Re: Brain size, IQ

Ralph L Holloway (
Mon, 16 Sep 1996 23:41:03 -0400

On 14 Sep 1996, Bryant wrote:

> In article <Pine.SUN.3.95L.960909233511.11048B-10
> > "Ralph L Holloway" writes:
> >
> >> Minor differences in our brain sizes seem to have little
> >> if anything to do with intelligence as far as I can tell.
> An anthro student emailed me a reference cited by Rushton which shows
> that neuron packing density and brain size correlate positively.

When neuron packing density is high, the cells tend to be smaller and have
fewer ddendritic branches. I sincerely doubt that that correlates
"positively" with brain size, which tends to show quite the opposite (see
Holloway 1968 in Brain Research for a review of these problems), i.e., as
the brain size increases so do the average perikarya sizes of the neurons,
tand the density thus decreases, and the glial/neural ratio tends to
increase, and the dendritic branching increases also, trends concordant
between ontogeny, phylogeny, and experiemntal manipulation of both
learning environments and hormonal milieux's (sp?). I think Rushton means
something else.

> Has anybody explored the hypothesis that developmental stability is
> responsible for brain size differences within populations? We recently
> established a negative correlation between developmental stability and IQ
> (measured as Cattell's culture fair test, which I believe tests spatial
> and mental rotation abilities).

What exactly is "developmental stability"?
R. Holloway