Re: Bipedalism in different substrates

From: NA Sides (nas_at_sonic.net)
Date: 06/14/04 

Date: Mon, 14 Jun 2004 18:48:47 GMT

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. 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.

NAS

Relevant Pages

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