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

Paul Crowley (
Tue, 30 Jul 96 13:25:47 GMT

In article <4tibn9$> "HARRY R. ERWIN" writes:

> 1. Hominoid infants whose mothers use an orthograde suspensory locomotor
> pattern hang on very well.

>From Schultz: The Life of Primates (1969) p. 233 "Infants of such
daring brachiators as all gibbons, usually continue to cling to
the mother's abdomen while being cradled on the flexed thighs of
the latter when hanging by her arms."

> The implication is that a major change in locomotor adaptation involves
> changing those motor programs. That's almost certainly why early apes were
> pronograde rather than orthograde
> [..]
> Now bring an orthograde suspensory primate down to the ground.

Why do you propose a suspensory stage? It requires two major changes
in locomotor adaptation. If the suspensory adaptation for most
hominoids was never much more than the bipedal capability of, say,
chimps, and the (formerly pronograde) territorial adaptations were
never lost, then there are no major changes of locomotor adaptations.
The only hominoids with a major change would be the gibbons, but as
they are the only ones to brachiate and as their distribution is
peculiarly limited, they can be regarded as highly specialised.

I suspect that far too much arboreality is being read into the
bones. If a fossil chimp or gorilla was dug up, I'm sure the general
conclusion would be that the animal was 100% arboreal. There is
unquestionably a strong bias in this direction. I wonder why?

> The motor
> program they use in the trees is suspensory climbing, and that does not
> convert easily into either terrestrial quadrupedalism or bipedalism. The
> 'reflexes' involving the hands are wrong, particularly when running, since
> rapid tactile feedback and response is what protects against damage. If a
> suspensory primate wants to move fast, it either needs to keep the hands
> off things (bipedalism), or it needs to protect the parts that damage too
> easily (knuckle-walking). Which one is followed up is a function of
> details of the biome.

I might accept this is we were 100% sure that the LCA was close to
a gibbon. How such an animal might "evolve" if it was "forced" onto
the ground is a moot point; however, it's an absurd proposition; it
would need to be artificially kept alive for some tens of thousands
of years in enclosures where it was well protected from competition,
predators and parasites.

Your scheme of things puts huge obstacles in the way of hominoid
evolution. Other primates have it much easier: no adaptation to
suspensory climbing; no re-adaptation to the ground. Are we really
sure our ancestors weren't baboons or monkeys? (Only joking).