From weighing wet brains at autopsy and calculating cranial capacity from skulls and external head measurements, it will be seen from modem as well as historical studies that Mongoloids and Caucasoids average larger brains than Negroids. The Mongoloid > Negroid finding is especially striking. When ad justments are made for body size, Mongoloids have even larger and heavier brains than do Caucasoids. Although sampling and methodological difficul ties may be identified in particular studies, results obtained from multimethod comparisons allow a triangulation on probable truth.
The racial differences in brain size show up early in life. Analyses of the U.S. Collaborative Perinatal Project discussed in chapter 2 showed that 17,000 white infants and 7-year-olds had significantly larger head perimeters than their 19,000 black counterparts, even though, by 7 years, black children were taller and heavier (Broman et al., 1987). In all groups, head perimeter at birth and at age 7 correlated with IQ at age 7 from 0.10 to 0.20.
Small differences in brain volume translates into greater brain efficiency and millions of excess neurons and helps to explain the global distribution of intelligence test scores. It will be seen that Caucasoids from North America, Europe, and Australasia generally obtain mean IQs of around 100. Mongol oids from both North America and Pacific Rim countries typically obtain higher means in the range of 101-111. Negroids from south of the Sahara, the Carib bean, or the United States obtain means of from 70-90. Studies of mental decision times, measured in milliseconds, which correlate with conventional IQ tests (chap. 2), show that Mongoloids have the fastest reaction times, fol lowed by Caucasoids, and then by Negroids.
Brain Weight at Autopsy
In a review highly critical of the literature on wet brain weight measured at autopsy, Tobias (1970) claimed that all interracial comparisons were “invalid,” “misleading,” and “meaningless” because 14 crucial variables had been left uncontrolled. These included “sex, body size, age of death, nutritional state in early life, source of the sample, occupational group, cause of death, lapse of
time after death, temperature after death, anatomical level of severance [of brain from spinal cord], presence or absence of cerebrospinal fluid, of meninges, and of blood vessels” (pp. 3 and 16/ Tobias pointed out that each of these variables alone could increase or decrease brain size by 10 to 20 percent, an amount equivalent or greater than any purported race difference. He equally opposed conclusions of race differences in structural variables such as corti cal thickness, size of frontal lobe, or complexity of the brain’s convolutions.
Because I was curious to know what the data would show, despite method ological weaknesses, and because I believed that the principle of aggregation (chap. 2) often cancels measurement error, I calculated the mid-points of the range of scores provided by Tobias (1970: 6, Table 2) and found that Mongol oids averaged 1,368 grams, Caucasoids 1,378 grams, and Negroids 1,316 grams (Rushton, 1988b). I also averaged a related measure, the “millions of excess nerve cells” estimated by Tobias for 8 subgroups and nationalities (1970: 9, Table 3). These were the number of neurons available for general adaptive purposes over and above that necessary for maintaining bodily functioning and were derivable from equations based on brain/body weight ratios (Jerison, 1963,1973). Tobias was skeptical of the value of this “exercise” and provided few details. Nonetheless, I found that in millions of excess neurons, Mongol oids = 8,990, Caucasoids = 8,650, and Negroids = 8,550 (Rushton, 1988c).
Subsequent to Tobias’s (1970) review, a major autopsy study was carried out by Ho et al. (1980a, 1980b) who provided original brain weight data for 1,261 adult subjects aged 25 to 80 from Cleveland, Ohio. Ho et al. excluded those brains obviously damaged and avoided most of the problems cited by Tobias. Sex-combined differences were found between 811 American whites (1,323 g; SD = 146) and 450 American blacks (1,223 g; SD = 144), a differ ence that, according to Ho et al., remained significant after controlling for age, stature, body weight, and total body surface area.
In the introduction to their article, Ho et al. (1980a) briefly reviewed addi tional literature from which I calculated that Mongoloids averaged 1,334 grams, Caucasoids 1,307 grams, and Negroids 1,289 grams. Averaging the three sets of estimates (Tobias’s review, Ho et al.’s review, and Ho et al.’s data), I found a sex-combined brain weight for Mongoloids of 1,351 grams, Caucasoids 1,336 grams, and Negroids 1,286 grams (Rushton, 1988b). Further, Ho et al.’s re view suggested that, whereas the Caucasoid brain weight began to decline at age 25, the Mongoloid brain weight may not do so until age 35.
Endocranial Volume
Many more studies have estimated brain size from cranial capacity, for, as J. R. Baker (1974: 429) remarked, “Skulls are many, freshly removed brains are few.” This literature too has undergone serious critiques, for example, by Gould, first published in Science (1978), and then his book, The Mismeasure
o f Man (1981). In particular, Gould re-analyzed Morton’s (1849) work, men
tioned in the last chapter, and alleged that the figures had been biased by “unconscious...finagling” and “juggling” (1978: 503).
Gould (1981: 65) suggested how biases could be introduced into such data:
Plausible scenarios are easy to construct. Morton, measuring by seed, picks up a threateningly large black skull, fills it lightly and gives it a few desultory shakes. Next, he takes a distressingly small Caucasian skull, shakes hard, and pushes might ily at the foramen magnum with his thumb. It is easily done, without conscious motivation; expectation is a powerful guide to action.
TABLE 6.1
S. J. Gould’s “Corrected” Final Tabulation of Morton’s Assessment of Racial Differences in Cranial Capacity