"Didier A. Depireux" wrote:
> The posting about the girl and her thalamic damage and related
> microcephaly reminded me of a question I have always had. In a chicken and
> egg type of question, I always wanted to know whether the skull determines
> the size of the brain, or does the brain determines the size of the skull?
>> In other words, if you have a small head, is it because you have a
> small brain; or is it that if you have a small brain, you skull will be
> small. I would assume that the space between the brain surface and the
> skull is a constant.
>
I don't think you can really separate the two, as they are developmentally
connected (like all the various parts of the body). i.e., if you have large
hands, you also have large metacarpals and phalanges to "fill" those hands. So
you're right - it is exactly a chicken-and-egg type question.
Of course, on a species (rather than individual) scale, the size of the skull
and brain is constrained by the size of the female pelvis, which in turn is
constained by the biomechanics of bipedalism.