Re: Bipedalism in different substrates
From: Pauline M Ross (pmross_at_ross-software.co.uk)
Date: 07/20/04
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Date: Tue, 20 Jul 2004 17:46:41 +0100
On Tue, 20 Jul 2004 03:55:59 GMT, "Bob Keeter" <rkeeter@earthlink.net>
wrote:
>>[Pauline]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-)
Yes, sure. And it is interesting that the great apes are all
classified as having less than the full complement of fur, and also
have a similar distribution of eccrine glands, not to mention having a
larger body than most primates and no tail. It is possible that the
effects of water on the ground are more widespread than generally
supposed.
>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.
Yes, they must have had ancestors, but those ancestors were never
anywhere where they could get fossilised, apparently. Their current
environment is certainly very wet, although it is year-round-rainfall
wet rather than water-on-the-ground wet. Whether it is wetter than the
'typical hominid environment' (well-watered?) is debateable.
>
>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?
Not me, no, I don't know enough about either of them to try to fit
them into a family tree. I leave that sort of thing to the
professionals.
>
>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?
Well, no, because all the early hominids were found in pretty dense
woodland which would (presumably) be acidic. Actually, savanna fossils
are tricky too, because anything left out the open is mauled by
scavengers and trampled to dust by the local heavyweights.
>
>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-)
You'd be surprised. Try this one:
Muskiet/Fokkema/Schaafsma/Boersma/Crawford 2004 'Is Docosahexaenoic
Acid (DHA) Essential? Lessons from DHA Status Regulation, Our Ancient
Diet, Epidemiology and Randomized Controlled Trials' American Society
for Nutritional Sciences J Nutr 134 183-186, 2004
There's quite a growing body of evidence regarding our requirements
for certain elements common in seafood. I agree there's not much in PA
directly supporting AAH, but then no one is actively researching it.
Recent research (eg Reed and others) has been more in line with AAH
than earlier conventional thinking.
>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?
And could we penetrate very dry areas without any technology either?
All apes (including humans) are naturally creatures of wet (or
wettish) tropical zones. The spread into temperate, cold and dry zones
is very recent.
>ANd what degree of wading, and "less than otter" aquaticism, would
>possibly lead to hairlessness on the upper body and arms? 8-)
You're getting mixed up, Bob. Wading => bipedalism, swimming =>
hairlessness, subcutaneous fat.
>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!
Well, there's a nice damned-if-you-do and damned-if-you-don't
statement. I see now why discussion with you is such an uphill battle.
Essentially you are saying that an aquatic explanation is out of court
no matter what.
But I think the key is in the 'quite a few years'. I agree modern
humans are (essentially) land mammals, but how long have we been so? I
would say we have only been unequivocally terrestrial since the advent
of agriculture (say 10 kya); before that *most* populations lived
close to large bodies of water *most* of the time.
So that means that (for most populations) that any adaptation to
terrestrial life is very recent and still ongoing. That's why we
haven't yet lost our SC fat, for instance, which is generally
counter-productive on land.
>> [Pauline] 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.
There are lots of reasons for SC fat (in aquatics), and I'm inclined
to think that streamlining is as important as anything else, perhaps
more important than insulation. But insulation is *always* beneficial
in water, I would have thought, even in the tropics. On land, of
course, fat is very much counter-productive in the tropics.
Buoyancy may or may not be useful, it depends whether the animal is a
surface or bottom feeder. Again, waders are unlikely to evolve SC fat,
that would need full immersion (ie swimming)
>
>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!
Not quite out of answers yet, Bob :-) As I said above, I see wading as
the driver for bipedalism, and swimming (or complete immersion of some
sort) as the driver for SC fat and furlessness, but the proportions of
each (and of arboreal or terrestrial locomotion) would have varied a
great deal. So no contradiction.
-- Pauline Ross
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