Cranial Capacity of Real and Imagined Races of Man

The fine art of turn of the century physical anthropology involved measuring the size of the skull (and therefore the size of the brain) to determine the innate capacity of the different “races” for civilization. It was commonly held that such morphological investigations had yielded “scientific proof” of the biological superiority of some races over others. This business was closely tied to Polygenism which emerged in the 18th century. Leading scientists considered races to be species separately created by God. After the acceptance of Darwinian evolution in the late-nineteenth century, the polygenic outlook was modified. The “races of man” were now thought to have evolved, pace Wallace (1864), from different primates or early hominids in more or less absolute isolation from each other.

Perhaps the most influential high racialist, certainly from a historical perspective, was Ernst Haeckel (1834–1919). Whereas Social Darwinism was used to justify laissez-faire capitalism in the Anglo-Saxon world, Haeckel emphasized the struggle for survival between the races as the motor of history. Our man celebrated the vanishing of weaker races and the proliferation of the vigorous ones. The Nazis were big fans. Indeed, National Socialism was nothing but “applied anthropology.” Haeckel’s thought formed the central theorem of Nazism; it was “the only element of the Nazi era which was neither modified nor manipulated in response to strategic or tactical requirements” (Rich 1973).

After Auschwitz, overt racialism was abandoned by mainstream anthropology. But it continued to thrive on the margins. The last hurrah of anthropological racialism was probably Carleton S. Coon’s Origin of the Races (1962). Coon pushed the idea that human races were different subspecies that had evolved in parallel with little or no contact. Himself a one-time president of the American Anthropological Association, he was harshly condemned by the then president, Washburn, at the 1962 meeting. At the end of the speech, the audience stood up, cheering.

Besides the racialized trauma of the mid-century passage, there was mounting evidence that all extant humanity could trace their lineage to Africa in the not too distant past so that not enough time had elapsed for the emergence of subspecies in humans. Of course, there is substantial biological variation in humanity. But it was by then understood that racial taxonomy was a poor way to understand this variation. Human biological variation is largely within populations; and even between populations it varies continuously, not discretely (a necessary implication of racial taxonomy). The modern understanding was captured by Frank Livingstone in the same year as the last hurrah of racial anthropology: “There are no races; there are only clines.

The fine art of human craniology survived in paleontology departments. Dealing with fossils from millions of years ago (Ma), there was much less at stake in morphological taxonomy. Nor was it a secondary issue. Hominin are classified above all by cranial capacity. Indeed, the definition of the genus Homo boils down to hominins with a cranial capacity greater than 600 cubic centimeters (cc). Early hominins, although committed bipedals (including late pre-Homo tool-manufacturers) are placed in different genera above all because their brains are considered too small. Figure 1 displays the evolution of average hominin cranial capacity by taxon.

Figure 1. Average cranial capacity by hominin taxon.

Two observations. First, H. neanderthalensis had slightly bigger brains than H. sapiens. This calls into question either the equation of cranial volume with intelligence, or our name, Homo sapiens, ie “wise guy.” Second, the averages shown in Figure 1 conceal massive variation as well as the exponential growth in hominin cranial volume. Figure 2 is more revealing. Note the log scale of the time axis. What the figure shows in exponential growth in human cranial volume since we split from our common ancestor with the chimps 7 million years ago (Ma).

Figure 2. Hominin cranial volume. Source: Spocter (2007).

The mixing of genera in Figure 2 would perhaps scandalize a purist. Figure 3 zooms into the past two million years; the Age of Homo. Red represents Neanderthal crania; blue, H. sapiens; and black, other “species” in the genus Homo.

Figure 3. Cranial volume in the genus Homo. Source: Spocter (2007).

What of the races imagined by the pioneers of craniology? Given all the hullabaloo, surely there was some empirical basis for the alleged racial differences in cranial capacity? Indeed, as late 1994, Rushton, the high racialist out-of-time, argued in Race, Evolution, and Behavior that Black crania were 80 cc smaller than White crania, which in turn were 17 cc smaller than Asian crania (thereby reversing the classical ordering claimed by high racialists: White > Asian > Black).  I have found that it is always a good idea to check such claims. Table 1 shows the summary statistics for cranial volume by “race.” The data is taken from the US Army’s ANSUR II Male working database which contains a total sample of 4,082 subjects. In order to calculate cranial capacity we use the formula from Rushton (1993).

Table 1. Cranial volume by “race.”
Source: ANSUR 2 (2012), author’s computations.
“Race” Num Mean Std Min Max Range
White 2,817 1,474 84 1,198 1,818 620
Black 642 1,489 91 1,148 1,792 644
Hispanic 440 1,465 85 1,185 1,767 582
Asian 117 1,471 87 1,256 1,725 469
Other 66 1,481 88 1,308 1,655 347
All 4,082 1,476 85 1,148 1,818 670

Turns out, it is precisely the other way around. On average, Black men’s crania are 15 cc larger than White men, who in turn have crania that is on average 3 cc larger than Asians. Of course, these differences are utterly insignificant in light of the substantial variation. For instance, 15 cc is a trivial 0.18 standard deviations. Indeed, the most important numbers in Table 1 are in the last three columns. They emphasize the dramatic scale of the variation at the individual level. The range for both Blacks and Whites is well over 600 cc! The standard deviation of cranial capacity for the other “races” in America is comparable. The only reason the range is lower is because of smaller sample sizes. Figure 4 shows a boxplot of the same data. Racial taxonomy gives us no handle at all on the variation in human craniology.

Figure 4. Boxplot of cranial volume by “race.” Source: ANSUR 2 (2012), author’s computations.

If you want to try this at home, you don’t need to make complicated measurements of your head. Instead, you can proxy cranial capacity by head circumference. Figure 5 shows the tight linear relationship. It also displays the estimated regression line, which you can use to get a quick and dirty estimate of your cranial volume.

Figure 5. Head circumference and cranial volume. Source: ANSUR 2 (2012), author’s computations.

Caspari et al. (2017) made a compelling argument that human subspecies are not a logical impossibility. Many extinct hominins in the genus Homo weren’t other species. Rather, they were human races or subspecies. H. erectus may indeed have been a different species since it diverged from our lineage 2 Ma; perhaps enough time for speciation. (Biologists reckon that across the animal kingdom speciation takes about 1 Ma.) But our last common ancestor with Neanderthals, Denisovans, as well as the ghost populations whose signature is all over our genome but whose fossils have yet to be found, lived some 600 Ka (thousands of years ago). That’s enough time for raciation but not speciation. More importantly, we interbred with these humans; not now and then but continuously after our multiple dispersals from Africa between 130 Ka and 40 Ka. (As we surely did with other races in our African homeland early in our career.)

H. sapiens emerged 200 Ka in Southern Africa and spread to East Africa soon after. (The “purest” H. sapiens today are the Koisan, the Kalahari Bushmen.) Meanwhile, Eurasia was populated by a number of now-extinct human races. For some half a million years then, we were genetically isolated from the hominins who populated Eurasia. Moreover, even by the standards of the late Pleistocene, Neanderthal populations were very small and isolated. Population densities were extremely low. And in the face of the violent glacial-interglacial whipsaw of Pleistocene Europe, they found themselves periodically isolated in refugia below the Alps. Dating in the Neanderthal world must have been tough! The prolonged isolation and extremely low population densities well-approximate the extended isolation of the races of the high racialist imaginary.

But isolated or not, Neanderthal were definitely people. From Capari et al. (2017):

Neanderthals were capable of complex behaviors reflecting symbolic thought, including the use of pigments, jewelry, and feathers and raptor claws as ornaments. All of this is probably evidence of symbolic social signaling, complementing the evidence of complexity of thought demonstrated by the multi-stage production of Levallois tools. Neanderthals were human.

Moreover, the notion that our race had cognitive advantages over the other races has to be abandoned. The difference wasn’t brains. Perhaps it was grandparents. … I am only half-kidding. The decisive difference seems to have been different life histories. Our race lived dramatically longer. And it is that which admitted a quantum leap in dynamism via the intergenerational transmission of knowhow and knowwhere and so on. More on that another time.

Figure 6. H. sapiens (Libben) and H. neanderthalensis (Krapina lx) survivorship curves.

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