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

Paul Crowley (
Thu, 01 Aug 96 14:31:11 GMT

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

Paul Crowley wrote:
> : 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).
> We're orthograde, not pronograde, in our anatomy.

But all primates are orthograde.

> : Why do you propose a suspensory stage?
> Because we've got good evidence for it (Dryopithecus).

You'd have to say Dryopithecus is ancestral for it to be good
evidence of a suspensory stage? Is this what it comes down to?
I suggest that there is a serious conflict between your account of
the time new motor programs take to develop and a suspensory stage.

A much simpler explanation for our suspensory adaptations can come
from looking at the infantile and juvenile behaviour of the larger
apes. Like all other primates they have to be able to cling to
their mothers almost from birth. As they grow, there is great
survival value in being able to clamber around smaller branches of
trees, both to escape predators and to get food (fruit, nuts and
buds) that the heavier adults cannot reach. While they are the
size of gibbons their behaviour can be roughly gibbon-like.

It would follow that our ancestors were probably ground-based
primates for 15-25 Myr. The niche is much larger. It is also
probable that knuckle-walking is an ancient adaptation. Was there
any post-cranial material for Ankarapithecus?