9 ms·
Twins reared apart do not exist
- tptacek 11mo ago(David Bessis is a fan favorite here, and Paul Graham makes an appearance.) Related, from last year: https://news.ycombinator.com/item?id=42200209 https://news.ycombinator.com/item?id=42200209
- bell-cot 11mo agoIn my mind, the bigger issue with twin studies trying to show that (say) IQ is highly genetic is that humans do not reproduce by cloning. And regression toward the mean is very much a thing for heritable traits. In other words - Junior should not be presumed to be smarter, fitter, more deserving, or destined for success, just because his parents did well. No matter how attractive that conclusion might sound, to people who consider themselves to be the "better" sort.
- DaveZale 11mo agoiq 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
- tptacek 11mo agoWhoah, no, there is definitely not a consensus for 50-80%, and most of what's being published now refutes the 80% end of that range --- the 80% estimates come from underpowered studies like MISTRA that improperly assumed independent environments for twins reared apart.
- DaveZale 11mo agookay, I saw the paper saying 500 genes are involved. So does a single number for iq mean anything? Does the number depend upon what is tested?
- tptacek 11mo agoWe have essentially no mechanistic understanding of gene/intelligence interactions. Rather, we have cohorts of people tagged with traits (educational achievement, tested IQ, height, etc), all sequenced, and then we can run correlation surveys across all their genomes to identify correlations between alleles and traits. When you do that, you get 10-30% heritability numbers; the gap between that and the range for MZ/DZ twin studies (the 50-80% you often see) is "the missing heritability problem".
- DaveZale 11mo agodoes epigenetics play a significant role? Within one lifetime or several generations?
- tptacek 11mo agoWay above my pay grade. Probably! Or probably not?
- red75prime 11mo ago
- dragonwriter 11mo agoThat 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.
- bell-cot 11mo agoYes-ish. Hence my use of "issue". The problem is most people's zealous desire to read socially self-serving conclusions into any data they can find on such subjects. And when they really like the Q.E.D. punchline, humans have very low standards for the "logic" used to reach it.
- ionwake 11mo ago"most people's zealous desire to read socially self-serving conclusions into any data they can find" what planet are you living on? also your comment was completely incorrect and missing the entire point of twin studies.
- jagoff 11mo ago[flagged]
- tptacek 11mo agoI 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!)
- jagoff 11mo agoI, and clearly many others based directly on your comment assertion, clearly disagree. Whether or not you like MISTRA, “they left out the non-identical twins” is a side issue, and the broader evidence that IQ is substantially heritable is extremely strong. Even if DZA were excluded, MZA alone provides a solid heritability estimate. The DZA sample was small and noisy, and MISTRA uses other twin and family data. Plus, meta-analyses confirm high IQ heritability, typically 0.5-0.8; Later structural-equation models applied to the full MISTRA cognitive dataset (MZA + DZA) estimated the heritability of general intelligence around 0.77, essentially the same ballpark as the original simple estimate. laplab.ucsd.edu. Intelligence is highly heritable, potentially reaching 80% in adulthood, supported by further studies like the Haworth et al. meta-analysis, showing age-related increases in heritability. Strong evidence for polygenic and SNP heritability is shown from Plomin & von Stumm's 2018 research, showing how polygenic scores predict general intelligence. Adoption studies further support the genetic influence, as adoptive siblings show weaker correlations compared to biological ones. Environment is certainly NOT outweighed entirely or beyond merit, but evidence clearly shows the "uncomfortable" result having strong support despite desperate attempts to debunk. In short; the op's story only works if including the DZA data actually drags the heritability estimate down into trivial territory. It does not. Later analyses of the MISTRA sample that explicitly include both MZA and DZA twins and use full structural-equation models estimate heritability of general intelligence (g) at about 0.77 in adults. https://laplab.ucsd.edu/articles2/Lee2010.pdf https://laplab.ucsd.edu/articles2/Lee2010.pdf That is higher, if anything, than the original approximate 0.70. In other words: The alleged “suppressed control group” does not turn the result into “no heritability”. The more sophisticated models using that very same DZA data still say “IQ differences in this adult sample are heavily genetic.” You just don't like this data, and don't want to accept it, because of the implications.
- deleted 11mo ago[deleted]
- jagoff 11mo ago[flagged]
- jagoff 11mo ago[flagged]
- tptacek 11mo agoThis literally doesn't say anything. It's a lot of words, but you've managed to reproduce the exact position the author of the article has. For those wondering what the trick was here: this comment forwards the 40-80% h2 numbers from twin studies, then says "molecular genetics show real, replicable genetic signal for intelligence", rather than showing the 10-30% h2 numbers those studies generate. It's practically nobody's position that there's no linkage between genetics and intelligence (that would be weird indeed), but it's important for this comment for you to believe that's the counterargument --- otherwise the comment doesn't make sense.
- andriesm 11mo agoThe real question is whether genetics is a substantial or a negligible influence on intelligence (or proxy measures like IQ). If genetics is less than 5 percent I would consider that something worth ignoring. If it is 10 percent it is substantial enough to make a difference at the extremes. If it is 20 percent that is real serious business. Anything higher means we should really sit up and take notice of this fact.
- skybrian 11mo agoWhy is that? Odd that the article claims otherwise: > 50% may sound like a solid heritability figure, but the associated correlation is rather modest.
- AnthonyMouse 11mo agoAnother issue is, what is it that you're trying to use it for? If you're arguing against a eugenicist then it's not just about the percentage, in that case you have to distinguish between genetic and heritable. Suppose that there are some set of four genes that, in just the right combination, are worth 5 IQ points. That's, by definition, genetic, but it won't have a strong correlation with heritability because every kid has four chances to get the combination wrong. Or, if the combination does something bad, four chances to get it right even if their parents didn't. So past performance is no guarantee of future results. By contrast, if you're trying to decide whether to allocate more resources to kids who already show promise, you care about the individual's natural potential rather than the statistical probability that it will be similar to their parents, so it doesn't matter what was more likely, it matters what actually happened. And by the point you're performing the evaluation, you can't go back in time and change things like the prenatal environment for someone who is already born, so in that context those things belong in the "nature" column and "nurture" only gets the things you could still affect.
- keiferski 11mo agoIt’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. Ironically IQ is also popular amongst people in a very different situation, that is, people that aren’t actually successful “in the real world” but score highly on aptitude tests. Their high scores serve as an identity pedestal to look down upon others and set themselves apart from the masses. This seems to be the primary demographic of IQ-requirement organizations. Now of course there are scientific studies on this topic, but let’s not pretend like this is a cultural meme because writers like Cremieux are just tirelessly searching for the truth, no matter what ideological consequences that may have. They quite obviously have a viewpoint first and then work backwards from there to justify it. As a meta comment: the whole obsession with IQ as a kind of unchanging permanent quality seems very much out of tune with how biological systems actually work, and is kind of a remnant of a Platonic worldview. That is, it’s not dynamic/process/system oriented in the way that nature actually works, but instead is in search of eternal qualities á la Plato.
- dijit 11mo agoSmart 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.
- Etheryte 11mo ago
- andy_ppp 11mo agoYou can see this type of thinking in the absolute certainty that the YC interview process finds every billion dollar company that apply. I’m unconvinced and think a lot of the people who joined those early batches and made so many great companies were changed by their environment not by being filtered for credentials or genetic gifts.
- andai 11mo agoRe: Von Neumann IQ Pill https://archive.ph/6tOQF https://archive.ph/6tOQF
- pendenthistory 11mo agoI trust my own observations and my conclusion is that heritability is very strong. This is not a view that was imparted on me, quite the opposite. Growing up in a western country I was led to believe we are all blank slates, and I truly believed it. Once I started spending more time around the opposite sex some doubts started to emerge. Once I became a parent it became very apparent that this ideology had no basis in reality. Kids come with a personality, batteries included, and it's very easy to point out even individual behaviors that originate with either parent. Boys and girls are also very different on average. It's insane that we have somehow convinced ourselves that this is not the case, and I will surely be attacked by just pointing this out. I don't need twin studies to understand this basic fact, a fact that's been apparent to everyone throughout history, except for the past ~40 years in the west.
- lapcat 11mo ago> 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.
- lostmsu 11mo agoThe author of this piece totally ignored that heritability is only part of the genetic lottery.
- lapcat 11mo agoWhat do you mean?
- lostmsu 11mo agoThat heritability doesn't cover all genetic factors. E.g. out of 100% of IQ variation 50% might be inherited, but that doesn't say that the rest is nurture, right? It can still have a huge factor of genetic lottery. E.g. isn't heritability the mean of the genetic effects, but there's also the rest of the distribution (std. dev)?
- comrade1234 11mo agoWhen I was an undergrad (or maybe it was grad - it was a long time ago) we learned about the Minnesota twins study that attempted to find the strength of genetics in personality. The study developed new statistical techniques to measure this and can to the conclusion that genetics is very strong. But now you hear nothing about this study. I'm not sure if it's because the results are tainted by eugenics, or if the techniques they developed were wrong...
- tzs 11mo agoYou hear something about it if you run the article through a screen reader. :-)
- comrade1234 11mo ago[flagged]
- davidbessis 11mo agoWhat you call name-dropping is justified by the need to clarify the stakes and be transparent about where the criticism is coming from. If the article is too long for you & you're already familiar with the notion of heritability, you can go directly to the "The Dog Eat My Control Group" section near the end.
- IAmBroom 11mo agoSo, you admit you DNRTFA, and yet complain about what's not in it?
- tptacek 11mo agoI think you're going to find "I refused to read the article" is not a very effective persuasive strategy on HN. Especially when your opening bid is a restatement of what the article is about!
- sjducb 11mo agoIt seems surprising that IQ would not be heritable. Literally everything else is heritable. Height, skin colour, sporting ability, body weight, eye colour, cancer risk, most disease risk, beauty. Why would IQ be mostly random when other things are very heritable? Occums razor says pick the simplest hypothesis that explains the data. The onus is on the blank slate crew to find some good data to demonstrate that IQ is not mostly heritable.
- bloppe 11mo agoIQ 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.
- davidbessis 11mo agoOf course IQ is heritable to a certain degree. Why do you pretend to see blank slatism where there is none?
- IAmBroom 11mo agoAnother strawman from someone who DNRTFA. No one here, including the author linked, is suggesting what you propose.
- tptacek 11mo agoThen be surprised, because we have comparative numbers (across a variety of different methodologies) 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.