[Taxacom] Ageism and classification

Richard Zander Richard.Zander at mobot.org
Wed Apr 22 11:23:11 CDT 2009


A Web-based science encyclopedia:


has an article by Peter A. Ensminger:


which says in part:


"Evolutionary taxonomy can be considered a mixture of phenetics and
cladistics. It classifies organisms partly according to their
evolutionary branching pattern and partly according to the overall
morphological similarity. Evolutionary taxonomy is basically the method
used by the early evolutionary taxonomists and is also called classical
taxonomy. The major limitation of evolutionary taxonomy is that it
requires a highly arbitrary judgment about how much information to use
for overall similarity and how much information about branching pattern
to use. This judgment is always highly subjective, and makes
evolutionary taxonomy a very poor method of classification, albeit one
that survives in the hands of certain older taxonomists."


Anent "older taxonomists" let's discuss tree-thinking. In "Mathematical
Taxonomy" by N. Jardin & R. Sibson, 1971, John Wiley, New York, on page
150 it says: "Prima facie the case for using numerical methods of
automatic classification to construct taxonomic hierarchies for all
kinds of organisms can be made to appear quite strong. The case rests
upon the following assumptions. First, the purely phenetic approach to
taxonomy must be accepted. Secondly, it must be assumed that automatic
classification based upon an adequate selection of populations and
attributes can be guaranteed to produce optimal phenetic


This is from 1971. What are the results of phenetic cluster analysis?
Trees. Parsimony analysis also generates trees through a nonultrametric
method based on a simple model of evolution of traits), and I have it on
good authority (Pierre Legendre, pers. comm.) that parsimony analysis
really is cluster analysis. Cluster analysis, whether phenetic or
phylogenetic or even MCMC Bayesian, produces trees and does not identify


Evolution does not act by clustering. It acts by descent with
modification of one biological entity (identifiable at some degree of
resolution) into another. Paraphyly is one method of identifying an
ancestor at some degree of resolution. 


"Automatic classification" by clustering methods to create trees as
hierarchical sister-groups has been around since the late 1960's and is
now at least 40 years old. Clustering methods with morphology and
molecular data are valuable in investigating evolution, but more
information may be had about evolution than that obtained from
clustering methods and presented to us in classification via holophyly. 


I think it is time for students to confront their doddering geezer or
geezette professors of phylogenetics with a paradigm change that calls
for an eclectic approach to evolutionary content in classification, and
reject holophyly (and other automatic or judgment-free aspects of
phylogenetics) in favor of recognition of paraphyly and autophyletic
products of descent with modification based on reasoned and seasoned
judgment of all available information about evolution.


Richard H. Zander 
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Missouri Botanical Garden
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richard.zander at mobot.org
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