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The possible loss of two fig leaves in anthropology...
Ralph L Holloway (rlh2@COLUMBIA.EDU)
Sun, 5 Feb 1995 22:31:40 -0500
in this newsgroup, and I've posted a few thoughts recently, I'd like to
take a a more daring tack. For the thirty years that I have been teaching
physical anthropology I've always taught my students that (1) there is no
known solidly empirical demonstration that there exists a strong
relationship between the size of the human brain and intelligence,
however measured, conceived, etc; (2) there are no known demonstrated
important organizational differences known in the structure of the brain
between different racial groups. I used to belabor these seemingly
obvious points by pointing out that the total range of human variation in
brain size equaled roughly 1000 grams (or cc's, or ml) --remembering the
old chestnuts of Anatole of France (1000 or less) and Jonathon Swift and
Turgeneev ( about 2000 or more)-- and that this variation is about the
same (if not more) than the total evolutionary change from
australopithecines (450) to modern Homo at about 1450 (in cc's). How then
could we talk about brain size increase being such an important variable
in hominid evolution? How could we talk about minor differences in brain
size being of any importance between living human populations? (I'll bet
this sounds familiar, doesn't it...?).
Two recent publications are leading me to re-examine the above.
(1) Andreason et al, 1993, Intelligence and brain structure in normal
individuals, Am. J. Psychiatry 150:130-134, have studied MRI in a sample
of normal healthy adults, and found significant correlations with
"full-scale IQ" and intracranial volume, cerebral , temporal lobe,
hippocampal, and cerebellar volumes (not caudate or lateral ventricular
volumes), after partialling out height (which has a high correlation with
brain size). The correlation coefficient was up to .38 for the
cerebrum, .46 for temporal lobes, .44 for cerebellum, .42 for
hippocampus. Gray matter correlated at .35. To me, these are pretty high
correlations, but as the authors suggest, leaves much of variance to be
explained by variates other than brain size. Then there are the reports
found in Rushton's book and recent editorial in Intelligence 19, 263-280
(1994). All require careful study to see if such results are replicable.
(2) Of more interest to me is something I've been sitting on for about
ten years, which was a data set comparing the volumes of primary visual
striate cortex (Brodmann's area 17) between caucasians and Australian
aboriginals. That study has at last been published and shows that the
volume of primary visual striate cortex in Aboriginals is roughly twice
the volume of that in caucasian brains. It holds in both sexes. Here is
the reference: Klekamp et al (1994) Morphometric study on the postnatal
growth of the visual cortex of Australian Aborigines and Caucasians. J.
Brain Research 35(4):541-548. This correlates very well with several
studies which have shown higher scores in visual acuity among aboriginals
(see in particular, Kearins (1981) Cogn. Psychol. 13:434-460. This occurs
in peoples whose brain weights are significantly smaller than those for
caucasians. The authors are very very careful not to rule out nutrition
and growth factors, but for my part I have difficulty in NOT believing
that the main factor is neurogenetic, since the difference is very great
and nutritional diffderence do not normally 'cause' such a magnitiude of
structural difference. (See also Reidel et al 1994 on the postnatal
growth of the cerebral cortex in Aboriginals in the same journal, issue,
pps. 531-540., which makes a strong case for nutritional factors in such
growth.)
I had the opportunity to discuss this with the Australian
paleoanthropologist, Alan Thorne, who mentioned this research at a James
Arthur Lecture on the Evolution of the Human Brain in NY, in which he was
concerned with the sophistication and antiquity of Australian Aboriginal
art. I was delighted to hear him remark that the australian aboriginals
were quite pleased to learn that their brains were somewhat different
from those of Caucasians !!
For decades now, it has been just fine to talk about biological
variation in our polytypic species from the neck down, but the gratuitous
assumption that somehow the central nervous system was spared
similar variations, however formed, of this, our most important and
wondrous organ of adaptation, has left me a virtual closet-case in
anthropology. I frankly love the fact that we are so variable, I find it
a beauteous thing, and I strongly believe that racial prejudice cannot be
fought without open and honest acceptance of our variability. In fact,
whatever the small differences in organization or size of the brain, our
abilities and shared intelligence are so overlapping that discrimination
is simply inherently stupid, because it robs the world of much needed
excellence which exists in all populations. Frankly, I embrace this
diversity, and will continue to study it.
OK, let the storm commense... Ralph L. Holloway
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