
Not optimized for intelligence, optimized for neural efficiency.
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?
there are very good reasons for evolution to explore all the corners that it can easily cut
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.
look at very smart people, look at very dumb people. Is the difference due to neural efficiency?
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.
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.
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.
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)...
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?
Yeah and also we used to have a much better sense of smell. Smell is also used for identification (it seems, in most mammals except humans) and for that the more compounds you detect at the lesser concentrations the better. With mercaptans I think it’d be related to bacterial toxins in rotting meat, which kill at absurdly low concentrations. We can’t detect poisons themselves but we can detect other stuff that goes along with it.
Yeah, that’s the point—those who live next to the coast (within what ever range you can have a preventable iodine deficiency—right next to the coast maybe nobody ever gets it, but some distance inland...) could evolve taste for seaweed based on some other compounds or their combination, to get iodine.
Would that fit food transportation patterns? I’ve never heard of seaweed being collected and shipped in large quantities. Most communities were generally pretty self-sufficient as far as food goes. If you don’t have optional access to seaweed, there’s not going to be anything evolution can exploit—you’ll just get entire communities of deficient people.
Which apparently did exist historically: https://en.wikipedia.org/wiki/Cretinism#History The consequences are pretty severe: starting from birth, retardation, small size, frequent infertility. And lots of variation within villages and between regions—which sounds like there would have been a lot of selection pressure for particular food preferences, within-village and between-village, but there doesn’t seem to’ve been any kind of adaptation.
What I mean is that a lot of people live quite close to the coast, where they could either go to the trouble of finding more kelp (as people do for salt) or not.
I think it’s just that there wasn’t enough generations and enough pressure. Adaptations like being able to drink milk do occur in a short timeframe, but those could have attained full adaptation in 1 mutation, while this may be the sort of adaptation where 1 mutation only yields a slight preference.
edit: or it may be that iodine deficiency is historically recent and sufficiently rare to result in any specific adaptations. I was basing it on Lithuania which has iodine deficient soil even fairly close to the coast, but that state of affairs may be geologically recent.
Something else with regards to IQ… regarding the variance of IQ (and potential for any breeding). There’s a correlation between the IQ of spouses, which implies that variance is larger than it would have been otherwise (high IQ genes combine more often than they would with random mating). I imagine that the level of correlation between IQ would be dependent on the social institutions and equality (as in a very gender unequal society, there’s no selection mechanism at play, or at least, no direct selection). This also serves as an existing breeding program within the general population (if you look at just the high IQ population and ignore what the rest are doing), with the advantage of not destroying genetic diversity. (Something like Aktion T4 has all the potential of losing those high IQ genes that can backfire when combined with ‘wrong’ genes or the copies of themselves—selective breeding can easily backfire (and does when selectively breeding animals) ).
What would cause iodine deficiencies to be recent? As far as I know, remedies using seaweed go back thousands of years; that was enough time for milk and altitude adaptations in some populations, and it seems to me that fixing iodine deficiency would be much more valuable if possible: being completely lactose-intolerant is not nearly as bad as being a shriveled retard who’s infertile.
By recent I meant last ~20 000 years. The lactose tolerance is an exceptionally simple adaptation: full adaptation in 1 step. Whereas I’d imagine available mutations for seaweed craving could only produce a slight preference for a wide class of foods with the first mutations.
Also it may be that there is such an adaptation, it’s just that it’s in a sub-population where it gone unnoticed. In either case we have an apparent fact that there’s no such adaptation, even though it would seem to be advantageous. Which perhaps can’t tell us much about why but can tell us not to expect more complex adaptations to that specific problem.
edit: also, isn’t iodine only necessary for the synthesis of thyroid hormones? In principle it ought to be possible to evolve not to need iodine in the first place, but that obviously won’t happen if iodine is common enough.
I suspect such an adaptation would have been noticed. There’s a stupid number of studies in which the researcher takes urine/blood samples from women, measures iodine levels or a proxy for iodine level like TSH, and do a followup on the infants, and, mirabile dictu, the infants tend to have smaller heads or other problems in a fairly linear correlation with the mothers’ deficiencies. (Seriously, there’s like 1 a week of these in my Pubmed alerts for iodine, it’s quite a nuisance. Who funds this crap?) It’s common to record race or ethnicity as part of the covariates; if someone had found an interaction where, I dunno, Europeans were immune to iodine deficiency, I figure I would have heard about it because it would be so much more interesting and sexy a result than the usual one.
I’m not sure. It may be that iodine is the only way to do the things it does in mammals—either because it’s a local optima or global. For example, you can theoretically have blood which doesn’t require iron for hemoglobin (which requires iron), as demonstrated by octopus blood using hemocyanin which relies on copper rather than iron, but no matter how little iron is available, it’s hard to see mammals ever evolving hemocyanin and abandoning hemoglobin. And more generally, now that the arsenic-bacteria seem to have been debunked, there doesn’t seem to be any replacement at all for phosphate in key roles like ATP; if Earth-life has no access to phosphate, it’s doomed.
(Of course, some other examples suggest the other way: humans lost the ability to synthesize vitamin C a while ago, and could probably recover it; but there’s never been enough selection pressure.)
But they wouldn’t be immune to deficiency, merely eating a diet that prevents the deficiency, through some sort of craving for seafood which is virtually impossible to discern from cultural. We do seem to have a preference for variety in food.
My understanding is that it is used in signalling molecules used to control growth, but is not used in any key steps in main metabolism itself. Animals can survive on very little iodine, it seems—stunted and not growing right, but i’d imagine given enough time evolution would find a way to re-do that growth control using another molecules for hormones.
Also cranial capacity is in fact correlated to iq
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.
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.
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?
What gwen said. Also the majority of Singapore is ethnic Chinese, whose ancestors came from higher latitudes.
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.
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)
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.
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.