Re: Bipedalism in different substrates

From: Bob Keeter (rkeeter_at_earthlink.net)
Date: 07/18/04 

Date: Sun, 18 Jul 2004 18:48:38 GMT

"Pauline M Ross" <pmross@ross-software.co.uk> wrote in message
news:kccif0hqk9ihpj9tbr5kk5ds5ob1bthdd2@4ax.com...
> On Sat, 17 Jul 2004 01:46:52 GMT, "Bob Keeter" <rkeeter@earthlink.net>
> wrote:
>
> >Now, Pauline. Is this an answer to the question posed in the quote you
> >so generously included above? OBVIOUSLY something favored bipedalism
> >or we would not be bipedal. Wading is one of the options as is the need
> >to free up the forelimbs for flying, but some options can be discounted
> >quite easily for one reason or another. Im asking that you apply the
same
> >logic to the "wading" hypothesis as you did elsewhere. Step by step,
> >with your own intellectual honesty vetting the conclusion of that
logical
> >process! 8-)
>
> The logic in the quote above is that if a species shows adaptations
> for activity X, then it must have been doing a certain amount of X. So
> if hominids show adaptations for bipedal locomotion, then they must
> have been doing a certain amount of bipedal locomotion.
>
> But (so far as I know) there are no specific anatomical adaptations
> just for wading. In other words, a species which wades is not
> distinguishable at the skeletal level from one which is terrestrial
> (just as otter skeletons are apparently indistinguishable from weasel
> skeletons).

8-) Ah yes! Logic is rather difficult there, but you came through with
flying colors!

There is NOTHING that would absolutely and unequivocably demonstrate
bipedality (in the gross form) as a wading or as a walking adaptation?
Perhaps a bit fast dismissing that, and of course in the world of absolutes
there is almost always a chance for an exception. . . . BUT which way
would the exception work! For example, I might agree whole heartedly
with your suggestion if you ONLY included the skeletal geometry above
the ankle. The knee and hip adaptations to a wading or walking existence
would be logically identical, in spite of Algis' "sidestep shuffle". 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 (and I include all the way back to at least the apiths
since
we have a very good idea of what their flesh as well as bone foot looked
like.)
to wading in your typical marsh or swamp. Now considering such things as
pounds per square inch of foot area, the arched bones in the foot and the
relatively long and narrow design, is that foot better adapted to a
terestrial
walking gait or an aquatic wading gait? Your call, so long as you provide
the justification.

> So all you can say is that hominids must have been doing a fair amount
> of bipedal walking, but whether on land or in water is impossible to
> say, and as for why - well, living analogues are the best place to
> start looking for reasons.
>

Bingo! "Living analogs" for obligate bipeds are few and far between, and
separated by enough evolutionary timeline as to be pretty marginal. On the
other hand, we have some really close relatives that are at least capable of
significant bipedal locomotion. 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). Could we possibly presume that
if we had an ancestor that was at least as committed to bipedalism as the
bonobo, it
would also wade quadrupedally? Perhaps a reach. . . but speaking of
reaching. . .

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. .
. . .

Wading in water deeper than the reach of the arms length would be a logical
waste of time! Furthermore, wading in water equal to or less than the
length
of the arms would have absolutely no COMPULSORY impact on bipedalism!

> >Yep. BUT the sampling techniques used for these isotopic studies depend
on
> >powdering and even vaporizing a small sample of the enamel for the mass
> >spectrometer. I would think that it would be difficult to the point of
> >impossible
> >to extract enamel from only one year's deposit much less any subset of a
> >year.
>
> OK, thanks, but that means that the 'tree-rings' are probably not
> relevant in the context of isotopic analyses.

Straight up, you are right, the point is that the enamel is laid down over
time.
A given concentration of isotopes in the "total sample" either imposes
a relatively constant rate of isotopes in the enamel accumulations or some
VERY high shorter term spikes in the isotope. Im thinking that the "very
high"
might just be TOO HIGH even with the idea of a seasonal gorging on
drowned zebras!

> >
> >When analyzed the carbon isotopes showed a carbon accumulation that could
> >be explained by the diet of a savanna-living hyena. Hyenas eat meat, one
> >way or another, year round.
>
> 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?

> 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?

As for the mix. . . . I would say that, above all else, would indicate that
the
environment changed, that there were some "individual preferences"
exhibited, etc. In an open forested environment I would have expected a mix
and would have been shocked not to see it.

Is this the article that you were referring to:

THE CARBON ISOTOPE ECOLOGY AND DIET OF AUSTRALOPITHECUS AFRICANUS AT
STERKFONTEIN, SOUTH AFRICA.
Conclusion: The stable carbon isotope ratios for ten specimens of
A.africanus from Sterkfontein Member 4 show that this species of hominin had
an unusually varied diet with a sizable component of C4-based foods. These
could have included C4 grasses and sedges and/ or the insects and
vertebrates that eat these plants. The C4 dietary component varied
considerably from one individual to the next with a mean of about 40% and a
range between about 30 and 60%. When the results of four specimens of A.
africanus from Makapansgat are added to those from Sterkfontein, the C4
component can be seen to vary from nearly 0 to 60%. This range is wider than
that observed for any other species of early hominin, or indeed for any
non-human primate, fossil or modern. It indicates that A. africanus was an
exceptionally opportunistic feeder: the ultimate in hominin adaptability.
Such adaptability would have contributed greatly to its survival skills in
the changing environments during this crucial stage of human evolution.
These results show that hominins had become savanna foragers for a
significant part of their diet by ca. 3 Ma. The critical point when they
emerged from the forest to sample savanna foods can only be established if
the newly-discovered "forest hominins" of South and East Africa are
subjected to the same isotopic analysis.
van der Merwe N.J.,. Thackery J.F., Lee-Thorp J.A., Luyt J. Journal of Human
Evolution 44(2003), 581-597

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?

And yes it would be a real "*** kicker" if our newfound friend
Sahelanthropus ended up with hyena-like enamel as well, wouldnt it! ;-))

> >Could you point me at that paper on the isotopic variation by the way?
8-)
>
> Nikolaas J van der Merwe, J Francis Thackeray, Julia A Lee-Thorp,
> Julie Luyt 'The carbon isotope ecology and diet of Australopithecus
> africanus at Sterkfontein, South Africa' JHE 44 (2003) 581-597.
>
> They get a range of C4 from 30% to 60% (with Makapansgat included that
> becomes 0% to 60%). I only seem to have the printout, but 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.

> >> >[Bob] ABSOLUTELY! If there was every a profound point of agreement
> >> >you have found it. We were always NEAR water, just like most other
> >> >totally non-aquatic mammals!
> >>
> >>[Pauline] Hey, we agree on something :-)
> >
> >Does that mean that you REALLY do agree that even totally non-aquatic
> >mammals are still "tied" to water? What kind of "non-aquatic" mammal
> >would you be referring to? After all that would set a "threshold" for
> >example.
>
> I agree that we (ie our ancestors) were always near water. I don't
> think I would agree that most other totally non-aquatic mammals are
> always near water - it kind of depends what you mean by 'near'. Is a
> chimp always 'near' water? How about a giraffe?

Yes, a chimp is always NEAR water even though many rarely bother with
it. Certainly the chimps that live in the more open areas will prefer to
stay
in those areas also well supplied with drinking water.

Matter of fact, a giraffe is a very good example to consider! Its
definitely a
creature of the "open forest", totally specialized to pick the tender mimosa
or accacia leaves out of the tops of the scattered trees. It can go for days
without
water, but eventually, must still do its awkward "kneel-down" to get a
drink.

> >
> >If a mammal was "less connected" to water than an "X", it is by
definition
> >non-aquatic! That would be a very powerful statement dont you think?
> >8-) Powerful and at the same time very "sticky" from a logical
standpoint
> >wouldnt you say? ;-)
>
> You're in binary mode, Bob - aquatic/non-aquatic. In the real world,
> there is a continuum.

Perhaps. but there has to be a line above which there are no aquatic
animals and another line below which there are no terrestrial mammals.

> >If anything, I would offer that the "sweating" is clear and "obvious"
> >proof that our ancestors (you pick the point in time) had to exist in
> >a hot, and at least relatively dry climate. The simple reason is that its
> >only in such a climate that sweating is at all efficient.
>
> I agree. Hot, dry and with abundant water to replenish that sweated
> off. And Paul's point about salt is a good one.
>

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-)

> You see, again you are in binary mode. You assume that a hominid must
> have cooled off *either* by dunking in water *or* by sweating, but the
> two could easily have developed in concert. When you are right beside
> the water, you take a dip to cool off; when you have to spend time
> away from the water, you sweat to cool off. Hominids probably always
> exploited a variety of local resources, so sometimes they would be in
> or near the water and sometimes not.

My point, my ONLY point is that when in the water, sweating is useless
and when using sweat for evaporative cooling, you cant be in the water!

The same animal COULD switch gears between these modes in a matter
of seconds, its just that you cant do both at the same time.

>
> [Snip maths]
>
> >Pauline, have you ever spent any time in a very hot, very dry place?
> >You will go through water like its going out of style. But quite frankly
> >so long as you have plenty of water to push through your marvelously
> >efficient evaporative cooling system you can survive some very ugly
> >ambient temperatures.
>
> Yep. Lived in Texas for 3 years, toured all round the SW states, did a
> fair amount of walking around in very hot, very dry places. I found I
> had to drink pretty much continuously, although I suppose anyone who
> was used to being outside would need to drink less.

Not really. The cooling requirement is a function of body temperature, mass
metabollism, etc, but for all intents and purposes, everyone is just about
alike.
Those with more experience in hot & dry climates just SEEM to not need as
much water at least in part because of how they dress or handle themselves.

Thats not scientific but is at least based on 15 years or so in the desert!

> >
> >I agree entirely with the proposition that a hominid would be in woodland
> >areas near water, but I would also contend that at least the margins of
> >the true grasslands and virtually all of the "open woodland" areas would
> >be viable. 8-)
>
> Yes, absolutely. I think hominids were always generalists, exploited
> whatever was available.

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-)

> > So long as they can be close enough to open water to get a
> >good filling drink once a day, and you will be surprised at just how much
> >a hominid can drink after a long day in the sun, they dont even need
> >a water skin or ostrich shell.
>
> I'm not sure that humans can drink just once a day. A lot of
> open-grassland grazers can do that, but I don't think humans can.
>

8-) Humans need around 2.5 liters of water a day for normal existence, but
can
get by on quite a bit less. Consider some of the "shipwreck" sagas and the
"starvation
rations" imposed. Not that it is good to do, but possible to do would make
a
lot of difference in survival situations.

> >> [Pauline] OK. Clubs are a possibility, digging sticks a bit more of a
stretch,
> >> but we can agree that it is all conjecture - or, as I prefer to put
> >> it, there is no evidence... ;-)
> >
> >Did you say that! If so, Im claiming a major coup! "There is no
evidence"
> >is a damn-fine phrase. Remember it.
>
> Oh, I will :-) But remember that PA has precious little hard evidence
> of any kind. A few well-scattered fossils and artefacts, some
> ecological data, extant species and some genetic data. And every last
> bit of it disputed and argued over. It's astonishing how much
> information people manage to glean from so little base data, but it
> does suggest caution; your Sponheimer/Lee-Thorp paper is based on just
> 4 samples of A. africanus, for example.
>

Gleaning information is one thing, fabricating hypotheses is another. And
for
that matter, fabricating hypotheses is not inherently a bad thing. Hanging
on
to hypotheses even after the evidence points a different way, is somthing
else entirely. 8-) Worse is presenting hypotheses as if they were
"obvious"
fact.

> >> [Pauline]But I do wonder why you feel such a missionary zeal to reform
all us
> >> poor misguided folks...
> >
> >Perhaps the same reason you want to "reform" all of us poor misguided
> >savanna folk!
>
> But I don't. I actually don't care what you (or anyone) thinks.
> Everyone is welcome to look at the evidence (such as it is) and make
> up their own minds. I enjoy our discussions, but I have no thought of
> 'reforming' you; the objective (for me, anyway) is simply to clarify
> my ideas and learn something in the process.

Worthy ambitions that I also share. You would be surprised at how much
I learn just by researching my "refutations" of the AAH! (or maybe not!!)

Regards
bk

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