Re: bipedalism and AAH

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patdooley@aol.com (Pat Dooley) writes:
Nicholls writes :

<< deletions >>

>> That is, the studies which I have cited repeatedly disproves
>> the assumption that bipedalism is less efficient that
>> quadrupedalism at least when it comes to walking. The
>> measurments were taken on chimpanzees because they are living
>> and it is somewhat difficult to take these readings on fossils.

> Energy efficient or survival efficient?

> Is an ape going through the process of radically altering its
> pelvic structure, the length of its legs, its internal
> anatomy, the shape of its spine, the position of its skull,
> and all the other structural changes associated with true
> bipedalism, going to be as efficient at bipedalism as
> quadrupedalism during that process?

What we KNOW (i.e., have data to support) is that chimpanzees
walk bipedally and walk quadrupedally and that one mode of
locomotion is not more energetically efficient than the other,
despite the fact that chimpanzees are knuckle-walkers and
therefore specifically adapted to quadrupedalism.

The common ancestor was NOT a knuckle-walker and very likely
had a more generalized morphology than a chimpanzee. You
constantly miss this point and it is extremely important. We
don't have to go from a chimpanzee pelvis to a human pelvis or
a chimp spine to a human spine.

> At various points during that process, both quadrupedal and
> bipedal efficiency are going to be reduced to the point where
> neither is as good as the starting point - 100% quadrupedalism
> or the end-point - 100% bipedalism, either in energy efficient
> terms or surival efficiency terms.

You assume that the common ancestor was a quadruped. I do
not. I assume the common ancestor was an arboreal ape and
that knuckle-walking and bipedalism are secondary adaptations
originating at the time of the pongid-hominid split.

> Evolution doesn't give you a sub-optimal holiday while you
> evolve an optimal solution - the principle of
> non-disadvantageous intermediates.

Once again, there is no such principle and once again
evolution does not produce optimal solutions -- only solutions
that work better than other solutions available at the time
using materials at hand. Optimal solutions can only be
executed when organisms are designed from scratched.

You know, the creationists over on talk.origins use this exact
same argument to tell us that such things as the eye or a
birds wing are evidence of intelligent design and not
evolution. They see these as optimal solutions and all
intermediates, by definition, sub-optimal and therefore
unworkable.

>> My point is that the common ancestor was not a knuckle-walker as has
>> been fairly well demonstrated, that it was most likely an arboreal
>> ape (clearly indicated by Lucy's limb bone proportions and curved
>> toes) and very likely a suspensory feeder. The latter adapation
>> would predispose it to be a biped when it moved on the round, much
>> the same as gibbons and spider monkeys who are modern suspensory
>> feeders. This is not to imply that humans are descended from either
>> spider monkeys or gibbons.

> Your spider monkeys or gibbons are a red herring.

I see. Spider monkeys and gibbons are red herrings but whales,
manatees and dolphins are not? At least I'm in the right
mammalian order.

> I think you are putting yourself out on a limb by claiming Lucy was
> a suspensory feeder. There is no earthly reason why such a
> suspensory feeder should become bipedal in the human sense.

I didn't claim Lucy was a suspensory feeder. I said that Lucy
is descended from a suspensory feeder and as I have continued
to point out, suspensory feeders tend to be bipeds when they
are on the ground. Behavior, then morphology. Protohominids
begin the behavior to increase their resource base when
forests begin to shrink.

> (Standing or walking on two legs for short periods does not
> qualify as bipedalism, despite what some posters claim.)

Most primates engage in a variety of locomotor behaviors.
Chimpanzees knuckle-walk, walk and run bipedally, climb, jump
and even brachiate. It is therefore not an anomalous behavior
in primates. It is, in humans, anomalous only to the extent
that humans are specialized bipeds. That's just the way
evolution works.

-- 

Phil Nicholls                     "To ask a question you must first

Department of Anthropology           know most of the answer." 

SUNY Albany                                      -Robert Sheckley

pn8886@cnsunix.albany.edu            SEMPER ALLOUATTA

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