Re: Bipedalism and theorizing... was Re: Morgan and creationists
Paul Crowley (Paul@crowleyp.demon.co.uk)
Fri, 02 Aug 96 16:40:53 GMT
In article <herwin-0108962057150001@news8.erols.com>
herwin@gmu.edu "Harry 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.
>
> No, not all primates are orthograde. Assignment: read a good book on
> primate anatomy.
The othograde posture of the trunk is a well known characteristic
of primates; only the very smallest tend to be pronograde, and we
are not concerned with them in this discussion. All I have to hand
is Schultz: The Life of Primates. Page 51 reads:
"The admirable grace with which gibbons can brachiate at high
speeds had not apparently become perfected until farily recently
. . . With brachiating locomation the trunk, naturally, is held
in an upright position . . . . The erectness of the trunk, however,
is not at all typical of brachiating primates only, but is really
maintained by all primates with widely varying degrees of complete-
ness during arboreal locomotion, as well as sitting which forms a
considerable part of their daily life."
> > > : 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.
>
> We've also got anatomical evidence. Can you hang by your hands?
Just about; but, taking size into account, I'm far worse than most
monkeys. I'm perfectly happy having a quasi-chimp as an ancestor
but I don't think I (or it) ever had a quasi-gibbon as one. This
is partly for the reasons you gave -- it would have involved too
many drastic changes to the motor programs.
> Science is about creating a network of tested propositions that reinforce
> each other. There is such a network associated with the assumption of a
> suspensory stage in our evolution. It includes a good deal of hominoid
> post-cranial material from the Miocene and Pliocene. It includes hominid
> post-cranial material. It includes anatomy.
You have presented no reasoning (except the old one about a change in
climate causing something uncertain) or referred to any hard evidence.
When poor scientists congregrate in an area with little firm data and
a history of numerous previous wrong judgements the result is often
a defensive attitude which leads to bad thinking and unquestioned
(and unquestionable) assumptions.
> > 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?
>
> No, it does not follow. You're about 30 years out of date.
Hopefully, we'll get an answer from fossil data someday. Maybe
a 15 mya knuckle-walker, or DNA evidence that (say) gorillas
speciated around 20 mya.
Paul.
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