Re: Bidpedalism

5 Jun 1995 20:24:49 GMT

Ralph L Holloway ( wrote:

: Where in the world is the evidence to show that gorilla and chimps are
: probably more terrestrial than A. and Homo habilis ("Of course...").

Oxnard, Order of Man, Yale University Press and University of Hongkong
Press, 1983. AL-288 and OH-62 both have hands more adapted to climbing (in
terms of stress analysis) than Pan and Gorilla. It's also of interest that
the Mountain Gorilla climbs _down_ to the ground and takes off
cross-country when threatened. As I indicated, that's hardly the behavior
of an arboreal animal. My guess is that terrestrialism is a consequence of
increased weight. In the middle to late Miocene, we start to see bigger,
more specialized apes. The really big African apes became quadrupedal on
the ground and developed knuckle-walking. The medium-sized ones retained
bipedality (and hence climbing ability). That later turned out to be
preadaptive for living in the savanna for both Paranthropus and H.

: It's one thing to claim that Australos and Homo habs have retained some
: primitive features in their locomotory activities, or were able to do
: more than we thought before in an arborial econiche, but it's something
: else again to say "of course..." chimps and gorillas are more
: terrestrial! And just which Homo habilis specimens are you talking
: about? OH 8? OH 62? KNM ER 1470 and other KNM stuff , particularly
: femoral fragments? You've got habilines at 1.8 MYA and clear-cut erectus
: Nariokotome youth) at 1.6 MYA, with narry an indication in the latter of
: any arborial locomotory adaptations. Have I missed something, not to

KNM-ER 15000 is certainly the turd in the punchbowl. Except for the brain
size (and a few details), he might fit in fairly well with the current
population of the area. His ancestry, though, is unclear. H. rudolfensis
(1470)? Maybe, but he doesn't fit in with most of the habilines.

The problem with H. habilis is that the only well-known skeleton is
OH-62, which has an inter-memb. ratio of 0.95 (about equal to the low end
of Pan) and hands adapted for minimizing stress while climbing. (This is
more adaptive than what is seen in Pan!) The knees are OK for a biped. The
elbows of 3735 are braced against dislocation. Even more so for A.
afarensis (except AL333 and AL333-w series) and A. africanus. See Senut
and Tardieu in Ancestors.

Bipedalism is less specialized than quadrupedal knuckle-walking. The bones
in both Gorilla and Pan form a supporting structure that is stressed to
handle compressive forces. They may resemble our bones, but they are more
specialized. The hands in the gracial species are not like those of G/P or
like ours--they resemble Pongo in their curvature and appear stressed to
handle suspensory forces. Perhaps P/G are more arboreal than the gracials
were, but that would imply that the selective forces on P/G in terrestrial
mode are much greater than the selective forces on P/G in the arboreal
mode, and the reverse for the gracials. I can buy that, I suppose, but
with difficulty.

: mention the Laetoli footprints a couple of million years earlier? I'm

I understand they don't fit the A. afarensis foot.

: all for expanding our consciousness regarding early homs retaining some
: arborial skilss, but statements like Erwin's go too far. Ralph Holloway.
: On 4
: Jun 1995, HARRY R. ERWIN wrote:

: > Not really. A selective advantage need only exist for a few hundred or
: > thousand generations for the corresponding features to fixate. Not long
: > at all. BTW, Mountain Gorillas find terrestrial movement an advantage
: > when dealing with the threat of a predator--to the point that they will
: > usually climb down from a tree to flee on the ground. (Of course,
: > gorillas and chimps are probably more terrestrial than A. and Homo
: > habilis.)
: >

Cheers --
Harry Erwin
PhD student in computational neuroscience: "Glitches happen" & "Meaning is