Re: Bipedalism and theorizing... was Re: Morgan and creationists

Wallace Neslund (
Thu, 11 Jul 1996 19:07:33 -0700

Gerrit Hanenburg wrote:
> I've looked up some species averages for life-history variables.
> -neonatal bodyweight:
> Homo sapiens-3300.0 g.
> Pan troglodytes-1756.0 g.
> -neonatal brainweight:
> H.sapiens-384.0 g.
> P.troglodytes-128.0 g.
> Ratio neonatal brainweight/neonatal bodyweight:
> H.sapiens-11.6%
> P.troglodytes-7.3%
> In my opinion these differences alone pose a different nutricional
> demand in that H.sapiens neonates need a higher daily caloric intake.
> This difference becomes even greater if we take into account the fact
> that a human infant has a far higher rate of braingrowth in the first
> year of life (almost tripling it's brainsize)
> Given that the infant subsists almost entirely on mother's milk during
> the first year of life,I thought that the caloric output of the human
> breast must be greater than in chimpanzees and that one way of solving
> the problem would be an increase in the amount of glandular tissue.
> This could explain part of the difference in breastsize between humans
> and apes.

You've made a good point. I agree that, due to rapid brain growth in an
Hss infant, it would need both greater quantity and possible quality of
milk to feed those specialized brain tissues. That brings up another
question, though. How much of the Hss breast is actually taken up by milk
producing mammary glands and how much is fat deposit? If the fat to gland
ratio is very high, then the size difference between Hss and other
primates cannot be explained by nutritional needs alone. By your figures
above, it appears that the Hss brainweight/bodyweigh is about 1.6 times
that of Pt. Since Pt females have very little visible breast development,
it would appear that the ratio of Hss to Pt breast size is greater than
1.6. This would imply there is an other/additional function to the


God knows, I don't. - Thomas Aquinas

He's so dumb, he not only doesn't know anything,
He doesn't suspect anything. - unknown