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Greg
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« on: July 22, 2002, 04:06:07 PM » |
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I would like to lay out an idea that is part of a paper I'm writing, partly to get discussion on this forum going, and partly to see now how dumb people think my idea is in order to soften the blow after press time...
Note that when new hominid finds are made, especially those that are named with a new species/genus, it is often commented that this increases the diversity of known hominids, and that this is more evidence that we should throw out old ideas about linear evolution of hominids and recognize and revel in the great diversity of hominid life back in the Pliocene.
(SJG would say: "You mean 'disparity' not 'diverity'" and I do, for those who wish to be careful about this term... I mean how many species around at one time.)
Of course, we have recognized a high level of diversity for decades now, but it is convenient in the popular press to keep throwing out old and dead ideas again and again, but that is not the point I wish to bring up here....
In looking at the current fossil record for hominids, there is a great deal of diversity from 3.5 mya or so until about 1.5. Prior to this there is less diversity at any given time. Although there are several different named species from 6/7 mya to 3.5, the diversity at any given time --- taking the fossil record at face value - is low, esp. rel. to that later time period.
In other words, the pattern of evolution of hominids in the late Miocene through the early Pleistocene is one with some but limited diversity for the first few million years, followed by a couple of million years of rather astounding diversity.
Since diversification (radiation, multiple speciation, etc.) is a sign of a big, important evolutionary event, I suggest two things.
1) The LCA split, i.e., the initial rise of hominids, was ultimately important but at the time not especially impressive as an evolutionary event, in that it did not lead to a major diversification of the taxon. Therefore, it is of note that the origins of bipedalism is not one of the most important evolutionary events per se as it is often thought to be (ultimately important, but at the time not - and this distinction is critically important!).
2) The real story of Australopith evolution is not the rise of Australopiths, but something that happened later, broadly between 4.0 and 2.0, really probably in two stages ca 3.3 and 2.6. In another paper just submitted, Richard Wrangham and I are suggesting that this was a shift to using USOs as fallback foods (instead of THV).
In the paper I'm working on now I intend to argue that the fossil record itself does NOT have a taphonomic bias that causes us to see little diversity early and lots later. But I won't argue that there. Instead, lets assume that the above is a hypothesis given the current pattern of fossils, that could be falsified by further fieldwork.
I also make a similar argument for geographical spread.
GTL
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