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Taxonomic philosophy (was Re: WHAT'S GOING ON?)



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Date: Sat, 01 Jul 2000 20:23:31 -0700
To: m_troutman@hotmail.com
From: Stanley Friesen <sarima@friesen.net>
Subject: Re: WHAT'S GOING ON?
Cc: kinman@hotmail.com, dinosaur@usc.edu
In-Reply-To: <20000630154138.11681.qmail@hotmail.com>

At 08:41 AM 6/30/00 -0700, Matthew Troutman wrote:
><<When strict cladists respond in this way, and infer that someone
>doesn't know the difference between dinosaurs (sensu stricto) and 
>dinosaurs (sensu lato, i.e., including birds), I think they hurt not only
>cladistic classification (which I use up to a point), but also cladistic
>analytical methods (which I find very valuable).>>
>
>How?  The driving force of life is evolution.  To exclude birds from the 
>rest of dinosaurs is not an evolutionary perspective.

As Dr. Ashlock would have said, cladistic classification ignores half of 
evolution, anagenesis, in its focus on cladogenesis.


><<This insistence that the rest of world recognize their terminology,
>and making fun of those who don't distinguish between dinosaurs (sensu 
>stricto) and a cladistic dinosauria (sensu lato), will only backfire, and 
>I would discourage such tactics.  I could care less if it turns 
>people  off to strict cladistic classification, but when it casts a cloud 
>over  cladistic analytic methodologies, then it really starts to irritate me.>>
>
>Without getting myself involved in whatever matter you are discussing let 
>me give you some historical perspective on cladistic vs. Linnean (or 
>whatever) classification:
>
>As I said above, cladistic classification is grounded in evolutionary 
>thought, where everything shares a common ancestor at some point on the 
>tree of life.

So is Mayrian and Ashlockian classification.  This is not a distinction.
[The original unmodified Linnaean approach is a different matter].

>   Defining groups by their common ancestry is not only convenient, it 
> makes sure that we will not be excluding organisms from the group in the 
> future, it is also evolutionary.  We have a more accurate picture of life 
> and how it changed because rather than vaguely tracing ancestries and 
> lineages on the Linnean chart (or whatever), we can identify where, for 
> example, birds and cabbages had their last known common ancestor.  We 
> can't do this as well in Linnean (or whatever) classifications.

That isn't the *purpose* of a Linnaean (or Mayrian) classification.  For 
that purpose we have cladograms (or other styles of evolutionary diagram if 
one wishes).  Why clutter up an evolutionary tree with irrelevancies like 
formal taxa anyhow?  All that is really needed are labeled nodes using a 
standardized, coherent system.

>theories of thought were easily accomodated by the Linnean system.  Since 
>relationships weren't inferred by Linnean taxonomy, essensialist, 
>non-evolutionist, systems such as typology could be utilized to their full 
>potential; there would be no muddy areas in the chart where reptiles 
>changed into birds, the basic types (the very root of the word typology) 
>would never change.  The very face of nature, that is evolution, would be 
>ignored.
>
>Linnean classification could be converted over to evolutionary 
>perspectives, but things get confusing:

Not really - not if you understand what is being done.  It only gets 
confusing if you try to use a classification as a substitute for a cladogram.

>were not living back 600 million years ago to witness the birth of 
>animals; the only way we can be scientific is by not explicitly positing 
>ancestor-descendent relationships, and letting the trees speak for themselves.

This is bogus.  An ancestor-descendent relationship is a meaningful and 
potentially testable hypothesis, even *without* time travel.  There is no 
requirement for direct observation.  (At the very least a sister species 
with no autapomorphies is best considered the probable ancestor of the 
other branch).

>   Only with greater magnification on the branches of the tree (and 
> perhaps the physically impossible time machine), can we tell 
> ancestor-descendent relationships.  Until then, we have to be scientific 
> and say only what we know for sure.

Science isn't about certainty.  If it were we would not be allowed even 
cladograms!  We are most assuredly not even certain about what they say.

>else on the planet (as were dinosaurs).  We most express things they way 
>that they are, evolutionarily.  To exclude birds from dinosaurs, not being 
>in keeping with the evidence at hand and certainly not looking at it 
>evolutionarily.
>Matt Troutman

Actually, to exclude birds from the dinosaur *clade* is not in keeping with 
the best current evidence.  But taxa need not be clades to be scientific - 
so long as the criteria for delimiting them are replicable.

- --------------
May the peace of God be with you.         sarima@ix.netcom.com
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