Re: Tiktaalik

[dinoboygraphics@aol.com]

> > > I disagree with the whole idea of "macroevolution". The kind of 
transformation I see involves a lot of rather small changes. It's just 
that some of those changes are rare (loss of gills, opercula, gulars, 
fin rays, gain of digits...) and photogenic. <<<

Sorry I'm a day late, but I had to jump in here; macroevolution is NOT 
simply "large scale changes" (and microevolution is not always less 
phenotypic change than macroevolutionary events).  Microevolution is 
change within a species, while macroevolution is evolution from one 
species into another, or "higher" level changes (whatever the heck that 
would mean now).  So the extreme changes wrought upon the domestic dog 
are microevolutionary events, while the almost unoticeable phenotypic 
changes in Australian green-eyed tree frogs accompanied reproductive 
isolation and speciation the last 8,000 years(mating behavior changed, 
as hybrids of two populations were less fit).

The distinction arose out of the days post Darwin when many biologists 
thought that natural selection could not alone account for speciation, 
let alone large scale changes.  Of course, back in the day of asking 
questions like how one "class" of vertebrates evolved from another 
"class", this meant that large phenotypic changes were indeed the 
domain of macroevolution.  But today biologists generally accept that 
large changes in body plan result from the accumulation of many small 
changes over time; there is scant evidence for even a weak version of 
Goldschmidt's "Hopeful Monster" form of phenotypic saltation.

While Gould, Eldridge, and Vrba (among others) have doubted whether 
speciation events are driven by natural selection (yes, punctuated 
equilibrium), in Gould's back-breaking The Structure of Evolutionary 
Theory he still invokes selection acting on species sorting over time 
(i.e. the most fit species surviving long enough to produce other, 
similar species) as the cause of some long term phenotypic changes, 
albeit not (usually) speciation.

The only field of modern biology I know of that still has a pluralirty 
of adherents who advocate non natural selection-based forms of large 
scale phenotypic change over time is structural developmental 
biologists (see Muller and Newman's volume Origination of Organismal 
Form for a nice survey of current thought along these lines...not that 
I personally advocate most of the ideas as driving forces in evolution, 
but it's interesting).

Back to painting and working on our Supersaurus mount...it's all up 
except the head and and hands and feet!

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com