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Re: bipedalism and AAH
Troy Kelley (tkelley@hel4.brl.mil)
Thu, 4 May 1995 15:14:03 GMT
Subject: Re: bipedalism and AAH
From: Kevyn Loren Winkless, umwinkl0@cc.umanitoba.ca
Date: 2 May 1995 17:50:24 GMT
In article <3o5rd0$kji@canopus.cc.umanitoba.ca> Kevyn Loren Winkless,
umwinkl0@cc.umanitoba.ca writes:
>In <1995May2.140337.1495@arl.mil> Troy Kelley <tkelley@hel4.brl.mil>
writes:
>
>>The second part of your statement is
>confusing: "More >generalized apes lacking the knuckle-walking
>adaptation would >undoubtedly be more efficient both running and
walking".
>>Do you mean apes or monkeys? I think both gorrillas and
>>orangatangs walk on their knuckles, like chimps. And you
>>say that they would be "more efficient both running and
>>walking" - which I think is the point of the argument - that
>>quadrapedialism is more efficient than bipedialism. So
>>why would hominids have ever adopted it?
>
>You're missing the point. It's not a matter of whether or not the
>generalized apes moving bipedally are more efficient than quandrapedal
>apes, but rather that for generalized apes moving bipedally is more
>efficient than moving quadrapedally _because_ they do not have the
>knucklewalking adaptation. Given a generalized ape, adapted to a life
in
>the trees, walking on two legs or walking on all fours is six of one and
>half-dozen of the other; neither is particularly comfortable. Should,
>however, circumstances and evolution gang up to force a life on the
>ground, the ape will have to get better at one or the other mode of
>locomotion, since brachiating is no longer an option. We might
speculate
>a common ancestor of chimpanzees and humans which was a generalized ape,
>used to the treetop life. Two populations of adaptation evolved when
>this ape was forced to the ground: a population which favored
bipedalism,
>and a population which favored knucklewalking. Voila! modern ape
>populations.
I think the point is "whether or not generalized apes moving bipedally
are more efficient than quadrapedal apes". I understand that you are
saying that generalized apes moving bipedally is efficient because they
they do not have the knuckle-walking option, but I do not think that is a
strong argument. The simple fact is that quadrapedalism is a much better
way to move around than bipedalism, therefore humans would have needed
intense selection pressures to adopt such a unusual means of
transportation.
This reminds me that some of the AAH theorists have hypothisized that
some homonids evolved separately on an island off the coast of Africa.
This is starting to have more appeal to me when one considers what easy
prey our bipedal ancestors must have been to most big cats and other
carnivores.
>>>Most animals on the savannah live NEAR a lake or river and
>>>visit them regularly. Few animals actually live at the
>>>waterhole or riverbanks because those areas tend to be haunted
>>>by predators as they are today.
>>I think the point here is that humans need much MORE water
>>than other savannah creatures. It is true that most animals
>>live "NEAR" a lake or river. BUT they might only have to
>>drink once a day, or once every couple of days. Some
>>herbaviors get almost all of there water needs from the
>>plants they eat and consequently almost never have to
>>drink standing water. Early hominids needed much more water
>>than other creatures of the savannah.
>
>Other apes habitually feed on fruits and soft greens, with the
occasional
>insect or small animal. Plenty of water in that diet. Furthermore, I
>suggest you measure out 0.7 L of water and look at it - its not that
>much. Considering that the grassland-dwelling ungulates you are making
>the comparison to have been evolving on the grasslands for quite a bit
>longer than apes have, it really isn't suprising to discover that
they're
>a little better at conserving water.
I am not sure I agree with that .7 L of water per day estimate. Also, if
you look at the rest of the quote he says that is "if it (the hominid)
retreated into the shade for a four-hour period in the afternoon." which
is quite a large variable. I have heard estimates that humans perspire
about a liter a day, which is probably where this quote came from, BUT,
that is if you do NOTHING else. If you include any physical activity,
like hunting or running from predators, the about of water lost by the
human body goes up dramatically. I don't have all the facts with me now,
and this information has been posted to this news group before, but the
fact is that humans, and probably our human ancestors are incrediably
poor at conserving the amount of water in our bodies. This would lead
one to speculate that early humans evolved in a habitat where water was
easily available, wouldn't it?
>
>>>Protohominids didn't just stand in the mid-day sun, they
>>>walked from the forest to that clump of trees 100 meters
>>>away because there was FOOD there.
>>Again, why would they walk bipedially when it is such an
>>inefficient means of transportation? If they where walking
>>from forest clump to forest clump they would have been
>>exposed to predators along the way, and those hominids
>>that were slow and bipedal would have gotten eaten before
>>any faster non-bipedal hominids.
>
>If we presume that the primary habitat for these hypothetical ancestors
>was close parkland, reasonably moist with fairly tall grasses and scrub
>brush (as would fit with a typically apish diet), then we might also
>presume that the entire troop didn't move bipedally - instead, only a
few
>walked upright so as to see above the terrain and note approaching
>predators, like gophers. As time went by, those apes who had advance
>warning had a better survival rate, and so bipedalism was a favored
trait
>in the population. In essence, our ancestors "waded" through tall
>grasses and such like to travel from one island of trees to
>another...perhaps they were driven from the forests by increasing
aridity
>in the environment and the resultant retreat of the forest itself.
Many animals use a bipedal stance to look for predators. Prarrie dogs for
example; but this does not mean that these animals adopt bipedalism to
escape from predators. I think that is the real point. So "bipedalism was
a favored trait in the poplulation" perhaps for predator location, but I
can't imagine that it would be favored for predator escape.
>
>>>It is also noteworthy that proboscis monkeys have not lost
>>>body hair, gained subcutaneous fat. They are able to walk
>>>bipedally without shortened pelvises, realigned muscles or
>>>locked knees. In effect they do what nearly all primates do
>>>from time to time -- walk bipedally. I have been arguing this
>>>point forever it seems. Behavior before morphology.
>
>>You say "Behavior before morphology" but it does not
>>support your argument in this case, which is, why haven't
>>"proboscis monkeys lost body hair and gained subcutaneous
>>fat". Perhaps their behavior is coming before their
>>morphology.
>
>But in this case there is no sign of a trend in that direction, and no
>evidence that it would be an advantageous development. If that could be
>shown, the case would be much stronger for a similar background for our
>own ancestors.
>
Evolution takes a long time. And lost of body hair and subcutanous fat do
not fossilize, so I think it is difficult to determine whether the P.
monkey "shows a trend in this direction".
Troy Kelley
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