Twins Reared Apart Do Not Exist

iq is "polygenetic" with the consensus estimates at 50-80% based on genes

success has components of luck as in "right place, right time" for someone with the right qualities and connections, and many of the very successful are quick to admit this

I am a 3rd generation machinist along the paternal line, and although the machines I operate are in expensive labs, those my father and grandfather operated were probably just as challenging. Engineering also seems to often run in the family. How much is nature and nuture? "It varies" is a safe response

That doesn't sound like a problem with twin studies exploring the degree to which IQ is genetic, that sounds like a problem with people treating aggregate tendencies and associations as a basis for individual discrimination.

I think it's pretty funny that no matter how straightforward the methodological critiques of 90s-vintage twin studies are, they always elicit responses as if the critiques were metaphysical, rather than (for instance) deliberately excluding the dizygotic twin control group from MISTRA because it revealed the studies findings were just noise.

The truth is, for these kinds of studies, the whole enterprise might as well be metaphysical; people saying these kinds of things have formed a religious conviction about the heritability of behavioral traits, and their real objection is that science continues to be done on the topic at all. Ironic, given the frequency with which they complain that this science is suppressed.

(I too have a near-religious conviction about this subject, though in a different direction; I do not, however, pretend that conviction is itself a methodological critique!)

Which exact passage of my piece triggered this bizarre interpretation? What made you jump from "someone criticizes a 1990 paper in Science for withholding critical control group data" to "this person is subject to magical thinking"?

As it happens, I often run into trouble due to my conceptualist views on the foundations of mathematics (that is, I'm a hardcore physicalist & anti-Platonist cognitivist, which is quite rare among mathematicians), so I find your criticism particularly unfair.

In contemporary human populations living in typical modern environments, a large share (roughly half or more in adulthood) of the differences in IQ between individuals is associated with genetic differences.

The evidence is overwhelming in that direction:

Twin & family designs: h² ~0.4–0.8, often ~0.7–0.8 in adult samples like MISTRA.

Adoption: people resemble their biological relatives more than their adoptive relatives in IQ, despite strong environmental differences.

Molecular genetics: polygenic scores and GCTA show real, replicable genetic signal for intelligence.

What it does not mean is that:

1. IQ is fixed at birth in a way that cannot be influenced by environment.

2. IQ differences justify any sort of discrimination or moral ranking.

Those two points are where people tend to clutch their pearls and panic. Just because we have noticed an uncomfortable truth does not mean that it is valid to use it in a discriminatory manner; the issue becomes that people will inevitably do so, thus those "in power" cripple the theory in the crib so as to avoid the fearful and uncomfortable implications.

For full clarity: I didn't flag your comment (at least, not intentionally, as I never even thought about doing that)

Now the substance:

"The alleged “suppressed control group” does not turn the result into “no heritability”."

=> Of course not, did anyone claim there was no heritability? But

1/ It's not "alleged", it's printed black on white in the paper.

2/ There is no excuse for suppressing control group data (it's like suppressing the placebo arm of a drug study).

3/ It does turn the result into "junk", and it does establish a definite case of scientific malpractice among people arguing that IQ heritability is 0.70.

As for later analyses, they weren't the topic of my post, but that doesn't mean they're casher.

Smart people tend to have gifted children, this is, unfortunately, factual.

Being smart is a poor proxy for success, you have to have access to the right knowledge and resources at the right time, and often the “smart” move is short term.

It could be argued (and often is), that the reason intelligence is strongly predicted based on heritage (though of course: not guaranteed) is due to your parents interactions with you as a child.

like many things, I’m not qualified to answer.

Sufficed to say that some of the smartest people I personally know are more limited in their success than some of the confident yet much less intelligent people I know: who seem to be, in general, much more successful.

> It’s not that surprising that many successful people seem to be strong fans of heritability, or more broadly, of the idea that metrics like IQ point to some sort of “universal independent” metric of value. To do otherwise requires living one’s life in cognitive dissonance; how could they be worthy of such riches while others struggle to just pay the bills?

It doesn't require any such thing. It doesn't take a super genius to understand the roles of chance and circumstance have on one's lot in life.

> the idea that metrics like IQ point to some sort of “universal independent” metric of value

What’s particularly annoying is that this can so easily be proven false. No amount of heritable IQ points are gonna help if you’re born to a starving family escaping genocide in Sudan.

But also, “IQ” has been a useful characteristic for a few decades to maybe a few centuries at most. For most of human existence, pure physical strength was likely much more useful than the ability to do abstract thinking.

So even if we accept all these easily disproven ideas, it’s still clearly evident that the fact that they’re in a position to benefit from these supposedly heritable traits is only because they happen to be extremely fortunate to be born in a time and place where these traits are actually valuable.

Several 9s of humans that ever existed would have found an Einstein level of genius worthless

> It’s not that surprising that many successful people seem to be strong fans of heritability, or more broadly, of the idea that metrics like IQ point to some sort of “universal independent” metric of value. To do otherwise requires living one’s life in cognitive dissonance; how could they be worthy of such riches while others struggle to just pay the bills? Surely success and intelligence is just an inborn thing, and thus inevitable and unchangeable. There’s nothing they can do, and it was always going to end up that way. Inevitability erases any feelings or guilt or shame.

I've never understood the idea that winning the genetic lottery somehow makes a person more "deserving" or "worthy" than another. To me, the whole idea of "meritocracy" is a moral abomination.

> It’s not that surprising that many successful people seem to be strong fans of heritability, or more broadly, of the idea that metrics like IQ point to some sort of “universal independent” metric of value.

I agree that that could be a motivation. But I would also say that having a motivation for a given result doesn't preclude that result. That is generally true in science.

I'm not an expert. But there seems to be fairly overwhelming evidence that some significant amount of intelligence is heritable. That IQ is a reasonably good measure (or proxy) for intelligence. And that IQ correlates well with a lot of other things like educational attainment and income.

That doesn't mean that your genes determine your future. But it does suggest that some people are "born" in a better position than others -- aside from their socio-economic status.

This shouldn't be controversial. Height is well-known to be heritable. Being tall gives you a better shot at making the NBA. The same is true for many other things.

There's also the problem that many "IQ" tests are heavily biased toward a Western, Anglophone education.

Being able to correctly say, for instance, which of four options a "façade" is most like has nothing to do with inherent intelligence; it has to do with whether you were taught the meaning of the word "façade", and the four (often somewhat uncommon) words presented as the choices. The same is true for any of the questions that are, even in part, testing your vocabulary.

Presenting such a test to two people, one of whom was educated at a private school in New York City, and came from a family that highly valued reading and education, and the other at a public school in rural upstate NY, and came from a family that thought it was "too woke" for boys to read books, it is painfully obvious which one will do better, regardless of any genetic factors.

> The question never was about whether or not genetic differences contribute to the spread of intellectual talent—they obviously do. The question always was about the “interesting place” Paul Graham talked about, the meaningful space between genetic potential and actual achievement, and whether or not it really existed. And, at 30% or 50%, this place surely exists.

In the exact same boat here.

Also count me in for disallowing childless people in many of societies political leadership positions. A position I would have found ludicrous 10 years ago. ;)

It’s just not possible to understand the best way forward for the species if you haven’t procreated.

> I trust my own observations and my conclusion

Why would you decide to hold a position strongly based on a minuscule and extremely biased sample set and reject even considering data and studies outside of your immediate experience?

Unless you’re afraid your conclusion might be challenged? Wouldn’t it be interesting either way? Either to find out that your children are typical or to find out that you and they are special in some way?

I understand many people are not interested in or curious about science, but don’t understand people who are both disinterested but also strongly hold particular positions on scientific questions.

People in general don't like being told they're wrong. This means that arguments that challenge status quo get suppressed. Science isn't magically immune to this just because you add a label "it's scientifically proven, bro!". Therefore, a lot of research on controversial topics can be safely discarded simply because people doing the research have lots of reasons to be biased. This is especially relevant in social sciences, because it's a bottomless pit of controversial topics, and has almost zero possibilities of repeating an experiment. Sure, we have 50 years of research proving that children are blank states, but it's important to remember that eugenics were deeply rooted in science too. It's just that different societal attitudes expected scientists to come up with different scientific results, so they did. Think of a society-wide version of corporate-sponsored research centers that are expected to massage the results until they match the desired outcome.

Another thing is that sometimes it might be beneficial to believe something that isn't true. If you knew for a fact that tomorrow 99% of population will suffer extremely painful death then from the point of view of an individual the correct move would be to commit painless suicide, but the survival of humanity relies on everyone believing they'll be all fine. This is obviously a caricatural example, but there are lots of such lies that keep the society going, and "we're all equal" is just one of them.

Personally, I find it extremely difficult to believe that we'd be born equal, because evolution works only if some individuals are better than others, and I strongly believe that evolution is a thing.

The belief system opposing "very strong heritability of intelligence" isn't "blank-slatism". Plenty of researchers who believe there are only weak connections between genes and intelligence also reject the strong-form blank slate hypothesis, to the point where, when I see people bring "blank slate" into a conversation, I immediately have to convince myself that they're not just trying to stop the conversation.

The comment you wrote really isn't a response to anything this article said.

My father was told all his life that he had the same character than his mother, and until I was 10, I was told I showed the same character as my grandfather (I still have his walking cadence and posture).

My father is adopted.

The article only asks the question of scientists have data to conclude that IQ is inherited. The author is only saying that there are so many problems with the data, that correlation without causation is possible.

You hear something about it if you run the article through a screen reader. :-)

Another strawman from someone who DNRTFA.

No one here, including the author linked, is suggesting what you propose.

Then be surprised, because we have comparative numbers for basic phenotypical traits like height and complex behavioral phenotypes like intelligence and educational achievement, and they do not line up. You're not supposed to use that razor to blind yourself.

IQ is not "mostly random". It's highly correlated with the quality of your education. Kind of like how height is highly correlated with childhood nutrition, and sporting ability is highly correlated with practicing sports.

The article is about how hard it is to tease these confounding factors apart. A highly intelligent parent is likely to prioritize their children's education. A hypothetical study that concludes "intelligent parents raise intelligent children" could easily be construed in favor of either the heriditarian or blank-slatist perspective.

Of course IQ is heritable. Why do you pretend to see blank slatism where there is none?