No, that's not how this works. You can't just say "twin study" and dispel the environment(s), and, in fact, GWAS is pushing things in the opposite direction (people will argue by how much, but the direction is clear).

Split twins strongly backs genetic component, and heritability is also significant. There's nothing to dispell, environment does seem to be a factor in negative direction, so that's undoubtedly a big factor as well. But low IQ people having low IQ children is going to explain a lot of it - no need to be a "social darwinists" to believe that.

Split twins does the opposite: separated twins IQ-test outcomes track the SES of the families they go to. But "twin studies" is science at the level of "The Bell Curve", which is 30 years old.

At this point, you kind of have to want IQ to be genetically determined (in any meaningful amount) to believe it is.

> Split twins does the opposite: separated twins IQ-test outcomes track the SES of the families they go to.

Consider me convinced if you can source this - I'm not finding anything but opposite - that they strongly correlate the older they get (IQ test).

Read Turkheimer.

Something more specific ? Couldn't find anything directly saying what you're claiming here.

I was interested if my info was out of date so I found this https://www.sciencedirect.com/science/article/pii/S019188692... which basically again confirms genetic IQ factor in adults is major. Separated twins correlate, siblings corelate less and virtual twins (same age unrelated siblings) corelate way less.

Anyway I'm no expert on this, but I've heard this view from multiple credible sources and the more I dig in the more it seems supported.

What were those credible sources?

First one that comes to mind is The Blank Slate from Pinker, but I have read that like 15 years ago. But it did shape my view on the subject and I have seen this topic come up many times since.

I don't remember anyone disputing strong genetic component of IQ, other than people uncomfortable with implications. And I am not even that interested in the social implications, but more practical issues like IQ improvement (basically 0 impact from what I have seen other than being physically fit/exercising), implications on parenting (you cant imprint your desired outcomes on your children and need to play to their innate interests and strengths/weaknesses), etc.

I'm sorry, but this is a persistent myth about this space. Lots of research is done every year on the genetic components of behavior and cognition. The field doesn't see it as a yes/no question; there are questions about how far you can get with classic twin studies vs large-scale GWAS, questions about the malleability of intelligence, questions about the validity of IQ tests (see things like test-test reliability), questions about the meaningfulness of psychometric "g", all actively studied.

Again you can just go read Turkheimer's Vox piece for an refutation of your "basically zero impact" thing.

My big thing here though isn't to convince you that you're wrong about your belief that intelligence is innate and fixed. Rather, it's that you opened this thread with a citation to heritability research, and your usage of "heritability" was broken and misleading. With that cleared up, I don't think we need to drag this out.

Just a reminder about GP's original comment:

> This is guaranteed to be a strong factor, there's plenty of evidence on IQ heritability and correlation with income.

> Just because it doesn't predict the outcome fully doesn't mean it's insignificant.

I'm just trying to figure out what your argument was, since it looks like you're trying to convince GP of what they already believed. Income isn't genetic after all.

You've clipped out the question that comment replies to, which was about the genetic determinism of IQ.

Turkenheimer: https://web.archive.org/web/20191231135901/http://pdfs.seman...

> Results demonstrate that the proportions of IQ variance attributable to genes and environment vary nonlinearly with SES. The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse.

[....]

> In the low-SES group, the intraclass correlation was .63 for DZ twins and .68 for MZ twins, consistent with h2 of .10 and c2 of .58; for the high-SES group, the DZ twin correlation was .51 and the MZ twin correlation was .87, consistent with h2 of .72 and c2 of .15.

[...]

> In the fractious history of scientific investigations of the heritability of intelligence, the effects of poverty, and the relations between them, there has been only one contention with which everyone could agree: Additive models of linear and independent contributions of genes and environment to variation in intelligence cannot do justice to the complexity of the development of intelligence in children. Only recently have statistical models and computational capacity advanced to the point that less simplistic models can actually be fit. Although there is much that remains to be understood, our study and the ones that have preceded it have begun to converge on the hypothesis that the developmental forces at work in poor environments are qualitatively different from those at work in adequate ones. Clarification of the nature of these differences promises to be a fascinating, and hopefully unifying, subject for future investigation.

The Bell Curve is a great book that is unfortunately maligned by people that dislike what it says but all too often have no actual arguments against what it says.

Separated twin studies show conclusively that IQ is (partially) genetically determined as does, yknow, all common experience and intuition.

Can you name three people who practice in this field (Turkheimer, who I named upthread, is a harsh critic of the book and a giant in this field) who agree with your take here?

> whether or not you wear lipstick has high heritability.

Think about this example. The genetic factor here is massive, much higher than anyone is claiming for IQ. Can you imagine how hopelessly lost you would be if your analysis of lipstick distribution in the population focused on its heritability and link to genetics?

An even bigger issue you immediately run into in these conversations: someone will say "I don't mean heritability that way, I mean genetic heritability". Which, whatever, except: now you've discarded all the science. The papers you'd draw these numbers from are referring to heritability in its technical sense, not in some message board sense.

Yes. I mean, either you're talking about statistical properties of a population or you're talking about something else. These discussions usually devolve into "something else" almost immediately.

I mean I still fail to see how comparing these three scenarios

- genetic twins separated at birth

- genetic siblings raised in same household

- genetically unrelated same age siblings adopted in the same household

are teasing out anything but an underlying genetic component and reproducing in studies

You can have intuitions about any of these issues, but you can't use heritability research as evidence for them without understanding the technical meaning of "heritability". That's all that's being said here.