Re: AAT Theory

Gerrell Drawhorn (
13 Nov 1995 10:13:31 GMT

Troy Kelley ( wrote:
: Subject: Re: AAT Theory
: From: Benjamin H Diebold,
: Date: 8 Nov 1995 21:58:03 GMT
: In article <47r95b$> Benjamin H Diebold,
: writes:
: >
: >Why not take the predation during travel between trees as a selection
: >pressure to develop better bipedalism? May the better bipedalist win!
: >
: >Ben

: Because quadrapedalism is generally faster and more efficient than
: bipedialism. So really, why should one abandon quadrapedalism for a less
: efficient mode of transport, in a dangerous environment?

McHenry and Rodman have shown that for chimpanzees knucklewalking or
bipedalism are equally efficient. As far as speed, ever see sifakas when
they move terrestrially? They are quite fast in a bipedal mode.

Hominoids are pretty poor terrestrial quadrupeds until they solve the
problem of stabilizing the wrist joint. The African apes have developed
special features in their wrist and digits that allows knuckle-walking.
Orangutans lack these features and must shamble awkwardly across the
ground. Hylobatids do not even attempt to place their dainty wrists on the

A. afarensis and the new material of A. anamensis shows none of these
specialised traits for knuckle-walking.The common ancestor of
apes-hominids would therefore be unlikely to have them. Given the
evolutionary constraints facing an ancestral hominoid first utilizing
terrestrial habitats, the real question may not be "Why did humans become
bipedal?", but " why did the African apes develop knuckle-walking?"

Jerry Drawhorn