Re: An alternative to ST and AAT

John Waters (
8 Nov 1996 05:45:44 GMT

Paul Crowley <> wrote in article
> This raises a very interesting point. For some 2.5
million years
> (until about 2.5 mya) hominids could not stride and
probably could
> not run; if they could, they certainly did not do it
well. The
> australopithecines had short legs, long arms and no
> So why did they maintain this very strange morphology for
so long?
> What could have been the evolutionary pressures keeping
them like
> that? And change what allowed them to adopt the, more or
> modern form?
> Has anyone attempted an answer to these questions?

JW: For what it's worth, the HBT explains that the hominid
delay in switching to a highly efficient form of bipedalism
was caused by the problem of the overheating baby. When a
hominid baby was carried in its mothers arms, the baby's
core body
temperature would rise.

In very hot conditions, the baby would die of heatstroke if
carried continuously by its mother. The pressure for
efficient bipedalism created an evolutionary demand for
less infantile body hair, increased number of sweat glands,
the moulting of the foetal hair etc., to combat infantile

The maternal adaptations were an increase in subcutanous
fat levels in the chest/breast region, and on the hips.
These are the places where the infant comes into contact
with the mother. The fat prevented the mother's own
internal body heat from being conducted into the infant.


John Waters is the author of "Helpless as a Baby",
a book concerned with general and human
evolution. It may be accessed at URL