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Re: Feduccia's allegations

At 1:32 PM -0800 1/23/03, ekaterina A wrote:

We should keep in mind that primitive and derived forms often coexist together. For example knuckle walking great apes coexist with the erect humans, the brachiating lesser apes, the old world monkeys, the tarsiers and lemurs. One cannot deny that many of these forms retain primitive characters and are good approximations for reconstructing of the various ancestral states leading to humans. Hence the Sinitic fossils do provide good approximations for the ancestral states in the emergence of birds, though they may be co-eval or later than A'pteryx.

It's not quite that simple, because the originals don't stand still; they also evolve, as we're beginning to see with Sahelanthropus, a hominid which dates from around 6 million years ago and is either in the human or gorilla line (that's still under debate). Other early hominids also show a mosaic of features. Yes, some of the original features are still there -- but without access to the originals. As you say below, it's important to be careful in interpreting mosaicism. -- Jeff Hecht

Another point is that one should very cautious in interpretting the mosaicism of derived characters in organisms coming from major transition zones in evolution. They mosaicism is most likely to result from reversal rather than independent gains. I interpret this a arising from the following: evolutionary phenomenon: 1) There is very rapid colonization of a niche with all derived characters associated with the transition arising quick succession. 2) There is heavy competition in the new niche and hence selection for some forms that can exploit both the new niche and their old original niche more effectively. The forms that do this gain greater access to resources. This effect selects for certain reversals. 3) These reversal occur in parallel in different lineages resulting in mosaicism.