Re: First Family and AAT

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ghanenbu@inter.nl.net (Gerrit Hanenburg) writes:

>hubey@pegasus.montclair.edu (H. M. Hubey) wrote:

>>Head up is the natural position for any land animal that gets
>>thrown in the water. I assume that the legs would hang down and
>>that in shallow water they'd be in contact with the bottom. If the
>>body is more upright (i.e. so-called streamlined) it would be able
>>to stay in deeper water for the same length appendages.

>This is not really an answer to my question.An upright position may be good
>for an ape in the water,this doesn't mean it is also a good position for an
>ape on land.The AAT has to answer the same question that other theories
>concerning the origin of bipedalism have to answer.
>For what reason did the aquatic ape maintain its wading position on land?

The difference is that you are discussing a time period of very
short (nearly zero on evolutionary scale) length and also the
time period in which these humanoid/apes would have gone into
water. Certainly an ape that stays in the water for a day is
going to come out looking the same way it went in.

I (presumably along with the AAT proponents) was referring to the effect
of staying in this aquatic environment over a long period of time.
That is, those apes with longer legs and more upright postures would
have more chances of survival and hence producing others like
themselves.

>The experiments have already been done by mother nature. All *we* have to
>do is gather the data and do the analyses.In the case of Cetaceans and
>manatees the outcome seems to be loss of hindlimbs while in the case of
>pinnipeds there is reduction of the hindlimbs which also have become much
>less efficient in terrestrial locomotion.In the case of hippopotamus the
>experiment is still going on,so keep watching carefully. :-)

Unfortunately we weren't around at the beginning of the experiment
so we don't reall know what they looked like. We have some bones
from various time periods which we can put into some kind of order
by resemblance and we "assume" (i.e. theorize) that we are seeing
the evolution of the same animal. We don't know what conditions caused
these animals to stay in water permanently. We don't know what would
have happened if conditions had changed and they had come out of
the water. We don't know what will happen to rhinos. We don't know
of otters and polar bears will lose their fur and their legs too.
I'd guess that the standard theory will fudge something like this:

If the polar bear spends more and more time in the water
it will become aquatic and more like whales etc. If the
environment forces it to spend more time on the outside
it will lose its webbing, etc etc.

>As in dogs.A species like Mesonyx had limbs specialized for cursorial
>locomotion.

Well, this certainly changes things. It's hard to imagine
a scenario in which say a dog will lose its legs, its fur
and become like a porpoise [with the caveat of course, that
if it was forced somehow to spend more and more time in the
water with no chance for it to come out and live on land].

>So my problem is (for example):why should the kneejoint in an aquatic ape
>begin to become adapted to weightbearing while in fact it didn't have to
>bear much weight?

I don't know and I think there may be many questions like this
that are not answered. Why would a lizard lose its tail, get longer
legs, a smaller jaw, start to carry it eggs in its body etc. That's
what it boils down to in the end. The animals higher on the scale
have longer legs (and a more developed brain) so they don't need
large tails to keep their balance. Since they are more nimble they
also don't have to scraping the ground either. Why would all that
happen? The hip joint would change to allow the rear legs to get
under the animal; different bones in the legs get to grow at
different rates, etc.

>Why should it begin to develop a relatively (compared to apes) high
>bicondylar angle in order to bring the knee closer to the midline of the
>body so that the centre of gravity of the body need only move a short
>distance to bring it above the stance leg while such a problem of gravity
>was hardly present in the water? etc.etc.

Well, if longer legs and straightening of the pelvis are beneficial
to help the animal escape to deeper water, then the rest of the
changes might be attributable to changes on land. That is, if no
other changes took place, so that the animal was a clumsy walker
on land (albeit with long legs and a more erect posture) then
perhaps the survival value of the being able to move about
quickly on land might explain the rest.

If we had to explain every change in every animal with this
kind of rigour maybe many of these animals could be proven
not to have really evolved :-)..

-- 



				Regards, Mark

				http://www.smns.montclair.edu/~hubey

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