Re: Bipedalism in different substrates

From: Bob Keeter (rkeeter_at_earthlink.net)
Date: 07/20/04 

Date: Tue, 20 Jul 2004 03:55:59 GMT

"Pauline M Ross" <pmross@ross-software.co.uk> wrote in message
news:aatmf05j5kr0f8epc2k3p07mr4lsv9vb0q@4ax.com...

Snip. . . .

> >Not that it could possibly prove a thing, but would you expect to find
more
> >zebra fossils around a water hole at the edge of a forest or spider
monkey
> >fossils in what was a grassy plain?
>
> I would expect to find *all* fossils near water, since that's where
> they are created (except for a small number in caves). That's why
> Reed's paper is so interesting, in that she bypasses the taphonomic
> bias of location of deposition by looking at the morphology of the
> fossil species. Most people look only at the terrestrial fossils and
> ignore the aquatic ones, thereby creating a different kind of
> taphonomic bias.

Yeah, and we have already been over that rather unsuccessfully.
Particularly when I tried to use her selections of "modern equivalents"
for her analytical ancient environments. Particularly distressing since
Ross herself selected the modern ecologies as being at least in a
"macro-environmental" and taphonomic sense as the root of her
analysis!

> >We also know that the mere existence of a wet environment does NOT
> >greatly influence the evolution of primates, at least not in the sense of
> >the influences that we would be discussing.
>
> Most primates are highly arboreal, so water on the ground doesn't
> affect them at all. They can stay in the canopy. The great apes are
> different in being larger than average so they can't use the lighter
> branches at the extremities to get around. Inevitably they are more
> likely to have to come down to ground level and (if there's water
> around) get their toes wet.

And our close ape relatives are, along with us, probably the least
arboreal of all primates. . . . . So water on the ground would obviuosly
"effect" them more than a spider monkey, even if the ONLY effect
was to get their toes wet! 8-)

> [Snip]
> >So, if the ancestors of chimps, bonobos and gorillas have been
consistently
> >exposed to a wet environment, actually WETTER than typical hominids
> >perhaps, and for a longer term than the hominid line, why are they not
> >better
> >adapted to that environment than your notional "aquatic hominid"?
>
> Well, now, how do we know what sort of environment the ancestors of
> chimps, bonobos and gorillas have been exposed to? We have a fair idea
> where they were some 15+ Mya, and we know where they are today, but in
> between? How many fossil chimps have been found? None, yet quite a
> number of hominid fossils have turned up.

Well, we know that the chimps, bonobos and gorillas did not just spring
up out of the earth 5mya, so. . . . they must have had ancestors, and the
smart money says that their ancestors likely lived in something close to the
current environments. These current environments are much wetter than
the typical hominid environment.

By the way, where do you place oreopithicus and pithecantropus? I thought
that you were once saying that they were the likely chimp ancestors or
something close to that?

Now that you mention it. . . . I wonder why the fossils of many forest
dwellers are so rare in comparison to savanna dwellers? Could it possibly
be that the more acidic soils of the forest just dissolve bone material
more than the mud of a savanna water hole? Could that possibly contribute
to the accumulation of hominid fossils and the obvious rariety of
fossil chimps and gorillas?

> So either chimps and gorillas are actually descended from some of
> those hominids (a bit radical, but it has been suggested), or they
> were somewhere else altogether at the time. And since virtually all
> fossils are deposited in water, the 'somewhere else' would have to be
> somewhere without large bodies of water.

True. Have you ever seen a desert flash flood? May be the ONLY serious
water in a decade, but it still drowns and buries fossils-to-be.
Snip>

> >But "evidence" is not a hypothetical "conclusion" drawn from that bone.
> >The bone is irrefutable. The interpretation of the distal end wear
pattern
> >as being from performing the Austrailian crawl to excess, is NOT
evidence!
>
> Interpretations are not hard evidence, true. But an interpretation by
> a reputable scientist in a peer-reviewed journal is certainly
> acceptable *at some level* as evidence (at least until a new fossil
> turns up or someone finds a flaw in the methodology). And while the
> bone itself is irrefutable, virtually everything about it (age, size,
> shape, markings, etc) is subject to interpretation to some degree.

And the interpretations of reputable scientists in peer-reviewed journals
supporting, actually SUPPORTING, even the vaugest tenets of the AAH
are to be found in . . .er . . . in . . . 8-)

> [Snip]
> >And the fact that our closest cousins have spent millions of years more
> >than hominids, living in exactly the environments you would say our
> >ancestors were molded by, have NOT adapted with ANY of the
> >above "aquatic features" is a non sequiteur?
>
> As I said above, there is no evidence of precisely what environment
> they lived in. We can make assumptions, but that is all they would be.

And if we made those assumptions, exactly how far could we "extrapolate"?
Could we make that assumption and then use it as justification for a host
of perceived "adaptations"?

> >If you take the four great Africa apes (us included) and ranked them
> >in order of their tolerance for dry climates, it would appear to be
> >Gorilla, bonobo, chimp and last (and most tolerant) hominids.
> >Yet the underlying theme of the AAH is that hominds got to where
> >we are today only because of adapting to a wet environment!!!
>
> And if you ranked them in order of their tolerance for *wet* climates,
> you would get (perhaps) chimp, bonobo, gorilla and (last and most
> tolerant) hominids. Modern humans are tolerant of almost any kind of
> climate, including desert and polar. Fossil hominids are found in (and
> therefore tolerant of) well-watered environments.

We are tolerant of the hard vacuum of space. . . . so long as the technology
supports it. If you could somehow take away human technology, do you
imagine that we could even penetrate the temperate zones?

Snip. . . .

> Well, that's an interesting paper and no mistake (although nothing
> about aquatic mammals). It does make the point that receptivity
> outside oestrus is a fairly common feature in primates, so humans may
> not be so far from the norm. He also suggests that constant
> receptivity may simply be a result of modern human living conditions,
> and that the natural condition would be much the same as with the
> other apes, which is certainly thought-provoking. Maybe there simply
> isn't a puzzle to be solved here!
>
> >But if the terrestrial explanations have hard and fast, existing and
> >observable analogs elsewhere in the animal world, would you call
> > them "convoluted"?
>
> There is no analog anywhere in the terrestrial animal world for
> year-round subcutaneous fat; for furlessness, there are only pigs (but
> these things have many analogs in the aquatic world). The standard
> explanation for human furlessness involves a level of heat-dumping
> unseen elsewhere in nature in a medium-sized animal, combined with an
> unusually prolific use of water and body salts, possibly combined with
> a locomotory method which is vanishingly rare. Wouldn't you call that
> convoluted?

ANd what degree of wading, and "less than otter" aquaticism, would
possibly lead to hairlessness on the upper body and arms? 8-)

As for convolution. . . . . 8-)

Can you agree that modern humans are land mammals and have been for
quite a few years? If so, why have we not "returned" to characteristics
driven by our terrestrial environment? If you say something to the effect
that the "aquatic adaptations" turn out not to be disadvantages in
terrestrial
evironments, by the way, you essentially disavow any connection of these
traits to a water envionment (for "dont care" states, there would be neither
a pro or a con selection process and simple random drift must be assumed
as the "cause".) 8-) If the traits have "other advantages" in a
terrestrial
millieu, then they dont even have the need for water to have been selected!

> >
> >On the other hand if the aquatic solutions began to defy the existing
> >examples,
> >and even contradict each other in modern species, do those start to feel
> >convoluted and contrived to you?
>
> Both subcutaneous fat and furlessness are commonly found in aquatic
> species, and are very rare in medium-sized terrestrial species.
> Where's the contradiction?

SC fat because there is no need for insulation in tropical streams, if
anything
there is a need to dump body heat, as we discussed elsewhere. If the fat
is for bouyancy, it would only have an effect when that portion of the body
is immersed, again running hard against the wading hypothesis.

Hairlessness, as a drag reducer, would ONLY be effective on those
parts of the body immersed in the water, and in an upright, wading
posture the presented area drag of the body will be many magnitudes
greater than the localized "skin effect" of a little hair.

Your choice. . . . do they contradict the wading hypothesis? If wading
is "out", the only thing you have left is to hitch a ride on the "swimming
like a fish" bandwagon, and I dont think that even you think much of
that fabrication! 8-) Whenever you get down to the "2+2=0" case
its time to look for other answers!

Regards
bk

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