Essentialism and such (was a bunch of previous subject lines)

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

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu]On Behalf Of
> Carl
> Sent: Thursday, October 26, 2006 8:47 PM
> To: dinosaur@usc.edu
> Subject: RE: Dinosaur a tecnical term; fish is not (was RE: Fish with
> milk (Sheesh spinoff))
>
>
> Elements are defined by their number of protons, and regardless of other
> variations, a given number of protons is _always_ the same for any
> example of that element, and anything having that number of protons is
> an example of that element regardless of its state.  So, in the sense
> that Webster and Goodwin mean it, the element has a universal and
> invariant essence at least as far as how we understand it.  This is true
> regardless of the time, space, historical background, or physical state
> of any particular example.

And herein lies one of the inherent (essential!) problem with using 
essentialism in biology.

Organisms are NOT history independant! We are, every one of us, a record of 
history. All protons are the same, each atom of a given
isotope identical in all aspects regardless of what happened to it before.

Not so with organisms, populations, and species. Our properties are highly 
contingent on events of our personal and evolutionary
histories. No two of us are identical. ("There is variation in all populations" 
being the first step in natural selection, after
all...).

But from a pragmatic level, essentialism & typism results in misleading 
science. A case in point: many of the Feducciaries (for
those new to the list, check out the archives) seized on Welman's analysis of 
the brain of the coelophysoid formerlly called
_Syntarsus_ (I'm going to miss that name) as demonstration that birds did not 
evolve from dinosaurs. Why? Because the brain of
_Syntarsus_ was too different from birds. And since _Syntarsus_ was a theropod 
dinosaur, its brain represented the "theropod type",
and therefore theropod brains could not have been the origin of bird brains.

This is hardly the only case of people using this sort of logic. It would make 
sense if such "types" (NOTE: we are NOT talking
"holotypes" here!) were real, but instead they aren't. There isn't a "theropod" 
type any more than there is a "dinosaur" type or a
"reptile" type. There is instead descent with modification.

Hope this helps,

                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
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