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Re: The Gathering Hypothesis, was Bipedalism and...
Rick Abrams (ricka@praline.no.NeoSoft.com)
14 May 1995 11:58:48 -0500
I've been enjoying the discussion in this newsgroup, so I thought
I'd toss out this idea as strawman argument. Most professionals
are having a problem explaining human bipedialism in terms of a
environmental adaptation. Maybe it isn't. Could it instead be
the result of sexual selection? Several primate species have
special features caused by sexual competetion. I can easily
see an upright posture used as part of a mating ritual (I'm
taller than my competetion). This could push the trait through
a brief awkward phase and the its other benefits would insure
its further development.
In article <60.1450.7295.0N1E0EA6@canrem.com>,
J. Moore <j#d#.moore@canrem.com> wrote:
>
>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)
--
rha
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