Re: Paleontology 1
Elaine Morgan (Elaine@desco.demon.co.uk)
Fri, 04 Aug 1995 11:45:04 GMT
Alex Duncan:
Yes, thank you, I am enjoying my tutorial (after all these years as
autodidact)
You say "In African apes smaller size might mean (most importantly)
different intermembral proportions. In modern gorillas, the
intermembral index is around 116, in chimps it is around 105, and in
bonobos it is around 100..."
It might mean that, or it might not. You are making an unwarranted
assumption that the difference in the intermembral index is a
consequence of size difference alone. There is no evidence for this,
and at least one piece of evidence against it. W.L.Jungers carried out
a comparative intermembral index projection between two primates who
differed considerably in size and it revealed near isometry for both
humerus length and femur length. The specimens were both human - a
Mbuti pygmy and a Caucasian. Isn't it usual for genuinely allometric
relationships (eg. surface-to-volume index) to hold true within species
as well as between them?
Surely it is equally or more likely that the intermembral difference
between the apes relates to different behaviour patterns. (And I
would, of course, relate the bonobo's longer legs to its
seasonally-flooded-forest habitat.)
I don't consider a suspensory existence makes bipedalism easier or
likelier. The two modes are in several respects diametric opposites.
Suspension stretches the spine; bipedalism compresses it. Suspension
means nil weight on the lower limbs ; b.p.means maximum weight on them.
As for "partially erect", if you mean erect from the pelvis upward,
then suspension is no more conducive to that than the posture of an
indri in a tree or a gelada sitting on the ground.
Ralph Holloway.
Thank you for clarifying convergence. You say: "I see a lot of
diversity of pongids throughout the Miocene and probably into the
Pliocene. I don't have any trouble believing that ttwo different
species of ape, living in roughly sympatric regions, could show
different adaptations....one becoming proficient at bipedalism, the
other at knuckle-walking."
I agree with you on the first sentence. The second one sounds quite
plausible as long as it is expressed in those generalised terms. It
only looks dubious when you get down to the nitty-gritty and try to
imagine exactly what an ape could have been doing in a tree that would
tilt it towrds bipedalism. As above, I don't go for suspension. I don't
go much for climbing either. All you can say for it is it leads to
hind-limb dominance. It doesn't lead to improved balance, or a more
bipedal-like head angle, or to alignment of spine and lower limbe, and
certainly not to straightening and locking of the knees. I get the
impression that any idea which might possibly shore up the
straight-line scenario gets accepted a tad too uncritically.
Elaine Morgan. "The devil is in the details."
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