April 15, 2012
Genetic Variant Influences Brain Size, Intelligence

While searching for genetic variants that impact a brain's risks of a variety of mental illnesses researchers have discovered a genetic variant that contributes to intelligence differences.

In the world's largest brain study to date, a team of more than 200 scientists from 100 institutions worldwide collaborated to map the human genes that boost or sabotage the brain's resistance to a variety of mental illnesses and Alzheimer's disease. Published April 15 in the advance online edition of Nature Genetics, the study also uncovers new genes that may explain individual differences in brain size and intelligence.

"We searched for two things in this study," said senior author Paul Thompson, professor of neurology at the David Geffen School of Medicine at UCLA and a member of the UCLA Laboratory of Neuro Imaging. "We hunted for genes that increase your risk for a single disease that your children can inherit. We also looked for factors that cause tissue atrophy and reduce brain size, which is a biological marker for hereditary disorders like schizophrenia, bipolar disorder, depression, Alzheimer's disease and dementia."

This isn't surprising. Since genetic sequencing costs have plunged by orders of magnitude researchers can finally collect enough genetic sequencing data to identify genetic variants that each make a small difference in intelligence. The evidence so far suggests that most intelligence-influencing genes each have only small impact. So large data sets are needed to order to pick up the signal from each genetic variant that has an impact on intelligence.

In an intriguing twist, Project ENIGMA investigators also discovered genes that explain individual differences in intelligence. They found that a variant in a gene called HMGA2 affected brain size as well as a person's intelligence.

DNA is comprised of four bases: A, C, T and G. People whose HMGA2 gene held a letter "C" instead of "T" on that location of the gene possessed larger brains and scored more highly on standardized IQ tests.

"This is a really exciting discovery: that a single letter change leads to a bigger brain," said Thompson. "We found fairly unequivocal proof supporting a genetic link to brain function and intelligence. For the first time, we have watertight evidence of how these genes affect the brain. This supplies us with new leads on how to mediate their impact."

More genetic variants that influence intelligence will be found this year and even more the next year and the following year. By 2020 I expect most of the genes that influence intelligence will be known. Small numbers of people will start doing embryo selection based on intelligence in this decade and large numbers of people will do so in the 2020s.

Share |      Randall Parker, 2012 April 15 12:17 PM  Brain Intelligence

James Bowery said at April 15, 2012 12:32 PM:

Where are Boas, Gould et al when you need them?

Actually, no one needs them. The social sciences including anthropology are firmly established theocracies utterly impervious to hate facts. Boas, Gould, et al did their work well.

interested said at April 15, 2012 2:11 PM:

Hmm, sample size in the tens of thousands, and two separate projects combined (these two findings replicate across the two). Further, since the variant affects both IQ and brain size, there is a little less room for a spurious effect. There have been a lot of false alarms in this area, but this looks more promising than any so far.

Mthson said at April 15, 2012 6:02 PM:

James Bowery:

It's going to be amusing when people like that quietly realize that they've been on the wrong side of history for 100 years, and that reprogenetics is the only way to end academic/economic inequality.

interested said at April 16, 2012 1:24 AM:

Bowery, according to Razib, the brain size and IQ boosting variant is most common in Africans, then Europeans, then East Asians. Just the opposite of observed aggregate phenotypes, and just what Boas et al might have hoped for. http://blogs.discovermagazine.com/gnxp/2012/04/common-variant-for-iq-gene/

Ronald Brak said at April 16, 2012 4:28 AM:

Thanks for that link, Interested. I was going to comment that they might have found a gene that affects skull size and I see from your link it is correlated with height.

Nic said at April 16, 2012 11:35 AM:

Interesting. Seems abit like the Rise of the Planet of The Apes scenario. I wonder if its possible to actually increase intelligence later on in life.

interested said at April 16, 2012 11:54 AM:

Looks like yet another false positive: the sample size for IQ was much smaller, and the correlation much weaker, than for brain size, and it hasn't shown up elsewhere. So the IQ claim is probably wrong.

James Bowery said at April 16, 2012 1:52 PM:

Interested, while it may be what Boas, Gould et al might have hoped for, it was naive of them to do so.

Once you admit aggregate phenotypes vary by geographic race, you're on a slippery slope to reality and the reality is that reality is what they needed to evade as reality is impervious to spin control.

I recall having a conversation with a young lady from Sicily about the large cranial capacity of Hawaiians and how it was a shame they didn't have more of Hawaii to reserved to maintain their linage. She objected that intelligence isn't correlated with brain size (she had, incidentally, a rather small cranial capacity for her size). I was quick to state that the exact opposite might be the case under some circumstances since, as has been shown in computer architecture, the region of control (the amount of space that signals must traverse in a clock cycle) is minimized in order to maximize computation flexibility (take branches, etc.). I also added that brain size might have some unknown function for organisms that must navigate the oceans -- such as cetacea and, of course, Hawaiians. That shut her up. It probably would have down-right scared Boas, Gould et al.

PacRim Jim said at April 16, 2012 2:42 PM:

Market opportunity: Fake genetic profiles that exaggerate the desirable and minimize the undesirable.

Mthson said at April 16, 2012 2:45 PM:


The Boas et al hypothesis is that it's a priori physically impossible for ethnic groups to vary in brain tendencies, and that it's bad faith to treat the subject in an honest scientific manner.

I remember how shocked I was as a young liberal science nerd looking forward to reading Gould's work, only to realize that somehow some of the most influential leaders of science are reduced to anti-science moralists when it comes to the science of humankind.

It's already been shown in previous studies that ancestry clusters vary in distribution of brain genes, with some genes that are common in some populations being completely absent at detectable frequencies in other populations.

If you're still placing your bets on the side of Boas et al, think carefully about whether they succeeded in stopping the advance of the study of genetics, and whether genetics as a field is going to become less important or more important in the future.

Ronald Brak said at April 24, 2012 7:01 PM:

Although a gene alelle has been found that appears to be related to higher IQ and this alelle is found more commonly in some groups than others, currently we can't actually say that differences in IQ between groups is due to genetic reasons. We'd have to look into it more deeply before we could say that. But what we do know is that differences in IQ between different regions is either not due to genetics, or the effect of genetics is not large. Currently IQs in sub-Saharan Africa are comparable to the IQs of white Americans in the 1950s. Obviously white Americans haven't undergone much genetic change since since the 50s, so it is clear that environmental changes rather than genetics resulted in the IQ increase. From this it is clear that environmental effects are sufficent to explain the difference between average IQ in the US and sub-Saharan Africa that exists today. This doesn't mean that there there isn't a genetic difference, but we know from adoption studies and for other reasons that if there is a genetic difference it can't be large. And we can't say which way it would go.

Just to be clear, this is not saying genetics does not ifluence IQ, it does, but regional genetic differences either do not have an effect, or have a very small effect on IQ. Also this does not mean that we can't identify other difference between regional groups as genetic. For example, indigenous Australians have better eyesight on average than more recent European or Asian immigrants and that difference is genetic.

Mthson said at April 24, 2012 8:12 PM:


Your data is inaccurate, and your moralistic certitude ("any genetic differences are fine, as long as they don't make me feel uncomfortable") has been making inaccurate predictions for decades. It's an old device of IQ-denialists to claim adoption studies etc. show genetics are irrelevant, when that's not the case.

Let's try something else. When do you predict average Latino American academic performance will catch up with Asian-American or Ashkenazi academic performance? The answer is never, because Latino-Americans were specifically filtered to be from the least-skilled tiers from their home countries, and Asian-Americans were specifically filtered to be from the most-skilled tiers. That's why Immigrants Do Not Improve Academically In Later Generations.

Similarly, average White American academic performance will never catch up to Asian-American or Ashkenazi performance.

Once you accept that ethnic groups in the US vary in IQ, it will be easier to accept that global ancestry clusters also vary.

Ronald Brak said at April 24, 2012 9:16 PM:

Mthson, are you saying that the increase in IQ scores of white Americans since the 1950s is due to genetics?

Mthson said at April 24, 2012 9:58 PM:

I'm saying that some groups increasing their average IQ scores to certain levels in certain circumstances doesn't cancel out everything that points to varying natural IQ levels in e.g. Africa & Asia.

Ronald Brak said at April 24, 2012 10:14 PM:

So you accept that environment accounted for the large change in IQ scores of US whites since the 1950s? So can you see that environmental factors can have a large effect on IQ scores and can be large enough to account for the current difference in IQ scores between sub-Saharan Africans and Americans?

Mthson said at April 25, 2012 3:34 AM:

The US white IQ even in the 1930s was higher than in Sub-Saharan Africa today. "Ulric Neisser estimates that using the IQ values of today the average IQ of the US in 1932, according to the first Stanford–Binet Intelligence Scales standardization sample, was 80" (source). In comparison, nations in Sub-Saharan African today that are more wealthy than US whites in 1932, like Botswana, average around 72 IQ.

Predicting the gap will close would need to be based on data showing the trajectory of IQ gains in different ancestry clusters. There will probably be at least small gains in both Sub-Saharan Africa and East Asia, but if the current IQ gap between people with the same income in those two regions is around 30 IQ points, both of them making IQ gains would not close the gap.

The Chinese at $8k GDP (PPP) per year outperforming Botswanans at $16k per year by a very large 30 IQ points would warrant a prediction that further wealth gains in Sub-Saharan Africa aren't going to have the preferred effect. Even a 10 point IQ disadvantage for a population with actually double the wealth would be enormous.

Ronald Brak said at April 25, 2012 3:59 AM:

So using the estimate you provide, you are saying that US whites increased IQ by 20 points since the 1930s due to environmental and not genetic causes?

Mthson said at April 25, 2012 6:02 AM:

Yes, but if you're assuming a priori that the presence or absence of the factors underlying the Flynn effect are the source for the Sub-Saharan vs. East Asian IQ gap, or for the Latino American vs. Asian American IQ gap, that wouldn't be warranted based on current data and trajectories.

Ronald Brak said at April 25, 2012 4:47 PM:

So your position is that environmental factors can result in a 20 point change in IQ, as evidenced by white Americans, and that sub-Saharan Africans currently have as much opportunity to make their IQs blossom as white Americans now do?

Mthson said at April 25, 2012 6:01 PM:

No, some groups increasing their average IQ scores to certain levels in certain circumstances doesn't cancel out everything that points to varying natural IQ levels among ancestry clusters.

Ronald Brak said at April 25, 2012 7:18 PM:

So you think that sub-Saharan Africans don't have as much opportunity to develop their IQs as US whites currently do?

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