Re: Bipedalism and other factors
Pat Dooley (patdooley@aol.com)
9 Jul 1995 19:55:45 -0400
>From: ghanenbu@inter.NL.net (Gerrit Hanenburg)
>What about this:
>
>Organisms that spend much of their time in (at least) chestdeep
>water will be selected to make use of Archimedean Law in an
>efficient way.I think that is by floating and/or swimming,not by
>walking upright.Walking upright is not an efficient way of getting
>around in chestdeep water.
It is efficient in shallow water, especially when you are looking
for shellfish and the like.
Human swimming is more efficient that quadruped swimming
precisely because bipedalism puts the body into a single plane.
(Even seen a chimp swim?)
>It 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.
You assume that the AAT claims bipedalism is an adaptation for
chest deep wading. I think it was more likely an adaptation that
suited shallow water wading and swimming.
Lucy, the first nearly complete skeleton of an Australopithecus
afarensis, had feet that were broader and larger than ours,
(35% of leg length instead of 26%). Her gait was described by
Roger Lewin as "not quite as bad as trying to walk on dry land
wearing swimming flippers but in the same direction."
Post Lucy, the major bipedal adaptations were longer legs, smaller feet,
and locking knees.
>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 remodeling in the direction of wateradapted
>locomotion.(i.e swimming and/or floating).
Compared to other primates, it may well be that bipedalism is
a partial adaptation for swimming, along with hairlessness
and a subcutaneous fat layer.
>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(webbed feet).
But none of these animals fill a niche that combines swimming and diving
combined with shallow water and shoreline foraging. The massive shell
middens left by many early human cultures attest to continued ability to
fill that niche.
>On these grounds I think it is unlikely that an anatomical change in
>the direction of bipedalism (on land) will begin to develop in an aquatic
>environment as proposed in the AAT.
>
>Gerrit
Redo your analysis using shallow water wading, and swimming, and start
with a semi-arboreal ape partially adapted to bipedalism.
Pat Dooley
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