For a long time I had argued, based on cranium data, that brain size has been increasing in the developed world by about 1.3 standard deviations a century. But then there was a paper published, which actually looked at secular increases in brain weight in various countries, and found very tiny increases in brain size. I quibbled with aspects of this study (especially the use of non-age controlled standard deviations to measured standardized changes over time), but ultimately agreed that brain size gains have been much smaller than I had thought. Still, it didn’t make any sense to me, given the much larger secular increase in head size, which is closely linked to brain size.
Well, now it seems I was right the first time. Brain size gains really have been about 1.3 standard deviations per century, just as I originally thought. This is evidenced by an extensive 19th century data-set by Broca which found male brains averaged 1325 g (1259 cm3 in vivo)and female brains averaged 1144 g (1087 cm3 in vivo). I suspect these brains were taken from people who died in their late 40s (typical of the time period).
To put that in perspective, a study by Ho et al (1980) found that White American men and women (who presumably died circa 1980) had autopsied brain weights of about 1392 g and 1252 g at age 60 and 1570 g and 1339 g at age 25 respectively. Assuming age differences in brain weight are linear, we can deduce that 48.5 year white American men and women dead circa 1980 had autopsied brain weights of 1450 g (1378 cm3 in vivo) and 1281 g (1218 cm3 in vivo) respectively. So summing up:
men | women | |
brain size of French 48ish year olds dead circa 1877 | 1259 cm3 | 1087 cm3 |
brain size of white american 48.5 year olds dead in 1980 | 1378 cm3 | 1218 cm3 |
absolute difference in 103 years | 119 cm3 | 131 cm3 |
standard deviation (sd) | 91 cm3 | 90 cm3 |
difference in sd units per century | 1.27 | 1.42 |
Averaging men and women together, brain size has increased by 1.35 SD per century.
Now a study of identical twins born with different nutrition levels suggests that malnutrition has virtually the same effect on later brain size that it has on later performance IQ (when both are measured in SD units), but has virtually no effect on verbal IQ. Thus if 20th century nutrition caused brain size to increase by 1.35 SD, it probably also caused Performance IQ to increase by 1.35 SD, so nutrition likely caused a 20 point per century rise in Performance IQ, a roughly 0 point per century rise in Verbal IQ, and about a 9 point rise in Global IQ.
In other words, nutrition explains about a third of the Flynn effect, which is 30 points per century. In other words, a third of the Flynn effect is a gain in real intelligence: biological intelligence. Another third of the Flynn effect can be explained by the rise in schooling, and the final third of the Flynn effect can be explained by people being raised in more educated affluent homes (similar to the well documented 10 point adoption effect)
Some would argue that socialization can not explain secular increases in adult IQ, because the effects of parenting vanish by adulthood, however the Dickens-Flynn models shows that to only be true within generations, not between them.
A good analogy for the Flynn effect would be if average height had increased by 2 standard deviations per century. and then it was discovered only about 0.66 SD of this increase were real. Another 0.66 SD was because people were wearing higher heeled shoes, and yet another 0.66 SD was because parents were raising their kids to stop slouching.
Nitpicking comment. Wasnt there a paper recently that suggested early death (under age 30) have on average a lower IQ than the survivors? So..would the people who are dead at 25 be a couple of IQ points lower than the population? Then the correlation between brain size and IQ…so would the slope of the linear approximation be steeper?
Pumpkin what do you think about making monthyl open threads?
I’d be willing to do that but a lot of the posts become open threads anyway.
What about C-section? It enabled big brained babies and mothers to survive. It broke the possible limit of brain size. Without C-section, most big brained people wouldn’t be alive today.
That certainly had some effect, but given that only a small percentage of babies were affected, and given the imperfect correlation between baby head size and adult brain size, the effect might be small.
Classic White Americans out of Irish or German or even English stock have much larger heads than French people.
Head size is more influenced by body size than brain size is. In the 19th century, Gratiolet claimed Germans had brains 100 g heavier than the French, but Broca argued the sampling was biased because Germans died younger and from violent causes (as opposed to death after illness which he felt shrunk the brain). Correcting for these two factors alone, Broca found French brains to be heavier than German brains, but Broca was French so he might have been biased.
Hey Pumpkin Person. Yours is one of the few websites I’ve been visiting regularly.
Your articles are always fascinating and intriguing.
I’ve noted that you do not have a “blog roll”, or any series of links to recommended sites.
Perhaps you can point me in a direction for some recommended reading, anything that captivates you. Websites as well as book would be good.
The same goes to you other readers and commentators here.
Thank you
– Wieland
I don’t have time to read many other blogs, but when I do, I usually check out Steve Sailer :
http://www.unz.com/isteve/
Several regular (or formerly regular) commenters on this blog have blogs that I try to check out:
AKarlin
http://www.unz.com/akarlin/
Racerealist
http://notpoliticallycorrect.me/
Alcoholicwisdom
https://alcoholicwisdom.wordpress.com/
Robert Lindsay
https://robertlindsay.wordpress.com/
Bruce Charlton
http://iqpersonalitygenius.blogspot.ca/
Bruce Charlton also has a book I plan to read
http://iqpersonalitygenius.blogspot.ca/2016/01/my-new-book-genius-famine-is-now.html
ruhkukah might be creating a blog
http://en.gravatar.com/ruhkukah
Hope I’m not forgetting any regular or former regular commenters. If so, please add yourselves.
Me!
Whoops, just saw you add me. Thank you kindly, PP. =^)
http://www.counter-currents.com/2016/03/genius-religion-and-compassion/
Perfectly said.
Didn’t brain size rise in the 20th century, which is attributed to better nutrition due to the industrial revolution? So with that brain size rise, IQ gains followed because of the .33 correlation (I think I remembered that post of yours correctly).
I read that Lynn paper you mentioned in your post the other day. I’m studying nutrition currently and am extremely interested in nutrition’s effect on IQ and brain size.
Here’s a good cite from Rushton and Jensen (2005):
“Studies of Korean and Vietnamese children adopted into White homes show that
although as babies many had been hospitalized for malnutrition, they nonetheless
grew to have IQs 10 or more points higher than their adoptive national norms. By
contrast, Black and mixed-race (Black–White) children adopted into White middle-class families typically have lower average scores than the White siblings with
whom they had been reared or than White children adopted into similar homes”
“Three studies of East Asian children adopted by White families support the
hereditarian hypothesis. In the first, 25 four-year-olds from Vietnam, Korea,
Cambodia, and Thailand, all adopted into White American homes prior to 3 years of age, excelled in academic ability with a mean IQ score of 120, compared with the U.S. norm of 100 (Clark & Hanisee, 1982). Prior to placement, half of the babies had required hospitalization for malnutrition.”
“In the second study, Winick, Meyer, and Harris (1975) found 141 Korean
children adopted as infants by American families exceeded the national average
in both IQ and achievement scores when they reached 10 years of age. The
principal interest of the investigators was on the possible effects of severe
malnutrition on later intelligence, and many of these Korean children had been
malnourished in infancy. When tested, those who had been severely malnourished
as infants obtained a mean IQ of 102; a moderately well-nourished group obtained
a mean IQ of 106; and an adequately nourished group obtained a mean IQ of 112.”
Click to access Rushton-Jensen30years.pdf
They bring up nutrition a few times in the paper. This is also seen in Italian immigrants (who are mostly from Southern Italy). I’m half Calabrese, so I know about the struggles of Italian immigrants in America and the conditions in Southern Italy that drove them to come to America.
Around 30 million Europeans are malnourished, so they come to America and they get an IQ boost due to better nutrition.
Pumpkin, how is the Matrix Reasoning susceptible to practice effects? Isn’t it designed in such a way that no matter how much time you think about the pattern, if you don’t have the power, you can’t do it?