Re: A *Dry* Discussion About The Origin Of Bipedalism

"rmacfarl" <rmacfarl@xxxxxxxxxxxxxxxx> wrote in message
news:1125301280.342279.221630@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> mclark wrote:
>> "rmacfarl" <rmacfarl@xxxxxxxxxxxxxxxx> wrote in message
>> news:1125114048.973601.63410@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> > Mclark,
>> >
>> > I'm interested in this idea you've previously floated about the origin
>> > of bipedalism being linked to arboreal origins. I know it's been
>> > brought up usually in opposition to all that wet theorising, but I'd
>> > like to hear you expound on your idea bit further. Care to have a
>> > crack?
>>
>> Well, if you ask me, I think this whole 90% twist from
>> horizontal to vertical is a response to the problem of moving
>> an increasingly large body through the branches of trees.
>> I think I had this conversation with Pauline a while back
>> and if I recall (without a search), I think that I said something
>> about the nature of trees (they have a vertical trunk, in most
>> cases, branches angle off from this trunk at increasing angles
>> as they move away from the trunk and that useful resources
>> are usually found toward the termination of these branches),
>> and that larger bodies would be restricted by certain physical
>> laws from employing the normal monkey modes of travel.
>> As these increasingly large apes were restricted toward the center
>> of the tree, they were increasingly relegated to vertical climbing
>> (the vertical trunk), prevented from brachiating (more central
>> branches are larger). That leaves them with the upper surfaces
>> of larger branches. Foraging, and supplementing their balance
>> with their hands by grasping nearby branches, these apes would
>> find themselves with their feet both *on the ground* and acting as the
>> sole interface with the substrate. Add this to the fact that running
>> along the tops of branches is actually *more* stable that walking,
>> and the observation that *sitting* adds its own set of variables
>> to the mix (changes to the lower spine) and you have a certain
>> inevitability to the notion that those apes thus pre-adapted to
>> bipedalism would find themselves moving bipedally when
>> ~whatever~ moved them to the ground.
>
> Hmm [grimace]. My experience of climbing is that when you have to try
> to get out to the further edges of a thin branch, the opposite to what
> you posit above applies. I prefer to get on all fours & grip on to the
> branch with my legs while I gingerly stretch out along a section that
> feels like it's about to give way under me.
>
> What I've seen of chimps suggest a similar approach. I have a mental
> image of males hunting by climbing outward on all fours toward a
> trapped monkey, for example.
>
> Also of course, the actual brachiating ape adaption is for suspense
> foraging - hanging under branch, cf. orangutans, as opposed to Old
> World monkeys that run on all fours along the top of branches.
>
> All in all when you're up in the treetops I'd feel more secure with 3
> or 4 points of contact when branch-walking than with 1 or 2. Hence I
> can't say I find this scenario convincing.

Which was my point, of course. Those 3 or 4 points of contact
are not necessarily the same branch. I can be standing on the
branch below me and support my large mass by bracing against
other nearby branches. Moving out to the periphery of the tree
in pursuit of either the monkeys or the foods they eat is a dicey
proposition. Monkeys know this and react to hunting groups
of chimps by retreating to the smaller branches. Chimps counter
this by hunting in groups. They know that they will be hard pressed
to follow a monkey from one tree to the next so they position
various of their fellows in the adjacent trees and "herd" the
unfortunate monkey from one expectant hunter to the next.
In the resulting confusion, amidst all the screaming and hollering,
the monkey is caught while trying to escape --by some chimp
strategically placed on a large branch.

I know the difficulty. The problem, as I see it, is how you
get an otherwise four-footed primate to stand up whilst
engaged in the normal, everyday activities of a quadruped.
It *may* be that these adjustments are the result of increasing
body size --which may be a reaction to something else (like
scarce resources or sexual politics). Increasing body size then
introduces all these other difficulties --how to move efficiently
in an environment with shrinking possibilities. If you're restricted
to the larger branches, you would be restricted in your adaptive
responses. Once you have a *climbing* orthograde ape,
moving it to the ground becomes a natural progression. Figuring
out what drove this move is another difficulty hinted at previously.
Were they pushed, pulled, what? Did they leave because the
trees dropped out from under them or were they drawn away
by the promise of more lucrative jobs in the city? I think that it
is pretty well established that at some point our ancestors were
*living* in trees. We now live on the ground. The first ground
personnal were large-bodied, obligate bipeds. The seeds of that
bipedalism *must* have been nurtured in the trees. The question
is how.

> Just my opinion, of course.

And merely mine.

>> "Whatever" could be
>> anything that would initiate the move from tree to terrestrial --
>> drying and cooling, which would disperse the trees, a mere
>> local preference for a food source on the ground, a population
>> shift in geography, etc.
>>
>> I think R.H Crompton has at least intimated much the same.
>> Check this out:
>> http://www.liv.ac.uk/premog/premog-pubs.htm
>
> Which of the papers was the specific comment in, do you recall?

No, I don't. I only know that Crompton has said much the same.
It wouldn't hurt to read what he has to say about the mechanics
involved.

Here is another one. Though slightly quirky, there are a
few gems scattered throughout:

http://www.alexandertechnique.be/English/sit_happens.htm

[..]
> Ross Macfarlane
--
"You might be right but, people shouldn't buy it unless you can
*demonstrate* it through logical reasoning and/or evidence and I just
don't think you have done that." ---Algis Kuliukas 08/14/05


.

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