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Re: tree-climbing hominids
Paul Crowley (Paul@crowleyp.demon.co.uk)
Mon, 09 Oct 95 08:44:43 GMT
In article <459c9p$6n3@geraldo.cc.utexas.edu>
aduncan@mail.utexas.edu "Alex Duncan" writes:
> Chimpanzees are "partially quadrupedal". They have a compromise anatomy
> that enables them to move reasonably well on the ground while still
> retaining arboreal capabilities.
The exchanges get longer and longer, and now we're getting bogged
down in definitions. I'll probably reply in detail later, but as
I see it the real difference between us is that you are proposing
a "partially bipedal" hominid which "retained significant tree-
climbing abilities". I can't accept this for numerous reasons:
a) You have not given the beginnings of an account as to how this
creature operated (nor AFAIK has anyone else). It's a hypothesis
which runs on a "wing and a prayer" and does not go beyond the
formulation of the words.
b) The problems it would have faced can be stated clearly; they've
been solved by all successful forms of life. You have hardly
begun to deal with them. They include: (i) night predation
(ii) infant care - both day and night (iii) food provision.
c) You have to set out the ecological niche that this creature
occupied for a few million years, bearing in mind that chimps and
other species were in there first. This new species either elbowed
them aside (virtually impossible) or it found a new way of life.
What was it?
d) You have to set out *why* speciation happened at all in the first
place. Why such an utterly peculiar creature (e.g. you and me)
emerged. If you're going to propose geographical separation, its
got to be drastic. The CA was fairly mobile.
e) You know exactly how it finished up (h.s.) and you know roughly
how it started (something like a chimp, or a gibbon, or something
in between) and you have pretty good fossils from 3.5 mya. You
have desperately little time into which you must put the development
of a new and radically different species.
f) You must clearly account for the reasons why the species adopted
such a new and radically new form of locomotion.
g) The above are the fundamental questions (ok, there's some over-
lapping) but there are also subsidiary ones on which so much
bandwith is wasted:- nakedness, sub-cutaneous fat, sweating, etc.
Your answer should additionally account for all these.
[ You have three hours to complete the paper. :) ]
Forget the peripheral stuff for the moment. Can you provide an
answer that goes to the core?
Paul.
> In article <813146042snz@crowleyp.demon.co.uk> Paul Crowley,
> Paul@crowleyp.demon.co.uk writes:
>
> >
> AD> Your entire argument rests on this incorrect premise. If, by "fully
> >> bipedal" you mean "bipedal in the same manner as modern humans", then you
> >> are incorrect. Your statement is not supported by the fossil record.
> >> The fossil record suggests that the hominid species that were extant
> >> between ~4.5 and 2.0 Myr WERE NOT bipedal in the same manner as modern
> >> humans, and that they retained significant tree-climbing abilities.
> >
> PC> I should have dealt with this last time. We are concerned with two
> forms
> >of locomotion: quadrupedal and bipedal. There is effectively no half-way
> >stage. (Obviously there must have been a transition, but it must have
> >taken place under very special circumstances - which is why the AAT
> >exists).
> >
> PC> I cannot really "prove" this. It is self-evident that any viable
> animal
> >must have an effective mode of locomotion. Being "partially bipedal" or
> >"partially quadrupedal" is NOT viable (except under those very special
> >circumstances). You simply have to think of your own anatomy. How
> >could it be modified so that you were less than "fully bipedal" and yet
> >still remain a creature that could thrive on the ground in Africa?
> >Life as a "fully bipedal" hominid would have problems enough. Anything
> >less is out of the question.
>
> Chimpanzees are "partially quadrupedal". They have a compromise anatomy
> that enables them to move reasonably well on the ground while still
> retaining arboreal capabilities. They do not move quadrupedally as
> efficiently as other quadrupeds (and yes, the efficiency of chimp
> quadrupedalism has been tested, and found wanting).
>
> The same kind of logic could be used to claim that a creature cannot be
> "partially terrestrial" and "partially aquatic", and by this logic we can
> demonstrate that seals, otters, frogs, salamanders and penguins don't
> exist.
>
> PC>Your "not bipedal in the same manner as modern humans" is just not
> >facing up to the issue, as is the retention of "significant tree-
> >climbing abilities". If hominids ~4.5 to 2.0 Myr were terrestrial
> >animals, they were either bipedal or they weren't. My own belief is
> >that they were not fully terrestial - they were partially aquatic -
> >but also that they were fully bipedal.
>
> Again, we only have to look at the organisms around us to see the
> problems with this statement. Using quadrupedalism as an analogy, your
> argument could be used to claim that if one is a quadruped, one must only
> locomote in a certain manner, one must have interlimb proportions of a
> certain value, one must have specific anatomy on the distal limb
> segments, etc. etc. etc. When we actually look at the various
> quadrupeds, we see all kinds of different anatomies and styles of
> movement. When we look at the hominoids, we see that in general,
> efficient quadrupedal movement has been compromised by the demands of
> tree climbing. And yet, chimps spend about 90% of their time on the
> ground. Your assertion that only one kind of bipedalism would work is
> also belied by a look at the animals around us. Humans are not the only
> bipeds. As Chris Brochu pointed out, macropodids are functionally
> bipedal, as are all theropods, some ornithischians, many early
> archosaurs, etc. For the most part, all these styles of bipedalism
> differ.
>
> AD> Well, aside from the obvious question of whether or not
> >> australopithecines were effective tree-climbers, the most important
> >> question would be whether or not they may have built nests in the trees
> >> as modern chimps do. Such nests would make sleeping in the trees a much
> >> simpler business.
> >
> PC>This is a non-starter. Chimps usually build their nests where two
> >trees meet. They use branches of about 2 inches in diameter from
> >both trees. They sleep grasping branches from both trees and infants
> >cling to mother. So no one falls off. If a leopard tries to approach
> >the mother detects it and shakes it off. Such an arrangement is
> >impossible without four grasping limbs in both parent and child.
>
> First, I question your assumption that this impossible w/out four
> grasping limbs; and, second, again you are mistaken in your understanding
> of early hominid anatomy.
>
> PC>Chimps have mastered the "safety at night" problem with a highly
> >specific and well-engineered solution. Early hominids also mastered
> >this problem in another highly specific manner. You know the AAT
> >proposal. Savanna/mosaic proposals are conspicuous by their absence.
> >
> >> PC: At night? Lions, leopards and hyenas are nocturnal. Hominids are
> >> diurnal and effectively blind at night. They would only injure each
> >> other, and their females and young, if they were to use clubs and
> >> stones whenever they heard a rustle and thought a big cat was near.
> >> This must be one of the craziest ideas of all time. How much sleep
> >> would any of them get each night? What's the life expectation?
> >> Can you imagine the stress levels with the screams of the hyenas and
> >> the lions' growls?
> >>
> >> AD: Here I assume PC is refering to later hominids such as H. erectus,
> >> who presumably lived in fairly large groups, had a reasonably advanced
> >> tool kit that included the Acheulean hand ax, and might well have had
> >> fire. I agree that spending a night on the savanna under such
> >> circumstances would not necessarily have been easy, but not far from
> >> impossible.
> >
> PC>I was referring to all bipedal hominids - those which have lost the
> >grasping capacity in their feet. This happened long before the use of
> >fire (I put it at about 5mya.) I don't know when you date it. But
> >from then until the use of fire, you have an impossible dilemma.
> >
> >> AD: . . . prior to 1.8 Myr, we
> >> know that hominids had an anatomy appropriate to part-time life in an
> >> arboreal substrate.
> >
> >I just don't buy this. Either they slept in the trees (like chimps) or
> >they didn't. "Part-time life in the arboreal substrate" is empty BS.
>
> For the most part, all catarrhine primates practice "part-time life in
> the arboreal substrate". It is not empty BS. It is what primates do.
>
> AD> Essentially fully modern postcranial anatomy seems
> >> to arrive with the appearance of H. erectus. If we assume, for the
> >> moment, that H. erectus could not climb trees and wasn't safe on the
> >> ground, then I suppose we can entertain PC's suggestion that they must
> >> have utilized the abundant savanna islands to sleep on.
> >
> PC>What are these "savanna islands"? They're no suggestion of mine. My
> >islands are on the rocky marine littoral, nowhere near the savanna.
>
> Well, another problem rears its ugly head then. There is no question
> that H. erectus was capable of utilizing far drier and more open habitats
> than earlier hominids. They have been frequently found in depositional
> contexts indicating savanna, and even drier habitats. Additionally, they
> have been found in regions (e.g. Choukoutien, Swartkraans upper cave,
> Olorgesalie) where there were no bodies of water of any significant size
> whatsoever.
>
> AD> At this point of
> >> course, AAT has become a non-theory for the explanation of the origin of
> >> bipedalism, because bipedalism would have arisen prior to any aquatic
> >> stage. Additionally, the suggestion that 2 short distance swims daily
> >> (to the island and back) would have been a potent selective force is
> >> problematic.
> >
> >I'm lost here. You seem to be putting an AAT existence into the middle
> >of the savanna - or something?
>
> I'm not putting AAT into the middle of the savanna. That's where most H.
> erectus fossils are found. You suggested that hominids that couldn't
> climb trees must have slept on islands. The first hominids whose
> tree-climbing capabilities were as poor as ours are H. erectus.
> Therefore, H. erectus must have been the first hominids who were required
> to make use of aquatic resources in order to survive.
>
> AD> But a real issue is whether or not an H. erectus band would have
> >> been able to survive at night on the ground. Modern humans with tools
> >> not much advanced over H. erectus (e.g., !Kung) manage it without
> >> recourse to those abundant savanna islands (the islands are even more
> >> abundant in the near-desert the !Kung inhabit).
> >
> PC>Modern humans (e.g. !Kung) have a unique and powerful resource: *fire*.
> >Without that resource, hominid life on the ground is impossible.
>
> H. erectus also had fire.
>
> Your entire body of reasoning rests on a single premise: "any primate
> biped must have a form of bipedalism that is functionally equivalent to
> that of modern H. sapiens." I challenge you to question this premise.
> The world is full of animals who aren't particularly good at what they do
> (compared to other animals) but they do it anyway. Chimps are a prime
> example. They are not "good quadrupeds". Nonetheless, their form of
> modified quadrupedalism is their primary form of locomotion. I should
> also point out that the same argument is a potent one against the AAT.
> Humans are not particularly good swimmers. It has been pointed out 100's
> of times in this newsgroup that they would have made prime prey for
> African crocodylians. Once in the water, humans have virtually no
> defense against crocodyles. Suggestions that humans could just run up
> out of the water are a little pointless (especially if this is supposed
> to be the selective force that led to bipedalism) as humans move so
> slowly in the water, and quadrupeds are actually more effective waders.
>
> The best understanding of australopithecine anatomy is that it is a
> compromise between the needs to move on the ground and the needs to
> maintain arboreal capabilities. They did not have to the "best" at
> either one of these capabilities in order to survive. Their adaptation
> was a mosaic of abilities that enabled them to utilize resources in
> varied environments. Again, I point out chimps as an analogy. They are
> no where near as agile in the trees as gibbons or monkeys, and no where
> near as efficient on the ground as bovids or equids. Nonetheless,
> somehow they survive.
>
> Alex Duncan
> Dept. of Anthropology
> University of Texas at Austin
> Austin, TX 78712-1086
> 512-471-4206
> aduncan@mail.utexas.edu
>
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