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



Please read the following in the form of a question--
as this is squarely in my center of interest, I was
wondering if any evolutionary biologist readers have a
definitive opinion.

When the "switch gene" is lost, the only way to
recover it is through the spontaneous mutation and
subsequent conservation of a second gene w/ an
identical function, an improbable event that selection
cannot act upon or make more probable. A fortuitous
structure (sensu Dudley) can evolve into a wing
through a long series of less improbable events--
guided by selection as it goes. So, "simpler", but
actually much less probable.

I think.

--- Jeff Hecht <jeff@jeffhecht.com> wrote:
> >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
>
http://www.eeb.uconn.edu/Courses/Eeb477/Whiting_etal_phasmid_04.pdf#search='convergent%20evolution%20%20Phasmid'.
> 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 
> 
>