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Notes -
I realise this may come across as stirring the pot, but I hope I've been here long enough to have earned the benefit of the doubt.
In the context of the HBD debate, could someone please ELI5:
The concept of heritability and how it relates or doesn't relate to genetic causes of individual or group differences. I am aware of the "books at home" example. Is that all there is to it?
What precisely g is?
Steelman(!) Turkheimer's position. No, I don't want to hear about his politics.
Roughly summarise the position of Kirkegaard et al.
This whole debate always gets technical so quickly that I very often just get lost. I don't want to rehash the arguments here, I would like to understand the basics. But the waters are often so damn muddied (purposely so, I suspect) that it's very hard to get a grasp of what people are even fighting about.
Low-rigor response because I think you do have to study the object level a bit to evaluate the sides.
Precisely what its definition says. As Jensen himself put it:
This is the definitive blog post refuting a popular methodological criticism.
Do you mean what it corresponds to in reality? I suppose it's just a holistic brain performance index, that's also predictive of general health. There isn't one physical thing that creates g, but the sum of diverse brain factors (half of our genome gets expressed in the brain) ensures that it emerges in the factor structure of our mental abilities, conditional on similar amount of training useful for each, and that predicts both general functioning and peak achievement. It isn't surprising that our abilities are highly correlated. We have a very homogenous brain made up of extremely complex computational elements (neurons) implementing simple task-agnostic learning algorithms, so most of the complexity and variation of our basic architecture (though not specific structure acquired over the lifetime) is shared between neurons or in their generic connectivity. Random genetic errors or (non-localized) environmental insults create different perturbations of the neuronal function, but on the whole-brain level they all push the system away from its optimal regime, no matter what it's trying to learn or to perform. You're unlikely to score in the 99th percentile on arithmetic and 20th on vocabulary if your axonal conduction is shot or your synapses are too sparse or do not get pruned well or your total cell count is too low or if your cell migration was too noisy or intracellular metabolism is somehow defective. And even if you've somehow developed specific tricks to cope very well with your shortcomings in a given skill, on the population level the power of the general factor becomes overwhelming.
Much of the issue is reducible to signal/noise ratio. High-performing brains ride the edge of metastability and wrangle representations easily; low-performing ones waste power fending off chaos and lose track of the context.
But it is politics ultimately: we should be super, duper, ultra skeptical of HBD-related stuff and probably censor it for good measure, because Holocaust. He is leery of political implications of HBD acknowledgement regardless of specific merits of a given study.
Closer to the object level, I think he was recently steelmanned by Tailcalled:
Or put another way: the whole causal chain between genes and outcomes matters, for it may have links that depend on contingent properties of the environment. If proven, this would invalidate our assumption about this trait's heritability in a more general case. In our ancestral environment, smarter people probably hadn't been more myopic, because there had not existed the contingent segment «smart – reads a lot – sits indoors more than others – stupid monkeys haven't yet built good indoors lighting – not enough dopamine signaling in the retina – extended axial elongation period – myopia». It can be highly heritable, we can even find explanatory genetic polymorphisms – but the relationship disappears whenever we stop having our smartest children spend more time indoors with poor illumination. Likewise for all contingent chains. Therefore, even though everything is heritable, the first law of behavioral genetics does not mean that genetics is destiny or that people's phenotypes are molded by their genes in the intuitive strong sense the texture of their hair is.
This line of critique is pretty old, used by Lewontin etc. already, and is fair enough on its face, but assumes that some common mitigations psychometrists know about are insufficient, and it's only when it comes to proving this that we see clearly how Turkheimer is politically driven.
Roughly:
We are living in a saturated and humane age. Human brain development is actually surprisingly robust and insensitive to inputs that are scarce in developed economies (even if some of them were scarce not so long ago in the past), and human cognitive development mostly proceeds close to the optimal way so long as you don't severely and obviously fuck up brain development or deviate far from low-effort common sense in nurture. Thus, developed societies have exhausted reasonable interventions that target contingent hazards disproportionately affecting g in different demographics; probably all hazards that bring down g in the population at large. While some differences in positive factors remain, they're long in the diminishing returns regime for more advantaged groups, as far as intelligence is concerned; and negative factors are similarly minor and maintained not by any iniquity, scarcity or coercion but out of their free choice by people who are worse off; and the rest is completely unsystematic. There's no low-hanging fruit left. No more toxic lead paint we can scrape off walls of homes where redlined minorities live, no malnutrition we can solve with food stamps, no miracle iodine-enriched brain-enhancing diet that only upper class kids are getting, no worms in ponds peasants have to drink from, no education reform that can remove some unnecessary cultural pressure. We've optimized and homogenized our environment to the point that practically all subpopulations realize the same, very high, percentage of their genotypic potential for g that is possible at the current technological/infrastructural level, and so differences in outcomes predicated on differences in g are explained by true differences in heredity, and are not amenable to elimination via any social policy change we'd recognize as fair.
Mostly the same logic applies to non-cognitive factors that influence outcomes, if to a lesser extent.
This model is corroborated by an extreme wealth of evidence and by the complete failure to create a competitively powerful model that rejects its premises, despite nearly a century of trying to do so, generous investment and genuine desire of talented researchers. This knowledge is being obfuscated and suppressed by political means.
Thank you! Very helpful.
Two more questions if you'll indulge me:
What are the most common anti-HBD arguments you encounter that aren't sophistry?
Gun to your head, what are the most persuading arguments against the position that the observable inter-group IQ gap is genetic in origin to a significant degree?
For me it was Chandy's research with IRS data that showed that income reversion to mean was the same for Black girls as for the White population. I suspect he's just doing something stupid but I can't dismiss the results especially since they are based on the largest sample ever collected in this space.
Thanks! Could you elaborate a bit? What makes this a good argument? What does it imply?
First off, it's Chetty. Sorry! I got him confused with a paper on distributed deadlock detection.
Chetty managed to convince the IRS to give him detailed income data on... everybody. Yes, literally everybody. It's a sociologist's wet dream. Anyway, he did a bunch of analysis comparing parental vs. child incomes. The idea is that populations tend to mean-revert but they do so differently across races, etc... Whites mean-revert to a higher income level than blacks. It's a neat way of getting rid of the influence of starting conditions. The study itself is here: https://academic.oup.com/qje/article/135/2/711/5687353. The precise graph I'm talking about is here: https://academic.oup.com/view-large/figure/201514598/qjz042fig5.jpg.
A lot of HBD arguments rely on the assumption* that Black underperformance is due to genes. However, there isn't much of a reason that Black women should consistently have better IQ-related genes than Black men (or at least none that I've heard yet). If outcomes between Black women and Black men diverge substantially, that implies that Black underperformance might not be related to their genetics after all.
That's not "the same for Black girls as for the White population", it's the same for black women and white women, the white male curve is noticeably higher. And on a meta level, it's always suspicious when a paper drops categories midway through. Whatever conclusions you want to infer from this graph, they would be much firmer if it also had asians.
Good catch on white women vs. white men. I wonder what causes the difference. I do think your comment on Asians is a bit of a non-sequitur.
Why a non-sequitur? Earlier parts of section IV show a higher steady state for asians than for whites, then they get dropped from the comparison. If they were included in this graph, it would either show that their advantage is also mostly male and asian women match white women, in which case maybe this graph says a lot more about gender than about race. Or the asian over white advantage is maintained for both genders, which would make for a much stronger anti-HBD argument. Because one of the more appealing HBD talking points imo is that by Occam's razor the black/white gap and the white/asian gap have the same basis.
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"Books at home" is presumably shorthand for a wide range of parenting practices, and indeed I would bet that it originated as a relatively easily measured proxy for parenting practices.
Btw the graph from here happened to be going around today; it shows a large gap in cognitive skills between identical and fraternal twins, but also a substantial gap between siblings raised together and siblings raised apart. (Note that some small pct of the difference between identical and fraternal twins might conceivably be caused by parenting, since at least in the past parents often tended to treat identical twins identically-- dressing them the same, etc -- which might also manifest itself in forcing both to experience some of the same experiences (eg, if one wanted to take violin lessons, both had to). Again, I would guess that would have a very small effect even if true, but of course that is a guess).
Also, one consideration that I never see mentioned in popular discussion of HBD is potential congenital, but not genetic, causes. Eg if poor people have dumber kids than other people, is it all either genetics or upbringing? Or is some the result of greater propensity for drinking, drug use, poor diet, etc during pregnancy?
So if this were a HBD discussion someone would quickly point out that propensity for drinking is also partly genetic, therefore ???
I do not understand why this is brought up so often. Presumably you could claim that there is a policy solution for this (i.e. preventing pregnant women from drinking) and therefore the difference resulting from this type of parenting behaviour (even if it is partly genetic) is not set in stone?
Everything is genetic at some point. Without arms, it is more difficult to steal. Having arms is genetic. Do you deduce that stealing is genetic? Then everything will be genetic. But everything will also be social, political, physical, economical, sexual...
Drinking might be partly genetic, but a woman who has the drinking genes and does not drink (for example because she can't, as there is no alcohol in her country) will have healthier children than a women who drinks even though she has no drinking genes (say someone forces her to drink). So the gene is only relevant as a factor in the drinking behavior. The behavior is everything.
On the other side, if there is an intelligence gene, no circumstance will change the final result: she can live her life however she wishes, it won't change the result. The only important element is whether the children get the gene or not. The behavior is not relevant.
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Therefore this is a complicated issue, which is part of my point.
Yes, there are obviously potential policy solutions
Why can't it be brought up simply in order to better understand an interesting phenomenon? I saw an article the other day re why dogs cock their heads to the side when people talk to them. I read the article despite it having no policy implications at all.
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Just saw this posted today.
https://twitter.com/AporiaMagazine/status/1654233104523968512
It's not just partially genetic. The difference in intelligence between two individuals is mostly genetic. Most people, including the credentialled, naively assume the opposite, thus coming to incorrect conclusions about many social problems. That's one reason it gets mentioned a lot here. The other, more important reason, is that the Motte is one of the only places where a reasonable discusssion about HBD is allowed to take place. If we wanted to talk about baseball, there are a million other forums for that.
My apologies, that was awkwardly phrased on my part. What I meant was that I do not understand how the observation that many environmental factors could also be driven by genetics is a counter-argument to the position that in-between group differences are partly genetic. Yet I very often see that happening in HBD discussions.
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How is it possible you never saw it mentioned? Twin adoption studies specifically rule out these sorts of issues.
No, they don't. They rule out an argument that some part of the variation between identical twins raised together and apart is caused by the environment in the womb. But it does not rule out an argument that some part of the difference between identical twins born to a poor woman and identical twins born to a middle class person is caused by the environment in the womb.
They do rule out the argument that the variation between groups of identical twins of the same socio-economic class is caused by the environment in the womb, though.
Only if the correlation between identical twins of class X is identical to the correlation between identical twins of class Y. Is that what studies show? Because I know in other contexts the effect of genetics is mediated by socioeconomic status.
They don't need to be identical. The genetic correlation just has to be bigger than the SES correlation within a given SES group. Or you can just look at kids born to rich families but who got adopted out to parents of various classes.
It was my impression that this is what the studies, in fact, show. Maybe an earnest full-HBDer can give a link, I'm just a reluctant and partial one, that prefers the whole thing to be proven false.
I don’t know what you mean by the SES correlation within a given SES group. Within each SES group, every kid is coded with the same SES. There is no variation in SES to use to calculate correlation, is there?
Regardless, if there is a difference between the pct of variation explained by genetics in twins born to low SES mothers and the pct of variation explained by genetics in twins born to high SES mothers, then that difference is caused by something, right? That is true even if the genetic correlation is enormous.
Yes, but my question is whether such studies have ever been done.
There's still some income variation within a group, no?
Yes, but if the genetic correlation significant (doesn't even have to be enourmous) that already requires us to overhaul the way we talk about social issues. If you want to focus on the environmental things we can do to improve outcomes for people, go right ahead, but you can't presume isms because groups have different outcomes.
Once again, I believe so, but it would require digging through ages old SSC / TheMotte posts, or the materials of Kirkegaard / Sailer / Murray. I'm inclined to do neither, as I wish we could bury the whole idea.
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As a term of art--that is, aside from its colloquial sense--heritability is "the proportion of phenotypic variation (VP) that is due to variation in genetic values (VG)." This is a mathematical concept established on population-level statistics. I am not aware of the "books at home" example or what you take from it, so I'm afraid I am unable to tell you whether that is "all there is to it." But that link to Nature is a pretty short read, if you want to know more about how heritability factors into our understanding of highly heritable traits (like IQ).
G is also a mathematical concept that turns up in statistical analysis. Researchers who assign what are believed to be diverse cognitive tasks nonetheless observe high correlation in the ability to perform well on these tasks. G is the variable assigned to track that correlation. The fact that the correlation exists tends to undermine competing theories e.g. of "multiple intelligence."
Maybe to make it more of an ELI5, it's common in American culture to think of oneself as a "math person" or a "language person," or maybe even more particularly as a "history geek" or a "physics nerd." In all kinds of standardized testing we find it's actually quite unusual to be noticeably bad at, say, linguistic analogies, while being exceptional at, say, calculus. Even things like self-regulation tend to correlate with g--in a study of prison inmates, for example, populations with higher IQs were less prone to violence (PDF warning). While there are cases of extreme divergence (sometimes so extreme we call them "idiot savants"), statistically speaking high apparent cognitive ability is multi-domain.
Note that IQ is not the same as g, but is an attempt to measure g. Note that I also say "apparent" cognitive ability: you might argue that, for example, the ways in which we parse out "separate" cognitive tasks might not actually be separate, or something. It is important, in discussing intelligence science, to recognize just how much of a "black box" our brains still are to us. We can measure inputs and outputs, and we can even get some limited sense of what is happening internally, but beyond that most of our best guesses are inescapably statistical and of limited (but probably not zero) value at the level of individual humans. But in those analyses we find strong correlations of success across task domains (defined to the best of our understanding), which is extremely difficult to explain in the absence of something like g.
I know you've posed this as a "small scale question" but what position?
Again, you're going to have to be more specific.
Thank you! That is exactly the kind of answer I was looking for. Already learned a lot, thanks!
In a lot of HBD discussions I come across people who will claim that heritability is not identical to genetic causation. I do not understand on what basis this claim is made. To quote myself:
So g is essentially a latent contruct that is not directly measurable and IQ is our attempt to come as close as possible?
Turkheimer seems to be the poster child of the position that in-between group differences, especially as related to IQ, are not biological in nature. He very often is cited authoritatively in this regard. I am aware of his political position that this type of inquiry is unsavoury (and I agree to some degree), but I am not aware of the scientific basis of his argument. It seems to be some kind of "everything is heritable, we don't know what might be the case in radically different environments, so who knows?" which just seems nonsensical to me. I am looking for a good steelman of his position but I don't even know what his position actually is.
Likewise, Kirkegaard seems to be Turkheimer's main opponent. I tried making sense of some of his blog posts, but they are all way over my head.
As I said, I am in dire need of ELI5 because I don't even know what questions I should ask to improve my understanding.
E.W. Kirkegaard is nobody's main anything. He's a guy on the internet with a BA in linguistics, who changed his name and moved countries to try to dodge a piddling amount in a libel judgment.
If you're surveying a scientific argument and both parties are addressing internet randos as major players, you're probably in the wrong part of the argument.
((I'll acknowledge here that @DaseindustriesLtd has persuasively argued that credentialism is a form of censorship used to hold HBD down. It's a good argument, but one I find kind of funny coming from HBDers))
Where's a better place to look?
Murray The Bell Curve and Coming Apart. Then on the other side The mismeasure of a man 1996 edition by Gould.
Thank you! What are the main arguments fielded in the mismeasure of man?
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Consider the phenotypical trait "has two arms." Across a population of sufficient n, how "heritable" is "has two arms?" The answer is "not very heritable." Why? Because while there are probably some number of one-armed or no-armed individuals due to genetic mutation, most people who lack two arms have clearly-established environmental reasons for that (e.g. thalidomide, industrial accidents, etc.). So variation in armedness of the population is not predominantly explained by genetics. And yet it is surely true that you have two arms by virtue of your inherited genetic makeup!
On the other side, how "heritable" is "wealth?" The answer depends on your population sample, but often it is "very heritable!" Why? Well, in most places around the world, wealth is inherited (indeed, the word "inherit" originally referred to certain rights, long before we understood genetics) by operation of law. If wealth is concentrated in a few families (which is true in many human populations), then you would actually see a very tight correlation between the variation in genes and the possession of wealth, giving wealth a high heritability coefficient. Now it may well be that "making money" is something downstream of some genetically-affected trait, but still it seems unlikely that creating a clone of Donald Trump would guarantee you a being destined to inherit millions of dollars.
Examples like these have led to some fairly famous arguments that "heritability" ought to be jettisoned. But I find it difficult to take such arguments seriously, as they are in essence asserting that because observed correlations between phenotypical and genotypical variance do not definitively establish causation, we should stop caring about the correlations. This is the kind of attack that can always be raised against statistics--"oh, your correlations are spurious"--but I have yet to see any such attack that did not amount to an isolated demand for rigor. In cases like armedness or wealth, we can be pretty confident in our ability to see the spuriousness of the comparison. With something like intelligence, it's much more challenging, which is why we spend so much time crafting experiments intended to isolate relevant variables.
I don't know what it means to be a "latent construct" in this context. Probably g is not any one thing; cognition appears to be polygenic, so g is not only a function of having the right pieces, but also a function of how well those pieces work in concert. But yeah, IQ is one approach we've taken to, essentially, benchmarking g.
Yeah, I guess the steelman of his position, as I understand it, would be it's very difficult to compare populations, in part because the very process of population selection involves a choice. It's not that "everything is heritable" (armedness isn't!) but more like "a lot of high-heritability stuff is clearly not genetic, a lot of low-heritability stuff is clearly genetically determined, and your methods for selecting populations for analysis already have a variety of biases built in to them, so all you're really doing is laundering those biases through complex math." Whether you buy that argument is probably going to depend a lot on your own priors re: how much intelligence seems genetic, in the same way that armedness seems genetic. It's an oversimplification to be sure, but if you think "Bobby is smart" is more likely the result of the processes that make Bobby wealthy, or the result of the processes that make Bobby have two arms, you will very likely draw different conclusions about whether the heritability of intelligence (which is, undisputedly, quite high!) says something about the genetics of intelligence.
As someone who does not do a lot of statistical analysis, I often find this to be true of these arguments. I am more familiar with the philosophical problems (especially, the problem of induction) and I find even those quite perplexing! So I'm probably of limited help here. But it does seem to me that people like Turkheimer seem to be more interested in muddying the waters than in understanding and explaining observable correlations; this has a way of shifting extremely heavy burdens of proof over to the people who are actually looking at these correlations and trying, however imperfectly, to explain them. It's much easier to doubt an explanation, than to construct one. For me, as someone who is mostly an outsider to these arguments, the fact that any studies continue to suggest a genetic component to intelligence--never mind many studies!--seems significant, given the overwhelming amount of social and political pressure there is for people to adopt blank-slatism with regard to human cognition.
Thank you! That was the key to my confusion. For some reason I thought the comparison that is being made to figure out the degree to which genetic variance is responsible for phenotypical variance is always between siblings (which is of course one of the ways in which you can isolate the effect). I did not think about comparing two randomly chosen individuals.
Unless I am confused again, that's an independent variable you suspect is responsible for change in dependent variables but one which you cannot measure directly.
Could you give an example of what you mean by population selection here? Would Turkheimer argue that the populations we observe differences in are already subject to extremely potent social forces and it is therefore impossible to isolate genetic effects? But what about, e.g., twin adoption studies?
The mainstream opinion among geneticists seem to be that genes define the potential, the environment the degree to which it is reached. I don't think Turkheimer disagrees with that, only with the argument that in-between group differences are genetic.
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I think twin adoption studies that control for socioeconomic class show heritability cannot be boiled down to environmental stuff the parents do.
That one also always sounded like vodoo to me. I also don't like various statistical tricks they play to normalize IQ, though that one cuts both ways as far as political correctness is concerned.
I think "the general factor g of intelligence" is just "the principle component if you do principle component analysis on things that purport to measure intelligence". Like it definitely exists in the sense that PCA does indeed spit out a large first component if you do that. As long as all of the intelligence tests you're feeding into the statistical process meet some specific criteria (e.g. linearity, similar scale), it very strongly demonstrates that all of the tests are mostly measuring the same thing as each other.
To develop an intuition for what "the PCA spit out a large primary component" means in practice, let's consider an example housing dataset which includes attributes like price, number of beds / baths / parking spaces, presence of AC/heat, etc. If you do a PCA on that dataset, you get a primary component which explains 25% of the variance (and the next components explain 12%, 9%, 9%). Let's call this primary component the "general factor h of house-goodness". Sale price, number of bedrooms, and presence of air conditioning, in particular, are very strongly h-loaded, though every thing that would be nice to have in a house is positively h-loaded.
It's pretty clear that h reflects an actual thing, and that actual thing is probably approximated by "how good the house is". It's sensible talk about things like "high h houses that score low on the price test", or, as we say in plain language "nice houses that are cheap".
What the presence of h does not mean is anything like "this house scores higher on the number of bedrooms test because it has a high h factor".
You should view "the general factor g of intelligence" through that lens.
(cc @RococoBasilica, this seems relevant to your questions)
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So, Wikipedia defines heritability as "a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"
But in every single HBD discussion, there is someone claiming that heritability and genetic influence are not identical. They usually bring up something clearly environmental, such as "having books at home" and claim that this would also be heritable. I do think it has something to do with how many environmental circumstances such as parental behaviour might themselves be influenced by the parents' genes. But this doesn't seem like a refutation of genetic impact to me.
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