[Taxacom] another recent article in Taxon

Kenneth Kinman kennethkinman at webtv.net
Mon Mar 28 09:37:13 CDT 2011

 Dear All,
       Another very interesting paper was recently (December 2010)
published in the journal Taxon.  For those who haven't seen it,
especially zoologists who don't normally read botanical journals, the
abstract is given below.
Hörandl, E. & Stuessy, T.F.  2010.  Paraphyletic groups as natural
units of biological classification.  Taxon 59: 1641-1653. 
Despite the broad acceptance of phylogenetic principles in biological
classification, a fundamental question still exists on how to classify
paraphyletic groups. Much of the controversy appears due to (1)
historical shifts in terminology and definitions, (2) neglect of
focusing on evolutionary processes for understanding origins of natural
taxa, (3) a narrow perspective on dimensions involved with
reconstructing phylogeny, and (4) acceptance of lower levels of
information content and practicability as a trade-off for ease of
arriving at formal classifications. Monophyly in evolutionary biology
originally had a broader definition, that of describing a group with
common ancestry. This definition thus includes both paraphyletic and
monophyletic groups in the sense of Hennig. We advocate returning to a
broader definition, supporting use of Ashlock's term holophyly as
replacement for monophyly s.str. By reviewing processes involved in the
production of phylogenetic patterns (budding, merging, and splitting),
we demonstrate that paraphyly is a natural transitional stage in the
evolution of taxa, and that it occurs regularly along with holophyly.
When a new holophyletic group arises, it usually coexists for some time
with its paraphyletic stem group. Paraphyly and holophyly, therefore,
represent relational and temporal evolutionary stages. Paraphyletic
groups exist at all levels of diversification in all kingdoms of
eukaryotes, and they have traditionally been recognized because of their
descent-based similarity. We review different methodological approaches
for recognition of monophyletic groups s.l. (i.e., both holophyletic and
paraphyletic), which are essential for discriminating from polyphyly
that is unacceptable in classification. For arriving at taxonomic
decisions, natural processes, information content, and practicability
are essential criteria. We stress using shared descent as a primary
grouping principle, but also emphasize the importance of degrees of
divergence plus similarity (cohesiveness of evolutionary features) as
additional criteria for classification. 


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