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


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.

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

Ross Macfarlane

.