Re: Bipedalism in different substrates

From: Algis Kuliukas (algis_at_RiverApes.com)
Date: 06/15/04 

Date: 15 Jun 2004 08:34:28 -0700

NA Sides <nas@sonic.net> wrote in message news:<4orrc0lg14fprk30ie0hig0j79hhhcg4i4@4ax.com>...
> On Mon, 14 Jun 2004 16:39:24 GMT, NA Sides <nas@sonic.net> wrote:
>
> >On 14 Jun 2004 04:53:33 -0700, algis@RiverApes.com (Algis Kuliukas)
> >wrote:
> >
> ><snip>
> >
> >>'Does not contribute to the development of obligate bipedalism' - That
> >>is what is eluding you, Rick. Wading *does* contribute. Of course it
> >>does. The point you keep missing, forgetting (dodging?) is that at the
> >>land-water interface there is a gradient of depths. At the deeper end
> >>of the spectrum the ape has no choice if it can't swim very well, but
> >>is unlikely to swim even if it could. At progressively shallower
> >>depths is has more coice. It *could* go bipedally but is unlikely to
> >>do that, even when it could, because of a number of factors (there
> >>might be a wave, or a deeper pool or a deep muddy patch etc etc.) And
> >>so (are you getting this?) in shallow water you have a subtrate that
> >>is kind of a half-way house between the
> >>easy-to-do-but-noadaptations-required bipedal wading of apes and the
> >>more-tricky-and-likely-to-require-anatomical-modification fully
> >>terrestrial bipedalism.
> >
> ><snip>
> >
> >Hello, Algis. Could you clarify a point for me? Since immersion in
> >waist-deep or chest-deep water would have taken weight off the legs, I
> >don't see how it could have lead to obligate bipedality. It seems
> >that, by making it easier to retain an upright posture for longer
> >periods of time, this immersion would have eliminated the need for the
> >very adaptations that contribute to efficient terrestrial bipedality.
> >What selective factors would operate in a semi-weightless aquatic
> >environment that could contribute to adaptations for bearing and
> >efficiently moving body-weight on land?
>
> Sorry, Algis, I reread your post and it appears you may be claiming
> that selection for bipedality occurred in murky shallow water. I still
> don't see what factors would operate in such an environment.

No problem. The key point, I think, is that at the land-water
interface you almost always have *gradients* of depths. It's this
gradient that I think turned a wading ape into an obligate terrestrial
biped.

In waist deep water an ape needs no anatomical changes whatsoever to
move bipedally. It's tendancy for an upright posture, through it's
arboreality, and large size together make it the obvious mode of
locomotion - if not the only one. In waist deep to chest deep water
the effect of bouyancy would make upright posture (but not rapid
locomotion) practically effortless.

In slightly shallower water, some of this support is taken away and
therefore the ape would have to make slightly more effort to retain
the posture. But retain the posture it would, because the water would
still be too deep for risk-free quadrupedalism.

Even when the water was so shallow that quadrupedalism would be
risk-free it probably would still opt to remain bipedal in case of
waves, and/or dips in the floor of the river/lake/pool/sea, but at
such depths it's posture would require similar effort to that on land
and moving would be almost as energy efficient as moving on land too.

On the edge of the water, on shores and beaches, the land is
absolutely (by definition) flat, firm and vegetation free. It is the
*perfect* place for the human-like, inverted pendulum, energy
efficient bipedalism to work, and hence to have evolved.

I think this is the simplest, most plausible model for bipedal origins
going, and yet it is hardly mentioned in any of the texts because of
its obvious association with the dreaded so-called aquatic ape
hypothesis, which, apparently, just *must* be wrong. Human evolution
influenced by water? - Never in seven million years!

> How would
> mortality be greater among apes who went quadrupedal in such a
> situation? You suggest the possibility of "a wave, or a deeper pool or
> a deep muddy patch.." Why would quadrupedality be more dangerous in
> such situations? Possibly the quadrupedal ape would get dunked in a
> deeper pool but, assuming these critters couldn't swim, it shouldn't
> be in any more danger than a bipedal ape. It could simply stand up and
> then walk bipedally to shallower water.

The increased mortality of quadrupedal locomotion in water at waist
deep or slightly shallower depths is, I think, blatantly obvious. If
apes moved through those depths regularly then it seems pretty obvious
that over an evolutionary timescale any genes that gave a behavioural
tendancy for, or anatomical adaption to favour, bipedal locomotion
would be strongly favoured. Because such apes would also, by
definition, have to move through those gradients I was talking about,
the selection would also favour ever greater bipedalism in those
depths where the crude effect of drowning need not actually apply.
Logically, this would result in a positive feedback loop similar to
that argued by Aiello & Wheeler in their expensive tissue hypothesis.
But instead of meat acquisition driving brain growth driving increased
meat acquisition (and argument, incidentally that works even better
with fish) we have increased selection for bipedal locomotion at
deeper depths resulting in a greater tendancy for bipedal locomotion
in shallower depths which would lead to an even greater tendancy to
move in ever deeper depths.

This process would soon, naturally, result in hominids that were
bipedal, even on land and, as long as the substrate they moved through
was flat, firm and relatively vegetation free, this would be an
environment where the undoubted anatomical traits for highly efficient
humane bipedalism would have evolved too.

I hope this clarifies my thinking on the matter for you.

Algis Kuliukas

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