Interview with gwern

What do you think heritability means?

Farmers, who depend on this sort of thing, have it figured out:

> https://extension.missouri.edu/publications/g2910

Heritability is simply a measure of how much of the variation in a trait, like height or IQ, is due to genetic factors rather than environmental influences in a given population. Could be feedlot steers, could be broiler chickens, could be humans. In humans, traits like height are very highly heritable, at ~0.8. Certain others, like eye color, are heritable to ~0.98.

Right. It's a simple ratio of genetic variation to phenotypical variation. How does evidence of heritability support HBD claims, which are based on genetic determinism, a notion orthogonal to heritability?

I don't think that HBD claims -- at least, those made in reasonably good faith -- are based on genetic determinism. A Bosnian guy from the Dinaric alps is much more likely to be >1.8m in stature than a Pygmy. This is not predetermined as such, it's just that one population has something like +3SD in stature over the other. (An admittedly wildly extreme example!)

Differences in IQ between groups are apparently far more modest, but, however distasteful, it's still possible to speak of them, and it's possible to make statistical statements about them. My position is simply that, on the one side, it should be done in good faith -- and, on the other side, it shouldn't be seen as something heretical.

I don't understand the alternative interpretation you're alluding to. Stipulate the validity of IQ or the common g. If group variations in these metrics aren't caused by genes, why are they distasteful? If they are, you're describing genetic determinism, which, again, is orthogonal to heritability.

Heritability is a statistical concept, not a measure of genetic determinism. High heritability doesn’t imply that a trait one exhibits, such as IQ or height, is entirely predetermined by one's genes. Even eye color is only heritable to ~0.98. I'll grant that any trait heritable to 1.0 is indeed entirely predetermined by one's genes -- though, offhand, I'm not sure that such traits exist in humans.

That aside, we're getting into semantics. Whether you call it "genetic determinism" or "heritability," we're talking about durable group differences in genetically-mediated traits. And that is what people may find distasteful or even heretical.

Are we talking past each other? I'm saying: heritability is orthogonal to the question of whether a trait is determined by genetics. There are traits with no genetic component at all that are highly heritable, and vice versa. "Genetic determinism" doesn't mean "a guarantee that a group of genetically similar people will display a trait"; it means "the trait is causally linked to genes".

The semantics matter, because the evidence supporting HBD positions is stated in terms of the technical definition of heritability.

While I've got you, can I ask that you stop evoking "heresy" and "distaste" in this thread? I believe I'm making simple, objective points, not summoning opprobrium on your position.

Sure, heritability is orthogonal to the question of whether a trait is determined by genetics.

But traits like IQ, height, and eye color are both (A) highly heritable and (B) substantially shaped by genetic factors. In casual online discourse, I believe that (B) is usually taken for granted, so it's glossed over, and when people say that any given trait is "heritable" they're also assuming that (B) is true for the trait. At least, I am guilty of that lapse.

And I take your point about language.

When you say "substantially shaped by genetic factors", you should present evidence. It's easy to provide evidence for the heritability of intelligence (again, stipulating IQ), but as we've established, that begs the question of whether the genetic connection is correlation or causation. Environments are inherited, too.

There is growing evidence that group IQ heritability isn't evidence of genetic causation.

There's this: https://pmc.ncbi.nlm.nih.gov/articles/PMC5985927/

First sentence of the conclusion: "Genetic association studies have confirmed a century of quantitative genetic research showing that inherited DNA differences are responsible for substantial individual differences in intelligence test scores."

Related: https://www.pnas.org/doi/full/10.1073/pnas.1408777111

The trouble is that, like height, IQ is governed by a vast network of "genes of small effect," so a comprehensive view has proven difficult to nail down. Progress is apparently being made, though slowly.

> There is growing evidence that group IQ heritability isn't evidence of genetic causation.

What evidence do you speak of?

The Plomin and von Stumm study --- easy to find critiques of it! --- is about heritability. It cited unpublished GWAS data to claim polygenic scores would predict more than 10% of educational attainment, and thus intelligence. The educational attainment GWAS study that was eventually published found less than 5%. And remember, the twin study heritability data that most people cite in threads like this claimed over 50% (twin study heritability numbers for all sorts of traits are apparently overstated by factors of 2-4x, which is wild).†

An example of evidence against the reliability of educational attainment and intelligence heritability statistics: comparing intra-family heritability (across large numbers of families) to population-wide studies: for educational attainment, it turns out there's little correlation between the two; for simpler phenotypical traits, there's almost 100% correlation.

To sum this up:

1. The 2018 Plomin study gives sharply lower genetic/EA numbers than were floating around previously (say, from the Jensen-ist era)

2. Plomin's own numbers were preliminary and overstated

3. Researchers in the field criticized that study nonetheless

4. Subsequent studies on direct heritability and molecular heritability put even lower ceilings on it (basically, all credible behavioral trait heritability work has been done after 2018 --- and in fact this is broadly true of a lot of genetics work, not just trying to statistically mine behavioral traits out of genome scoring)

5. Even those results have flunked basic sanity tests (for instance, getting wildly different results in intra-family vs population-wide studies).

It's not looking good for people fixated on this idea.

† I'm being very loosy-goosey with the numbers and units here

I don't doubt that there are methodological and empirical problems all around. The scientific literature on these points is a mess.

We might want to look at the fundamentals: How is IQ qualitatively different from height, eye color, schizophrenia -- or any other highly complex, heritable polygenic trait? (One could also extend this to the many traits that animal breeders keep an eye on.) None of them have been fully pinned-down yet, but I don't believe that they can't be fully described in principle.

It's true that GWAS for intelligence explains <5% of variance today, but GWAS for height was in the same position a decade ago. Today polygenic scores for height predict over 40% of variance.

One obvious difference between what is known about the heritability of height and what is known about the heritability of intelligence or educational achievement is that when you put height heritability to the test, for instance by checking to see if the intra-family studies agree with the population-level studies, the height heritability stuff holds up, and the EA/IQ stuff does not. Another might be that successive rounds of study of simple phenotypical traits like height have not demolished previous estimates of heritability, while that has in fact happened in the EA/IQ case.

All this happens before we even reach questions about test-test reliability of IQ, or of whether gene-environmental interactions are uniform between Europe and other population cohorts (they do not appear to be!). It defines away SES confounding (which appears to be a significant issue). It has thus far largely ignored epigenetics. And, of course, for it to mean anything, the hypothesis also has to defend the idea that IQ/EA, at least in its genetic component, is immutable.

All that aside, I'm mostly just here to say that simple heritability statistics don't say what people on HN seem to think they say.