Re: Bipedalism in different substrates

From: NA Sides (nas_at_sonic.net)
Date: 06/30/04 

Date: Wed, 30 Jun 2004 14:46:10 GMT

On 29 Jun 2004 16:51:33 -0700, jae@ucdavis.edu (Jason Eshleman) wrote:

>Pauline M Ross <pmross@ross-software.co.uk> wrote in message news:<9d43e0l3tetlk9pttq19051eutqhq3l0l0@4ax.com>...
>> On Tue, 29 Jun 2004 14:56:25 GMT, NA Sides <nas@sonic.net> wrote:
>>
>> >Perhaps, in turn, Jim was taking the word of AAT advocates :0).
>>
>> You think so??? :-)
>>
>> >Apparently babirusa cross rivers in order to get to feeding areas on
>> >the other side, but actually forage on land for fruit and plants,
>> >including "the coconut-sized pangi Pangium edule, which has a seed
>> >containing toxic hydrocyanic acid." They may eat muds containing clays
>> >that function as chelating agents. Also apparently their digestion is
>> >specialized with pre-gastric fermentation that allows them to get some
>> >nutritional benefit from cellulose.
>>
>> Wow, thanks! I suppose the 'crossing rivers' bit is where the
>> 'affinity for water' comes from. I suppose if they do that often
>> enough, that makes them sort of semi-aquatic.
>
>I'm greatly bothered by terms that seem to have no definition or
>defintions that don't lend any real utility. In these discussions,
>"semi-aquatic" seems to be such a term. It's being used to describe
>creatures who may spend months at a time in the pelagic but do come
>ashore (e.g. elephant seals) down to creatures who cross rivers
>periodically. Clearly, the selective pressures relating to water in
>such creatures vary dramatically. I'd suggest that if the term
>"semi-aquatic" is applied to both the babirusa and the elephant seal
>it's a term that's sufficiently vague as to be near-useless in the
>context of selection for aquatic adaptations. The former, though able
>to get out of the water, are completely dependent on swimming for
>their survival. The latter appear to be terrestrial foragers who, so
>long as they've got a way to stay hydrated (something all mammals,
>terrestrial, arboreal, aquatic, subterranean or otherwise need to be
>able to do) would seem to be able to survive just fine without ever
>going for a swim.

But they move through water more than do chimps! Algis seems to think
this is an adequate definition of "aquatic." Perhaps Pauline and he
could discuss the matter and arrive at some more accurate definitions
of terms like aquatic, semi-aquatic, partially aquatic or whatever. We
can always hope that such a development will occur, but it would
probably be unwise to hold one's breath while waiting. Most
aqua-proponents seem quite content with the vague use of terms.
Precise definitions would just cramp their style.

>The term "hairless" is similarly ill-defined, especially when it comes
>to correlating it to creatures who are "semi-aquatic." While the
>fully aquatic marine mammals have lost virtually all their hair cover,
>I'd argue that their hairlessness is qualitatively different from
>ours. We've got hair over much of our body and considerable hair atop
>our head (which, despite special pleading to explain away, will get
>wet [especially among those who cannot cut their hair] when you try to
>swim at any speed). Including humans and whales in a broad category
>of "hairless" misses extreme qualitative differences that may very
>well make any correlation to a particular adaptation meaningless.

Picky! Picky! Picky!

NAS

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