IQ differences of identical twins reared apart are influenced by education
sciencedirect.com
sciencedirect.com
It might be useful to look at any twin study through this lens; if we know for sure the genes are the same and nature is off the table, how much variance remains?
- Genetics (DNA seq)
- Epigentics (Histone acetylation, base methylation etc)
- Brain wiring from experiences
- Chemical impact from experiences, e.g. nutrition, toxins, sunlight, muscle dev etc etc.> - Chemical impact from experiences, e.g. nutrition, toxins, sunlight, muscle dev etc etc.
Are these not all part of the nurture / environment bucket? Or are we drawing a hard boundary between nurture (eg, parenting) and environment? (eg, lead in the pipes)
For example, epigentics is sort of both "nature" and "nurture", in that you can pick up these traits, and pass them on/get them passed on.
Heritable epigenetics is a nascent field. We have yet to get any real promising research showing it even occurs to a significant degree in human.
I would assume it's not a significant factor until we can find even some minimal evidence to suggest that it's an influence in humans. Even then, my guess is that the impact would be minimal. I know this is contrary to a lot of the "trauma passed down through epigenetics" narratives that are going around, but the actual science is in a very different place than the popular understanding of the topic.
Epigenetics is most definitely a factor in humans.
Heritable epigenetics is a different story. There is some early evidence suggesting that transgenerational epigenetic effects appear in humans, but it's very early. Some of the first claimed discoveries of transgenerational epigenetic inheritance in humans turned out to be mistakes by researchers. A lot of the theories about human transgenerational epigenetic inheritance revolve around exposure to famines and food crises, which is unfortunately complicated by the way food crises shape dietary behaviors and eating habits which are also passed down via tradition (not genetically).
The difficult part is that journalists often use "epigenetics" to refer to heritable epigenetics, and a lot of commenters make the same mistake.
Put simply, the common epigenetics between twins need not be held in common with the parents.
Sure, but that wouldn't be relevant to twin studies because both twins would be exposed to the same environment.
The pop culture discussion about heritable epigenetics tends to assume influence outside of in utero conditions or crossing multiple generations. It's where the "generational trauma is in your genes" idea came from.
I have three kids with two different women. All 3 are blonde-haired/blue-eyed. I have brown hair and green eyes, my ex has brown hair and blue eyes, and my spouse has blonde hair and blue eyes. Not as interesting I suppose. Yes, they're all my kids biologically. :)
I am curious about the influence on height by self-limited diets in children who are picky eaters. Is there some self-regulation process that decreases pickiness when nutritional status is at risk?
Oddly, denial of these other variables has become core to scientific racism (https://en.wikipedia.org/wiki/Scientific_racism). For example, a Danish white supremacist named Emil Kirkegaard went so far as to create a fake journal (https://en.wikipedia.org/wiki/OpenPsych) to publish flagrantly incorrect papers on IQ that try to deny these factors and paint the IQ of non-white countries as low, with the only explanation being their “inferior” race/genetics. In fact, he just recently wrote a new “paper” (https://openpsych.net/paper/85/) that has been widely retweeted by supremacists on X.
Scientific racism has always operated this way. When it wasn't fabricating evidence, it was cherry-picking or failing to account for environmental causes. It would be interesting to see how historical claims made in this context hold up (I would expect to see changes that negate the claims; something that comes to mind is that the Dutch were one of the shortest peoples in Europe, but later in the 19th century became one of the tallest).
> flagrantly incorrect papers on IQ that try to deny these factors and paint the IQ of non-white countries as low, with the only explanation being their “inferior” race/genetics
I think the more important point we need to remember is that even if we were to discover that some groups have a genetic predisposition for higher IQ (putting aside the controversial nature of IQ to begin with), those with predisposition for lower IQ are still human and thus still owed what is due by virtue of their basic human dignity. It's also possible that over time, adaptation would change this predisposition. Populations aren't static.
https://theinfinitesimal.substack.com/p/the-missing-heritabi...
In particular, see the third chart, "GREML-WGS heritability estimates," which shows that heritability for height is pretty much the same when they try to adjust for environment in different ways, while the estimates for IQ vary a lot.
Gusev seems convinced that some environmental effect is inflating heritability estimates for IQ that are based on twin studies.
Nature is not off of the table. We've just traded problems with calorie quantity to quality.
condition US prevalence
hypertension 49%
obesity 40%
metabolic syndrome 40%
prediabetes 38%
fatty liver disease 25%
diabetes 16%
coronary disease 5%
if we know for sure the genes are the same and nature is off the table, how much variance remains?
(I think it can't possibly be entirely off the table, since we have mechanistic understanding of some gene-mediated cognitive disabilities).
Incidence of undiagnosed digestive and sleep disorders, like celiac disease and sleep apnea, respectively. "Catch-up" growth occurs almost universally after treatment starts, which means that the growth trajectory was lower than the "genetic potential", and likely remains so for children who can't access treatment.
Multiply across any number of silent or untreated disorders, sensitivities, or insufficiencies.
Adult height also isn't 90% heritable in the US. It only reaches that high a percentage of heritability in studies involving closely-related populations. In which case, of course; in populations with low genetic and cultural diversity and moderate or high variability, small differences are magnified.
For example, check out this mess:
> “Unfortunately, there is one significant issue with the aforementioned data: schooling. Seeing as the majority of work to date includes only aggregate data, it is impossible to account. The first concerns small N: seeing as most publish studies only include a handful of TRA data, there is a lot of room for error and over.
Unfortunately, there is a largely unaccounted for confound in this aggregate data which may make generalized analysis questionable: schooling.”
This is not an ad-hominum, but does put into question the statistical training backgrounds of both of these authors to accurate assess the data.
This is true of virtually all university research. Statistics is far more nuanced than what a semester course can teach you. And the incentives to publish can cause bad actors to use poorly defined surveys or p hack or whatever.
This makes the awkward wording even more confusing. I don't understand how a professional author who appears to speak English very well would write so poorly and not follow up with edits.
FWIW I find this research to align on my thoughts about the IQ - IQ is not a constant but a function of multiple variables, where one of the variables is most likely an education.
For instance, I am pretty sure that drilling through the abstract mathematical and hard engineering problems to some extent during the high-school but much more during and after the University, develops your brain in such a way that you become not only more knowledgeable in terms of memorizing things but develops your brain so that it can reason about and anticipate things that you couldn't possibly do before.
The strange thing is that the corresponding author and the co-author appear to be english speakers, as far as I can tell. I googled the primary author and found a YouTube channel where someone by the same name speaks clearly about neuroscience. Maybe I'm looking at another person with the same name and middle initial who also happens to speak about neuroscience and brain development?
yet iq inheritability is only a bit lower, around 80%
IQ tests are far from perfect, but when the same test is administered to different groups under the same conditions it can be reasonable to draw some signal out of the differences between groups.
Generally in a study like this the people administering the test wouldn't even know which group each person belonged to.
It's common knowledge that IQ tests aren't perfect, but your linked paper doesn't debunk their usefulness in a study like this. Not unless the researchers unblinded themselves and offered one group a large reward, which would be a much bigger problem than the use of IQ tests.
There's likely no such thing, so your best bet is to conduct the tests under a variety of conditions and aggregate the results. This has been the case for IQ for almost a century.
This study found that adding or removing rewards for performing well can pretty dramatically impact performance.
"it is unclear to what extent the positive manifold reported in intelligence research since Spearman (1904) might be explained not through a shared component of intellectual capacity, but through a shared component of effort or time investment in testing tasks."
So, yes, we don't know, but the ways we don't know should also include "we don't know if iq testing is even measuring intelligence rather than stick-to-it-ness".
Also, NCBLA standardized testing has demonstrably ruined education in America.
Incorrect, IQ is a composite measure correlated with fluid reasoning, crystallized knowledge, working memory, processing speed, and spatial ability. It's true that you can't naively use IQ to compare two diverse groups, but you can correct for this with a large enough sample of any two groups. This idea that it's biased towards western culture or education is vastly overblown.
With IQ tests, the only thing you know that if 2 people fill it out and one of them scores higher, they have a higher IQ. Based on this you can sort people into a list by increasing IQ, but the standard distribution is implied not discovered.
This is like having a double-sided scale and a bunch of weights - you can similarly compare the weights to each other, and sometimes the arm of the scale will lean to the left, sometimes to the right, by a little or lot - you can postulate that the weights are normally distributed are normally distributed, but they are absolutely not required to be (I can choose them any way I like), so your assumption would be wrong. We know this because we have a direct, not just a comparative measure for weight.
I could make up an imaginary 'weight point' scale based on these comparisons, and say weights A is 5 WP heavier than B and C is also 5 WP heavier than A.
But A might be 100g, B might be 1g, and C might be 1kg.
This is what I think of when I see studies clamining the difference between 2 groups was 5 IQ points.
It's not nothing, but IQ is already a little squishy. No one's IQ is a single number. But the article also goes into problems with the study and other potential issues.
Basically, they're saying there is this pattern in the data as recorded, but there are multiple confounding factors and issues with collecting the data in the first place.
(It's also just fine if we disagree about this --- researchers do too!)
Even height and weight change throughout the day. People are typically taller and lighter in the morning than in the evening. Weight especially is variable, it can fluctuate up to 5 to 6 pounds.
If someone is 15 points above average, they are in 84th percentile, or in top 16%.
The smartest kids are smarter than ever before. They're absolutely rocking the house. The problem is that the "middle class has been gutted". Kids who were kinda smart, or kinda dumb, are now lumped in with kids who probably need Individual Education Plans (IEPs). This lowers the educational standard for almost all students - though of course the most well-off among us (educationally, rather than monetarily) are not only not suffering, they're thriving.
That is provably incorrect, as since Victorian times people lost around 14 to 23 IQ points on average. Notably, the corrected scores have continued on a downward trend for the past century.
People are not getting smarter, as recent events have shown. =3
Only if they’re wealthy or get extremely lucky and live near a randomly good school. By many metrics I was the smartest in my class, but my family had little money and lived in a rural area with a single underfunded school. I spent my days in class with kids that were still struggling to sound out “cat” in third grade. A few times a week I got to spend an hour in “gifted” class but that was mostly art projects, nothing that would help make up for the rest of the day being wasted.
The standard public Chinese education turns out better 90th percentile than our 99.9th percentile house rockers.
How to confirm this? Talk to PIs and others hiring researchers. Home grown talent doesn’t even come close. It’s very upsetting.
The dumbing down of education goes further than what you note, though. Think of classical education and the formation of the human person (I'm not talking about "Dead Poets Society" ersatz, but the real deal). Think of the principles behind the trivium and quadrivium. In the best case, we are producing superficially technically savvy barbarians. Schools are effectively savage factories, and universities are laughable and should be ashamed of calling themselves universities.
There's nothing logical about brains; they work on heuristics built on reflexes and associations. Logic is something we learn through physically interacting with the world, and from sitting in class. As you learn it, your thinking about other things gets better. When you read great old Chinese philosophers like Mozi struggling but managing to make good arguments without syllogism, it's a reminder that syllogism is something that is invented. It survives because of its unreasonable effectiveness compared to considering what the ancient heavenly kings had done.
It also helps your soul to remember that a lot of people you're arguing with have no idea what a logical argument looks like. They think that an argument is when you try to shut the other person up. It's not their fault, they just literally don't know. They're not arguing in bad faith, they don't know what good faith looks like because the educational system has failed them.
That's actually probably a very difficuly topic: cam we devise a test that measures intelligence irrespective of education (i.e. training)?
Presumably one could do similar identical twin studies on half-marathon race times and SAT test scores. Does no one bother with those, because widespread awareness of half-marathon training regimens and SAT prep courses would spoil the (desired) illusion of some "innate superiority of blood" being measured?
Yes, and some of those have been done: SAT scores correlate very strongly with IQ.
There are two different kinds of IQ tests: convergent and divergent. Convergent tests are more common and test either knowledge or pattern matching. These tests are called convergent because they are a center of truth and conformance to that truth is the measured performance criteria.
Divergent tests measure the individual's creativity and abstract reasoning. The source of truth is the quantity of diversity of results submitted by the participant.
The implicit success criteria for convergent testing is reading comprehension. A person with dyslexia, for example, will perform worse on these tests irrespective of their learning speed, learned knowledge, intellectual curiosity, or creativity. This is a form of bias. Other forms of bias include memorization of terms, such as SAT preparation.
To further complicate things these measures typically only account for academic intelligence. Other forms of intelligence include social intelligence, spatial intelligence, creativity, conscientiousness, and so forth. In the concept of multi-dimensional intelligence, which is what is actually addressed in practice in the real world after high school, academic intelligence alone has very little benefit. Its like height in basketball where after 6.5ft all other factors become more important for all participants.
No, it's what they were designed to do - help identify people that may need specialized help because issues like learning disabilities.
> To further complicate things these measures typically only account for academic intelligence. Other forms of intelligence include social intelligence, spatial intelligence, creativity, conscientiousness, and so forth.
The two major IQ tests (Stanford Binet and Wechsler) test visual-spatial reasoning, abstract reasoning, verbal and nonverbal reasoning, working memory, processing speed, inductive/deductive reasoning, attention, concentration, etc.
These tests, if properly administered (individually in person by a professional) work well for figuring out who in school needs extra attention or requires further evaluation. Their use beyond that is questionable.
When I listen to Steve Jobs, I hear someone who has very strong ability to sift through noise. So Jobs couldn’t see engineering in a new way like Elon does but Elon couldn’t do what Jobs did either.
Regarding Zuckerberg, from what I’ve read he is the Bill Gates type where he has the traditional variant of high IQ, aka raw hardware/horsepower but lower on creativity/imagination side.
So intelligence seems to have different shapes and sizes.
That didn't mean they were unintelligent. It meant that them trying to explain the flurry of ideas in their head was like me trying to type with mittens.
Of course, knuckleheads can also sound like that, but for different reasons. That kind of rambling doesn't imply that the speaker is a dumbass. It definitely doesn't guarantee that they're a genius.
I don't dispute the differences in intellectual capacity between people but IQ tests are like weight lifting contests between people who didn't train to lift weights.
I don't understand why the scientific community keeps using methods that are so flawed. Perhaps it's due to my own lack of information.
The only way I could see IQ tests being a valid measurement of intellectual capacity is if participants were brought to the same level of knowledge and skills, and then were made to train for the IQ test using the exact same means, and even then cultural and language barriers must be accounted for.
Even if these twins have an identical intellctual capacity and they both had the same exact education, and same exact grades, that still doesn't mean they applied and exercised their brains in the same way for the questions of the IQ tests.
IQ tests to measuring intellectual capacity (instead of knowledge level) are like polygraphs to mesasuring truthfulness in terms of accuracy.
For measuring strength, i stand by my earlier correlation with weight lifting. If two people can dead-lift 500lbs, I only know that both participants are have reached that level of strength. What I don't know is how much effort each participant put into getting to that level of strength, which would tell me their natural muscular capacity per effort. IQ tests deceptively seem like they tell you what someone's capacity for intellect is, but they only tell you where that person is right now. Maybe that person worked hard and the score is their max, maybe the person rarely applies their brain to demanding tasks and this is their mid-level capacity.
My point is,it isn't just education or just genetics, it is also personality, effort, motivation. For all I know,someone with double-digit IQ score can work out their brain for a year and hit genius level. Choice. Can a person choose to be a literal idiot and succeed? Certainly, people choose to be incurious and ignorant all the time. Women can body-build and be as strong as many regular men for example. But simply because of a hormone difference, they have to work out a lot more than men to reach the same level of muscular strength. And men who never work out can be as weak as women who never work out.
There is also the question of brain development. Maybe the effort you put has different effect depending on age. small efforts at a young age at applying your brain might have huge impacts, where as if you're a teenager or an adult, applying the same effort might yield less results.
I mean, personally, if I tired, if I ate too much, or too little,if didn't get enough sleep, if I am distracted by something, if I'm unprepared and thus second-guessing myself, these are some of the things that throw me off wildly when taking exams. I've seen huge differences by simply getting enough sleep and calories.
There is no way that asking the same set of questions to to large population (even with control populations in place) can account for all the presumptions of the test.
The reason I mention this is because I see the exact same problem with IQ tests. It emphasizes certain types of intelligences and ignores others. Human intelligence is extremely multidimensional and a single number is simply incapable of representing its overall quality. For example, there are people who score poorly in IQ, but are superhuman in remembering places and navigating their way around complex routes. Meanwhile, many high scoring ones become hopelessly lost, failing to institute or follow even simple mitigation strategies for that problem. There are situations where this determines whether you live or die, and your IQ score becomes worthless indicator of even your survival.
Overall, afaik, again, problem solving often needed in our society correlates with this: "general intelligence". When people say: "But there are many ways to approach a problem, many types of intelligence".
This very well may be, but data consistently shows that people having high IQ scores solve different problems better. So, contrary to popular belief, people having higher iq in general have better talent for languages, same with understanding others emotions and using it to your advantage ("emotional intelligence").
As for reframing an issue and solving it in a different way. This may be valid approach (to teach people etc). But IQ is also time-measured. If your new approach does not help you to solve previously unseen problems quickly, it is not noticably increase your intelligence.
Thus, we see consistently that people cannot really prepare for iq tests much. You only get a few points more if you prepare. Same difference as if you are sleep-deprived.
I'm not sure you're right about the trainability of tests, either.
We don't have any real evidence of "different types of intelligences". People with high IQ just tend to be better at all cognitive tasks than people with lower IQ. That's why it's considered a reasonably good measure of the g factor. People with higher IQ also have better memory recall.
While you're right that that IQ isn't the full story of a person's abilities, it's use for diagnosing people that may face challenges in a traditional learning environment well motivated. All of the examples you mention of people scoring poorly on IQ and facing challenges in school supports the use of IQ, it doesn't discount it.
That would imply that a person with a high IQ score is uniformly better at every task compared to a person of lower IQ. But that's absolutely not what's observed. People show better skill levels at different tasks. A person who's bad at math may instead be a natural-born singing sensation. This is why I said that a single number is just incapable of representing intelligence. The mathematical dimensionality of the quantity called intelligence is just too high. You'll need a bunch of numbers - a vector, at the minimum. And even that can't be used for comparing people's intelligence. It can only be used for assessing someone's suitability for a particular task. Basically, IQ score is a scalar that is used to represent a vector, discarding very important information in the process.
> People with higher IQ also have better memory recall.
There are people who recite entire Shakespeare plays without understanding a sentence in it. I have also seen people who recall long derivation sequences using Maxwell's equations exactly and score well on exams, without having any clue as to what the del (∇) operator even means in practice. Needless to say, they have difficulty adapting that information to a novel situation. Memory recall is just one aspect of intelligence. There are other cognitive skills required to make that memory useful. This again goes back to my previous conclusion. A single number is quite meaningless at best and utterly misleading at worst.
> it's use for diagnosing people that may face challenges in a traditional learning environment well motivated. All of the examples you mention of people scoring poorly on IQ and facing challenges in school supports the use of IQ, it doesn't discount it.
On the contrary, it just misleads the educators to the student's real abilities. It ignores and hides the atypical talents that students possess. All it can do is to predict if the student will do well or not in generalized education and standardized testing, because they follow the equally illogical concept of using standardized pedagogy on everyone, neglecting their uniqueness. So, even if we accept your claim that the IQ score predicts their performance in schools, it means that the score has the very narrow scope of testing someone's capability to learn under a standardized curriculum. That's far too narrow to be identified as an indicator of intelligence. And even after identifying the students who are going to struggle, IQ gives no clue as to how to remedy that. All it does is put a dunce label on these students who might otherwise have done better. It does more harm than good.
No it doesn't, that's why I said "tend to".
> On the contrary, it just misleads the educators to the student's real abilities. It ignores and hides the atypical talents that students possess.
The test simply doesn't measure atypical talents, so there's no "hiding". That's why I said the test is used to identify people who will face challenges. What happens next has nothing to do with the IQ test and everything to do with other methods of assessment that should be used. Every test has limitations that those applying the test should understand.
> That's far too narrow to be identified as an indicator of intelligence
That's why it's a (strong) correlation and not a strict equality.
Look, jumping height has been empirically demonstrated to be a good predictor of overall athletic performance, and you're coming here and saying that there exist some people without legs that can do more pull-ups than most people with legs. That's all well and good, but that doesn't somehow refute the idea that jumping height is a good predictor of overall athletic performance. It's just a complete red herring. If you happen to encounter someone without legs, then use a different test.
People with legs who don't exhibit good jumping heights but are very good at some specific athletic challenge could exist, but they tend to be good only at that specific challenge (and ones that are very, very similar). This is a completely different thing than the general factor of fitness, which is correlated with all sorts of physical abilities, just like general factor g is correlated with all sorts of cognitive abilities.
So this study has 87-52-25=10 data points? Am I reading this correctly? Quite the reach to conclude what the article claims, if so.
Authors plead innocence!
52 pairs similar schooling 25 of these had very similar schooling
Thus the math becomes "87-52=35". 35 data points. Not spectacularly high regardless.