As Borsboom notes, intelligence and height are pretty different. Intelligence is measured and defined as a between subjects latent variable. Height, on the other hand, is not defined as in terms of between subject differences, but in terms of an empirical concatenation operation.
They are pretty clearly different! It is crazy to see many prominent intelligence researchers think this is even remotely controversial. A lot of them have convinced themselves that any sort of criticism of intelligence research is ideologically motivated or something, which is pretty unfortunate.
I am really glad that you are popularizing the criticisms of hereditarian/race science research that have always been met with vitriol and negativity by those specific communities so it has been hard to actually openly argue about them. You are really doing a great public service.
Thanks! Yes, what has surprised me is how much internal conceptual debate there has already been between the various IQ schools and the psyshometricians, which is then completely ignored in the public discussion.
And yeah I didn't get a chance to work in my favorite point from Borsboom et al. 2003 (https://pubmed.ncbi.nlm.nih.gov/12747522/) which, as you note, draws a really important distinction between the measurement of height and the latent variable analysis of IQ:
"But what about variables like height? Is it not unreasonable to say, “If Einstein had been taller, he would have been able to reach the upper shelves in the library”? No, this is not unreasonable, but it is unreasonable to assume a priori that intelligence, as a between- subjects latent variable, applies in the same way as height does. The concept of height is not defined in terms of between-subjects differences, but in terms of an empirical concatenation operation (Krantz, Luce, Suppes, & Tversky, 1971; Michell, 1999). Roughly, this means that we know how to move Einstein around in the height dimension (for example by giving him platform shoes) and that the effect of doing this is tractable (namely, wearing platform shoes will enable Einstein to reach the upper shelves). Moreover, it can be assumed that the height dimension applies to within- subject differences in the same way that it applies to between- subjects differences. This is to say that the statements, “If Einstein had been taller, he would have been able to reach the upper shelves in the library” and “If we had replaced Einstein with a taller person, this person would have been able to reach the upper shelves in the library” are equivalent with respect to the dimension under consideration. They are equivalent in this sense, exactly because the dimensions pertaining to within- and between-subjects variability are qualitatively the same: If we give Einstein platform shoes that make him taller, he is, in all relevant respects, exchange-able with the taller person in the example. We do not object to introducing height in a causal account of this kind, because variations in height have demonstrably the same effect within and between subjects. But it remains to be shown that the same holds true for psychological variables like intelligence."
Yes! There has been significant conceptual debate within psychometrics. There is a really good presentation by Borsboom on the philosophy of psychometrics (https://vimeo.com/256145513) that touches on those debates and provides a really good introduction of the field. I really recommend it to anyone that is interested in psychological measurement or even measurement theory in general.
I think part of the reason those things are ignored in the public discussions is because they are just too dry and esoteric, and they are just too negative. People tend to want to be positive about their research when they communicate it to the public or even think about it at all. As Borsboom jokingly says in the presentation above, if you raise those questions in a conference, you won't be invited to any party. There is also the fact that there is a pretty significant disconnect between psychologists that study those areas and the psychometricians. I think the field has been set back quite a bit because of that. There is an interesting dissertation to be written about this for a sociologist/philosopher of science and try to trace it back to the controversies of behavioral genetics and intelligence research and the legacy of scientific racism and/or the sociobiology wars.
In general though my impression is that the field has started, slowly but surely, moving away from the dominance of latent variable models and stuff like network models are growing in popularity (doi.org/10.1146/annurev-clinpsy-050212-185608). As a biologist, I find network models way more realistic and reasonable than latent variable models for sure!
"We know this because we have estimated a parameter called molecular heritability, which tells us the upper bound on what a genetic predictor could ever achieve."
Could you talk more about how we know that molecular heritability represents the upper bound of heritability? My impression was that not all SNPs have been discovered, and these have polygenic effects that are hard to define. So how can you know that the maximum possible genetic effect on IQ and other traits has been discovered?
TLDR: Molecular heritability is an upper bound on what you can predict *from* all the molecular data you have typed (regardless of whether you identified the specific mechanisms). But in general the typed molecular genetic variation appears to explain most (>80%) of the total genetic variation.
While modern behavioral genetics will be able to identify specific mechanisms of gene-environment interactions which may then cascade into seeking or creating a new environment (I hit a note once, so I get music lessons, and on and on..), the specifics of which genes get methylated doesn't add that much yet. The best paper I've read on misuse of heritability in the context of among-group differences in IQ is from 1995 by Ned Block, https://www.sciencedirect.com/science/article/pii/001002779500678R , and that article leans heavily on Lewontin 1984.
Great article! Hope you [or some affiliate that has the time] expands this into a book with extensive lay person support. It's nightmare arguing about this stuff at the barbeque !
I dont understand how IQ is this nebulous? Environmental factors can unilaterally wash away any genetic link? Then despite environemntal factors the Chinese and Europeans (living all over the world) have a similar IQ as they do to their people living in their native homelands. Wouldnt that alone prove genetics? Who is convinced that parents with advanced degrees and difficult, highly technical jobs wont on average have more intelligent children than someone with low skilled felon parents? Education and lead free painted homes dont explain this
Your claim about IQ in Chinese and Europeans is not verifiable and is likely incorrect. We don't have good estimates for the average IQ of people in mainland China; the current "estimates" come from the "research" of Richard Lynn, a self-described scientific racist who cherrypicked country-level IQ data (for example, ignoring lower scoring samples for China and choosing samples from universities for his estimates).
Chinese immigrants in the US are subject to substantial selection bias, with 55% of foreign-born Chinese-Americans (62% of Chinese-Americans are foreign born, and most of the remaining 38% are their children) earning a bachelor's degree compared to ~15% of Chinese people living in China. Chinese-Americans should be getting (and likely would get) higher IQ scores, on average, than their mainland Chinese counterparts.
By the way, during the Cold War, various studies showed that the average IQ of East Germans and West Germans differed by 8 points or more, which suggests a strong environmental effect on IQ (because those two groups should be nearly identical from a genetic perspective).
Great article. Let's try to make things more intuitive. Height is the combined length of many bones, some people have long legs, other long torsos, some both. Yet it can be measured very simply. But the underlying structures are complex. My 185cm height number does not say whether my shin are short or long. In some sense, "height" is not a thing, not an irreducible essence at least, it is an aggregate of many things. It is the combined outcome of shin growth, spine growth etc. etc. when we think of a measurement as a thing, it is called reification.
IQ measurement is very complex. The underlying structures hence must be really complex and thus intelligence is even less of an irreducible essential thing as height is. It is a measurement of the combined effect of many things. Many abilities.
The reason IQ is useful is that it correlates with success with many tasks in modern life. g-loaded tasks. Not all tasks are g-loaded (e.g. running is not), but many are, those that contribute to life outcomes the most (except for those people whose life outcome is e.g. Olympic gold in running). IQ is basically a measurement of adaptation to modern life. Balancing checkbooks etc. it is not a single unified essential irreducible "intelligence thing", but an aggregate measurement.
In 1930 a European hunter went hunting in what would later become Kenya. And he was amazed. He spent his entire life with European hunters and no one of the could read tracks so well as the native African villagers. They would look at a track and say "young pregnant female elephant, no, not the same one as yesterday, a different one". OTOH some of them spent years serving in the British military and could not speak a word of English. Were they high IQ or not? I think this is not a sensible question. It depends whether you put elephant tracks on the test or English words. Why were they very good at learning reading tracks and not good at learning English? No one really knows.
"In 1930 a European hunter went hunting in what would later become Kenya. And he was amazed. He spent his entire life with European hunters and no one of the could read tracks so well as the native African villagers. They would look at a track and say "young pregnant female elephant, no, not the same one as yesterday, a different one". OTOH some of them spent years serving in the British military and could not speak a word of English. Were they high IQ or not?"
Good question.
Or, to provide an example with some similarities: the cognitive ability to notice the subtleties required to detect and follow a game animal path in the Amazon rain forest has a lot of similarity with the skills required to find the correct answer in an RPM test. But while indigenous rainforest hunters are taught to hone that ability early on--and hone it further, with practice--the cognitive acuity is connected with the motivation provided by the requirement to find food, evade predators, steer clear of poisonous plants, etc. Life and death concerns. The same child might very likely exhibit only puzzlement if requested to apply those skills to an RPM. The RPM is a joke, comparatively. The crucial difference partakes of a values question, one might say.
By comparison: high performers on the RPM who have resided in comfortable civilization all their lives and decide to take a challenging vacation in remote Amazonia are liable to find themselves very much out of their depth if they stray only a few hundred yards away from the cleared patch of their campsite. They might not even be able to find a wildlife path in the Pennsylvania woods. That's abstract pattern matching and progression for real, under conditions less controlled than the quilted rectangles of RPM diagrams. Granted, tracking skills require a lot of inductive practice, and the questions on RPM are commonly expected to be solved on first exposure to the test. But, Really. It's conceivable the only thing RPM reveals is a relative knack for understanding what's to be solved for, and how. It's not nothing; "eductive intelligence" is undeniably involved. But that's only one component of Intelligence- and the possibility that people might use workarounds or a productive emphasis on other intelligence aspects hasn't been given much examination (it may resist the simple resolution of a standardized test.) And the RPM may be more widely used on account of its convenience and "lack of culture bias" than for its reliability at assessing the broad-based foundation(s) that might be said to add up to "general Intelligence." Whatever that is.
No. Why? Have you seen a Raven's Progressive Matrices? I think that is where the shape rotator meme comes from. It is an engineering skill test for people who never studied engineering.
RPM is a test for recognizing patterns, that essentially asks the same question throughout, adding increasing amounts of subtlety and difficulty. It rewards maximum fidelity to finding a fit to yield a uniform result in the patterning of each diagram. RPM implicitly advantages the test-takers most inclined to require that quality as a cognitive focus. And also assumes that test subjects are uniformly motivated to "find the right answer" without any particular motivation other than performing as well as possible in accordance with the requirements of the puzzle. It resembles Sudoku in that respect.
Unsurprisingly, some test subjects with diagnosed ASD show a marked improvement over their scores on a test that incorporates a heavy verbal component, like the Wechsler (which has been modified to incorporate some elements similar to RPM, but still relies heavily on verbal inferences and skills.)
I'd venture that any test subject without literacy skills does require some oral instruction, in conjunction with a prep question or two, in order to have some idea of what's being asked. But in my opinion, RPM isn't all that easy to explain orally; for one thing, there's no way to review the instructions again. Simply presented cold, as a set of questions, it isn't necessarily all that intuitively obvious to understand what the test wants. Notwithstanding the "nonverbal, cultural bias free" selling point of the RPM, so heavily touted by those who view it as definitive and conclusive at measuring "IQ."
Intelligence is a much more complex phenomenon than height and so its genetics is much more complicated than the genetics of height. The most likely explanation of the 'missing heritability problem' is that as more information comes in the gaps will become smaller and converge with population heritability. This is the latest iteration of 'egalitarianism of the gaps' argument and the safe bet is that it will end the same way the others ended.
The trend so far has been that as more information comes in, we learn that the genetic studies have confounding we didn't initially know about, and the gap with twin studies grows. I think the most likely explanation of the missing heritability problem is that twin studies are inflated by environmental differences, as has been known since the 70's (https://theinfinitesimal.substack.com/p/twin-heritability-models-can-tell) and also shown with modern quantitative methods (https://pubmed.ncbi.nlm.nih.gov/30104764/).
But at the same time, more information has come in supporting the hereditarian hypothesis. For example, it is now possible to see if higher white ancestry correlates with higher IQ among African Americans and it does. Conversely, there is no additional evidence in favour of any of the proposed environmental mechanisms for racial differences in IQ. The missing heritability problem is interesting, but the smart move is to wait and see before overturning decades of cumulative research all pointing in one direction.
Admixture analysis is just another way of measuring environmental correlations, it neither supports nor refutes either hypothesis (see examples here: https://x.com/SashaGusevPosts/status/1713626146963599712). But I can think of quite a few genetic predictions from hereditarians that have not held up:
1. That IQ is just genetics and non-shared environment with negligible cultural influence: indirect effects in genomic studies clearly show there are vertical cultural influences.
2. That outcomes like educational attainment are highly heritable and will be easy to build genomic predictors for: one of the largest genetic analyses of any trait is of educational attainment (n=3M) and showed <5% of the effects are actually causal families. In general IQ/edu is one of the least heritable traits of all tested.
3. That genetic effects on common traits would differ substantially between populations: no, causal effects are nearly identical between populations (https://pubmed.ncbi.nlm.nih.gov/36941441/).
4. That cognitive function is under strong and recent selection: No, IQ exhibits one of the weakest signals of selection if not entirely neutral.
5. Recent polygenic selection is widespread and acting on many traits (e.g. Steve Hsu predicting this: https://infoproc.blogspot.com/2012/08/recent-human-evolution-european-height.html): No, evidence of polygenic selection turned out to be a false positive and if it exists at all it is so weak as to be undistinguishable from population structure.
6. There will be large rare variant effects on IQ and rare variants explain the bulk of heritability. Nope, recent exome-wide studies show tiny contributions of rare variants (https://www.nature.com/articles/s41588-023-01398-8).
The missing heritability "problem" is just a specific example of a broader problem where hereditarians overfit to observational data and now that none of their forward-looking predictions about genetics have held up, they are inventing artifacts (or, as you are doing, simply continue to claim that it "all points in one direction").
Admixture analysis was originally suggested by environmentalists because they thought it would disprove the hereditarian thesis. Then when it didn't, they changed their mind and decided that it didn't mean anything. This is a consistent pattern of environmentalists for 50 years. There remains no hypothesis that can explain, at all, racial gaps in IQ by environmental means, whereas the genetic hypothesis is parsimonious and fits the data. All attempts to increase intelligence of low-IQ racial groups, up to and including relocating children to new families have failed miserably. Maybe environmentalists struck a pot of gold this time with the missing heritability problem, but, more likely, it's just a complex puzzle that will take many decades to solve without changing the basic picture.
It turns out that the scientific method is a test of specific hypotheses, not a test of the people that proposed them. Where scientists propose parameters and then develop methods to estimate them in an unbiased manner, "race scientists" simply walk through the garden of forking paths until they find a correlation that "looks right". Regression to the mean in siblings, admixture analysis, the method of correlated vectors / Jensen effect (essentially all of The G Factor), the national IQ nonsense, are all examples of this. When it is pointed out that their analysis in fact cannot distinguish between multiple hypotheses (often trivially so), they do not attempt to improve their methods -- as an actual scientist would -- but either fall back on an appeal to some environmentalist authority or argue that they're just providing one piece of evidence in a broader narrative, as if a pile of garbage can turn into gold if you simply pile it high enough.
You will note that the 6 examples I mentioned above were not "X hereditarian said analysis Y would prove hereditarianism" but "X parameter turned out to be Z instead of Y which is not consistent with a hereditarian model". Also none of the points were about "the missing heritability problem", which seems to have become a kind of verbal tic to avoid actually having to consider new evidence. Highly correlated effect sizes across populations have nothing to do with missing heritability. Estimates of indirect/cultural transmission have nothing to do with missing heritability. You get the idea. The thing to do here is to acknowledge that your statement "decades of cumulative research all pointing in one direction" was incorrect, and grossly so.
It gets estimates that are ballpark consistent with (non-genetic) multigenerational studies. However, it is almost certainly the case that assortative mating is NOT just happening on the phenotype, so this is a very simple model. I think it would be helpful if behavioral geneticists proposed more explicit models of rGE besides VCT and how to test them.
Don't really have a horse in this race but if you are using the numeric value of IQ for one of your variables and you assume that your candidates all come from say 1.5 sigma above the mean then you are including 6.5% of the population in your study. However, only 2.25% of the population is above 2 sigma. So really, 65% of your sample would have an IQ between 122 and 130. The noise in the IQ test accuracy seems likely to swamp out much of your signal.
This is very interesting. Was just discussing this with some friends (mostly mathematicians, some applied, one neuroscientist - please be patient with us).
Some questions that arose:
1. Are we talking about childhood IQ, or IQ in late adulthood? The latter is apparently affected much more strongly by genetics - or is that bunk?
2. What about epigenetics? (I know, I know, that is mostly about telling a cell that it's supposed to be a brain cell and not a liver cell, rather than some sort of reborn partial Lamarckianism - but let's talk about the latter). Does that play a role in intelligence, and if so, how inheritable is it?
3. A friend says: "As far as I can tell, he makes a really good point about genes and environment being correlated and therefore this causes big problems for interpreting (maybe even defining) heritability. His solution then seems to be to take the interpretation that minimizes genetic influence, and defines heritability to only include fairly direct effects. That’s fine as one interpretation — and a good interpretation as a geneticist — but it’s not the only one and probably a bad one from a sociological perspective." What is your take on this?
This is an interesting and important finding, but boy is it hard to follow along with exactly what all these different statistical measures actually mean.
I mean, I still believe that conclusion, but I have to concede its more because of the authoritativeness of the source than my being able to reconstruct the argument myself. And I'm pretty smart. How would one communicate these findings to people of average smartness and more suspicious of scientists as a source of unbiased information?
That's a good question, what do you think would help? So far I've tried to (a) simplify the intuition as much as possible; (b) explicitly quote from other papers in areas that might be seen as controversial. Would it be useful to try to get rid of any jargon entirely? Or provide a shorter overall summary? Something else? There are only ~3 core concepts involved here (population heritability, direct heritability, genetic correlation, factor analysis) but each one is unfortunately hard to be precise about without getting into jargon.
Really glad to see you cite Borsboom.
As Borsboom notes, intelligence and height are pretty different. Intelligence is measured and defined as a between subjects latent variable. Height, on the other hand, is not defined as in terms of between subject differences, but in terms of an empirical concatenation operation.
They are pretty clearly different! It is crazy to see many prominent intelligence researchers think this is even remotely controversial. A lot of them have convinced themselves that any sort of criticism of intelligence research is ideologically motivated or something, which is pretty unfortunate.
I am really glad that you are popularizing the criticisms of hereditarian/race science research that have always been met with vitriol and negativity by those specific communities so it has been hard to actually openly argue about them. You are really doing a great public service.
Thanks! Yes, what has surprised me is how much internal conceptual debate there has already been between the various IQ schools and the psyshometricians, which is then completely ignored in the public discussion.
And yeah I didn't get a chance to work in my favorite point from Borsboom et al. 2003 (https://pubmed.ncbi.nlm.nih.gov/12747522/) which, as you note, draws a really important distinction between the measurement of height and the latent variable analysis of IQ:
"But what about variables like height? Is it not unreasonable to say, “If Einstein had been taller, he would have been able to reach the upper shelves in the library”? No, this is not unreasonable, but it is unreasonable to assume a priori that intelligence, as a between- subjects latent variable, applies in the same way as height does. The concept of height is not defined in terms of between-subjects differences, but in terms of an empirical concatenation operation (Krantz, Luce, Suppes, & Tversky, 1971; Michell, 1999). Roughly, this means that we know how to move Einstein around in the height dimension (for example by giving him platform shoes) and that the effect of doing this is tractable (namely, wearing platform shoes will enable Einstein to reach the upper shelves). Moreover, it can be assumed that the height dimension applies to within- subject differences in the same way that it applies to between- subjects differences. This is to say that the statements, “If Einstein had been taller, he would have been able to reach the upper shelves in the library” and “If we had replaced Einstein with a taller person, this person would have been able to reach the upper shelves in the library” are equivalent with respect to the dimension under consideration. They are equivalent in this sense, exactly because the dimensions pertaining to within- and between-subjects variability are qualitatively the same: If we give Einstein platform shoes that make him taller, he is, in all relevant respects, exchange-able with the taller person in the example. We do not object to introducing height in a causal account of this kind, because variations in height have demonstrably the same effect within and between subjects. But it remains to be shown that the same holds true for psychological variables like intelligence."
Yes! There has been significant conceptual debate within psychometrics. There is a really good presentation by Borsboom on the philosophy of psychometrics (https://vimeo.com/256145513) that touches on those debates and provides a really good introduction of the field. I really recommend it to anyone that is interested in psychological measurement or even measurement theory in general.
I think part of the reason those things are ignored in the public discussions is because they are just too dry and esoteric, and they are just too negative. People tend to want to be positive about their research when they communicate it to the public or even think about it at all. As Borsboom jokingly says in the presentation above, if you raise those questions in a conference, you won't be invited to any party. There is also the fact that there is a pretty significant disconnect between psychologists that study those areas and the psychometricians. I think the field has been set back quite a bit because of that. There is an interesting dissertation to be written about this for a sociologist/philosopher of science and try to trace it back to the controversies of behavioral genetics and intelligence research and the legacy of scientific racism and/or the sociobiology wars.
In general though my impression is that the field has started, slowly but surely, moving away from the dominance of latent variable models and stuff like network models are growing in popularity (doi.org/10.1146/annurev-clinpsy-050212-185608). As a biologist, I find network models way more realistic and reasonable than latent variable models for sure!
It's not nature vs nurture. You nurture nature.
This is fantastic once again Sasha. This is a minor quibble but I would refer to the race "scientists" as race "scientists".
Thank you! Good point
Why such disrespect?
because their arguments don't deserve anything better. At least, not the ones I've read.
"We know this because we have estimated a parameter called molecular heritability, which tells us the upper bound on what a genetic predictor could ever achieve."
Could you talk more about how we know that molecular heritability represents the upper bound of heritability? My impression was that not all SNPs have been discovered, and these have polygenic effects that are hard to define. So how can you know that the maximum possible genetic effect on IQ and other traits has been discovered?
Hi Ian, it took me a bit but I expanded on the differences between molecular and family-based heritability estimates here:
https://theinfinitesimal.substack.com/i/148251755/okay-but-why-do-you-think-twin-estimates-so-much-higher
TLDR: Molecular heritability is an upper bound on what you can predict *from* all the molecular data you have typed (regardless of whether you identified the specific mechanisms). But in general the typed molecular genetic variation appears to explain most (>80%) of the total genetic variation.
Thanks I'll read it with interest!
While modern behavioral genetics will be able to identify specific mechanisms of gene-environment interactions which may then cascade into seeking or creating a new environment (I hit a note once, so I get music lessons, and on and on..), the specifics of which genes get methylated doesn't add that much yet. The best paper I've read on misuse of heritability in the context of among-group differences in IQ is from 1995 by Ned Block, https://www.sciencedirect.com/science/article/pii/001002779500678R , and that article leans heavily on Lewontin 1984.
Nicely done.
I have added your article to my burgeoning education graph:
https://embed.kumu.io/c3b449cc0b3a9558b8e2b1e8f7f4bf4b
This was super interesting on its own but also as a primer on the current state of genetic research.
Thanks for the like. If you like short stories, I post 2 or 3 a month. The next one is out on Saturday. Take care.
Great article! Hope you [or some affiliate that has the time] expands this into a book with extensive lay person support. It's nightmare arguing about this stuff at the barbeque !
I dont understand how IQ is this nebulous? Environmental factors can unilaterally wash away any genetic link? Then despite environemntal factors the Chinese and Europeans (living all over the world) have a similar IQ as they do to their people living in their native homelands. Wouldnt that alone prove genetics? Who is convinced that parents with advanced degrees and difficult, highly technical jobs wont on average have more intelligent children than someone with low skilled felon parents? Education and lead free painted homes dont explain this
Your claim about IQ in Chinese and Europeans is not verifiable and is likely incorrect. We don't have good estimates for the average IQ of people in mainland China; the current "estimates" come from the "research" of Richard Lynn, a self-described scientific racist who cherrypicked country-level IQ data (for example, ignoring lower scoring samples for China and choosing samples from universities for his estimates).
Chinese immigrants in the US are subject to substantial selection bias, with 55% of foreign-born Chinese-Americans (62% of Chinese-Americans are foreign born, and most of the remaining 38% are their children) earning a bachelor's degree compared to ~15% of Chinese people living in China. Chinese-Americans should be getting (and likely would get) higher IQ scores, on average, than their mainland Chinese counterparts.
By the way, during the Cold War, various studies showed that the average IQ of East Germans and West Germans differed by 8 points or more, which suggests a strong environmental effect on IQ (because those two groups should be nearly identical from a genetic perspective).
interesting read, insightful too
Great article. Let's try to make things more intuitive. Height is the combined length of many bones, some people have long legs, other long torsos, some both. Yet it can be measured very simply. But the underlying structures are complex. My 185cm height number does not say whether my shin are short or long. In some sense, "height" is not a thing, not an irreducible essence at least, it is an aggregate of many things. It is the combined outcome of shin growth, spine growth etc. etc. when we think of a measurement as a thing, it is called reification.
IQ measurement is very complex. The underlying structures hence must be really complex and thus intelligence is even less of an irreducible essential thing as height is. It is a measurement of the combined effect of many things. Many abilities.
The reason IQ is useful is that it correlates with success with many tasks in modern life. g-loaded tasks. Not all tasks are g-loaded (e.g. running is not), but many are, those that contribute to life outcomes the most (except for those people whose life outcome is e.g. Olympic gold in running). IQ is basically a measurement of adaptation to modern life. Balancing checkbooks etc. it is not a single unified essential irreducible "intelligence thing", but an aggregate measurement.
In 1930 a European hunter went hunting in what would later become Kenya. And he was amazed. He spent his entire life with European hunters and no one of the could read tracks so well as the native African villagers. They would look at a track and say "young pregnant female elephant, no, not the same one as yesterday, a different one". OTOH some of them spent years serving in the British military and could not speak a word of English. Were they high IQ or not? I think this is not a sensible question. It depends whether you put elephant tracks on the test or English words. Why were they very good at learning reading tracks and not good at learning English? No one really knows.
"In 1930 a European hunter went hunting in what would later become Kenya. And he was amazed. He spent his entire life with European hunters and no one of the could read tracks so well as the native African villagers. They would look at a track and say "young pregnant female elephant, no, not the same one as yesterday, a different one". OTOH some of them spent years serving in the British military and could not speak a word of English. Were they high IQ or not?"
Good question.
Or, to provide an example with some similarities: the cognitive ability to notice the subtleties required to detect and follow a game animal path in the Amazon rain forest has a lot of similarity with the skills required to find the correct answer in an RPM test. But while indigenous rainforest hunters are taught to hone that ability early on--and hone it further, with practice--the cognitive acuity is connected with the motivation provided by the requirement to find food, evade predators, steer clear of poisonous plants, etc. Life and death concerns. The same child might very likely exhibit only puzzlement if requested to apply those skills to an RPM. The RPM is a joke, comparatively. The crucial difference partakes of a values question, one might say.
By comparison: high performers on the RPM who have resided in comfortable civilization all their lives and decide to take a challenging vacation in remote Amazonia are liable to find themselves very much out of their depth if they stray only a few hundred yards away from the cleared patch of their campsite. They might not even be able to find a wildlife path in the Pennsylvania woods. That's abstract pattern matching and progression for real, under conditions less controlled than the quilted rectangles of RPM diagrams. Granted, tracking skills require a lot of inductive practice, and the questions on RPM are commonly expected to be solved on first exposure to the test. But, Really. It's conceivable the only thing RPM reveals is a relative knack for understanding what's to be solved for, and how. It's not nothing; "eductive intelligence" is undeniably involved. But that's only one component of Intelligence- and the possibility that people might use workarounds or a productive emphasis on other intelligence aspects hasn't been given much examination (it may resist the simple resolution of a standardized test.) And the RPM may be more widely used on account of its convenience and "lack of culture bias" than for its reliability at assessing the broad-based foundation(s) that might be said to add up to "general Intelligence." Whatever that is.
"The reason IQ is useful is that it correlates with success with many tasks in modern life."
Maybe. But it may correlation more strongly with brainwashing (imperial conditioning).
No. Why? Have you seen a Raven's Progressive Matrices? I think that is where the shape rotator meme comes from. It is an engineering skill test for people who never studied engineering.
RPM is a test for recognizing patterns, that essentially asks the same question throughout, adding increasing amounts of subtlety and difficulty. It rewards maximum fidelity to finding a fit to yield a uniform result in the patterning of each diagram. RPM implicitly advantages the test-takers most inclined to require that quality as a cognitive focus. And also assumes that test subjects are uniformly motivated to "find the right answer" without any particular motivation other than performing as well as possible in accordance with the requirements of the puzzle. It resembles Sudoku in that respect.
Unsurprisingly, some test subjects with diagnosed ASD show a marked improvement over their scores on a test that incorporates a heavy verbal component, like the Wechsler (which has been modified to incorporate some elements similar to RPM, but still relies heavily on verbal inferences and skills.)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4148695/
https://link.springer.com/article/10.1007/s10803-008-0667-2
https://pubmed.ncbi.nlm.nih.gov/17680932/
Exactly with the RPM you dont even need to know how to read
I'd venture that any test subject without literacy skills does require some oral instruction, in conjunction with a prep question or two, in order to have some idea of what's being asked. But in my opinion, RPM isn't all that easy to explain orally; for one thing, there's no way to review the instructions again. Simply presented cold, as a set of questions, it isn't necessarily all that intuitively obvious to understand what the test wants. Notwithstanding the "nonverbal, cultural bias free" selling point of the RPM, so heavily touted by those who view it as definitive and conclusive at measuring "IQ."
Intelligence is a much more complex phenomenon than height and so its genetics is much more complicated than the genetics of height. The most likely explanation of the 'missing heritability problem' is that as more information comes in the gaps will become smaller and converge with population heritability. This is the latest iteration of 'egalitarianism of the gaps' argument and the safe bet is that it will end the same way the others ended.
The trend so far has been that as more information comes in, we learn that the genetic studies have confounding we didn't initially know about, and the gap with twin studies grows. I think the most likely explanation of the missing heritability problem is that twin studies are inflated by environmental differences, as has been known since the 70's (https://theinfinitesimal.substack.com/p/twin-heritability-models-can-tell) and also shown with modern quantitative methods (https://pubmed.ncbi.nlm.nih.gov/30104764/).
But at the same time, more information has come in supporting the hereditarian hypothesis. For example, it is now possible to see if higher white ancestry correlates with higher IQ among African Americans and it does. Conversely, there is no additional evidence in favour of any of the proposed environmental mechanisms for racial differences in IQ. The missing heritability problem is interesting, but the smart move is to wait and see before overturning decades of cumulative research all pointing in one direction.
Admixture analysis is just another way of measuring environmental correlations, it neither supports nor refutes either hypothesis (see examples here: https://x.com/SashaGusevPosts/status/1713626146963599712). But I can think of quite a few genetic predictions from hereditarians that have not held up:
1. That IQ is just genetics and non-shared environment with negligible cultural influence: indirect effects in genomic studies clearly show there are vertical cultural influences.
2. That outcomes like educational attainment are highly heritable and will be easy to build genomic predictors for: one of the largest genetic analyses of any trait is of educational attainment (n=3M) and showed <5% of the effects are actually causal families. In general IQ/edu is one of the least heritable traits of all tested.
3. That genetic effects on common traits would differ substantially between populations: no, causal effects are nearly identical between populations (https://pubmed.ncbi.nlm.nih.gov/36941441/).
4. That cognitive function is under strong and recent selection: No, IQ exhibits one of the weakest signals of selection if not entirely neutral.
5. Recent polygenic selection is widespread and acting on many traits (e.g. Steve Hsu predicting this: https://infoproc.blogspot.com/2012/08/recent-human-evolution-european-height.html): No, evidence of polygenic selection turned out to be a false positive and if it exists at all it is so weak as to be undistinguishable from population structure.
6. There will be large rare variant effects on IQ and rare variants explain the bulk of heritability. Nope, recent exome-wide studies show tiny contributions of rare variants (https://www.nature.com/articles/s41588-023-01398-8).
The missing heritability "problem" is just a specific example of a broader problem where hereditarians overfit to observational data and now that none of their forward-looking predictions about genetics have held up, they are inventing artifacts (or, as you are doing, simply continue to claim that it "all points in one direction").
Admixture analysis was originally suggested by environmentalists because they thought it would disprove the hereditarian thesis. Then when it didn't, they changed their mind and decided that it didn't mean anything. This is a consistent pattern of environmentalists for 50 years. There remains no hypothesis that can explain, at all, racial gaps in IQ by environmental means, whereas the genetic hypothesis is parsimonious and fits the data. All attempts to increase intelligence of low-IQ racial groups, up to and including relocating children to new families have failed miserably. Maybe environmentalists struck a pot of gold this time with the missing heritability problem, but, more likely, it's just a complex puzzle that will take many decades to solve without changing the basic picture.
It turns out that the scientific method is a test of specific hypotheses, not a test of the people that proposed them. Where scientists propose parameters and then develop methods to estimate them in an unbiased manner, "race scientists" simply walk through the garden of forking paths until they find a correlation that "looks right". Regression to the mean in siblings, admixture analysis, the method of correlated vectors / Jensen effect (essentially all of The G Factor), the national IQ nonsense, are all examples of this. When it is pointed out that their analysis in fact cannot distinguish between multiple hypotheses (often trivially so), they do not attempt to improve their methods -- as an actual scientist would -- but either fall back on an appeal to some environmentalist authority or argue that they're just providing one piece of evidence in a broader narrative, as if a pile of garbage can turn into gold if you simply pile it high enough.
You will note that the 6 examples I mentioned above were not "X hereditarian said analysis Y would prove hereditarianism" but "X parameter turned out to be Z instead of Y which is not consistent with a hereditarian model". Also none of the points were about "the missing heritability problem", which seems to have become a kind of verbal tic to avoid actually having to consider new evidence. Highly correlated effect sizes across populations have nothing to do with missing heritability. Estimates of indirect/cultural transmission have nothing to do with missing heritability. You get the idea. The thing to do here is to acknowledge that your statement "decades of cumulative research all pointing in one direction" was incorrect, and grossly so.
I ran some simulations here assuming a model where cultural transmission is directly on the phenotype that spouses are sorting on:
http://gusevlab.org/projects/hsq/#h.b5cuc8jc2dvc
It gets estimates that are ballpark consistent with (non-genetic) multigenerational studies. However, it is almost certainly the case that assortative mating is NOT just happening on the phenotype, so this is a very simple model. I think it would be helpful if behavioral geneticists proposed more explicit models of rGE besides VCT and how to test them.
Don't really have a horse in this race but if you are using the numeric value of IQ for one of your variables and you assume that your candidates all come from say 1.5 sigma above the mean then you are including 6.5% of the population in your study. However, only 2.25% of the population is above 2 sigma. So really, 65% of your sample would have an IQ between 122 and 130. The noise in the IQ test accuracy seems likely to swamp out much of your signal.
This is very interesting. Was just discussing this with some friends (mostly mathematicians, some applied, one neuroscientist - please be patient with us).
Some questions that arose:
1. Are we talking about childhood IQ, or IQ in late adulthood? The latter is apparently affected much more strongly by genetics - or is that bunk?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270739/?fbclid=IwY2xjawFTM1ZleHRuA2FlbQIxMAABHdGvcZgSUpqK7aOSCcgUUIVNogZQcUIKeGtUeJDUDxD9cVdaNLkmvWzl4Q_aem_Vo32aqtMZXG1bVHpJySaXg
2. What about epigenetics? (I know, I know, that is mostly about telling a cell that it's supposed to be a brain cell and not a liver cell, rather than some sort of reborn partial Lamarckianism - but let's talk about the latter). Does that play a role in intelligence, and if so, how inheritable is it?
3. A friend says: "As far as I can tell, he makes a really good point about genes and environment being correlated and therefore this causes big problems for interpreting (maybe even defining) heritability. His solution then seems to be to take the interpretation that minimizes genetic influence, and defines heritability to only include fairly direct effects. That’s fine as one interpretation — and a good interpretation as a geneticist — but it’s not the only one and probably a bad one from a sociological perspective." What is your take on this?
This is an interesting and important finding, but boy is it hard to follow along with exactly what all these different statistical measures actually mean.
I mean, I still believe that conclusion, but I have to concede its more because of the authoritativeness of the source than my being able to reconstruct the argument myself. And I'm pretty smart. How would one communicate these findings to people of average smartness and more suspicious of scientists as a source of unbiased information?
That's a good question, what do you think would help? So far I've tried to (a) simplify the intuition as much as possible; (b) explicitly quote from other papers in areas that might be seen as controversial. Would it be useful to try to get rid of any jargon entirely? Or provide a shorter overall summary? Something else? There are only ~3 core concepts involved here (population heritability, direct heritability, genetic correlation, factor analysis) but each one is unfortunately hard to be precise about without getting into jargon.
It might just require me to reflect on the core concepts until I understand them fully and then reread the piece.
I sympathise with science communicators like yourself. Making complex ideas accessible to laymen is really hard!