knuckle-walking (was: hominid classification)
kinman2 at YAHOO.COM
Tue Aug 10 22:54:59 CDT 2004
Given John's latest response, I will henceforth waste no more time looking for molecular support specifically linking hominids and orangutans. The African ape clade (Gorilla, Pan, Australopithecus, Homo, among other fossil genera) seems to have support beyond that of the molecular data:
Perhaps the most interesting morphological synapomorphy for the African clade is the so-called "stiff wrist"----formed by a shelf of bone preventing the wrist from bending backward much more than 30 degrees. This "stiff wrist" aids in knuckle-walking in Gorilla, Pan, and is also present in the earlier Australopithecus species (anamensis and afarensis). The abandonment of knuckle-walking by the hominid line (as bipedality became more "obligate") was a gradual process, so whether A. afarensis knuckled-walked at all doesn't really interest me that much. By the time of Australopithecus africanus, knuckle-walking was pretty much abandoned in favor of a flexible wrist that was free and flexible for a variety of tool-usage (which would culminate in weapons for hunting). This link between morphology and behavior (and the gradual, concerted evolution of both) is something I find very intriguing and less vulnerable to the weaknesses of arguments based on molars (which can more easily fluctuate with diet).
THEREFORE, my efforts thenceforth will concentrate on two African ape topologies: (1) Hominidae as splitting from a Gorilla-Pan clade; and the somewhat more popular (2) Gorilla as splitting from a Pan-Hominidae clade. Frankly, the third alternative (Pan splitting from a Gorilla-Hominidae clade) doesn't seem to have any serious support. If the orangutan-Hominidae adherents can't (or won't) find or even look for molecular support for their hypothesis, I give up on them.
My postscript and John's responses:
>P.S. I am really trying to keep an open mind about the orangutan-human relationship, but I haven't found any molecular evidence supporting it (and I have tried) and you still have not presented any either.
You have decided that DNA base sequence similarities are the necessary proof of phylogeny in which case of course no other evidence has any bearing on the matter. Maryellen Ruvolo shares exactly the same view.
>Attacking the chimp-human molecular evidence won't get the job done. You have to find some molecular support or your morphological data will just be dismissed.
This is a read herring for human evolution as the molecular stuff cannot address the phylogeny of fossil forms. Just dismissing morphology as having no weight against DNA base sequence similarities means that all fossils are uninformative - completely. Might as well be a creationist.
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