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The Gathering Hypothesis, was Bipedalism and...
J. Moore (j#d#.moore@canrem.com)
Wed, 10 May 95 15:09:00 -0500
Um> >Actually, as Phil Nichols has pointed out (repeatedly!) in this
Um> >newsgroup, actual tests with chimpanzees has demonstrated that even
for
Um> >those knuckle-walking apes, bipedalism is no less efficient a mode
of
Um> >getting around. So the entire above argument is meaningless; the
Um> >question has been answered by scientific experimentation.
Um> Yes, this is the case, but this also assumes that the common
ancestor
Um> was a knucklewalker. My explanation above covers the possibility
(which
Um> seems to have been repeatedly asserted by AAH proponents) that this
Um> ancestor was as yet just a generalized primate, unspecialized for
either
Um> knucklewalking or bipedalism. The question I was replying to was:
why
Um> would an unspecialized primate develop toward bipedalism rather than
Um> quadrapedalism (or something to that effect)? Anyway, we're saying
the
Um> same thing (I think you might have confused what I wrote with
inclusions
Um> from previous posts).
Um> ...Kevyn Winkless.
I don't think I confused the posts, no; my point was that *even for a
knuckle-walker*, the *actual evidence* shows that bipedalism is as
efficient as knuckle-walking. And we know that gibbons and siamangs
(typically branch-swingers) walk bipedally when on the ground. And we
know that chimps and gorillas stand bipedally sometimes when gathering
food, and that chimps occassionally walk bipedally when carrying food.
Both also use bipedalism during threat displays.
So we know that bipedalism is not that difficult or unlikely even in
modern apes. It could very well be even easier for an early ape-like
ancestor if it were less specialized than these modern apes.
As for "Why?", that is, in a way, a question for philosophy rather than
evolutionary studies. Although it's common to ask "why?", it invites
adaptionist scenarios, and therefore "just-so" stories. A question that
makes just as much sense, but isn't often asked, is "*Why not?*".
What we see when we ask that is that all these methods worked pretty
darn well, up to a point. The three methods I'm talking about being
branch-swinging/climbing, quadrupedalism, and habitual bipedalism --
note also that of these main methods of getting around precluded
use of the others. That is, chimps and gorillas use quadrupedalism
(they knuckle-walk), but also occasionally use bipedalism, and both
climb and swing. Orangs and gibbons climb and swing, but also
occasionally use bipedalism, but also use quadrupedalism (in trees for
gibbons); humans also can and do use all three, although with their long
legs, their quadrupedalism tends to either crawling on hands and knees,
or when climbing up a slanted surface or tree. No hominoid uses one
method of locomotion exclusively.
While these methods all worked, as I said, pretty well up to a point
(they're all still around), the bipedal method allowed for more
expression of skills that were probably already in the population.
While chimps use tools, for instance, even fashioning them to their
liking, they're hampered in the ability to carry both tools, and things
to use those tools on, by the fact that their most common mode of
movement doesn't allow them to carry as much. At first this probably
wasn't such a huge difference, but even this small difference could make
the difference between a potential habitat being marginal or unuseable.
This would open up more areas as useable for bipedal tool-using
hominids, as opposed to quadrupedal tool-using apes ("proto-chimps").
Over time (a whole lotta time) the environments useable and available
for hominids grew, due to more and better tool use, and this worked in a
feedback fashion with brain growth (a bigger brain isn't necessarily
better, but can be if you're an animal that already has a use for that
brain, such as figuring out food sources in new types of environments,
or new uses for old tools, and ways to make new tools [just to name a
few]). This allowed hominids to utilise more and different habitats,
while other hominoids were restricted to still-extensive (until
recently) and viable habitats, but not as many different ones as
hominids.
So the question should be "*Why not?*" Why shouldn't some individuals
or populations at the time of the split from the CA (common ancestor) of
humans and African apes take to hominid-style bipedalism, while others
went the quadrupedal route? Still others may have become orang- or
gibbon-style tree-swingers, with that branch of the family dying out.
To paraphrase, "some look at evolution and ask 'why?'; I look at it
and ask 'why not?'" To ask "why" invites an adaptionist story.
Jim Moore (j#d#.moore@canrem.com)
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