Re: Dino Birds (was Re: Dinosaur = extinct animal)

[chris brochu <cbrochu@fmppr.fmnh.org>]

Dinogeorge@aol.com wrote:
> 
> In a message dated 7/12/99 10:50:51 AM EST, cbrochu@fmppr.fmnh.org writes:
> 
> << Dinogeorge@aol.com wrote:
>  >
>  > In a message dated 7/12/99 9:00:56 AM EST, cbrochu@fmppr.fmnh.org writes:
>  >
>  > << The overall point is that paraphyletic assemblages, above the species
>  >  level, are subjective, have no biological reality, and are not
>  >  recognized in modern systematics. >>
>  >
>  > Paraphyletic taxa certainly have "biological reality," whatever that is. If
>  > monophyletic taxon A and included monophyletic taxon B are "biologically
>  > real," then so is the paraphyletic taxon A-B, the set of organisms that are
>  > in A but not in B.
> 
>  No, it isn't, because we're subjectively deciding what to subtract from
>  A. >>
> 
> Not to be misunderstood: If A is >any< monophyletic taxon and B is >any<
> monophyletic taxon included in A, then the taxon A-B is as "real" as A or B.

In set theory, yes.  Biologically, no.  "Real" biological groups are
delimited by natural, external bounds that exist beyond human
subjectivity.  Common ancestry forms such a basis - provided we agree
that evolution has occurred, divergence events form the lower bounds of
groups. 

For more about this, I've been reading Ghiselin's latest book, which is
now in paperback:

Ghiselin, M.T.  1997.  Metaphysics and the Origin of Species.  State
University of New York Press, Albany, 377 pp.

chris


-- 
----------------------
Christopher A. Brochu
Department of Geology
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, IL 60605

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