Re: An alternative to ST and AAT

Paul Crowley (
Wed, 06 Nov 96 22:05:07 GMT

In article <> "Phillip Bigelow" writes:

> Actually, the only creature to walk EXACTLY like a human is a modern
> human. Australopithecenes did not have the hip/foot/ankle/arch
> structure to walk "just like a <man> <sic>".

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 waist.

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 less,
modern form?

Has anyone attempted an answer to these questions?

Anyway, here's a try:
The australopithecines needed to climb _palm_trees_ for food
(mostly dates) and possibly to escape predators. Their short
legs and long arms evolved for this purpose. Some authorities
(e.g. Stern & Susman) claim that their apparently curved phalanges
and other features clearly indicate that they were adapted to
climbing trees. I suggest that their adaptations are all for
this highly specialised form of climbing.

At about 2.5 mya there was a change. This could have been
brought about by a climatic one causing a decline in palm trees.
Or possibly one population made a breakthrough; it might have
discovered that a "rope" (a long piece of fibre) made such
climbing easier. Intra-species competition would soon cause a
rapid evolution of shorter arms, longer legs and the development
of a stride.

Of course, I base the species at sea-level, obtaining a
significant proportion of its diet from shellfish. So that
the rich food enabled the increase in brain size and allowed
the species to ride out possible climatic and vegetation changes.

Has this theory major holes? Can anyone suggest another?