Is the inequality of intelligence increasing?

“The inequality that matters,” as they used to say:

In a large US-representative adolescent sample, a Flynn Effect was found for IQs ≥ 130, and a negative effect for IQs ≤ 70

IQ changes also differed substantially by age group

A negative Flynn Effect for those with low intellectual ability suggests widening disparities in cognitive ability

Findings challenge the practice of generalizing IQ trends based on data from non-representative samples

So maybe yes — beware!

Here is the paper, via the excellent Kevin Lewis.

Comments

This is an expected byproduct of assortative mating. I expect a comment from Arnold Kling.

Or charles murray because he says what we are all thinking....

I’m surprised it took this long for mating to get assortative. Being married to someone with a vastly different IQ sounds awful. Did people in the past not have substantive conversations with their spouses?

I don't think Hugh Everett remembered that he had a wife after they were married.

Life previous to 1900 for vast majority of people was nasty brutish and short. Living with an unintelligent spouse was the least of their problems.

If you made it through childhood you'd likely make it to your 60s

The Flynn effect is about dumbing down the test.

"If you made it through childhood you'd likely make it to your 60s"

45% of people who were alive at age 10 were dead by age 60 in 1851 England. Which was almost certainly better than the world average.

https://ourworldindata.org/uploads/2017/08/Survival-Curves-UK.png

That was then, this is now. Since then we have developed vaccines, anti-biotics and better hygiene.

If you were the one teenager (out of 20) in your village with 130 IQ, then there was approximately one teenager with an IQ of 115 of the opposite sex and 5 over 100. For most of human history, that was the available dating/marriage pool.

Richard Herrnstein argued this in his influential 1971 article in The Atlantic Monthly: "I.Q."

It sounds plausible, but is it true?

Dalton Conley is currently testing this by taking DNA sampled from elderly Americans and their spouses, scoring for the educational attainment polygenic scores from Lee et al's huge 2018 study, and comparing it to scores for younger spouses.

So we might have a pretty good test of the Herrnstein Hypothesis of increased assortative mating published within a couple of years.

Conley's first try at this using primitive PGS early in this decade did not support the Herrnstein Hypothesis, but his next try using the latest PGS will be more informative. I look forward to hearing his results.

It's hard to argue with RatInACar's math... A narrow dating pool makes regression to the mean happen very quickly. Digging up the 1971 Herrnstein article right now.

Marriage has always been fairly assortative: most people married within their social class, broadly defined.
Mating? Well off men would philandering on the side generally with socially inferior women. That still happens, but with effective birth control and safe and legal abortion it doesn't tend to produce offspring.

"wealthy men would philander on the side," you don't think poor men and women cheated? you are a real class bigot. karl marx would be proud of you.

Mating has probably been assortative for a while. But on your comment within an SD doubt any gap is a huge deal, and most people lack intellectual interests where it would comes to light (the vast majority of high IQ college grads are still virtually without intellectual curiosity and mostly conform to the same set of beliefs).

Assortative mating, if it has increased, probably due to financial divergence by education and increases in sex parity in education, and work (more likely to meet). Likely not the benefits of spousal debates!

Even if you have no intellectual interests in common, you can get a good sense of someone’s IQ from how they handle certain situations, their judgment, skills, and even ability to banter. IQ affects a lot, and I think there are many benefits to having a spouse who has a similar or maybe slightly higher IQ than oneself!

Assortative mating probably has increased because people today get the chance to meet a lot more people before they settle down so they hold out for a better match. My parents married in their early 20s after they both only dated each other. I married in my early 30s to someone who is similar in IQ and most personality dimensions after several prior relationships with people who were less so. With the rise of online dating, people in their 20s now are even better able to find closer matches. The modern system seems better to me—many older couples seem to be miserable, constantly fighting, or simply indifferent to each other because of personality incompatibilities. Lots of people don’t find anyone today, but that still seems to be a better fate than being socially pressured into a marriage with someone very different as happened in the past.

I'm sure you can, but most people are around IQ 100, and it there are bigger personality incompatibilities and personality problems than an IQ difference, unless it's really serious, like matching above 115s with sub 85s and the like. For most people, character traits matter more, unless the gap is absolutely enormous. IQ matters more mostly indirectly, for reasons of income and so on.

On the broader question of whether more choice and mobility in personal relationships is better or worse, I usually tend to come down on the side of worse. Superior personality matching is probably not worth the downsides of increases in self-promoting personality traits, echo chambers, loneliness, etc. I would conjecture it is probably better for society as a whole and for individuals on aggregate for people to seek happiness in relationships they do not totally choose than to seek happiness by disposing of every relationship that does not meet their ideals. There's a happy medium of course. I think the older marriage system met this better than the modern system, but this is mainly speaking from my extended personal family experience.

I'm not sure assortation has increased at all really. Seems pretty high in traditional cultures with higher stratification and social barriers, even though it is not mediated much by individual choice. It would be interesting to see if couples who meet via online dating, or who marry later, tend to have happier relationships or more similar personalities, controlling for prior pre-relationship fixed characteristics (e.g. if people who marry late tend to be neurotics, their relative unhappiness doesn't really tell you much about what marrying late does for your happiness and so on). I would very much expect not to find the results you'd expect.

Well I have seen a study showing that couples who met online have significantly lower divorce rates (https://www.marketwatch.com/story/what-online-dating-could-do-to-divorce-rates-2017-10-16). But you might be able to get different results depending on which fixed effects you control for.

Maybe for >130.

For <70 this is more likely to be previously unviable children being born in the NICU and surviving. We’re solidly into disabled territory.

Mercy, friends: IQ is what IQ tests measure! Why must we even care?

I suppose it's the correlation with life outcomes

And neighbourhood outcomes. And national outcomes.

All right, all right, but aside from the sewers, the roads, the literacy, what have the Romans done for us?

All right, you get out of here, before I have at you!

Yeah, and temperature is what thermometers measure, and pressure is what barometers measure, .....

Yet, you cannot meaningfully measure the boiling point of water simply using a thermometer (though you can compare different boiling points, of course), as the boiling point changes due to the pressure as measured by a barometer. Single measures of complex situations tend to be worth very little, when they are not misleading.

Admittedly, maybe you have never done any cooking in Denver - where the boiling point of water, as measured by a thermometer is 95 °C or 203 °F - which is what the thermometer measures, even as the water is at a roiling boil.

So, it appears that the study crystalizes that puberty is a real problem for everyone - except the exceedingly intelligent.

Who, as we all are undoubtedly aware, are the people having as much sex as they want.

"...among a representative sample of American adolescents ages 13–18 (n = 10,073)"

The people that overdose by 25 YO starts around that age. There's people who uses drugs as hobby and there's people that loses 5 IQ points by age 18.

Is it really a "Flynn Effect" if we get to these levels of splitting where we are very unsure we are talking about a stable population that is in some sense the same over time?

I'd add that the thing with the "Flynn Effect" is that it's not always g-loaded. Things like Raven's Matrices that are meant to be pure, have the confound of being exposed to "Flynn Effect" secular increases that is uncorrelated with other subtest performance.

This effect may just tend to be about assortative mating and cultural isolation by people who are increasing exposed to such an effect, not a g-loaded effect.

Raven's matrices are a good example of something that looks culturally independent but in fact are partially testing whether one has been exposed to the concept of symmetry groups.

Good point. Drumpf's has trashed America's standing in the world and ruined our alliances with his lies. https://www.bbc.com/news/business-50633500

A hypothesis for the negative effect at low IQ is increasing abilities to save borderline infant mortality cases which nevertheless live with impairment from the trauma.

Per Wikipedia: Flynn in his 2007 book What Is Intelligence? further expanded on this theory. Environmental changes resulting from modernization—such as more intellectually demanding work, greater use of technology and smaller families—have meant that a much larger proportion of people are more accustomed to manipulating abstract concepts such as hypotheses and categories than a century ago. Substantial portions of IQ tests deal with these abilities. Flynn gives, as an example, the question 'What do a dog and a rabbit have in common?' A modern respondent might say they are both mammals (an abstract, or a priori answer, which depends only on the meanings of the words dog and rabbit), whereas someone a century ago might have said that humans catch rabbits with dogs (a concrete, or a posteriori answer, which depended on what happened to be the case at that time).

I often contrast useless skills with useful skills. What's a useless skill? Most white collar skills. What's a useful skill? Most blue collar skills. Yet, those with useless skills have on average higher IQs than those with useful skills, and they are paid a whole lot more for their skills (even though they are useless). Those with useless skills are often referred to as knowledge workers, implying that those with useful skills are, well, unknowledge workers. I don't doubt that the knowledge workers at Boeing who were responsible for the 737 Max have high IQs. I don't doubt that the knowledge workers at our largest banks who design creative ways to shuffle paper at great profit to the shufflers if not the unknowledge workers have high IQs. I don't doubt that the knowledge workers at Google and Facebook who design creative ways to mine data have high IQs. But in a crunch, I'll take the unknowledge workers with useful skills even if, or maybe because, they have lower IQs.

"...those with useless skills have on average higher IQs than those with useful skills, and they are paid a whole lot more for their skills (even though they are useless)."

Which makes them very useful skills indeed.

As Cowen points out in his prior blog post about measuring productivity, maybe we are measuring useful wrong, assuming as we do that someone who collects large sums for his skills must be providing something useful.

George Orwell made this point nearly 90 years ago in "Down & Out In Paris and London." Is that where Cowen got it?

It is a skill that is by virtual definition useful to the one who pays them for it. How else would you measure usefulness?

"I often contrast useless skills with useful skills. What's a useless skill? Most white collar skills. What's a useful skill? Most blue collar skills. ... and they are paid a whole lot more for their skills (even though they are useless). "

You're a Lawyer. Do you tell your clients that your skills are useless before or after they've paid you?

In a crunch, I'd take the unknowledge workers with useful skills. I am the first to acknowledge that I, a lawyer, have mostly useless skills, although my skills are highly valued by others with useless skills: we stand united in our highly compensated uselessness. I do believe in markets, but I've noticed that those who worship at the alter of markets don't actually believe in markets: they are the first to intervene in markets if markets, left alone, were to produce a result that would cause those with useless skills to suffer. Is it a market failure that those with useless skills have the most influence on policies that benefit those with useless skills the most? My saving grace is that I do have clients with useful skills. They understand that in a world that values useless skills they must have advice from someone with useless skills that are valued in said world.

"My saving grace is that I do have clients with useful skills. They understand that in a world that values useless skills they must have advice from someone with useless skills that are valued in said world."

I'm assuming from your answer to my question that you do indeed tell your clients you have useless skills. Are you then saying your clients are stupid, and pay you even though they realize you are useless? Or are you saying you are essentially a Con man, tricking your customers?

Let's say you're one of those useless criminal lawyers, and a plumber with very useful skills is arrested and charged with a murder he claims he did not commit, and he comes to you, prepared to pay your large sums of money to help him get out of jail and be acquitted of his charges. Would you tell him, no, you can't do that, because your skills are useless to him? Or would you make it clear that your skills are not merely useful, but essential to his life and freedom?

The basic idea is that if someone is willing to pay large sums of money for your skills, they must be useful to that person. Which is all that really counts, literally, when it comes to anything being useful.

It might be intelligent to start abbreviating "the excellent Kevin Lewis" to TEKL.

It is a natural result of useful applied knowledge being closely guarded in non tradable sector activity. But it is also a result of this activity still having to rely on other existing wealth in order to be economically - hence socially - feasible. A marketplace for time value could address the problem, because new time value markets would allow aggregate time value (alongside money) to serve as a conduit for knowledge dispersal, maintenance and preservation. Plenty of applied knowledge essentially worked this way for centuries before it was absorbed into 20th century institutions. Many individuals were once were able to take part in useful knowledge applications with others in the past without the expected monetary compensation of the present. Today, without the expected status of "appropriate" accreditation or workplace titles, it is difficult for them to do so. Hence their intellectual use potential atrophies.

Exactly. When Einstein thought up general and special relativity and Newton developed the calculus, they had time value markets from which they were able to purchase their ideas for mere pennies. The current system, with its niggardly hoarding of precious knowledge, is oppressive to people without access to intelligence markets.

I am beginning to doubt the claims of intelligence and genius being worth all that much,

Given that we have a President who claims to be

A Stable Genius.

My wife volunteers as a tutor for kids who are having problems in school. She says these are smart kids. What is common to most of them is that they are constantly moving. Apartment rents, moves to other neighborhoods. Their lives are not stable, some visit the dad on the week-end, they are in a different school every few years. Their learning is not tracked or corrected as they move from school to school: so, she has them work on math multiplication and division tables, get involved in reading, etc.

My problem with IQ measures or these statements is that we ignore the low hanging fruit, the things that can be changed with just a little effort and attention.

The cake is not baked.

Good anecdote. All the carefully done studies though say that interventions like this have very limited long term impact on intelligence measurements or life outcomes. Happy for you to prove me wrong by linking to the appropriate N Large study.

Give me the studies and post the links below.

Chris, I am still waiting for your carefully done studies. I have mine in hand and will post the links when you post yours.

Go ahead and post your carefully done studies on ineffectiveness of reading interventions.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3950413/#!po=1.92308

From the NIH.

There’s also a meta-analysis showing interventions work short term but fade out quickly. This is IQ, not reading or arithmetic.

As far as tutoring goes, I can’t help but think your wife is doing good work and helping kids get closer to their potential.

Ske[. The article you posted doesn't address intervention for reading skills or math. Did you read it? It is about general intelligence and cognitive interventions.

Am still waiting

I’m gonna be charitable and assume you opened the link without reading the rest of my comment.

Oh, I see now, you expressly disclaimed responding to information on the effects for intervention for on reading and math, but instead created a non-response by changing the subject to cognitive interventions to increase intelligence.

Well, I will have to tell my wife that her efforts will not increase intelligence, but will increase reading abilities and math skills.

But, those commercials say that if you take this pill that is based on jellyfish it will help your mind.

What I like about this site is how people ignore their own revealed preferences: how parents get help for their children in math with paid for tutoring, how parents help their kids read, or help them with homework.

All for naught because it won't help them, but don't tell the kids. Keep it a secret.

In summation:

I praised your wife for doing good works for the less privileged. I specifically said IQ, or indirectly G is unaffected. This is a fact, replicable by hundreds of studies.

I then expressed my admiration for your wife’s work in helping children reach their own potential.

Well, I again state my admiration for your wife’s efforts to help children reach their potential. She’s doing great work and is worthy of admiration and respect!

I’m all in favor of paid tutoring and free materials like my home, NYC does for students.

Free tutoring! Free books! We agree! Unfortunately, we disagree on the outcomes.

The poorest demographic is dominating admissions to the top schools here. And now the poorest people will be locked out because of their skin color.

So...to be clear. Democrats want the poorest demographic to be shut out from high performing schools because there’s too many poor Asians represented at public schools.

You can be as polite as you wish, but you have shifted the argument to intelligence, and not the effectiveness of reading and mathematical interventions.

Do you really disagree on the outcomes of reading and math interventions?

And, what is the point on shifting the discussion to Asians?

Bringing everything back into focus again: it is not about changes in intelligence, it IS about the effectiveness of intervention for math and reading.

And, again, the challenge put to Chris, and now to you, is list the studies that show reading and math interventions are ineffective. Post the links to the studies below, and I will post my links to studies.

Well I would have thought the onus was on you for making the claim in the first place to justify your case, but whatever, Scott Alexander, as usual, does a great job of discussing all the relevant evidence here about the impact of teachers;

https://slatestarcodex.com/2016/05/19/teachers-much-more-than-you-wanted-to-know/

TLDR: yes good teachers can improve in-year grades, but long term impact on things that matter (wages etc) is small.

It just might be that other factors are important -- Self-discipline, doggedness and having mentors to imitation, for starters. If you haven't seen some of your less talented school peers perform way beyond expectations and some of the brightest ones failing to achieve their "potential," you haven't been paying attention.

I like the idea of schools that bring out the best in students instead of sorting them by presumed g-scores. Reading and math skills, like unfamiliar languages and music, tend to reward practice and more practice.

In addition, there is that old bugaboo: Regression to the mean. It's real.

"TLDR: yes good teachers can improve in-year grades, but long term impact on things that matter (wages etc) is small."

I feel like the two of you are talking past each other.

Yes, the research says that good teachers don't have much of a long term effect above the current median teacher.

However, Bill's point is still correct.

"she has them work on math multiplication and division tables, get involved in reading, etc ... we ignore the low hanging fruit"

Teaching to our current standards almost certainly has a large effect on wages and productivity. There's plenty of evidence to indicate being able to read, write and do basic arithmetic are extremely valuable skills that can reliably be taught to a large percentage of children. Though it doesn't necessarily require a "good" teacher to teach the basics.

So yes Bill, teaching the fundamentals is low hanging fruit and worthwhile.

And yes Chris, the current research says that, good teachers don't seem to matter since even an average teacher can teach the fundamentals.

Has anyone studied this potential phenomenon for physical capability? It seems a similar bifurcation has happened there; top athletes are bigger, faster, stronger in almost any measurable way. And yet the overall population has higher obesity levels, flattening life expectancy, etc.

If the above is true for physical capabilities, then it doesn't seem much of a stretch to think that other human traits could/would have seen a similar split?

There is a story, [perhaps an urban legend, that pro athletes are born in similar parts of the year. They end up as the biggest kids in their grade, "do good in sports" and so pursue those skills.

Perhaps there is a flip side? Were nerds the youngest in their grade, physically less able, and so directed to bookish pursuits?

I've heard of this, and could be part of the explanation (if this split is indeed true).

Intuitively, I've long thought the 'reach' of information that has been attributed to concentration of economic success could/should also apply to many of these other areas. e.g. If you're motivated to become an athlete, it is so much easier today to learn how to eat, train, etc. Likewise, it is easier to be smarter younger than in the past. Or if you have a marketable skill, you can use it across a much bigger marketplace. Or if you're a company, it is easier to ID the ways that you need to change to....you get the idea.

What I haven't seen (outside of some nods towards it in this blog) is a holistic, comprehensive set of studies that examine this quantitatively across these different areas. so I'm left with my conjecture.

+1
'tis the Age of the Infovore. Average is Over.

Boy, did anyone else click on "Get rights and content?" That "I would like to..." drop-down list is a doozy. It's probably worthy of an MR topic just by itself. Surely 23 "modes of intellectual use" for a paper written to expand public knowledge is a bit absurd.

Anyway, I don't see how anyone can attempt an intelligent reply without seeing the graphs, the actual change in distribution.

A paper whose content was almost certainly produced with public funds.

Elsevier is a racket.

Was the standing assumption of this post that our remote ancestors lived in a golden era of "intelligence equality" from which civilization's advent has hurled human intelligence (or the myth of "intellectual egalitarianism") into the abyss?

--or was the working assumption that the advent of civilization and modernity were contributing to the equalization of intelligence (is anyone daring to quote Howard Gardner?) up to some unspecified point, after which egalitarian gains in human intelligence somehow collapsed along the way?

Nature itself may no longer favor our adaptive usurpations of intelligence, which helps explain the rise of Zika and other dread communicable neuropathic diseases. (Why do Americans today hear far less about Zika than we were hearing from media/entertainment channels only two or three years ago? Too scary for Americans to contemplate? Comparative analyses of capitalist/market responses versus socialist/centrally planned responses to Zika could tell us something about human adaptability, surely. Separately, a publicized and well-documented examination of how Zika's advent is changing calculations of contemporary eugenicists and birth control advocates might be salutary.)

Nature isn't a conscious entity sitting atound plotting in her laboratory how to screw us humans. Zika is nothing but an evolutionary accident, not something deliberate.

--in which case intelligence itself is just as much an evolutionary accident, no? (Do check out the literature: I've read numerous accounts which do seem to attribute reflective consciousness to evolutionary processes: Tyler Cowen himself seems pleased to attribute cognitive powers to the ideological processes of fabled "progress".)

Cf. "Intellectual: one who deems hypertrophy of the mind just compensation for constipation of the soul". (Psychic constipation left unchecked commonly leads to cognitive constipation, which is never relieved simply by logorrhea.)

If humanity has thoughtlessly unleashed Technogenic Climate Change as the case seems to be developing , "intelligence" may yet show just how maladaptive it can be for the survival of all terrestrial life.

In individual cases the mutations that produce either exceptional intelligence or defective intelligence are accidents, yes.

Can someone please explain to me why we use the term "IQ" instead of test score, or academic outcome, or something else that more clearly indicates that this is not just some immutable genetic endowment? The very notion of a Flynn effect tells us these things do change over time, which is clearly the product of better nutrition, education, etc., not that we are somehow evolving as a species to be smarter within a single generation. I find the obsession with "IQ" troubling and indicative of a clear bias around wanting to believe this about genetics.

For sure, and just to throw one out there, as the attention economy evolves, attention that generates high test scores may expand or contract in different childhood cliques.

A kid that doesn't do homework, but is on his phone all day, is certainly prepared differently for life, and we probably don't know what that really means.

A good way to think of it is nature sets the height of the bar, nurture gets you over it.

We don't actually believe that education generates intelligence. If we did, then we'd just put the Ivy League in charge of the Global Education Project and have them start Ivy Leagues all over the planet. A million Harvards would bloom and everybody would be as smart as Robin Hanson.

*response to JL

But the Flynn effect indicates there is no way to really know this unobservable bar so talking about this in terms of "intelligence" clearly biases the conversation toward assuming it mostly nature. We simply don't know the interaction effects.

Obviously education generates "intelligence". A 20-year old who did not attend a single day of school/instruction would likely score precisely "zero" on a general aptitude test. If you can't read you won't be able to access the test. Yes there are diminishing returns to education over time but that's a separate argument.

I stand by the statement that we should not be talking about IQ or "intelligence", or at the very least heavily qualify these things as conditional on education and other inputs throughout life.

IQ tests don’t rely on schooling. Nor literacy.

Education does not create intelligence. There are tens and tens of millions of educated Americans who score lower than Chinese illiterate peasants.

I’ve never understood the gut reaction to denying one of the only replicable conclusions from psychology.

Liberals (and everyone else) need to decouple intelligence from moral worth. G exists, and current twin studies peg G at about 86% genetics.

G has no moral valence. It just is what it is.

"Liberals (and everyone else) need to decouple intelligence from moral worth."

That won't happen any time soon.

Question, would income affect cognitive abilities? IE, if you are poor, stressed to the max, and struggling would that reflect in lower IQ scores on test? I wasn't sure where the research was on that?

No, not really. The Bell Curve covers this in its second section. They go through dozens of statistical comparisons using the National Longitudinal Survey of Youth, where IQ results from childhood and early adulthood are available, as well as parental socio-economic status, a composite of income, job prestige, and years of education.

They tried innumerable variations, which are documented in the footnotes.

Online can resourceful human beings find a number of videos documenting slime mold problem solving (maze navigation).

Some studies suggest that slime mold problem solving for maze navigation exceeds the abilities of many human subjects through age four.

How can this paper (or the commenters here) not address a racial component to this?

For IQ 130, the proportion will be overwhelmingly white, Asian, and Jewish, and disproportionately male.

Now, now,none of that kind of talk here, don't you know that talent is evenly distributed through populations all around the world? I'm assured that this is so by the best people.

Okay, I had also included this in my original comment. Not sure why it didn't make it in:

"For IQ < 70, the proportion will be overwhelmingly black and Hispanic, and disproportionately male."

Factoring in race is important since it helps hone in on an explanation of the cause, with the most parsimonious one being changing demographics resulting from immigration.

Intellectual disability is orthogonal to race, with the exception of autism which is actually higher in white populations.

So...no. Immigration would if anything have the opposite effect.

And around the time of the First World War, when this social Darwinist garbage along with its measurement became en vogue, Jews in the US were the biggest losers in the US IQ sweepstakes! They are certainly not losers today.

If you can't measure what you want to measure, measure something else, anyway.

Blacks have IQ scores falling somewhere between 85 and 90. Assuming an IQ standard deviation of 15, translates to between 9% and 15% of blacks having an IQ less than 70.

Hispanics have IQ scores falling the low 90's. For Hispanics (assuming at std.dev = 15), between 5% - 7% fall below 70.

Allowing more people into the country with the IQ characteristics above will produce greater variance in the native Bell curve, which naively assumes a mean of 100. Along those lines, the US is going from a society that broadly required one bell curve for capturing societal IQ, to one where 3-4 curves (with different means between 90 - 105) are needed. The most obvious place this will show up is the tails, +/- 2 standard deviations.

To not account for changing racial composition at the low and high-end of IQ bell curves is dishonest social science, plain and simple.

I think "dishonest social science" is redundant.

This. Let's go back to Economics Stats Bootcamp.

Suppose you have one normal distribution with a mean of 100. Then add another smaller population distribution with a mean of 93, and another population with a mean of 107. If you try modeling them all with one distribution, you get a seemingly fat-tailed distribution, with the same overall mean.

Not saying this causes the increased cognitive inequality or that genetics drives intelligence, but if you look at the fastest-growing immigrant populations -- Hispanics (IQ ~ 93) and East Asians (IQ ~ 107) -- it explains it fairly succinctly, to the point, it should be on the short list of candidate hypotheses.

What is tiring about the posts above is that they really don't discuss more recent works on this subject and how it always turns to race.

Unfortunately, I have lent this book to another person, but there is an excellent chapter on this subject (IQ, environment, networks), in the new book by Stanford Econ Prof. Matthew O. Jackson.: The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviors

Of course it turns to race.

IQ is the mystical woo that mediocre people cling to in the vain hope of believing themselves a part of some aristocracy of birth.

Intelligence is largely hereditary. It's a valuable trait, which means evolution will select for it. Consistent with this, people marry within 5 below to 5 above IQ points of each other.

The tabula rasa theory of human development is back there with phlogiston and the crystal spheres.

Creationists don't believe in evolution despite the mounds of evidence and anti-IQers don't believe in hereditary intelligence despite the mounds of evidence.

I'm dubious about "intelligence is largely hereditary". Even discounting the environmental factors, there's the reality of spontaneous mutation which is much more common than people think. Geniuses, and at the opposite extreme, people of defective mental ability, are likely just to be the results of genetic accidents, not of parental endowment.

Some people will have more and better grey matter than others, like every other bit of physical material in your body. Otherwise evolution wouldn't even be a phenomenon.

It's ironic that people who would laugh a Creationist out of the room think human evolution stopped 100,000 years ago and only happens from the neck down.

Adopted twin studies show fairly unequivocally that intelligence is largely nature, not nurture, in the real world. Somewhere, between 60% to 80% of an adult's intelligence, can be explained by the parents' intelligence, regardless of socioeconomic upbringing.

Granted, it’s not the laboratory-based smoking gun, which would be a link to specific genetic combinations.

https://medicine.jrank.org/pages/2465/Intelligence-Family-Twin-Adoption-Studies.html

But obviously, evolution HASN'T selected for it, since various cultures throughout human history have risen up, only to collapse; Persia, Egypt, Rome, Byzantium, China, MesoAmerica and Europe have all taken pride of place in human accomplishment, and all collapsed one way or the other.

If evolution were selecting for inherited intelligence some sort of pattern would have emerged, don't you think?

Yes. Human progress from hominid to Neolithic Man to the Bronze Age and beyond. Obviously things like disease, famine, violence, hubris, etc. happen too.

If evolution was selecting for intelligence, wouldn't a super intelligent strain of humans achieve enduring dominance?

Where are they?

The Trump Administration, duh

Diminishing returns. Height is an advantage, but evolution doesn't select for ten feet tall humans.

Evolution is also fluid and neutral. In an environment where physical strength is more advantageous than abstract thinking, you'll get less Bill Gates and more Mark Rippetoe (just to pull some names out of the hat). But intelligence seems to be evolution's winner. If you're still an actual hunter-gatherer, it's only because the more intelligent farmers have agreed to keep you in a human zoo.

Since this is MR, I assume you have this generally Whiggish outlook on everything including evolution, where we continually evolve to Utopia, and you apply that model to everything. But that's not really how it works.

Humans are themselves the superintelligent strain that nature has selected for. And continues to select for, which is what accounts for the rise of civilization and our incredible technological advances over the last few millennia.

Is there a study on IQ and hotness? I'd think that might matter also.

"Is there a study on IQ and hotness?"

There have been numerous attempts to complete such a study, but the researchers keep getting distracted...

If you are a guy, then yes, since intelligence is strongly correlated with height.

Found an unpaywalled copy and 'redd it'. Very interesting. My immediate sense is that the spread between the high-iq and low-iq increases as more years of education accumulate. So my immediate off-the-cuff possible interpretation is education helps wire up IQ into later adolescence (past around age 15, puberty?) longer for those with higher IQ's to begin with. Diminishing returns to education set in earlier at lower IQ's. (I reserve the right to update my speculations blah blah.) (File under The Case Against Education.)

Growing up, I recall people heading off on different tracks around 8th grade, 10th grade, 12th grade, then finally the smartest of the smarts heading to grad school. Intelligence hits its hereditary barriers along the way and begins to "crystallize." If it were otherwise we could educate everybody into Ph.D.'s. Then, all the Ph.D.'s would start getting multiple Ph.D.'s. Finally, after 60 years of education, you'd be a mentalist demi-god.

That's why Head Start and other early interventions are so much fun for the tabula rasa advocates. Most human children can be coached to good results with shapes and letters and simple math. But when you start throwing long division at them a percentage won't get it. The percentage who can't handle algebra will be higher, and higher still for more abstract mathematics. So by the time cute little neotenous humans become big, surly teenagers, most reformers have lost interest and go back to promoting young moms listening to Mozart.

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