Re: Brain Development

Ralph L Holloway (rlh2@COLUMBIA.EDU)
Sun, 5 Feb 1995 12:57:57 -0500

We are really at a loss with deciphering knowledge regarding variability
in thge brain and behavioral variability into something causal from that
which is purely correlational. The cold weather scenario is interesting,
but then again there is an association between body mass and brain weight
that appears tro be a positive correlation at roughly .35 max. What
strikes me sometimes ( and see also the Beals et et paper in Amer.
Anthrop., back a few years ago that showed a clinal distribution between
cranial capacity and latitude world wide) is the possibility that there
is so little knbown about differences in behavioral variation, that I
often speculate to my students that black (read African) brains might be
more metabolically efficient than white brains in that the behavioral
distributions are roughly equal while the black brain has less weight in
the tropics, reflecting a possible advantage in terms of metabolic
efficiency. It is intriguing that among Bantu in S. Africa, there appears
to be no difference in brain weights when compared to S. African whites.
Of course this was before recent data (which Rushton has mentioned)
indicating that recent studies using MRI (magnetic resonance imaging)
shows higher corrleations between brain size (but how excatly measured?)
and IQ's, around .6 . If these studies are replicated, it does suggest
the end of one of anthropology's traditional fig-leaves, that thewre is
no relationship between brain size and behavior. I'm open to the
demonstration, but until then, I am struck by the enormous degree in
overlap between brain sizes and behavioral complexity that society finds
n Sat, 4 Feb 1995, Read, Dwight ANTHRO wrote:

> Holloway has already pointed out the factual problem with the claim:
> "Ice would advance, creating harsh conditions that required intelligence to
> cope with, and then recede creating a rich, abundant environment that
> spurred fairly rapid bouts of speciation."
> (which is a statement previously posted as a brief synopsis of a longer
> argument by Calvin (?) on the ice age as a driving mechanisim for increase in
> brain size in hominids).
> In addition to factual problems, this type of argument tries to convert
> association (actually, it is even wrong on the association as Holloway notes,
> but even if it were not factually wrong...) into causation without
> establishing a plausible causal mechanism. As stated, the argument applies
> equally to ANY species, hence EVERY species subjected to the rigors of the
> Ice Age should demonstrate "rapid bouts of speciation" and development of
> intelligence. Failing that, at most there is association (assuming the
> argument was not factually incorect) and no causal link between ice ages and
> change in hominid brain size.
> D. Read