Re: Bipedalism and theorizing... was Re: Morgan and creationists
John Waters (jdwaters@dircon.co.uk)
23 Aug 1996 07:37:31 GMT
John Hawks <hawksj@umich.edu> wrote in article <32186E6A.18BD@umich.edu>...
>Therefore, if your hypothesis is correct, then we
> should see evidence for expanded brain size in hominids contemporary
> with or even predating the evidence for bipedalism.
>
>
> John Hawks
>
JW: Thank you, John, for your carefully considered reply.
The evolution of the increase in infantile helplessness is
not dependent upon an increase in brainsize. It can be due to
a reduced body size. In cases where a specie needs to develop
an improved power to weight ratio, this can be achieved through the
development of a slimmer and slighter body structure.
It is extremely unlikely that such a morphological
change would be accompanied by any reduction in the size of
the species' head. The proto-hominid would still need the same
degree of brain power to search for food etc. In addition, it
would still need the same size of teeth and jaws to mastigate
its food. So the proto-hominid would evolve a slimmer and slighter
body, while still maintaining the same head size. These
characteristics would be inherited by the infant/embryo, with
the result that the relatively large head would create birthing
problems, resulting in the death of a small proportion of infants
and their mothers.
This evolutionary birthing problem can be quite easily
resolved through minor changes in the regulatory genes responsible
for fetal development. In essence, (as you have correctely stated),
the head/brain development is retarded, so that at the time of
birth, the head is relatively small and can pass through the
pelvic canal. The head/brain then completes its fetal development
outside the womb.
So this then is the other side of the story. It is
not a question of an increased head size, but rather a
reduced body size. This sort of development is entirely
consistent with the known environmental conditions of the
time. It is hypothetical, but it closely fits the facts.
John Waters
PS. I posted this yesterday, but it doesnt seem to have reached
the newsgroup. I apologise if this amounts to a duplication.
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