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January 14, 2006
Walk Like a Hominid
John Hawks has an interesting discussion of a paper by Craig B. Stanford published in the most recent issue of the American Journal of Physical Anthropology. The paper is called, "Arboreal bipedalism in wild chimpanzees: Implications for the evolution of hominid posture and locomotion."
The following is from the paper's 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. This paper reports on a sample of bipedal bouts, recorded ad libitum, in wild chimpanzees in Bwindi Impenetrable National Park in southwestern Uganda. The Ruhija community of chimpanzees in Bwindi displays a high rate of bipedal posture. 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.
But Hawks wonders how this applies to hominids.
The fundamental question about early hominids is why they abandoned the ability to be facultative quadrupeds. That is something that chimpanzee positional behavior isn't going to tell us -- after all, chimpanzees take on bipedal posture in ways that don't compromise their quadrupedal abilities.
Hawks looks at various possibilities to explain bipedalism in hominids and is not overwhelmed by any of them. Both his post and Stanford's article are worth reading. The former is free; the latter will cost you 25.00 unless you subscribe to the American Journal of Physical Anthropology. I'll be going to the library to read Stanford's article.
Posted by Duane Smith at January 14, 2006 10:02 AM | Read more on Paleoanthropology |
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Comments
Hawk's post was really interesting. Definately a lot there to think about.
Posted by: afarensis at January 14, 2006 8:46 PM
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