Thinking positively: The genetics of high intelligence
sciencedirect.com
sciencedirect.com
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.
And the very definition of "intelligence" is incredibly complex and slippery, which is one of the reasons why I've always found trying to summarise such a complex property into a single numerical value such a silly exercise.
More on this here: http://slatestarcodex.com/2014/08/11/does-the-glasgow-coma-s...
NB I say that as someone who got a very high IQ test result - which didn't exactly convince me that IQ tests are a good idea....
Intelligence really isn't "multi-faceted" (read Gardner's own admission that his theory never panned out) and it isn't ill-understood (refer to the Nature or Nurture interview with Nancy Segal on YouTube).
There's two reasons people say that. One is, they fared badly on a test and want to dismiss it, and the other is, they fared well on a test and are bashful about it.
Also, IQ tests are meant to measure a person's intelligence, not to convince them that IQ tests are "a good idea" - for that you would have to study Psychometrics.
I worked on AI research for a number of years and my strong opinion is that our understanding of general intelligence is, as some wit put it, "pre-Newtonian".
Intelligence is neither well defined nor well understood. It is fairly controversial stuff.
But you're right that this doesn't tell you much about any of the individual dimensions. Maybe adding a variance across dimensions, so two numbers, would be more useful.
* Social class
* Assortative mating
https://www.newscientist.com/article/dn12993-chimps-outperfo...
Of course, genetics probably plays a role in that, too.
And seems to produce a higher incidence of autism too, if the anecdotes are to be believed...
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.
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...
> One thing we have to be wary of in this calculation of persistence is surname changing. If people going to the university born with the surname Anderson were changing this to Wigonius, then there would appear more persistence than there really was. The biographical sources for some of the student nations at Lund and Uppsala, Blekingska, Göteborgs, Skånska, Smålands, and Vermlands at Lund, and Östgöta at Uppsala, allow us to estimate the fraction of Latinized surnames which were newly adopted in each generation at the universities, since it gives fathers’ and mothers’ surnames for most students also. Figure 19 shows what fraction of students in each generation inherited rather than adopted a Latinized surname.18 For the earlier generations, 1730-1819, 96% of students acquired the name by inheritance from their father. However, 1820-1909 that proportion fell to 88%, even though by design these are all surnames that first existed before 1730.19 This will bias upwards my estimate of b, but can be corrected for by calculating for each period a b based just on the relative representation of the surname among the inheritors in that period.
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.
I know very intelligent and very stupid people all over this income range, with no obvious pattern.
The more interesting question is which correlations are strongest. I can't find a link, but I read a study that came out a few years ago that showed the biggest correlation with financial success was the parents' income levels. That is, controlling for the intelligence of the parents, an average-intelligence person born to wealthy parents was more likely to be financially successful than an above-average-intelligence person born to poor parents.
That may also be obvious, but it has more effect on the veracity of the common view of our society being a meritocracy.
> That may also be obvious, but it has more effect on the veracity of the common view of our society being a meritocracy.
Why? There's nothing about that that speaks to how much of a meritocracy we are. Parents' financial success directly measures everything that contributes to financial success (rather than, say, a subcomponent); you'd expect it to be highly informative.
The result you cite still holds when both children are adopted away. Is that support for the view of society as a meritocracy?
In a meritocracy, as I understand the idea, one's success is based on ability and talent rather than on class privilege or wealth.
If the biggest factor in your success is your parents' wealth, doesn't that suggest we might not have a pure meritocracy?
Do you have a link to the study? I don't remember the part about it still holding true when children are adopted away. That is an interesting finding. It would support your point (I think the point you're making, at least) that it's not necessarily parents using their class/wealth to bolster their children, but instead the parents have the proper mix of traits (intelligence, grit, ability to delay gratification, etc.) that results in financial success.
Nor do I. Who decides what abilities are important? How do they go about measuring them?
However, I do think it is "bad thing" for members of the elite to believe that we live in a meritocracy – when we do not, IMO. Skimming that Guardian article, I think my feeling is similar to the criticism put forth there. The notion that we live in a meritocracy creates a sense of entitlement and superiority in the elite. That is, if you believe we live in a true meritocracy, then those on top are there because they're smarter and harder working, and those on the bottom are there because they're less intelligent and/or aren't working as hard. Said more simply, meritocracy results in the feeling that you deserve your riches, and they deserve their poverty.
Whereas, in reality as I see it, your financial success is dependent on many factors outside of your control. Sure, most successful people are fairly smart and work hard, but many less successful people also have those qualities. The other factors contributing to success are things largely summed up by Warren Buffett's notion of the "Ovarian Lottery".
I'm not advocating a meritocracy. I'm advocating an honest assessment of society and the factors contributing to financial success.
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.
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.
Actually height is unlike intelligence since there is one gene on the Y chromosome that has a very large influence on height. There are no such genes for intelligence as this study and many others has found.
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.
because this is an 'assumption' not a logical 'conclusion'.
This study does support what previous studies have found from when people looked for genes that had a large positive effect on intelligence and failed to find any.
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.
> 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]
http://www.drtomascp.com/uploads/PersonalityIntelligence_IJS...
Which seems to provide some (weak) evidence against that:
"The hypothesis of a significant correlation between various Big Five personality traits and intelligence test scores was only partially supported. Only Conscientiousness was significantly related to psychometric intelligence, correlating with BRT scores. It is worth noting that the correlation was negative, indicating that higher conscientious participants tended to have lower gf."
I'm far from an expert though, so I can't say how good that study is.
I have no idea how football fairs, but you can debate the usefulness of that as an objection to the validity of IQ with someone else.
> 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...
In an modern developed economy, where you'll be more likely to do well if your IQ is high, some people will have inherited alleles which tend to raise their IQs and make them well-adapted to their environment, others different alleles which make them poorly adapted.
And, on top of that, there's an environmental, or rather cultural component.
A better question is, how much education in biology and psychology is needed to appreciate these findings?
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.
To actually try to explain the design here:
we think intelligence is caused by thousands of common genes, each of which slightly helps or hurts. When you have thousands of independent genes, then they add up to a normal distribution like the one we see when we measure a lot of people's intelligence. The exception is that there are too many retarded people; if the normal distribution was the whole story, then retarded people would be as rare as geniuses, but they are much more common than that. We explain there being too many retarded people by saying that they have one or a few very rare mutations, mutations which are very harmful. But another theory might be that the retarded have very few normal intelligence genes, or that intelligence genes don't simply add up but interact in complex ways, or that they have very harmful environments. How do we decide which theory is right? Well, we look at the retarded people vs their siblings; if their parents were lacking a lot of good genes, or they were being raised in a toxic waste dump, then we would expect the siblings to also be near-retarded themselves since they also inherited few good genes or are affected by the toxic waste. But they're not; they are almost average! This is more consistent with there being one bad mutation and the retarded sibling had bad luck than the other theories. This theory has since been confirmed by finding hundreds of unique and harmful mutations in retarded people. So we conclude that the effect of intelligence genes is indeed a normal distribution, with an occasional bad mutation overriding that and making someone retarded.
This immediately raises a question. If we admit that on the low end intelligence may be controlled by a single rare mutation, why not on the high end too? Maybe there are special genius genes floating around. This would be important because it means that you can't make much progress by just looking at the genes of regular people, and it also means that SNP studies will be extremely limited in what they can find. How can we check this? We can do the same thing as on the low end: if there is a special genius gene, then geniuses will have much higher IQ than their siblings do, who will be close to average; but if their parents have lots of good genes and there is no single special gene, then the siblings will also be well above average and similar to their genius sibling.
Using a very large set of siblings and twins, OP finds that very intelligent twins/teens are similar to their siblings. So this is the opposite of the retardation findings. There are rare genes for retardation, but there are not rare genes for genius.
Not necessarily. This is something you might expect if intelligence is a net fitness advantage and it is in a mutation load situation where rare variants need to be purged to keep things constant. But if intelligence is only worthwhile up to a certain point and it is controlled by frequency-dependent selection, or there is heterozygote advantage, or if intelligence is not necessarily reproductively fit at all, or other situations, then there could certainly be rare variants of large positive effect. (I would not have bet on their existence for many reasons, but not because it's impossible.)
To give an example, your claim would predict that there is no such thing as a single mutation which increases muscle mass a lot because it's a complex system affected by a lot of genes; yet nevertheless, there is a single mutation affecting myostatin which makes humans and pigs and dogs much more muscular, and it's even been edited into pigs with CRISPR this year and last year into sheep and cows. Presumably the reason that not all animals are ultra-strong thanks to the mutation is that it causes birthing difficulties and increases metabolic demands considerably, and so despite the obvious advantages of being ultra-strong, it's not actually fit.
To use your myostatin mutation example, the increase in muscle mass does not lead to significantly faster animals as the supporting structures are not there to utilise this increased muscle. Human intelligence is an emergent trait like speed determined by the co-ordination of many sub-systems.
These sort of emergent traits are almost never positively controlled by single large positive alleles. The one major exception are systems that are under different selection in males and females (e.g. height, plume color in birds, etc). In these examples two different systems have emerged controlled by the sex of the individual, but you don’t tend to find single genes that contribute massively in a positive way towards variation within each sex.
As an aside I remember reading a paper from long ago that suggested that high intelligence was the result of the relatively absence of mutant alleles at the various intelligence loci. When you look at the effect of null mutations at these loci the effect on intelligence is very low (less than a point for most). We all carry a large number of mutant alleles so the suggestion is that those with a high intelligence just happen by chance to have a lower frequency of negative mutant alleles. The interesting thing about this hypothesis is it would suggest that high intelligence is the default and low to normal intelligence is the result of mutational load. This is defiantly something that we can explore in the future as we get whole genome data from large numbers of people.
Some years ago, I read something that suggested otherwise. IIRC, it suggested that we had some idea of what alleles positively influenced intelligence based on the fact that Ashkenazi Jews were something like 2% of the population but had won something like 10% of Nobel Prizes and about 60% of the population had one or more alleles for serious genetic disorders known to impact neurology.
I remember this in part because, although I am not Jewish, I have one of the genetic disorders they tend to carry.
As far as I am aware there in no genetic disorder that only Ashkenazi’s suffer from that is not also present in the rest of the human population, the only difference is frequency.
As far as I am aware there in no genetic disorder that only Ashkenazi’s suffer from that is not also present in the rest of the human population, the only difference is frequency.
Do you honestly see no possible connection between these two things?
That's a serious question, not intended as argumentative per se.
I don’t think anyone has shown that being a carrier for any of the common mutations found in the Ashkenazi population increases intelligence in a measurable way, but if anyone knows of such a study I would love to read it.
www.kuro5hin.org/story/2005/7/29/20293/9910
Edit: It contains the stats I was trying to reference above but was misremembering. They are 3% of the population and 27% of U.S. Nobel Prize winners.
They have? I'm not aware of any GWASes targeting intelligence using Ashkenazi samples.
It leads to significantly stronger animals. That's not useless, for either prey or predators.
> Human intelligence is an emergent trait like speed determined by the co-ordination of many sub-systems.
We don't know what human intelligence is on a neurological basis. Imaging studies are linking it to a number of things, but it's still preliminary and so it's premature to baldly assert that there's no possible single mutation which might help.
> As an aside I remember reading a paper from long ago that suggested that high intelligence was the result of the relatively absence of mutant alleles at the various intelligence loci.
Mutation load hasn't been found to be strongly correlated with intelligence in studies which have looked at it directly, and the GCTAs already upper bound any such effect: "The total burden of rare, non-synonymous exome genetic variants is not associated with childhood or late-life cognitive ability", Marioni et al 2014 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3953855/ "A genome-wide analysis of putative functional and exonic variation associated with extremely high intelligence" http://www.nature.com/mp/journal/vaop/ncurrent/full/mp201510... , Spain et al 2015
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.
The same can be said with drugs -- any chemical that your body could have reasonably produced on its own should be expected to reduce your reproductive fitness. So brain drugs should nearly all have side-effects.
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.
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.
> (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.
The question you ask for yourself is "how do I live well?"