RE: TRUTH AND "TRUTH"

[christopher brochu <cbrochu@fieldmuseum.org>]

>-----Original Message-----
>From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
>Matthew Troutman
>Sent: Friday, October 13, 2000 5:20 PM
>To: dinosaur@usc.edu
>Subject: TRUTH AND "TRUTH"
>
>
>Chris Brochu wrote:
>
><<1.  We stopped worrying about Linnean ranks because they have no
>biological reality and can seriously mislead people.  They were made for a
>world view that did not account for evolution.  Good riddance to them.>>
>
>and Tom Holtz (looking forward to the Gaia paper) also wrote:
>
><<We could take the typological approach and say "aha, this specimen does
>not fit the features required to be a carnosaur, so it has to be in some
>other category".  Or we can take an evolutionary approach, sort out the
>distribution to the best of our current ability, and see what results (in
>this case, that tridactyly evolves independantly in derived carnosaurs and
>in coelurosaurs).
>
>If your goal is recovering the history of life, then I recommend using a
>repeatable scientific methodology.  If your goal is nice, neat lists of
>names, then typology is fine.>>
>
>Why? Alls it boils down to is semantics. Either used by the Linnaean System
>or the Cladistic system. I have no problem using the Linnaean system an I
>don't see how it does not take into account evolution. This means that
>Huene, Nopcsa, Ostrom, didn't believe in evolution because they USED the
>Linnaean system? This doesn't make sense. You can easily use both Linnaean
>higherarchy with cladagrams and not use new 'node' names. I know because
>I've done it.




I think you're confusing two different issues here, and it boils down to
the confusing definitions out there of the word "cladistics."

A systematist has several operations ahead of him/her, from describing new
species-level taxa ("alpha-level taxonomy") to organizing biodiversity
("phylogeny reconstruction) and naming the groups discovered through that
process ("nomenclature" or "taxonomy").  "Cladistics" can be used to
describe either of the last two of these - either a method of phylogeny
reconstruction (specifically, maximum parsimony analysis) or a method of
naming groups (phylogenetic taxonomy).  This is why I rarely use the term
at all anymore - it means way too many things to too many people.  People
like Dave Hillis and Kevin de Quieroz are "cladists" insofar as they apply
phylogenetic taxonomy (and phylogenetic nomenclature - see below), but they
advocate likelihood-based methods of phylogeny reconstruction (and are
hence not methodological "cladists.")

We can go a step further with phylogenetic taxonomy, in which only
monophyletic groups are recognized, and use evolutionary relationships as
the basis of group meaning - this is phylogenetic nomenclature, which is a
somewhat different beast from phylogenetic taxonomy.  In either case, one
could (if one so wishes) use Linnean ranks - the choice of whether or not
to use them is completely independent of the phylogeny reconstruction
algorithm used or the philosophical basis behind the groups one observes.

I, personally, take that step.  Ranks, as first applied in the 18th
century, were constructed in a world view in which biodiversity was seen as
an expression of God's mind - by studying the organization of diversity, we
approached God's thoughts in the same way we can approach an author's
thoughts by reading an author's works.  This was a very typological world
view, in which taxa were seen as diverging to greater or lesser degrees
from some sort of ideal "type" that existed in God's consciousness.

Taxonomy as a whole played a surprisingly small role in Darwin's work.
This isn't to say it played NO role (it certainly did), but what Darwin and
his contemporaries saw was a hierarchical arrangement that looked an awful
lot like something evolution would produce.  So they simply translated the
old Linnean framework into a Darwinian model.  So of COURSE people like
Nopcsa, von Huene, and Ostrom were evolutionists, even if the system of
ranks they applied to their taxonomy long predated evolutionary thinking.
That Dinosauria is nested within Archosauria, and that Theropoda is nested
within Dinosauria, is true whether we place the monniker "order" in front
of Dinosauria or not - the hierarchical arrangement, not the ranks, is
evidence of evolution, and it is that (and that alone) which is fully
compatible with evolutionary thinking.

What do the ranks actually MEAN biologically?  THe answer, frankly, is
zilch - in fact, they were never meant to convey biological information in
the first place.  What does the phrase "Dinosauria is an order" actually
MEAN, besides the implied equivalence to the order Crocodylia or the order
Primates?  I can see how ranks can be used to organize taxon names, but
there are lots of ways of doing that, including indented lists, that are
just as efficient.  The goal of modern systematics is to express
biodiversity in evolutionary terms, but the ranks don't do anything to
further that goal.  Try it yourself, Tracy - take the ranks away from your
Linnean hierarchy and see if they really, truly diminish the information
being conveyed.

Furthermore, they do genuinely mislead people.  I've seen talks where
workers cited the higher "speciation rates" of some "families" over others,
when one could break the fast-evolving "families" down and lose the
pattern; in this case, the pattern reflects arbitrary naming principles
rather than real biological phenomena.

As Shakespeare had Laertes say (Hamlet), "O my offence is rank, it smells
to heaven."




chris



_________________________
Christopher A. Brochu
Department of Geology
Field Museum
1400 S. Lake Shore Drive
Chicago IL 60605

312-665-7633 voice
312-665-7641 fax
cbrochu@fieldmuseum.org