Re: Brain Size and Tools I

Ralph L Holloway (rlh2@COLUMBIA.EDU)
Sat, 4 Mar 1995 22:25:51 -0500

I certainly don't know the answers to problems posed by Larry Mai. I
would point out that the fossil record is simply inadequate to
demonstrate the kinds of relationships that might falsify hypotheses
regarding the so-called 'constraints' on brain enlargement. Two useful
sources I've seen (one to be published in the near future)are the 1993
issue of Behavioral Brain Sciences that featured Dean Falk's "Radiator
Hypothesis". The useful part is really the discussion that followed her
presentation. The evidence for any dramatic change in venous drainage
patterns between early non-gracile (A. africanus) australopithecines such
as the robust forms or those earlier at Hadar isn't available. There is a
real question as to exactly what the marginal-occipital venous drainage
pattern 'proves' (e.g., read Kimbel's and others'comments). The second is a
paper
that will appear in CA (Current Anthropology) which looks not only at the
brain and its thermoregulation, but also the internal organs, which
happen to be very expensive metabolically. The author(ess) Leslie Aiello
makes an interesting argument regarding a change in dietary habits and
reduction of the guts, which might in turn have lessened the severity of
one constraint sufficiently.
As for encephalization, my reading of the fossil evidence suggests anything
but homogeneous processes at work over time. There are, as there were
even in the horse brain, periods of time when brain size increase appears
to be allometric and other times when it was not. The habilines are a
real problem here: is 1470 (?rudolfensis) the same critter as all that
stuff from Olduvai? I don't think so, but the postcranials for Olduvai
show something quite small, whereas if the femoral stuff from East Lake
Turkana is associated with 1470-like crania, one would probably have to
explain the increase in brain size as almost wholly allometric. And then
there is KNM-ER 1590, which is clearly larger than 1470... Worth
remembering too is the fact that all body weights are guestimates, and
these can vary quite a lot depending on the statistical techniques used.