On page 124 of scholar Stephen Jay Gould’s The Mismeasure of Man, he writes about a fascinating era when men of eminence (culturally recognized Geniuses; Nobel Prize winners) donated their brains to science.
Some men of genius did very well indeed. Against a European average of 1,300 to 1,400 grams, the great Cuvier stood out with his topheavy, 1,830 grams. Cuvìer headed the charts until Turgenev finally broke the 2,000-gram barrier in 1883. (Other potential occupants of this stratosphere, Cromwell and Swift, lay in limbo for insufficiency of record.)
The other end was a bit more confusing and embarrassing. Walt Whitman managed to hear America singing with only 1,282 grams. As a crowning indignity, Franz Josef Gall, one of the two founders of phrenology – the original “science” of judging various mental capacities by the size of localized brain areas – weighed in at a meager 1,198 grams. (His colleague J. K. Spurzheim yielded a quite respectable 1,559 grams.) And, though Broca didn’t know it, his own brain weighed only 1,424 grams, a bit above average to be sure, hut nothing to crow about. Anatole France extended the range of famous authors to more than 1,000 grams when, in 1924, he opted for the other end of Turgenev’s fame and clocked in at a mere 1,017 grams.
While Gould doesn’t report the average eminent brain, a simple way to estimate it is to observe the range, from the largest Genius brain (Turgenev; 2021 g) to the smallest (Anatole France; 1,017 g), and take the midpoint: 1519 g. However as scholar J.P. Rushton has explained, brain weight increases by 9% postmortem so I will divide this figure by 1.09 to get the in-vivo weight which gives 1394 g. Now to convert brain weight to volume, you multiply by 1.036 which gives 1444 cm3
How does this compare to normal men of that generation? The average year and average age when these two eminent men died was 1904 and 72 respectively. Meanwhile data from the general population shows that British men who died in 1907 (average age 47) had a mean brain weight of 1372 g. But these men were born 28 years later (on average) so to make their brain weights comparable we adjust for age by noting that from age 25 to 80, brain weight varies negatively with age by 2 g per year, so general population British men of the same average generation as Turgenev/France would be 1316 g. Dividing this by 1.09 and multiplying by 1.036 reveals this generation of men had a mean volume of 1251 cm3, 193 cm3 smaller than the average Genius of that era. Since Rushton’s military data shows that the cranial capacity standard deviation (SD) in white men is 91 cm3, the average Genius had a brain 2.12 SD bigger than normal!
Corrected for reliability and range restriction, the true correlation between IQ and brain size is probably 0.5, suggesting the true correlation with g (general intelligence) is 0.53. This correlation is far from perfect, and suggests that the brain size of Geniuses regresses precipitously to the mean (see validity generations). To correct for this regression, we divide the average Genius brain size (+2.12 SD) by 0.53 which gives an average IQ on a hypothetically pure measure of general intelligence of 4 SD above white men (IQ 162)! However because the typical IQ test “only” has a g loading of about 0.85, Geniuses should regress 15% to the mean on an IQ test and average 153 when tested (assuming the test has sufficient ceiling). Indeed an important study of extremely eminent scientists found they had a mean tested IQ of 150.