During the 1990s to the early 2010s, it had become well documented the brain-size IQ correlation among adults living in developed countries was about 0.4. Then in 2015, a meta-analysis by Jakob Pietschnig, Lars Penke, Jelte M. Wicherts, Michael Zeiler, and Martin Voracek surfaced claiming the brain size-IQ correlation was only 0.24! The paper argued that the 0.4ish figure that was typically cited was inflated by publication bias and these authors went out of their way to counter this.
While much of the HBD-o-sphere and academic community uncritically accepted the results of this meta-analysis and routinely cited it in their articles, I was immediately suspicious and argued that failure to correct to for range restriction and other methodological problems had spuriously deflated the correlation and that the true correlation was much closer to the traditional 0.4 than to the 0.24 Pietschnig et al had reported.
Now a brand new meta-analysis by Gilles E. Gignac and Timothy C. Bates is being published in the peer reviewed journal Intelligence showing once again Pumpkin Person was right! The authors reviewed the research cited by Pietschnig et al but corrected for range restriction, test quality, and sample quality and a 0.4 correlation was found.
However even 0.4 might be an underestimate of the within sex correlation between brain size and IQ because no correction was made for the fact that some samples combined men and women which lowers the correlation because men have substantially larger brains than women, yet virtually the same IQs. The within sex correlation might be closer to 0.45.
It seems the brain-size IQ correlation is very similar to the height-weight correlation. In a sample of male university students, the heigh-weight correlation was about 0.4. Arguably brain size is to IQ as height is to weight. A big brain helps make you smarter just as a tall height helps make you bigger but just as large brains are only one cause of IQ, greater height is only one cause of greater size, and it’s possible for small brained people to be brilliant just as it’s possible for very short people to be huge, and vice versa.
A genetic basis for IQ?
The brain-size IQ correlation is controversial because it suggests IQ is a biological variable, which in turn suggests it’s genetic. While IQ skeptics have been cheering the failure of genome-wide association studies to identify many genetic variants associated with IQ, they would be wise to not get their hopes up. Davies et al (2011) genotyped 3511 unrelated adults and found heritabilities of 0.44 for crystallized intelligence (acquired knowledge) and 0.51 for fluid intelligence (abstract reasoning). Taking the square root of these heritabilities suggests the IQ phenotype-genotype correlation may exceed 0.7! It should be noted that unlike traditional twin studies which yielded even higher numbers, genome-wide complex trait analysis only quantifies the additive portion of heritability, so the full heritability may be higher still.
Of course as commenter “Mugabe” notes, research is needed across a much wider range of environments to determine whether these are independent genetic effects.
I think the fact that IQ studies which do not include race are accepted more easily is a sign that it stems from emotional investment and not necessarily conspiracy. RR where are you? Can you give that link to the Polygenic study on intelligence genes between races again?
Do you recall which one? I’ve linked a lot of those in the past.
I was stating reasons why I think HBD isn’t accepted in mainstream science, one being that no major genes have been found to cause intelligence, you stated that there was I don;t think it was that long ago. It was probably the most recent one.
I remembered. Here.
I await replication, even better if it’s a non-hereditarian who does it.
Even then, Melo, I have no idea how many points it causes (don’t kill me if it’s in the articles, busy writing a rebuttal to Robert Lindsay on testosterone) but those genes have to have ultra-small effect.
Thank you. I appreciate it.
If the genes are causal, the predicted relation/correlation to ability (at least between racial groups) so far detected may not yet be very precise.
Also, interestingly, it seems that some African populations score above some Amerindian ones (e.g. the Mandinka and the Yoruba above the Maya, Pima, and South American Indians; and the Biaka and Kenyan Bantu above the Surui and Karitiana) , and also overall in the “subcontinental average factor scores” where Sub Saharan Africa is just above Amerindians. The Papuans and Melanesians also score above Mozabites (Berbers) and Mayans.
(and of course the results may also be somewhat confounded by the complication Cochran mentioned; Africans possibly having their own alleles affecting IQ that are not detected—or as much picked up, etc.):
“If the genes are causal, the predicted relation/correlation to ability (at least between racial groups) so far detected may not yet be very precise/well understood.”
“If the genes are causal, the predicted relation/correlation to ability—or associated with selection for ability…, etc..”
“Of course as commenter “Mugabe” notes, research is needed across a much wider range of environments to determine whether these are independent genetic effects.”
You once said pumpkin that video games have increased chronometric scores, inflating the sampling scores. And that genetically chronometric scores are limited by neuron reset time. Training is maxed out by reset times of neurons and cannot make them faster then they can be because of genes.
Today it seems that humans live in way more complex environments than before. (The Flynn effect is both cultural and nutritional) But when compared to ideal conditions it seems that further increases are possible (like the video game example).
Usually, I feel confined and I do not have full awareness of myself. But just a while ago I listened to some anime music videos and had to integrate vision, motion, and sound. I felt more aware and it felt like my perceptions were enhanced. From my experience, most people have a very narrow focus. But think about if in the future people had to integrate all 5 senses in virtual realities that have shapes and sound that makes their experience super complex. Most activities people do, do not activate the entire brain at once. If in the future virtual reality could activate the entire brain at once then Intelligence increases beyond they Flynn effect would be a possibility. Eventually, they would max out but their complexity would make their brain fully active, i.e. max integration and synchronization. Using your whole your brain at the same time trains all parts to work together thus able to handle more information.
OK PP, I concede you were right (re our conversation last month).
Funny story. I saw Bates tweet a poll about brain size IQ correlation. I got into a small argument with him over brain size on Twitter. Didn’t know who he was. I laughed when I found out who he was after I read this piece.
Lars Penke said something too.
Heinrich Himmler said:
The fatal problem with the brain size theory is that there have been many documented medical cases of people having normal cognitive function with most of their brain removed
The most famous example is that of an Englishman who had “virtually no brain” but had an I.Q of 126.
The many cases of this happening make the whole brain size thing meaningless.
As a neurologist in a relatively small European country, i have seen 4 cases of normal children with more than 50% of their brains removed.
The first had an IQ of 99, the second 105, the third 102 and the fourth 114.
As i said in article brain size is to IQ as height is to weight, so tiny brained smart people are no different from very short huge people
Heinrich Himmler said:
can a trait have predictive value for a variable when the virtual absence of the trait has no effect on the variable ?
I think so because brain size is only one cause of IQ just like height is only one cause of weight. There are people with virtually no height (under 3.5 feet) who weigh over 300 lbs.
Heinrich Himmler said:
If brain size is one “cause” of I.Q then we should see a reduction in I.Q after 50% of the brain has been removed
If we amputate away 50% of a man’s height, then we will see a massive decrease in weight
the two are not the same
How do you know there’s been no IQ reduction unless premorbid IQ is known?
In this case a man who lost most of his brain ended up with an IQ of only 75 which is lower than 95% of America. For all we know his IQ might have been much higher had his full brain remained:
IQ measure semantic memory but not autobiographical memory and seems the correlation with the late is not higher.
IQ =/= intelligence.
But EVERYONE on psychometric kingdom already think like that…
Semantic memory can be autobiographic . Episodic memory is always autobiographic. I have no episodic memory but my memory about the facts that concern me is really good. An amnesic will have lost the semantic one about his self, not always the episodic one : that must be terrible !
I have over 10,000 memories. That is my Gues since I think about so many things that happened to me every day. They are semantic. But I remember the space and colors. I just do not physically see them like you see normally with your eyes. I have aphasia. I only see black when my eyelids are closed. But some part of my brain allows me to tell people what bible camp was like and what I did and some people there, lots of stuff. I know where the river was and the fields and the back path. It’s all together but I cannot see it. My earliest memory was Teenage mutant ninja cupcakes and the sandbox in the backyard of the house. I was 4 years old. I have no memories before 4 years old. Anyone know what that means?
can be, we have ”pure” autobiographical memory, blended memory and ”pure” semantic memory.
Cat, you’ve stated many times you are an aphantasic guy with episodic memory. That’s fine. The fact you repeat things endlessly is very autistic to me, but not the asperger way. Not only there is a quantitative spectrum of autism, but also differences in quality. Your denials should be against Asperger – i dont think you have that – but maybe you should study the different forms of autism that exist . As you’re very interested in analysing yourself, you wouldnt loose your time. And you could explain what you found. I also would love to read the opinion of the people here who have a polyphonic head 🙂
”The within sex correlation might be closer to 0.45.”
PP i think ‘within sex’, bigger brains are more associated with mental skills like better memory and multi-tasking ability, tact etc that an IQ test doesnt measure.
Women are probably better at multi-tasking though