Re: Bipedalism and theorizing... was Re: Morgan and creationists
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Mon, 15 Jul 1996 12:16:47 GMT
Paul Crowley <Paul@crowleyp.demon.co.uk> wrote:
>The phrase "bipedal chimp" is something of an oxymoron; it really
>can't be taken for a model. The big difference between bipedal and
>quadrupedal hominoids is that, when walking or running, one has a
>vertical trunk whereas the other has a horizontal one. This has
>drastic consequences. Imagine being a small infant -- Which would
>you find it easier to hold onto when your mother is being chased
>through the woods by, say, another hominoid?
Chimps,orangutans and gibbons frequently engage in orthograde
positional behavior,keeping their bodies in a vertical position.The
infants do not seem to have more trouble holding on to their mothers
in these situations.
If they can hang on in these situations then there is no reason why
they shouldn't be able to hang on to the vertical body of a
facultative or habitually bipedal hairy mother.
<diagram snipped>
>Apologies for the diagram; but I'm trying to emphasise a vital
>but usually ignored point. The engineering for bipedalism
>entailed radical changes. Whereas both the ventral and the
>dorsal positions are feasible for infants of quadrupedal animals,
>they are virtually out of the question for bipedal creatures.
But the changes in the pelvic,lumbar and thoracic regions do not seem
to be incompatible with an infant in ventral or lateral position.
In fact they may have profited from a more anteriorly oriented iliac
blade as a kind of natural support.
>It's an important point because once you accept that the ventral
>position was impossible for early hominids and that regular carrying
>in arms was most unlikely, then altricial infants, home bases,
>shared infant caring, a non-woodland habitat -- and much else --
>all necessarily follow.
But you assume that early hominids were fulltime bipeds.This was
probably not the case.They may have been arboreal to a considerable
degree.(now that we know of the Stw 573 hominid footbones from
Sterkfontein,which indicate a divergent and highly mobile hallux,this
seems more likely)
Early hominids do not show the fully developed suite of characters
that are associated with fulltime bipedalism in modern humans
and,given their small brainsize,didn't yet have secondarily altricial
infants.
Gerrit.
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