111 Comments

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.

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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."

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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!

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It's not nature vs nurture. You nurture nature.

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This is fantastic once again Sasha. This is a minor quibble but I would refer to the race "scientists" as race "scientists".

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Thank you! Good point

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Why such disrespect?

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because their arguments don't deserve anything better. At least, not the ones I've read.

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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.

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Nicely done.

I have added your article to my burgeoning education graph:

https://embed.kumu.io/c3b449cc0b3a9558b8e2b1e8f7f4bf4b

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This was super interesting on its own but also as a primer on the current state of genetic research.

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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.

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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 !

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interesting read, insightful too

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"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?

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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.

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Thanks I'll read it with interest!

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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

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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?

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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?

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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.

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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!

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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.

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"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.

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"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).

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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.

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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/

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Exactly with the RPM you dont even need to know how to read

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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."

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Aug 27Edited

The heritability estimates indicate that population heritability for height is 37%, while IQ is at 23% and educational attainment is only 12%. However, educational attainment shows a high genetic correlation with participation (r² = 0.72), and IQ is not far behind (r² = 0.39). This suggests that the observed heritability for IQ might be lower due to participant bias. If we adjust the heritability of IQ to account for this genetic correlation, it could potentially increase to about 35.4%. What do you think?

In fact, the selection bias in GWAS is also important for all characteristics, as mental illness, for example, also correlates with IQ. Speaking of IQ: it is more or less the best measure we have in psychology ...

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This is good intuition, but Schoeler et al. (https://www.nature.com/articles/s41562-023-01579-9) included a comparison of the raw population heritabilities with heritabilities estimated after re-weighting for participation and the results were only slightly different: "While heritability estimates were less impacted by weighting (maximum change in h2, 5%) ..."

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Aug 27Edited

Fascinating, but I wouldn't dismiss it just because it's low.

What do you think of this?

GWAS and twin studies are both quite robust, so rather than asking which is right, we should focus on understanding the reasons for the gap and trying to bridge it. It is plausible that both twin studies and GWAS are accurate to some extent. Twin studies focus on overall genetic influence, and GWAS focus on specific common variants. Twin studies may do a better job of capturing this parent-offspring heritability, while GWAS may struggle because they look at a more genetically and environmentally diverse population. If the GWAS estimated genetic correlation of a trait is substantially lower than the twin studies estimated heritability of the trait, it may indicate that the GWAS is missing important genetic components. Why not argue that the GWAS estimate is too low?

Another take: The assumption that twin studies and GWAS measure "different aspects of the same underlying phenomenon" may be too simplistic. In reality, they may measure fundamentally different things, with GWAS focusing on additive genetic variance and twin studies capturing a broader range of genetic influences, including dominance and epistasis, which could make direct comparisons problematic.

Still, your argument is pretty compelling!

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"GWAS and twin studies are both quite robust, so rather than asking which is right, we should focus on understanding the reasons for the gap and trying to bridge it. "

But there's another problem, one that I notice as common to all standardized tests of IQ: are a few broad-brush data correlations used as follow-up ("educational advancement", "occupational status", "income amount")really all that reliable to confirm that the tests are measuring what they claim to measure- the foundation of general intelligence, per se? Or are the tests simply reliable at the more modest goal of assessing scholastic skills, similar to an SAT, where modern society is more inclined to reward high performers; or a narrow set of aptitudes such as that measured by RPM, which might happen to correlate in alignment with in-demand (if narrow) skill sets like data coding and CGI? I notice a little too much vulnerability to the post hoc, propter hoc fallacy in the premises to be all that assured that IQ tests are assessing an ability as elusive as "intelligence", per se. Much less theeven more profound claims asserted in regard to measuring "general intelligence", aka "Spearman's g." In that regard, it's worth noting that Charles Spearman himself made statements in his writings that qualify and delimit his original measurement goal.

It also has to be said that a society with different norms and latitude for individuality from the US may incorporate various carrots and sticks to increase the odds of success and upward mobility in conformity with early expectations of achievement. Which is not to say that such incentives and disincentives are particularly lacking in American society; they just aren't encoded as rigidly.

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Alternative Hypothesis: Since GWAS do not sequence the entire genome but focus primarily on SNPs, they may underestimate the true genetic heritability of IQ compared to full genome sequencing. I find it hard to believe that the genetic heritability for educational attainment is genuinely so low. It’s not uncommon to see a “not-so-smart” child in a gifted family, which suggests that IQ and educational attainment may be influenced more by genetic factors than environmental ones. However, there seems to be greater variance between parents and children than we might expect based on traits like height, possibly because intelligence is inherently more complex. What are your thoughts?

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It's certainly possible that rare variants will explain some of the additional variance, though the initial studies of genes/exomes (which is where we would expect most of this extra variance to lie) are showing very little (summarized here: http://gusevlab.org/projects/hsq/#h.375v1ho0nj4).

Regarding seeing patterns in families, I would caution against that as heritability behaves very counterintuitively. For example, for a trait with 10% prevalence in the population (say, something like being noticeably "smart") even with a high heritability of 0.8 and *both* parents exhibiting the trait, the probability that the offspring exhibits it is just 55% (for a heritability of 0.2, this is 18%). Which is to say that even for highly heritable traits you would expect to see *many* families where both parents are in the top 10% and the child is not. Can you distinguish between 55% of families and 18% of families just from anecdotal evidence? I don't think I could.

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Thank you for taking the time to respond to all my comments. I really appreciate the debate!

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