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

on 23 Nov 2005 16:28:35 GMT, Philip Deitiker <Nopdeitik@xxxxxxxxxxxx> sez:
` 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.
` "
Ha! See, support for my Certified Wild Conjecture (hypotheses?
I don't need no steenkeen hypotheses) that bipedalism was encouraged
in concert with the appearance of openings in the forest cover
(step 0.25 in the emergence of savannah from rainforest), by
the need to stand on the ground and reach up to forage, amongst
the shrubbery which grew down to the ground to take advantage of
the edges of these open spaces and the partly shaded sunlight there.
This must have occurred in a pre-LCA ancestor whose brachiating
specialization made it quite prone to bipedal posture when
finding itself on the ground, otherwise quad or semiquad (k-walking)
locomotion would have won out. By contrast, the chimp line would
have developed in a region where this type of foraging was not
a large fraction of available options.

` "
` 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.
` "

--
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vincent@triumf[munge].ca Pete Vincent
Disclaimer: all I know I learned from reading Usenet.
.

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