Re: An alternative to ST and AAT

Gerrit Hanenburg (
Sat, 09 Nov 1996 10:37:54 GMT (Paul Crowley) wrote:

>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.

Australopithecines,as represented by "Lucy" (AL 288-1),did not have
long arms. The "intermediate" humerofemoral index (85) is the result
of a relatively short hindlimb. The forelimb already had proportions
similar to modern humans. (Jungers,W.M.(1982),Lucy's limbs:skeletal
allometry and locomotion in Australopithecus afarensis. Nature
But that is no argument against striding bipedalism and running,though
it probably was less efficient than in modern humans.

>So why did they maintain this very strange morphology for so long?

Why very strange? It's basically hominoid.

>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.

You acknowledge that the anatomy of Australopithecines could have had
something to do with selection for arboreality? That gives me a lump
in my throat,although I do think you're actually borrowing this piece
of your theory from others who conceived of the possibillity of
arboreality quite some time ago. There's nothing new here.

>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.

How exactly did they use this "rope" in order to make climbing easier?

>Intra-species competition would soon cause a
>rapid evolution of shorter arms, longer legs and the development
>of a stride.

That does not set your theory apart from landbased ones.
A longer leg has its advantages in a setting were you have to cover a
larger range (it makes bipedalism more efficient by increasing stride
length and decreasing stride frequency)

>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.

As I already pointed out in an earlier post,shellfish does not exactly
constitute a rich foodsource. Shellfish is particularly low in fat and
carbohydrates and not exceptionally high in protein.