Re: Bipedalism in different substrates

From: Pauline M Ross (pmross_at_ross-software.co.uk)
Date: 07/03/04 

Date: Sat, 03 Jul 2004 14:00:07 +0100

On Fri, 02 Jul 2004 23:27:20 GMT, "Bob Keeter" <rkeeter@earthlink.net>
wrote:

>8-) NO. Crossing rivers is simply not a driving factor in the evolution of
>zebras (in their case, mostly since ability in the water has so little to do
>with
>the drowning deaths). Zebras and wilderbeest drown because their comrades
>essentially trampple them to death in the wild crossing.

Yes, Bob, and which ones are more likely to get trampled, the good
swimmers or the less good? the first ones across or the ones in the
middle of the pack? the ones who find a safe exit route on the far
side or the ones who follow the crowd and find the bank slippery with
mud? You cannot seriously propose that an event that occurs several
times a year and causes multiple deaths is going to have no selective
effect, surely?

>For all practical purposes, ALL mammals swim. You really have
>to look hard to find a mammal that doesnt. As for red herrings,
>the point you make is extremely valid. Occasional, inconsequential
>(even if deadly) encounters with water will not force adaptations.
>That much is valid beyond belief. So long as it is applied rigorously.

I'm having trouble envisaging an event which is simultaneously
inconsequential and deadly :-) As to the proposal that all mammals
swim, I would put it this way: a conventionally quadrupedal mammal
finds it relatively easy to swim because their standard method of
locomotion converts easily to a swimming stroke. A zebra trotting into
a river and finding itself out of its depth simply continues to 'trot'
in the water, and ends up swimming; a basic doggy-paddle is not that
different. And, I repeat, if the price of failure is drowning, there
will be selective pressure on swimming ability.

[Re Potts' environmental selection paper]
>> [Pauline] But one of his difficulties is that he assesses habitat without taking
>> water into account. Even where it is clearly relevant eg in the
>> 'riparian-woodland scavenging' model, he emphasises only the woodland
>> part.
>
>*-) Is that a problem for him, or a problem for you?

It's a problem for him, of course, because he is missing a large
element of the picture. If you are discussing the influence of the
environment on human evolution, you should take *all* elements of that
environment into account, don't you think?
>
>> [Pauline] Yet we know from Kaye Reed's paper (don't we, Bob?) that
>> Australopithecus was found in well-watered woodland, and Paranthropus
>> in similar and somewhat drier habitats, but always including wetlands,
>> and early Homo in the same, plus some dry habitats. This gives a
>> uniformity to early hominin environments which Potts completely
>> misses.
>
>Pauline, I have NEVER claimed that an ancient homind could possibly have
>survived without water. I will even go so far as to suggest that we should
>add adjectives such as "reasonably plentiful". [Snip]
>ALL savanna animals must have ready access
>to water else they die! Simple as that. They die. No natural selection
>process, no evolutionary tendencies. If the water is not there, the grazers
>will die. So would ancient hominids.

Savanna-adapted animals must drink, but they don't need to drink as
often as animals from wetter terrain, and they drink a lot in one go.
Would you say this applies to humans?

But the issue is Potts' paper: he claims that there is no consistency
to the type of environments where hominins are found, yet Reed found
exactly that - they all include plenty of water. Not the occasional
water-hole or savanna-surrounded river, but "well-watered" and
"wetlands". If Potts had included water in his discussion of hominin
habitats, he would have had that consistency.

>By the way, how would you rate "fools" to "idiots" on the scale of
>sociopathic ad hominem on USENET?

This is tedious. I would rather ignore all this snide stuff, but since
you ask me directly, I will tell you: on a scale of 1 to Jason
Eshleman's little masterpiece, I would rate it a 1.
>
>So. . . . My contention goes something along the lines of you can lead a
>homind to water and eventually he must take a drink, but that does not even
>imply that he is irresistably forced to get his feet wet! 8-)

No, indeed, and modern chimps, say, who can get all the food they need
without doing so, will avoid water. But in the much wetter Miocene and
early Pliocene, there may well have been times when the food available
without getting ones feet wet was not quite enough, and those
individuals who were prepared to wade or swim would have done better
than those who were not.

>Water is not simply a recurring feature, its an absolutely essential
>feature, . . . . for at least drinking purposes. All other "purposes" need
>evidence.

There's very little direct evidence of what our ancestors were up to 2
or 5 or 10 Mya. We don't know directly whether they were wading, for
example, or what specifically they were eating. We have to look for
indirect evidence: what was the environment like? what food would have
been available? what do extant apes do in similar conditions?

>>[Pauline] If one is proposing a hypothesis for the evolution of a species,
>> one of the first and most important questions is: why did this happen
>> to *this* species? Were there other species in the same environment,
>> did they evolve the same way and if not, why not? The more unusual the
>> proposed explanation, the more searching these questions have to be.
>> Potts is proposing a unique-to-humans hypothesis, yet he never
>> addresses them at all. It's a major weakness, in my view.
>
>OK, lets see if I can get this straight.
>a) Any evolutionary process that could lead one species in a give direction
>should be expected to lead others in the same direction?

No, not really. Why should it? Evolution doesn't work that way. Even
very similar species might react to the same evolutionary pressure in
different ways.

But if you propose an explanation for some evolutionary change in a
species, part of that explanation must include the reason why other
species in similar conditions did *not* go that route. In other words,
you can't propose an explanation why something *did* happen, without
also explaining why it did *not* happen.
>
>b) An "explanation" that is unique to the human species is far fetched (or
>at least less credible) that a generalized process?

Any unique explanation is less likely than one which applies in
multiple cases, yes. You would investigate the more common possibility
first.
>
>c) The "more unusual the proposed explanation", the more questions must be
>asked and the more strongly the conclusions must be supported with facts?

I said "The more unusual the proposed explanation, the more searching
these questions [why other species evolved differently] have to be."
Conclusions always have to be supported with evidence (facts are thin
on the ground in PA).
>
>8-) Sometimes you truely surprise me! In this case, happily though!

That's because you think the 'aquatic' explanations are unusual :-)
>
>Lets start with "a"! If I consider all aquatic and semi-aquatic mammals
>under the weight of 150 lbs, and there are a host of them, did their
>adaptation to the water lead to the loss of fur or actually a thickening of
>the fur?

Well, now, all aquatic and semi-aquatic mammals under 150 lbs, so that
will include quite a 'host' of the smaller dolphins and porpoises,
right? So quite a few that have lost their fur. :-)

>Now lets look at "b". If I look at all of the other mammalian species that
>have successfully adapted to an aquatic or semi aquatic existence, I see
>NONE that have adopted the rather unique bipedal gait because of their
>contact with water. NONE!

But then of all the other mammalian species that have taken up an
aquatic or semi-aquatic lifestyle, I see NONE that started out as
arboreal apes. NONE! ;-)

>If an environment niche is sustainable it is not left empty nor is it abandoned.
>There have
>been huge areas of Africa (varying in size of course) entirely suitable for
>the aquatic ape constantly over the last 10my or more, yet there are no
>aquatic apes! Only us humans and the terrestrial apes are left, even though
>the proposed niche is very much there [Snip]

YES! Exactly.... only us humans and the terrestrial apes. Huge areas
entirely suitable, and only us humans and the terrestrial apes... If
an environment niche is sustainable it is not left empty nor is it
abandoned....

No aquatic apes? Now I wonder where they are? ;-) 

-- 
Pauline Ross

Relevant Pages

  • Re: Bipedalism in different substrates
    ... Wetland habitats are here and they always have been. ... the facts that Miocene apes of Europe & SE Asia must have lived around ... wading is the most likely to induce bipedalism, ... around 11% drag reduction in water. ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... >> foraging in a variety of areas and employing different foraging ... >> bipedally both on land and in water, but this would shoot down your ... >the facts that Miocene apes of Europe & SE Asia must have lived around ... Australian aborigines also survived in other habitats. ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... > sustained terrestrial bipedalism. ... I've been trying to explain why wading bipedally is a safer locomotion ... It gets apes moving bipedally in the first place, ... Regular bipedal movement in water for several million years before ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... Of course it's also true that apes can drown and I'm ... >> likely to drown than a wading chimp. ... continue insisting that the putative dangers of swimming are somehow ... >Both place hominids next to water throughout much of their evolution. ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... >>water into an argument against it being a selective factor then, ... > wading, therefore, would have saved lives. ... > in the thread, nobody was swimming. ... I argued that as apes, generally, are not good swimmers ...
    (sci.anthropology.paleo)
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