Re: tree-climbing hominids
Paul Crowley (Paul@crowleyp.demon.co.uk)
Sun, 08 Oct 95 09:54:02 GMT
In article <4528lp$9cl@geraldo.cc.utexas.edu>
aduncan@mail.utexas.edu "Alex Duncan" writes:
<references etc.>
Thanks for the long and careful reply and all the references. May I say
how much I admire your patience in dealing with us heretics. I know how
angry I am liable to get when I am criticised in my specialty by an
ignorant outsider. That they occasionally turn out to be right does
not help either. Your generosity and tolerance are impressive.
All that matters in Science is honesty, and with your apparent respect
for it I feel that we might be getting somewhere.
I will look up the references. I am not hopeful as all those that I
have studied are full of false assumptions. Since the time of Galileo,
those proposing a revolutionary change in a field of knowledge have
been advised to read the (often sacred) texts. (In his case, they
included the Bible and works of Ptolemy.) This advice, while well
meant, is invariably misconceived. The (sacred) texts mean a lot to
the orthodox; they say nothing to the heretic.
> 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.
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).
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.
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.
> 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.
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.
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.
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.
> 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.
What are these "savanna islands"? They're no suggestion of mine. My
islands are on the rocky marine littoral, nowhere near the savanna.
> 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?
> 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).
Modern humans (e.g. !Kung) have a unique and powerful resource: *fire*.
Without that resource, hominid life on the ground is impossible.
Paul.
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