Poor misunderstood Punctuated Equilibrium (was RE: Some thoughts on AVES )

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Robert G. Tuck Jr.
>
> > Evolution occurs through the accumulation of minute changes, not the
> sudden appearance of radical changes
>
> Gould and company might take issue with this statement.
> Personally, I await
> more data and take no sides in the matter.

Actually, the punc eq model does NOT advocate the sudden appearance of
*radical* changes, despite the fact that it is sometimes characterized as
saying such.

Instead it suggests that species remain stable for long periods of time, and
that speciation (primarily by allopatric speciation: peripheral isolates of
the main population) undergo change in a geologically short period of time.

However, those changes are not held to be *radical* changes (and is the
reason that punctuated equilibrium is not synonymous with Goldschmidt's
"Hopeful Monster" model).  Instead these changes are largely the minutiae of
interspecific differences: possibly some proportional shape changer, or
perhaps some minor discrete change (such as number of ribs on a clam shell,
addition or loss of a lens in the compound eye of a trilobite).

So the punctuations in punc eq are not supposed to be sudden major
reworkings of the body plan.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796