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Re: Reevolving bones?



Tracy Ford writes:

>Just another way for cladist to explain something to fit what they want,
>and not to see who impossible it really is. Reevolving a toe, that was
>totally lost, to be exactly the way it's suppose to be is totally insane.
>
>Is there any modern evidance to support this? In living genera?

Loads and loads and loads of it: reversals/atavistic traits are far from
"insane" or "impossible". To cite a few (sorry, no refs beyond a certain
Gould book, but these are widely known in evolutionary biology): horse's
toes, hen's teeth, numerous bones and muscles in birds (Raikow has
published a bit on this), ummm... humans, more amphibians than you can
shake a stick at (e.g. the plethodontid septomaxilla, I think), and so on.

Please, please, will people read some modern texts (i.e. after 1985 or so)
on evolutionary developmental biology? Maybe some papers on homeobox genes
or conservation of developmental programs? Especially when you're going to
base some phylogenetic supposition on it. Most evolutionary biologists
today have moved on from Dollo's Law, Cope's Rule, and other Victorian
metaphysical relics. Evolution is far more interesting than simple one-way
rules, so there's no way you can refute the feasibility of a given
phylogeny based on a speculation like "things don't re-evolve".

It would be better if someone cited a specific, recent, peer-reviewed paper
studying the morphogenesis of a closely related taxon (or better yet,
several taxa) that had repercussions for the morphological evolution of the
taxon in consideration (e.g. therizinosauroids; I don't know what you'd use
for comparison besides a bird and/or croc; lots of branch length there so
I'm not sure what you'd be able to say).

Since we're dealing with extinct taxa with no extremely close living
relatives to study (e.g. Deinonychus, Archaeopteryx and Mononykus aren't
alive, so we can't study their development), it's far more objective to let
the character distributions tell the story, and leave the invocation of
"special knowledge" of non-avian coelurosaurian developmental patterns and
processes out of the picture. Or do you have a live therizinosauroid hidden
away in a lab somewhere and have made some startling discoveries about it's
morphogenesis? If you do, the world is waiting for you to announce your
findings; otherwise, please, let's get on with some science and be honest
about what we do/don't know.

                        John R. Hutchinson
                 Department of Integrative Biology
                  3060 Valley Life Sciences Bldg.
                University of California - Berkeley
                     Berkeley, CA 94720 - 3140
                      Phone:  (510) 643-2109
                      Fax:    (510) 642-1822
         http://ucmp1.berkeley.edu/people/jrh/homepage.html