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Re: Yoyoism (was Re: Endothermic Crocs in Nature)

>From my very limited understanding of "evo-devo," which tries to integrate 
>genetic development mechanisms with evolutionary processes, this sort of thing 
>appears to happen because the actual mechanism by which traits development is 
>multi-level. One gene switches on another gene or set of genes that actually 
>express the trait. So, for example chickens may still have a gene capable of 
>producing teeth, but no gene is available to switch it on. In a more realistic 
>example, these lineages may have stopped switching on the genes for wings, but 
>retained the wing genes so they could be switched on later -- which is far 
>simpler than re-evolving wings. 

There's a lot more to be learned about these processes, and I think they will 
help explain some evolutionary puzzles -- Jeff Hecht

At 2:14 PM -0700 4/15/05, Dino Guy Ralph wrote:
>"Tim Williams" <twilliams_alpha@hotmail.com> writes:
>For example, I know of no "neoflightless" insects, nor
>"neoamphibious" proto-cetaceans.
>Many phasmids (stick insects) appear to be neoflightless, and secondary 
>flightedness has apparently evolved independently in four distinct phasmid 
>groups since this initial neoflightless event.  In fact, a couple of phasmid 
>clades apparently lost their wings, regained their wings, and lost their wings 
>yet again.  But don't take my word for it -- read the paper for yourself at 
> Figure 3 is particularly fun.
>I hereby coin the term "yoyoism" to describe this aspect of numerous reversals 
>of a particular character within a lineage.
>"Dino Guy" Ralph W. Miller III
>Docent at the California Academy of Sciences
>proud member of the Society of Vertebrate Paleontology