Re: Bipedalism in different substrates

From: Bob Keeter (rkeeter_at_earthlink.net)
Date: 07/21/04 

Date: Wed, 21 Jul 2004 01:40:13 GMT

"Pauline M Ross" <pmross@ross-software.co.uk> wrote in message
news:arqpf01raeg5usvso4tielsnlimgr9d0nd@4ax.com...

Snippage. . . .

> > On the
> >other hand, the foot is perhaps the most "telling tale". 8-)
> >If you have ever been wading in a wet swamp or marsh I will consider you
> >to be an expert on this subject, so. . . . how well adapted is the basic
> >shape of the homind foot [...]
>
> I'm going to pass on this one. I know zippo about feet, or anatomy
> generally. You tell me. But I feel that webbed feet are going to make
> one of their periodic appearances... :-) To forestall that, I would
> suggest that webbed feet are most useful for a) walking lightly over
> somewhat muddy or boggy ground, not for wading or swimming; and b) for
> swimming with a paddle-like motion, not the typical human kick-stroke.

Ever been scuba diving or snorkeling? What are those funny rubberized
things
that you put on your feet and why is it that you do so? Ever seen some of
those
"swim mittens" that are sometimes used? Interesting, VERY interesting what
technologically minded humans will do to themselves, on a very temporary
basis
to allow their supposedly aquatically adapted body actually perform
reasonably
efficiently in the water. . . . . Then there is the competitive swimmers
that get a
little bit overzealous with the razor to get rid of all of that non-existant
body hair
to minimize drag.

> > Bonobos, in spite of perhaps the closest to
> >bipedal geometry among the great apes, seem to prefer quadrupedal posture
> >when they wade (at least in the wild).
>
> Do they? I haven't seen anything to suggest that they *prefer* to be
> quadrupedal, only that they do so in shallow streams when foraging for
> food on the stream-bed.

Have you seen ANYTHING else that describes wading of bonobos, on a
habitual basis, performing some task with at least marginal "survival"
impact,
in the wild? If so, lets hear it! 8-)

> >Why would a hominid go wading in the first place? I would suggest that
> >it would for the same reason that the bonobo does, i.e. to secure food.
> >Now if you are wading around in the water somwhere between ankle and
waist
> >deep, where would the food almost certainly be? would it be in
overhanging
> >branches? (Sometimes) Would it be floating on the surface? (possibly) or
> >would it be lying on the bottom like the various things that bonobos
harvest
> >from their streams? Im sure that you see the direction we are going
here. .
>
> Again, you are assuming from one reference that foraging on
> stream-beds is the norm. I don't know that it is.

Well, exactly what would they forage if it was not on the bottom. Fresh
water
shellfish dont swim much at all, tubers (as opposed to the indigestable
stalks) of
sedges are under the water, on the bottom. What floats on the surface that
a
homind style digestive tract could process?

> >>[pauline] Yes, but that doesn't mean that the hominids ate exactly the
same diet
> >> as hyenas, does it? It means only that they had the same *proportions*
> >> of C3/C4 foods in their diets, which was intermediate between pure C4
> >> (grazers) and pure C3 (browsers and frugivores), but nearer the C3 end
> >> of the spectrum.
> >
> >I may need to re-read the paper, but I seem to remember that the apith
> >enamel was much closer to the grazers and carnivores that ate grazers
> >than to the browsers and fruit/nut crowd. The hyena is after all more
> >of a creature of the open than closed in forested environment dont you
> >think?
>
> In the 1999 Sponheimer/Lee-Thorp paper, the grazers (C4) had values
> around zero, while the browsers and frugivores (C3), including a
> couple of modern primates, had values around -12. The hyenas and
> apiths had values around -8, closer to the browsers than the grazers.
> That is consistent with a mostly fruit/nut/leaf diet with a sizeable
> chunk of grass-derived food as well. The later paper gives a mean of
> 40% for the C4 (grass-derived) component, but varying from 0% to 60%.

But you didnt address the question. Is a hyena a creature of the open or
closed
forest environment?

> >
> >> [Pauline]It is probably safe to presume that the hyenas were living
mainly on
> >> meat, but you can't make the same assumption about the hominids. They
> >> *could* have been entirely vegetarian and still had the same C3/C4
> >> proportions as the hyena. And the variation between individuals is
> >> quite large (-5.6 to -11.3).
> >
> >They could have? And exactly what native plant material could they have
> >eaten (and digested without cooking) that would have provided the
> >same "mix" as the hyena?
>
> The bulk of the diet (60% on average) would be the usual fruit, nuts,
> leaves; so only 40% from "grasses and sedges or animals that ate these
> plants or both". That 40% component could (theoretically) come from
> sedges or grass seeds, but I would think there was some meat in there
> (maybe some termites, maybe insects, maybe reptiles, maybe something
> larger, but most probably a mixture).

8-) Did you read the article on the 2my old blood samples from the
Sterkfontein stone tool? ;-)

Try it, you will like it!
http://www.abc.net.au/science/news/stories/s1156792.htm

> One interesting point from the 1999 paper is the indication that
> Paranthropus and early Homo had very similar overall proportions of
> C3/C4 to the A. africanus sample, despite Paranthropus inhabiting more
> open grassland environments than Apiths, and also despite Homo having
> stone tools to facilitate meat processing. I'm not sure what to make
> of that, but it is certainly consistent with your view that hunting
> predated the advent of stone tools.

8-)

> Another interesting point is the wide variation in C4 component
> between individuals (0-60%). I would account for this by proposing
> that some populations lived close to river crossings popular with
> migrating herds, so meat regularly arrived on the doorstep, while
> other populations got such a bounty rarely or never. How would you
> account for the variation - were some groups hunting and others not?
> Were some more successful than others?

Look to the modern chimp populations. Some hunt rather regularly;
others apparently never do (or at least are not observed to do so).

Hindus do not eat beef, Muslims do not eat pork, and I happen to
favor bacon cheesburgers, yet we are all of a single species.

> >Is this the article that you were referring to:
> >THE CARBON ISOTOPE ECOLOGY AND DIET OF AUSTRALOPITHECUS AFRICANUS AT
> >STERKFONTEIN, SOUTH AFRICA.
>
> That's the one!
>
> >"These results show that hominins had become savanna foragers for a
> >significant part of their diet by ca. 3 Ma. [...] ">
> >I would be lax if I did not call your attention to the next-to-last
> >sentence! 8-) By the way, I have no problem whatsoever with the idea
that
> >an apith might have been just as "at home" in a more closed woodland as
the
> >savanna. Do you?
>
> No, and I have no problem with "savanna foragers" either, but I don't
> think they were ever exactly savanna dwellers. Essentially, I think
> they lived in forest/woodland close to large bodies of water, but
> their ranges may well have included enclosed patches of grassland (ie
> grass more or less surrounded by trees) and some completely open areas
> too (ie parts of larger areas of grassland that happened to abut their
> forest). Plus lots of bush, of course - the classical mosiac habitat,
> in fact. Possibly the only difference between us is that I see it as
> well-watered woodland with bits of open territory, while you perhaps
> see it as open territory with bits of well-watered woodland.

Like I told you before. The same words with very different "pictures"!
;-) Seriosly though the difference between those two paradigms is as
small as a good monsoon or a dry summer. Hominids would have had
to survive in both to make a go of it. Adaptations that did not "make
sense" in both of the environments you suggest were almost certainly a
one way ticket to extinction when the other micro-climate appeared.

> >>[Pauline] I have a
> >> couple of other papers by Sponheimer and Lee-Thorp if you want them.
> >
> >Got a couple. Fire me the titles/urls if you dont mind.
>
> This one is more up-to-date:
>
> Sponheimer/Lee-Thorp 2003 'Differential resource utilization by extant
> great apes and australopithecines: towards solving the C4 conundrum'
> Comparative Biochemistry and Physiology Part A 136 (2003) 27-34
>
> The other turns out to be the 1999 one (must give saved papers better
> names!), but this one is interesting, not isotopes but tooth shape and
> wear:
>
> Teaford/Ungar 2000 'Diet and the evolution of the earliest human
> ancestors' PNAS Dec 5 2000 vol 97 no 25
>
> I can send you copies if you want.

Want! Thanks!

> >For a plant eater, with a prolific sweating reflex, salt would be
critical.
> >On the other hand, why dont lions seem to need salt licks as much as
> >ungulants? 8-)
>
> Good point. Do lions ever need salt-licks, or do they get all they
> need from meat? Of course their diet is 100% meat.

8-) Glad you noticed!

Actually, I would suspect that considerably less than 100% meat would
provide enough salt in the diet. Remember how "pollutants" tend to
accumulate in the top predators? Id suspect that the same would be
true of salt.

Snippage. . ..

> >But one has to wonder whether rubbing shoulders with chimps and
> >gorillas ancestors in what is today their native environments, or moving
out
> >into a new and different environment would be the most "common sense"
> >reason for our differences? 8-)
>
> The expression 'moving out into a new and different environment'
> worries me. Do you really think species do that? I would think it more
> likely that there was a widespread ancestral species which utilised
> arboreal and ground and water resources; as the climate changed, some
> populations found themselves in habitats which were richer in arboreal
> and ground resources (and became chimps and gorillas) and some found
> themselves in habitats which were richer in ground and water resources
> (and became humans). Without the water, this is not far from the
> conventional view.

Actually, until you get to how that water was utilized and how often it
was utilized, I dont think that its ANY different from the conventional
view! You would just require, for some reason, that the hominids switch
from a semi-arboreal, semi-terrestrial critter into a semi-aquatic, semi-
terrestrial critter instead of just making the transition directly to a
terrestrial
critter! Two major changes of venue versus a single transition. Hmmmmm
Even if I dont consider the context, one evolutionary path vs two is perhaps
not the most parsimonious would you say?

Snippage. . . . .

> Absolutely. The breeding habits of the hippopotamus, for example. Very
> educational. :-)

Absolutely!! Never know when I might need a new umbrella stand or four?
;-)

Regards
bk

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