To further test Richard Lynn’s theory that the Flynn effect is caused by nutrition and health increasing the size and functioning of the brain, I compared the U.S. army’s anthropometric data from 1966 with data from 2012, looking for evidence of brain growth since the Vietnam war. My source for the 1966 and 2012 data are THE BODY SIZE OF SOLDIERS _ U.S. Army Anthropometry-1966 and 2012 ANTHROPOMETRIC SURVEY OF U.S. ARMY PERSONNEL: METHODS AND SUMMARY STATISTICS respectively.
Adult male head circumference 1966
Adult male head circumference 2012
Adult male head length in 1966
Adult male head length in 2012
Adult male head breadth in 1966
Adult male head breadth in 2012
Adult male head height in 1966
Adult male head height in 2012
Discussion
By 1966 standards,adult male U.S. head circumference, head length, and head breadth increased by 0.83, 0.66, and 0.27, standard deviations (SDs) respectively, though head height seems to have decreased by 0.12 SD (sampling error?). On average adult male head size measures have increased by 0.41 SD, however a study by JC Wickett et al found that head circumference was the single best predictor of brain size, and head height may even be negatively correlated with IQ, though given the small sample size, it’s important not to over-interpret this.
According to James Flynn, performance on U.S. IQ tests has been increasing by 3 point per decade since the earliest days of testing. This would suggest an IQ increase of 13.8 points from 1966 to 2012 or about 0.92 SD. This is only slightly more than the 0.83 SD increase in head circumference over the same period. And army data may slightly underestimate the head size increases because in 1966, even sons of the elite were often forced to join the army because of the draft, while in 2012, the poor and non-white have been forced to do more than their fair share of army service. Adjusting for demographic changes in the U.S. army, the head circumference increase might perfectly match the IQ increase.
Pumpkin Person 
Very interesting post and something that seems to verify my suspicions. According to Lee Pearson formula the 1966 CC is 1471cc and for 2012 it is 1497 cc. That constitutes a difference of 26 cc which is a lot less significant than one might suspect while using HC alone it would produce a figure that is wildly different to this. Also what this means is that head shape has changes somewhat since then. Of course it is not the type of head shape change that would render the Lee Pearson formula outdated(as mentioned before only a more box headed shape would do that) but it is one that can change our perceptions somewhat. This is not verified by extensive research but my suspicion is that changes in child rearing may be the cause for this. In recent years the practice of alternating the baby’s sleeping position from side to side is becoming more prevalent as opposed to having the baby sleep face up. Over a period of time this can change the shape of the skull making it longer as opposed to shorter but taller.
Now I am not denying that brain size has increased but my feeling is that it is not as significant as some people think while it is hard to envision how this increase can carry on at the rate it is currently at(unless you believe in the “magic” of epigenetics).
Finally the research citing no correlation of IQ to head height is bunk IMO. There is no reason that I can think of that would make this rationally possible. Brain Volume is brain volume, doesn’t matter too much how it is shaped as long as it is not too ridiculous. In fact I would think that a taller head tends to move the shape of the skull to become more spherical, a spherical shape tends to be more economical not only in packing the most volume per given surface area but also in creating the shortest distance between any two points in the brain(relevant brain regions). This increases perceptual time. In fact it has been proven that women tend to outperform men on average in certain aspects of simple perceptual speed(mathematical computations for instance). This is due to the fact that they have smaller more brachycephalic heads which shortens the distance brain signals need to travel, this may sound insignificant but multiply that by millions of signals per second you can see that this tends to add up while it also reduces the possibility for signal loss or errors. Men tend to mitigate this by having thicker and more heavily myelinated axons which increases the signal speed, which means that even though a greater distance needs to be covered it ends up being done in a shorter period of time. This of course comes at a greater energy cost and cognitive real estate(takes up mare space). Luckily men do tend to have bigger brains which in men whose brains tick all the right boxes puts them at the top tier in virtually every cognitive field well in excess of the best of the best among women.
Note that despite the fact that men have more neurons overall women tend to have greater neuron density than men which further supports the thicker myelination theory.
Now I am not denying that brain size has increased but my feeling is that it is not as significant as some people think while it is hard to envision how this increase can carry on at the rate it is currently at(unless you believe in the “magic” of epigenetics).
In theory I see no reason why brain size could not have substantially increased. There have been substantial increases in height, weight, birth weight, athletic ability, life span etc, over the 20th century. Why not brain size? Richard Lynn’s argues there was a substantial decrease in brain size and height when humans switched from hunter/gathering to agriculture because of malnutrition and disease, and only with the advent of 20th century nutrition and health have we finally returned to our genetic potential.
On the other hand it could be that brain size is so important that it evolved to be less sensitive to fluctuations in nutrition. It may even be that whatever nutritional increase in brain size has occurred was offset by dysgenic decrease in brain size as some scientists argue genetic intelligence has been decreasing, though that’s speculative.
But given that IQ scores have increased by as much as 30+ points over the 20th century, for there to be little corresponding increase in brain size would call the validity of IQ tests into question.
Finally the research citing no correlation of IQ to head height is bunk IMO. There is no reason that I can think of that would make this rationally possible. Brain Volume is brain volume, doesn’t matter too much how it is shaped as long as it is not too ridiculous. In fact I would think that a taller head tends to move the shape of the skull to become more spherical, a spherical shape tends to be more economical not only in packing the most volume per given surface area but also in creating the shortest distance between any two points in the brain(relevant brain regions).
Ironically wickett et al. make the same argument, yet reach the opposite conclusion. They write:
The negative weight on head height for predicting IQ, g, and fluid ability is interesting because it suggests that the shape of the head, and not just the size, is important. Greater intelligence is predicted by a brain that is larger in the width and length dimensions, but smaller in the height dimension. Considering the shape of the brain, the effect of widening the brain and reducing its height is to make it more spherical. This may be meaningful given that a sphere is the most efficient shape to minimize the mean distance between points. This increase in efficiency may be important to high-level intellectual functioning.
However I agree with you on this point. Modern humans are known for our relatively high and spherical heads. This is one of the defining characteristics of our species and what differentiates us from archaic sapiens who had low and relatively long heads. Indeed the greater efficiency of our head shape may have helped us defeat Neanderthals, even though they were our equal in raw brain size.
“call the validity of IQ tests into question.”
IQ tests aren’t (construct) valid.
“Considering the shape of the brain, the effect of widening the brain and reducing its height is to make it more spherical.”
Yes well, that statement by wickett et all is, I’m sorry to be blunt, also bunk. A perfectly spherical head of 159x159x159 would produce the same cranial capacity as the current average of 131x154x199. Note how significantly increased the head height is compared to head breadth while there is an even more significant decrease(this time) in head length. So basically not sure what they were smoking but they make no sense.
“However I agree with you on this point. Modern humans are known for our relatively high and spherical heads. This is one of the defining characteristics of our species and what differentiates us from archaic sapiens who had low and relatively long heads. Indeed the greater efficiency of our head shape may have helped us defeat Neanderthals, even though they were our equal in raw brain size.”
I think we might be in perfect agreement on this point!
As for the argument regarding our brains finally bouncing back to the size prior to the advent of farming due to recent improvements in nutrition, I think there might be something to that. However, here is my interpretation of the data. IMO(note this is more speculation on my part, might need to do some more research on this) what has happened is that our brains have indeed shrunk during that time but the number of neurons remained roughly the same. Neuron density increases in order to accommodate the same number of neurons within a smaller volume. How is this achieved, I think by accommodating less fat, thus reducing the amount of myelin on axons. This may be something that is readily correctable on a mass population scale within a few decades which is why we have seen this dramatic increase in brain size. IMO, the level of genetic evolution required to increase the brain by 10% lets say is of the order of at least 10,000 years(through natural forces), certainly NOT one century.
So in my opinion what we have actually seen is mostly cosmetic. As for the flynn effect, this increase in brain size may have helped somewhat qualitatively by producing more reliable brain signals from better myelination. Add to that the compounding effect of improved ways of cognitive and psycho-emotional organization/management and teaching methods, we get the slow increase in IQ. I do believe that one can learn how to think more efficiently thus creating a slow cumulative increase in IQ over time(thus improving the software while the hardware that is more or less the same). Of course this is mitigated by aging, lack of motivation and the fact that we don’t live long enough to see this increase reach any significant level. But with improved learning techniques we can transfer this valuable knowledge to the next generation which then shows up in the research as the flynn effect. Nutrition/lifestyle obviously matter too but I think the true hardware(number of neurons/glial cells) remains fairly constant over time(minus any marked genetic deviation) and requires thousands of years for a significant change.
Correction: In the post above I wrote that a smaller rounder head increases perceptual time. What I meant to say was that it increases perceptual speed, in effect reducing perceptual time. Note that this applies to simple mathematical computations, when the complexity increased significantly and abstract reasoning, visualization, lateral thinking and the like are necessary, usually this engages multiple regions and the more neurons the better ie a bigger brain facilitates this better.
An interesting bit of info regarding this is the difference in brain size between men and women. Even though there are studies that point to this translating to a higher IQ for men it seems that once we break things down it looks like in actual fact women tend to outperform men marginally in Verbal IQ while men outperform women in Math/Logic IQ. However something that is often overlooked is that men significantly outperform women in visuo-spatial IQ by at least 1 SD. That is quite significant and it turns out that of all the cognitive acuities this is the most labor intensive and requires the most cognitive bandwidth. As noted by Rushton in one of his papers a good way of understanding this is by comparing computer processing power needed for regular computations vs 3D rendering, the latter requires far more processing power.
But women are probably better as social IQ, which is not well measured by IQ tests.
“But women are probably better as social IQ, which is not well measured by IQ tests”
So it seems, I think that this may be the case because they are more predisposed to concerning themselves with people rather than things. Apparently they are better at reading body language too but I think this has more to do with their role in society. At the end of the day the brain only has x amount of space, you devote an extra amount of real estate to one specific thing, this tends to come at the expense of other things. It is hard, perhaps impossible to be highly proficient in all areas. I’m sure there are some men who may be far better at social IQ than the best of women. I do however believe that there is such a thing as social IQ, I just think that women go about it differently to men.
Ultimately though this may be more circumstantial and just be speculation on our part. What we do know for sure and for me this is the deciding factor, is that men have bigger brains(more heavily myelinated neurons) they have more neurons overall particularly in the frontal lobe, men also tend to have more intra-hemispheric connections while women tend to have more cross hemispheric connections. There are also differences in certain brain regions where women have the edge but overall men have the edge in more regions than women. I’m guessing this has more to do with our roles in society and the general differences in interests between men and women. So obviously if we go by hardware men certainly have the edge. How we go about using that hardware is a different story.
if you control for fat-free body mass 77% of the male advantage in head circumference vanishes. Of course head circumference is only a rough proxy for brain size
Well I believe that even after correcting for height and weight men still have about 100 grams more brain mass than women. I believe that roughly speaking for every SD(3 inches) increase in height there is a requirement of no more than 30 cc to deal with that extra mass. Note that the only real cognitive drain that comes with an increase in body size comes from the skin(pain, touch, hot/cold) and partially the muscles and organs(pain). So even after some correction for unaccounted body fat we can see that there is a significant advantage for men up to 1 SD which actually accurately predicts the 2-7 IQ points advantage for men that is often reported. Use of encephalization quotient among humans is outdated, a more sophisticated way of working it out is through surface area. Besides there is ample real world evidence that points to this advantage for men although it is often suppressed by the PC narrative.
Here is another study that contradicts the reported negative correlation of head height with IQ
https://dokumen.tips/documents/head-size-correlates-with-iq-in-a-sample-of-hootons-criminal-data.html
Note that head height correlated at 0.14 vs head length at 0.13 while the highest correlation was with head width with 0.15.
Also worth noting is the fact that with the study you mentioned the range of head height was 14.6 cm to 17 cm. For a study of just 36 individuals that is astonishingly high. It basically amounts to the 99.9th percentile to 3+ SD above that. That is unheard of and likely points to some kind of methodological error. It may well be that a couple of individuals had cognitive deficiencies and also had freakishly tall heads…or it may well have confirmed my suspicions that Mr Wickett has some kind of bias against tall headed individuals(joking of course).
Another strange thing about the Wickett et al. study is that when I calculated the samples average cranial capacity using Lee & Pearson, it was an incredible 1675 cc!
It’s not surprising that they would get strange results given that they did so many different correlations on such a small and unrepresentative (sibling pairs) sample.
“Another strange thing about the Wickett et al. study is that when I calculated the samples average cranial capacity using Lee & Pearson, it was an incredible 1675 cc!
It’s not surprising that they would get strange results given that they did so many different correlations on such a small and unrepresentative (sibling pairs) sample.”
Yes well, Patrick mentioned something about how they measured the head height and it seems suspect(possibly taken from the bottom of the ear and not the ear canal). Also 14.6 cm is already too high for a small sample let alone 17 cm. Add to that your finding for their cranial capacity and it is obvious we have a bad study on our hands. I personally give little credence to studies with a low number of test subjects. You’ll be surprised how often i run into shoddy methodologies or outright miscalculations. This is why people are so incredibly misinformed about a whole host of things, it seems there is a study that supposedly validates every variety of opinion out there. As long as their is money to be made or egos to massage there is always a way to fudge the data. Of course in this instance I think it is more a matter of incompetence.
As far as I can see Lee & Pearson and Wickett et al. used different methods to measure the height of the head. Lee & Pearson were measuring from the top of the tragion, while Wickett et al. were measuring from right under the ear canal. That makes a pretty big difference, I think.
Oh well that definitely explains it, but why on earth would they do that? Clearly there is methodological error here, obviously that would factor in the length of the ear in the calculations and last I checked ear length has nothing to do with brain size/IQ. You may be on to something regarding possible mentally disabled people with low sitting ears being included in the study.
https://dokumen.tips/documents/head-size-correlates-with-iq-in-a-sample-of-hootons-criminal-data.html
In any case this study clearly contradicts Wickett’s work and confirms what we all know to be pretty obvious.
I just wanted to mention that the method JC Wickett et al used to measure the height of the head would also measure the position of the ears. In some cases of genetic mental retardation one symptom is low sitting ears. So maybe the negative correlation with IQ is not caused by a larger height of the head, but by the lower position of the ears.
Yes it did cross my mind that greater head height might be more prevalent among people with cognitive deficiency than say greater breadth or length. Another explanation for this could be that some populations around the world(India, Pakistan, south and central asia) that have lower brain mass overall also tend to have a higher head than average but also very short in length. They also have IQ averages in the 80s. This might be where the association came from.
I knew I had a rather big head but it was not a problem until I became bald and had to wear a hat to protect against the sun or cold weather.
I the found that it was almost impossible to get a hat, that fits my head.
I have to wear a size 8 or 63,5 cm hat.
Even in special hat shops that size can be difficult to find.
I believe the reason to my big head is, that I have a big brain however my says its because my skull is thick. Whatever the explanation it is a challenge now as I am older.