Re: Postural bipedalism may have preceded and not causally connected to walking.

rmacfarl wrote:
>
> Philip Deitiker wrote:
> > American Journal of Physical Anthropology
> > Early View: Published Online 15 Nov 2005
> >
> > Arboreal bipedalism in wild chimpanzees: Implications for the
> > evolution of hominid posture and locomotion (p NA)
> > Craig B. Stanford
> >
> > From abstract
> > "
> > Field observations of bipedal posture and locomotion in wild
> > chimpanzees (Pan troglodytes) can serve as key evidence for
> > reconstructing the likely origins of bipedalism in the last
> > prehominid human ancestor.
> > "
> >
> > "
> > In 246.7 hr of observation from 2001-2003, 179 instances of
> > bipedal posture lasting 5 sec or longer were recorded, for a
> > rate of 0.73 bouts per observation hour. Bipedalism was
> > observed only on arboreal substrates, and was almost all
> > postural, and not locomotor. Bipedalism was part of a complex
> > series of positional behaviors related to feeding, which
> > included two-legged standing, one-legged standing with arm
> > support, and other intermediate postures. Ninety-six percent
> > of bipedal bouts occurred in a foraging context, always as a
> > chimpanzee reached to pluck fruit from tree limbs.
> > "
> >
> > "
> > Most observations of bipedalism were made when the animals
> > were in treetops and the observer at eye-level across narrow
> > ravines. This suggests that wild chimpanzees may engage in
> > bipedal behavior more often than is generally appreciated.
> > Models of the likely evolutionary origins of bipedalism are
> > considered in the light of Bwindi bipedalism data. Bipedalism
> > among Bwindi chimpanzees suggests the origin of bipedal
> > posture in hominids to be related to foraging advantages in
> > fruit trees. It suggests important arboreal advantages in
> > upright posture. The origin of postural bipedalism may have
> > preceded and been causally disconnected from locomotor
> > bipedalism. Am J Phys Anthropol, 2005. © 2005 Wiley-Liss, Inc.
> > "
>
> Thanks Phil. So possibly a chimp-like, knuckle-walking ancestor becomes
> postural biped in an arboreal context, then later moves to a
> terrestrial context where it adopts obligate locomotive bipedalism
> (with vestigial signs of knuckle-walking). Convoluted, but not
> implausible.

Well, no, not convoluted. Primates are already predisposed to bipedal behavior
so since arboreal environments is a major habitat for them it's only "natural"
to continue that behavior on the ground.

> 179 instances of bipedal stance of 5 seconds' duration or greater. Data
> overkill? :-)

To the AA crowd, it is...
.

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