Thinking positively: The genetics of high intelligence

http://www.sciencedirect.com/science/article/pii/S0160289614001676

by gwern • 11 years ago

136 101 11 years ago

I would be very surprised if high intelligence was anything other than the extreme edge of a normal distribution of the human population. For it to be anything other than this it would require people of high intelligence to be a sub-population that did not breed with the rest of humanity.

yummyfajitas• 11 years ago

You could make this argument for any trait. However, some traits are the result of a single gene - e.g., sickle cell anemia and the accompanying malaria resistance. Yet some of these traits occur in large populations that are not strongly inbred.

danieltillett16• 11 years ago

Only single gene traits. Intelligence (however defined) is multi-genetic - there are thousands of genes that contribute to intelligence. Given this the only way that individuals with high intelligence could be anything other than edge of a normal distribution is if they were part of a human sub-population.

Edit. I should add that the humans are not completely one population because of genetic isolation and differential selection (especially over the last 10,000 years), but we are almost a single population. Like everything in genetics it gets fuzzy at the edges.

troels• 11 years ago

On the other hand - Chimps are significantly less intelligent than humans. So clearly, genetics play a role.

danieltillett16• 11 years ago

Of course genetics plays a role in intelligence (a very important role). In the case of chimps they are not part of the human population so they are not really relevant to any discussion about the genetics of human intelligence.

medymed2• 11 years ago

If raised in an affluent suburb, they might surprise you.

DonaldFisk5• 11 years ago

On many, but not all cognitive tasks:

https://www.newscientist.com/article/dn12993-chimps-outperfo...

Of course, genetics probably plays a role in that, too.

mgraczyk• 11 years ago

Subpopulations can be physically and temporally distributed amongst the greater population. As long as breeding is not statistically independent of intelligence, there will be a tendency for intelligence-related genes to clump together.

danieltillett16• 11 years ago

This is true, but to get extreme outlier sub-populations for a mulit-gene trait like intelligence would require pretty effective isolation. For any sub-population to be large enough to affect the distribution of intelligence across the human population, yet be able to maintain this isolation, is very unlikely.

vixen99• 11 years ago

'would require people of high intelligence to be a sub-population that did not breed with the rest of humanity' - which is increasingly what is happening with people of high ability & potential income of both sexes attending the same universities and mating. This polarization has been documented.

ansible• 11 years ago

This polarization has been documented.

And seems to produce a higher incidence of autism too, if the anecdotes are to be believed...

0xdeadbeefbabe• 11 years ago

I hope someone intelligent is working on intelligence reallocation.

astrodust• 11 years ago

There are a lot of highly intelligent people at all levels of income distribution, so while there might be a polarization effect, it's not to the point of being segregation.

Intelligence can help you gain wealth, but if you're never given an opportunity or don't have a lot of drive you'll struggle perpetually.

drumdance2• 11 years ago

It's happening, but I think it will take quite a few generations for it to become and independent trait of its own.

danieltillett16• 11 years ago

It would take quite a while for asortive mating to create a new human sub-population, but given the low fertility (through choice) of people with high intelligence such a sub-population can't form.

civilian2• 11 years ago

It's not even that mating like that is increasingly happening--- it's been that way in nobility for a long time.

What is the True Rate of Social Mobility in Sweden? A Surname Analysis, 1700-2012 http://www.econ.ucdavis.edu/faculty/gclark/papers/Sweden%202...

stephengillie• 11 years ago

It is - a family with low average intelligence can birth occasional individuals with much higher intelligence than their average.

lagadu• 11 years ago

For it to be anything other than this it would require people of high intelligence to be a sub-population that did not breed with the rest of humanity.

It is: we call it "social classes". Because intelligence correlates positively with success and because people tend to have children with other people from a similar social stratum, the exact situation you described emerges as a pattern.

bittercynic• 11 years ago

My experience doesn't bear this out. Though the few extremely wealthy people I know seem very intelligent, I don't think intelligence correlates with income for the $15K-$200K annual income range. (This is the best proxy I know of for social stratum here in the Bay Area.)

I know very intelligent and very stupid people all over this income range, with no obvious pattern.

douche• 11 years ago

Ashkenazi Jews would seem to be a well-studied sub-population that tends to possess above-average intelligence.

https://en.wikipedia.org/wiki/Ashkenazi_Jewish_intelligence

ZeroGravitas• 11 years ago

I notice in that page it compares the number of "full" Ashkenazi Jews in the population, to the number of people who won various academic prizes who had "full or partial" Ashkenazi ancenstry, which seems like a very blatant distortion.

On reading slightly further I see someone else has already spotted this and added that disclaimer to the text.

Seems like it would be relatively easy to compare like with like here, which makes me suspicious of why it isn't done. Does that mean that the effect disappears when you do that comparison? It's certainly going to be reduced.

danieltillett16• 11 years ago

Even if it were true that Ashkenazi Jews as a group had above average intelligence, there just are not enough Ashkenazi Jews in the world to have a significant influence on the distribution of human intelligence.

thaumasiotes3• 11 years ago

I would be very surprised if high intelligence was anything other than the extreme edge of a normal distribution of the human population. For it to be anything other than this it would require people of high intelligence to be a sub-population that did not breed with the rest of humanity.

Not at all. There could be a specific suite of traits that includes high intelligence, present in some people but not in most. Those people would have high intelligence, but they wouldn't be the extreme of the natural variation of the rest of the population. They would have gotten there by "cheating".

This is known to occur right now in human height. Men are taller than women. The difference is so pronounced that the human height distribution is not normal. The tallest humans (except Yao Ming) basically are the extreme of normal variation in men. But they aren't the extreme of normal variation in humans.

I hope you'll agree that "men" cannot be characterized as a subpopulation that doesn't breed with the rest of humanity.

danieltillett16• 11 years ago

Men can't be a sub-population by definition since men can breed with men. In regards intelligence both men and woman share the same mean. Given men have only one X chromosome we might expect that they might show a wider distribution in intelligence than women, but the evidence for this is controversial and airing it has a habit of losing you your job.

apalmer5• 11 years ago

Your second sentence is not logically implied by the first sentence.

It is not uncommon to have phenotypes that are expressed only rarely although the genes that code for the phenotype are widely dispersed. Many well known genetic diseases fall into this category.

danieltillett16• 11 years ago

Intelligence is like height in that it is multi-genetic (on the order of thousands of genes). Any trait that is determined by thousands of genes is going to show a normal distribution.

DonaldFisk5• 11 years ago

I don't think there's such a thing as general intelligence. You can be good at some cognitive tasks and poor at other cognitive tasks: https://en.wikipedia.org/wiki/Theory_of_multiple_intelligenc...

I also don't think you can separate genetic influences from environmental influences, i.e. one allele might make you do well in one environment and poorly in a different environment. This appears to the case for the 7R allele of the DRD4 gene: http://www.northwestern.edu/newscenter/stories/2008/06/ariaa...

I also don't think any genes actually code for intelligence as it's commonly understood. Intelligence is, basically, knowledge (including knowledge about how to acquire knowledge). Genes affect brain chemistry, which influences intelligence in different ways, within a given environment.

jessriedel2• 11 years ago

The theory of multiple intelligence you link to is in strong disagreement with the mainstream position of academia.

Intelligence tests and psychometrics have generally found high correlations between different aspects of intelligence, rather than the low correlations which Gardner's theory predicts, supporting the prevailing theory of general intelligence rather than multiple intelligences (MI).[19] The theory has been widely criticized by mainstream psychology for its lack of empirical evidence, and its dependence on subjective judgement.[20]

moyix2• 11 years ago

From the Wikipedia page you link on multiple intelligences:

Intelligence tests and psychometrics have generally found high correlations between different aspects of intelligence, rather than the low correlations which Gardner's theory predicts, supporting the prevailing theory of general intelligence rather than multiple intelligences (MI).[19] The theory has been widely criticized by mainstream psychology for its lack of empirical evidence, and its dependence on subjective judgement.[20]

As for your other points...

I also don't think you can separate genetic influences from environmental influences, i.e. one allele might make you do well in one environment and poorly in a different environment.

That's probably the case for some genes, sure. But finding strong correlations between twins raised apart would seem to indicate that many of the genetic factors are not entirely environment-sensitive.

I also don't think any genes actually code for intelligence as it's commonly understood. Intelligence is, basically, knowledge (including knowledge about how to acquire knowledge). Genes affect brain chemistry, which influences intelligence in different ways, within a given environment.

Twin studies seem to contradict this. From Wikipedia (heritability of IQ [1])

* Identical twins—Reared together .86

* Identical twins—Reared apart .76

So yes, environment has an impact, but there's still a high degree of correlation in intelligence between identical twins raised apart.

[1] https://en.wikipedia.org/wiki/Heritability_of_IQ#Correlation...

pippy• 11 years ago

Interesting, but tangently related: https://en.wikipedia.org/wiki/Robert_Klark_Graham

sygma• 11 years ago

Saw it on your monthly newsletter today. Thanks for compiling those!

dgrant• 11 years ago

Can someone explain this for someone like me with no education in biology or psychology?

JoeAltmaier• 11 years ago

Sadly that may be impossible. Metaphors are limited - the understanding gained is always flawed and rarely actionable.

A better question is, how much education in biology and psychology is needed to appreciate these findings?

nitrogen2• 11 years ago

This is an interesting point and reminds me of the difference between technical and verbal understanding:

http://www.yudkowsky.net/rational/technical/

jm_l• 11 years ago

For mentally challenged people, researchers have done an analysis of the distribution of certain genes that are associated with the handicap. They have shown with high likelihood that mental handicap is actually different than just being on the low end of the intelligence distribution.

This study tries to answer the question, "is the same true for high intelligence?" The two general theories are the Continuity Hypothesis and Discontinuity Hypothesis. As its name suggests, the Continuity Hypothesis predicts that the high end of the intelligence distribution is continuous; extremely intelligence individuals don't violate the intelligence distribution the way mentally challenged people do. The Discontinuity Hypothesis predicts the opposite.

By analyzing the genes of twins and other close family members, the researchers found strong evidence of the Continuity Hypothesis.

soheil• 11 years ago

I love how you accurately summarized a 10 page paper into a few concise sentences understandable most likely even by those on the low end of the intelligence distribution.

huangwei_chang• 11 years ago

Thanks a lot for the summary. It is way better than reading the paper (I tried).

btilly• 11 years ago

BTW evolution theory suggests a priori that the Continuity Hypothesis is more likely to be correct.

Intelligence is selected for in humans. Therefore any individual gene that significantly boosts intelligence should be expected to have already spread through the population. As a result we should not expect to find any rare genes that make people super-smart. So super-smart people get there with a combination of different genes, each of which contributes very little.

The bottom end of the scale is the opposite story. Evolution says that individual genes that hurt intelligence should be selected against, and are therefore expected to be rare. (Mutation says that they should not be non-existent, but they should be rare.) Therefore there is no surprise in finding rare individual genes that significantly hurt intelligence.

This pattern is not unique to intelligence. It is predicted for any trait that has actively been selected for by evolution over a long period. The top of the range should look continuous. The bottom of the range tends to be dominated by deleterious point mutations.

kylemathews• 11 years ago

The researchers did a study of Swedish military conscripts (98%) of male population. They tested if high-intelligence is as inheritable as general-intelligence. They found strong evidence that it does as siblings of high-intelligent soldiers also tended to more intelligent than the norm.

ambicapter• 11 years ago

How does that show anything. Can't you assume that siblings would be raised in similar environments?

gragas• 11 years ago

Abstract

High intelligence (general cognitive ability) is fundamental to the human capital that drives societies in the information age. Understanding the origins of this intellectual capital is important for government policy, for neuroscience, and for genetics. For genetics, a key question is whether the genetic causes of high intelligence are qualitatively or quantitatively different from the normal distribution of intelligence. We report results from a sibling and twin study of high intelligence and its links with the normal distribution. We identified 360,000 sibling pairs and 9000 twin pairs from 3 million 18-year-old males with cognitive assessments administered as part of conscription to military service in Sweden between 1968 and 2010. We found that high intelligence is familial, heritable, and caused by the same genetic and environmental factors responsible for the normal distribution of intelligence. High intelligence is a good candidate for “positive genetics” — going beyond the negative effects of DNA sequence variation on disease and disorders to consider the positive end of the distribution of genetic effects.

apalmer5• 11 years ago

More or less the main crux is high intelligence is just a 'normal' manifestation of regular genes.

Take height as an example, most people tall or short have 'regular' genetics for their height. A bunch of different factors play together along with the environment to lead to the height they actually have. its basically like a 1000 different genes interacting that each may give you or take a way a fraction of an inch and all together they sum up to your actual height.

However sometimes you have people who are dwarfs, these arent just a combination of many genes, there is a overwhelming specific set of a few genes that totally overwhelm all the other height genes and give you greatly reduced height. Similarly on the other end of the spectrum you have some forms of giantism where a few genes overwhelm all the other height genes and give you greatly increased height.

This study is more or less saying high intelligence follows a model like regular tall height, many different genes interacting to sum up to above average height. Not a model like giantism or dwarfism where a very limited number of genes overwhelm the 'normal' genetics of intelligence.

powertower• 11 years ago

They wanted to know what accounts for the difference between the high-intelligence group and the average-intelligence group.

(1) we conclude that high intelligence is familial, heritable, (2) and caused by the same genetic factors responsible for the normal distribution of intelligence.

The 1st part is simple to understand, what is confusing everyone is the 2nd part... As the combination of both parts does not make sense (due to the type of "interpretation" presented).

Here is the clearer version -

(1) They found that intelligence was mostly hereditary (inherited via genes passed on by parents).

(2) They further found that the top scorers could also be divided into their own bell-curve. That the high-intelligence group had there own distribution that followed the same pattern (which gives the bell-curve even more validity).

To understand #2 just imagine a smart kid (in high-school) getting accepted into MIT, and once in, that smart kid finding out that he is now just "average" compared to some of the others.

These conclusions are very politically-incorrect, especially for a progressive country like Sweden where you are not supposed to even acknowledge that different dog breeds have different behaviors.

escherplex• 11 years ago

Point number two above is well taken. Also there's more 'stretching' at the higher end. For example you may find a couple of individuals who can do complex del functions on a variety of topics in their head and somehow seem 'inspired' whereas others specialize on one arcane topic and spend countless weeks feeding research data into matlab or Wolfram apps while scouring onscreen .pdf tech archives for suitable algorithms they can adapt. But at this stage of the game functional genomics is in its infancy (you can't yet feed a genome's UCAG sequence into your 3D printer and expect it objectify a true object). For fuller understanding of implicit nature / nurture parameters concerning intelligence it may be more practical to select and isolate a suitably large sample from the center of the general population, where (dy/dx) = -yx is relatively flat, and insert such into a distraction-free positive artificial environment which focuses primarily on intellectual development and includes cognitive enhancement medical supplements such as nootropics or whatnot to varying degrees. Results may suggest high-intelligence is more latent than suspected, especially if sub bell curve distributions manifest.

josephjrobison• 11 years ago

Was hoping that thinking positively would help increase your own intelligence - seems to not be that way?

munchbunny• 11 years ago

Maybe not your intelligence. But this article is just about intelligence as a trait, not about how to live.

The question you ask for yourself is "how do I live well?"

throwawayaway• 11 years ago

So time for GATTACA right?

hyperion2010• 11 years ago

Actually not time for GATTACA because you'd have to tweak 1000s of genes not one. Which was the finding of this paper.

aklemm• 11 years ago

What if being retarded and being highly intelligent aren't ends of the same spectrum? High intelligence seems much more situational than being retarded. A retardation is fairly objective and would stand out in almost any scenario, whereas high intelligence can be invisible when the subject isn't taking an IQ test.

Thinking positively: The genetics of high intelligence

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