Re: bipedalism and AAH

Kevyn Loren Winkless (
5 May 1995 06:53:34 GMT

In <> Troy Kelley <> writes:

>In article <3o5rd0$> Kevyn Loren Winkless,
> writes:

>>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
>>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
>>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
>>and a population which favored knucklewalking. Voila! modern ape

>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

I think that you will find that this is not the case for the hypothesized
ancestor. If we are assuming a primarily arboreal life (brachiating
rather than branch-running) for this ancestor, there is no reason at all
to assume that quadrapedalism would be more efficient. Quadrapeds are
more efficient because _the curve of their spines_ acts as a spring to
absorb and release energy. A brachiating primate has no similar
structure (this is to the best of my knowledge with no references handy -
if anyone knows for certain let us know!), and in fact I would expect to
find an extremely flexible spine that would probably be very good at
absorbing impact energy and _diffusing_ it harmlessly (so as to reduce
whiplash-type injuries and so forth). Such a structure would likely be
equally efficient bipedally or quadrapedally if forced to operate on the
ground. Once forced into a habitual forest floor lifestyle, this would
leave the population with two equally effective directions to develop -
both modes of locomotion are equally inefficient to the species that is
not adapted to either - and as in my model differentiation within the
population resulted eventually in two distinct populations: one that had
improved quadrapedal locomotion, and one that had improved bipedal
locomotion. We are the result of the latter, all other ground-dwelling
great apes are the result of the former.

>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

Shoreline habitats have their own share of predators, particularly with
the extremely aquatic lifestyle often proposed by AAH proponents...sharks
etc. And in tropical waters hairlessness might even have been a
disadvantage - consider the wide variety of highly poisonous jellyfish
species which live in such warm climates. As for big cats, I have seen
film footage of a leopard which chose (wisely, in my opinion) to seek
easier prey when faced with the organized resistance of a forewarned
troop of chimpanzees...and leopards habitually feed on primates: baboons
and the like are a normal part of a leopard's diet. Quite possibly, the
extreme level of social organization and "close-knitness" and
"cooperativeness" of human social groups derives from a distant
ancestor...if chimpanzees were as organized as humans usually are, I
doubt any big cats would bother with them at all.

>>>>Most animals on the savannah live NEAR a lake or river and
>>>>visit them regularly. Few animals actually live at the
>>>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
>>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
>>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?

Actually, I have a problem with the 0.7L estimate myself...It does seem
to be a little low. What I was trying to point out is that it is not
necessarily safe to assume that a drastic change occurred in the
hypothetical ancestor's diet just because whatever-it-was drove the
population out of the forest. If the diet assumed by the ancestral
population on the savanna was at all similar to that of modern arboreal
primates, then there is plenty of water included in that diet. Take into
account the possibility that they merely travelled from clump to clump of
"vegetation islands" on the savanna, and what you essentially have is a
troop of apes moving from water source to water source. Maybe there's a
watering hole and maybe there's not, but certainly the vegetation will be
a little more water rich.

>>>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
>>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
>>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
>>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.

I depends. If one assumes that, like the prairie dog, watchers can just
sit up and look around, then yes I agree with you. But this is a family
group on the move. It makes sense that there be a mechanism for keeping
watch while continuing to move...especially if, as you say, they are in a
vulnerable position while they are moving across the open land. If
conditions favoured those individuals who could keep a look out while
moving for longer and longer periods of time, then you have a pressure to
develop better balance and more efficient posture. Incidentally, unless
there's something to climb or hide behind somewhere close, no
knucklewalker has a chance against a feline that's bearing down for the
kill unless its had ample warning...I don't think the efficiency of the
mode of locomotion would have significant impact in this scenario, though
it is an interesting question...I wonder if anyone can find literature on
efficiency? I know that quite a bit of work has been done among
arthropods, but I don't know of any detailed numbers on mammals of this
order of size.

>>>>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
>>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".

Yes! and this is my point. Citing such examples is unproductive unless
solid proof can be brought to bear which shows that proboscis monkeys are
evolving to converge with the AAH's hypothesized aquatic human ancestor
(or not as the case may be). Given the circumstances, there is not
evidence either way, and the best that can be said is that it is an
example of a monkey that does indeed like sitting in puddles, and so
proof that the hypothesis isn't entirely impossible. I cannot say that
it is anything in the way of support beyond this.

...Kevyn Winkless

"...I drank WHAT!!?" - Socrates