[Taxacom] FW: cladistic analysis for morphological characters -- UPGMA is not cladistics

Richard Zander Richard.Zander at mobot.org
Wed Nov 14 11:56:18 CST 2012


Dick:
I don't think that "botanists are constructing causal explanations for
the patterns that we see." Botanists are deducing causal explanations
from the clustering we see. The deduction is from an axiomatic
assumption that close clustering means close phylogenetic relationship.
This may be only obliquely true.

Take the example of a taxon near the base of a morphological cladogram.
It is similar to other taxa near the base of the cladogram in having
plesiomorphic traits. It turns up deeply nested in a molecular cladogram
of the same taxa, nowhere near the similar taxa in the morphological
cladogram.

A deduction is that the morphological cladogram is wrong. An inference
is that both cladograms are right, and the deeply nested taxon in the
molecular cladogram is ancestral to all the lineages distal to its
position in the morphological cladogram. With this induction, we have
lots of abduced evolutionary scenarios to test. With deduction, the
"explanation" is a might circular.

Richard 

____________________________
Richard H. Zander
Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299 USA  
Web sites: http://www.mobot.org/plantscience/resbot/ and
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Modern Evolutionary Systematics Web site:
http://www.mobot.org/plantscience/resbot/21EvSy.htm
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-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Richard Jensen
Sent: Wednesday, November 14, 2012 9:03 AM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] FW: cladistic analysis for morphological
characters -- UPGMA is not cladistics

Kirk,

Don't the branching patterns we see in cladograms (or the nested sets we
see in phenograms) imply a cause?  These groups exist for a reason - we
have identified characters and examined the distributions of characters
to determine if there are patterns.  We could argue that these patterns
are just chance consequences of developmental processes, but I would
like to believe that these patterns have a causal basis.  Our
recognition of, say, Spermatophyta (the seed plants) is based on our
understanding that these plants share an evolutionary history reflected
in their reproductive (and other) structures.  By examining the fossil
record and using the tools of evo-devo, botanists are constructing
causal explanations for the patterns we see.

Dick J




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