Brain capacity CC

Brain sizes(*) vary considerably within any species, but this variation is not usually related to intelligence. Instead, it correlates loosely with body size: large people tend to have larger brains. As a result, women on average will have smaller brains than men, and Pygmies will have smaller brains than Zulus, but the average intelligence of all these groups is, as far as we can tell, the same.

(*) Note: for convenience, I use the term "brain size" instead of "cranial capacity". Because the brain does not fill the cranial cavity, the brain size is smaller than the cranial capacity, but the latter value is, obviously, the only one that can be determined from a skull.

Figures for the average brain size of modern humans tend to vary between sources, but a typical value is 1350 or 1400 cc (cubic centimetres). The following figures should convey a feel for the normal range of variation in human skulls. Burenhult (1993) states that the 90% of humans fit in the range 1040-1595 cc, and that the extreme range is 900-2000 cc. S.J. Gould, in "The Mismeasure of Man", reviewed a 19th century study by Morton of 600 skulls which ranged from 950 to 1870 cc (and 25% of this sample was of small-statured Peruvians, so the figure of 950 cc is, if anything, lower than it might be for 600 randomly selected humans). Morton also catalogued his skulls by race, with the lowest average for any racial group being 1230 cc.

Various sources, some of them creationist, give lower limits for human brain size of 900 or 830 cc. The prominent British anatomist Sir Arthur Keith in 1948 gave 855 cc as the lowest known human brain volume (compared with 650 cc as the then highest known brain volume for a gorilla). Normal humans with even smaller brains have been found, but they are very rare. Microcephalics, who are subnormal in intelligence, can be as low as 600 cc, but this is a pathological condition and such skulls cannot be considered normal.

Hrdlicka (1939) examined the extremes of brain size in the 12, 000 American skulls stored in the U.S. National Museum collections. Of these, the smallest 29, or fewer than 1 in 400, ranged from 910 to 1050 cc. Hrdlicka states that the smallest skull in this collection, at 910 cc, appears to be the lowest volume ever measured for a normal human cranium. The low volume skulls were not primitive or aberrant in any way; their small volume was merely a result of the smallness of the entire skull. So although the extreme lower range of modern human brain sizes does overlap that of Homo erectus, their skulls are very different: in H. erectus, the brain case really is smaller in relation to the rest of the skull. In small modern humans, the skull proportions are normal and the brain size is small only because the skull is small. (Compare the Turkana Boy skull and a modern human here.)

Compare the above figures with the 5 measurable Java Man skulls. These average 930 cc, less than the minimum of the 600 modern skulls cited above, with the smallest being 815 cc. Moreover, unlike modern humans with low brain sizes, these skulls are very robust, with flattened braincases and large brow ridges.