Re: Palaeontology (1)
Phil Nicholls (pnich@globalone.net)
Fri, 04 Aug 1995 18:31:00 GMT
Elaine Morgan <Elaine@desco.demon.co.uk> wrote:
>
>Palaeontology.
>I have ordered from the British Library all seventeen of the refs.
>recommended by Alex Duncan. Six have arrived. The following are just
>preliminary observations.
>It has long seemed strange to me that the same facts can be so
>differently interpreted by people as intelligent as we all agree Alex
>(for instance ) is, and as I believe I am. (Don't take a vote on it)
>Increasingly I suspect we are making different assumptions about the
>timing and sequence of events.
>Look at these two statements in a paper by Susman, Stern, and Jungers
>(from : "Ancestors : the hard evidence.")
>(1) "In the wild, chimpanzees also spend a substantial portion of their
>time on the ground, as quadrupeds, but their manner of quadrupedalism
>is more costly than that of almost any other ground-dwelling
>quadruped. Compromise to increase the range of their habitat seems to
>be the best explanation for this apparently stable adaptation in
>chimpanzees."
>(2) "Bipedalism may have been a response to the need to travel to and
>among the ever shrinking forested areas."
>They seem to be saying: "The chimpanzee became quadrupedal because it
>needed to increase its range. The hominid became bipedal because it
>needed to increase its range."
>That is a perfectly tenable position, but only on the premise that the
>animals were aleady very different before either of them set a foot on
>the ground - eg maybe the prehominid ape was smaller-bodied, had a
>different intramembral index, etc. But this is pure speculations,
>isn't it? For all we know, at 4mybp all the African apes were
>small-bodied and resembled one another very closely. It has been
>suggested that the l.c.a. looked like a bonobo. The gorilla could have
>become larger much later - as late as 2mybp or even 1mybp. We have no
>fossils.
>If they did resemble one another closely, we would need a very good
>reason why one lot would respond to the advent of savannah mosaic by
>becoming quadrupedal and the other by becoming bipedal.
There are anatomical reasons to believe that the Gorilla and
Chimpanzee did not adopt knucklewalking until after the hominid/pongid
split. The position described above does not require a premise that
proto-hominids and proto-pongids were already very different. It only
requires that they developed locomotor specializations because they
occupied different niches. Proto-pongids stayed in the forest.
Proto-hominids exploited the forest/savannah interface zone and
eventually, as hominids, moved more and more onto the savannah.
>There is also an unwarranted assumption that the trend towards
>bipedalism postdated and was a consequence of the opening up of the
>forests and the advent of s/mosaic. That too is pure speculation,
>isn't it? Susman et al make a point of stressing that bipedalism did
>not arrive overnight. : "Far from being abrupt and complete, its
>evolution can be seen as having taken place over a considerable time
>span". I'll drink to that, If in the beginning they spent say 90% of
>their time in the trees and only occasional intervals locomoting at
>ground level (whether across grass or through water) it could have
>evolved very slowly indeed. It could have been under way, gradually,
>since the onset of speciation. It could have been a response to the
>same ecological event that caused the speciation. That would be
>elegant.
Morphological divergence is a result of speciation, not the cause of
speciation. Once speciation is completed there is a tendency for the
new species to show increased specialization in species specific
characteristics. Using the imagry of Sewell Wright, the move close
and close to one of the peaks in the adaptive landscape. Hence it is
very likely that bipedalism appeared shortly after speciation but only
because protohominids were exploiting a new niche.
>I'll come to Laetoli and all that jazz when more papers arrive.
I am on the edge of my seat.
Phil Nicholls pnich@globalone.net
"There is a grandeur to this view of life, with it's several powers, having
been originally breathed by the Creator into a few forms or into one; and
that, whilst this planet has gone cycling on according to the fixed law of
gravity, from so simple a beginning endless forms most beautiful and most
wonderful have been and are being evolved."
[Last sentence from _On the Origin of Species_, by Charles Darwin
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