Re: First Family and AAT
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Mon, 25 Sep 1995 09:51:55 GMT
szpltdwn@dale.ucdavis.edu (Gerrell Drawhorn) wrote:
> 2) Bipedal adaptations in early hominids appear to be mechanically
> designed to deal with increasing gravitational forces applied to the hip,
> hindlimbs and foot. Swimming would seem to completely release the
> hindlimbs from these verticle forces - selection would take the climbing
> foot, ankle and leg of an ancestral hominoid on an opposite trajectory
> than ultimately attained in hominids. Even wading by a quadruped would
> reduce these forces to some degree.
> I find it difficult to envisage a situation where the lateral
> system in the pelvic musculature, the increased surface areas and
>angulation of the knees, the development of the longitudinal and
>transverse arches of the foot, etc. could arise if animals were in an
>environment where they were buoyant. Either a lightly-built knuckle-walking
>or (more generalized) brachiator (not as specialized as hylobatines)
>would seem to provide a better progenitor than an aquatic form.
I wrote something similar a few months ago:
"It (the water) is not the right environment to select in favour of an
anatomical complex that suits bipedal locomotion because the upward pressure
of the water takes much of the load of the body off your lumbar spine,
pelvis and lower limbs.That load is exactly what is needed to remodel
the anatomical complex of an arboreal ape into that of a bipedal ape
that walks on land.
Without those gravitational forces there is no selection to remodel the
lower body in favour of bipedalism.Instead you would expect a kind
of "degeneracy" or remodelling in the direction of wateradapted
locomotion.(i.e swimming and/or floating).
Other mammals that have moved to the water have lost their hindlimbs
altogether as in whales,dolphins and manatees or they have
become much less functional in terrestrial locomotion as is the case
in pinnipeds,and where they kept their legs they became adapted to
swimming as in otters".
I thought that the AAT was overlooking some important physics.
I didn't get much reaction (maybe because I didn't formulate it very well or
the idea was considered too silly) Now that you bring it to the attention
again I'm curious as to how much response it will get this time.
Gerrit.
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