new hominid synapomorphy and thanks to all
kinman2 at YAHOO.COM
Wed Dec 29 16:59:45 CST 2004
To tell the truth, I think some people are a little too sensitive about milder forms of biological teleology. Apparently it was my phrase "evolved to" that evoked the reaction (over-reaction in my opinion). As for the "purpose" of a supraorbital torus, you might notice that I used the word "advantage" instead. In order for such a structure to evolve and persist (especially in different clades), it almost certainly conferred some evolutionary advantage. It takes energy to build up such a bony structure, and natural selection does not favor unnecessary expenditures of energy in the long run. So this definitely is a SCIENTIFIC question (not religious, unless someone tries to make it so). If a true supraorbital torus doesn't absorb masticatory stresses, then what advantage does it confer?
It might even have multiple advantages, such as with bird feathers, where thermoregulatory advantages probably preceded the later advantages of powered flight (a later exaptation). Bird feathers almost certainly did not evolve for the "purpose" of powered flight, but they did serve that "purpose" eventually. Perhaps a better term is "function", since it doesn't seem to ruffle the "feathers" of some biologists as much. I just don't think mild forms of teleology are worth the bother. By the way, I believe bird feathers may have originally evolved on the tail as an anti-predator device. They would have only later spread to the main body for keeping eggs warmer, and then even later for aerodynamic functions.
Anyway, rather than a bit of semantic teleology, I am far more concerned about using "mounded" brow ridges as a potential synapomorphy (which I assume Schwartz believes were then lost in later hominids). But these mounded brow ridges sound to me more like a plesiomorphy for great apes (compared to outgroups like gibbons and various monkeys). The derived state would be when the two "mounds" fuse together above the nasal region to form a continuous brow ridge (yielding a true supraorbital torus). The question is how many separate times this occurred in great apes. Separately in the chimps and in the gorillas (or only once as a single clade). Supraorbital tori presumably evolved independently in Homo erectus (as well as in a certain percentage of Australian aborigines and a few other modern populations). Does a supraorbital torus serve the same function in all of these apes? That's what really interests me at this point.
P.S. Your scoreboard seems rather inflated in favor of your point of view (as in the Ukraine, a whole new "recount" will probably be needed). :-)
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