[Taxacom] Knocking Hennig off his pedestal

Richard Zander Richard.Zander at mobot.org
Sun Jan 26 11:03:41 CST 2014


Well, as long as everyone seems to be weighing in on this, in my opinion
cladistics cannot determine monophyly. The assumption that an ancestor
can have only one descendent before changing into another species is
often wrong. One widespread generalized species can generate two or more
specialized descendant species without much change (swamping of
mutations, strong stabilizing selection). In such case, the rubric that
for every three species two are more closely related fails.  Thus, many
nodes in a cladogram are doubtless of the same name as one of the
sister-groups.

Phylogenetics assigns a node the role of locum tenens, a place holder
for a shared unknown species. Given that such a place holder is often
superfluous and non-parsimonious, the node becomes a locus pocus, a
magical organizing principle that ensures full resolution in a cladogram
when at the species level there can be no full resolution. Cladograms in
the literature are full of loci poci.


____________________________
Richard H. Zander
Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299 USA  
Web sites: http://www.mobot.org/plantscience/resbot/ and
http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Evol. Syst.: http://www.mobot.org/plantscience/resbot/EvSy/Intro.htm
UPS and FedExpr -  Missouri Botanical Garden, 4344 Shaw Blvd, St. Louis
MO 63110 USA

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Patrick
Alexander
Sent: Saturday, January 25, 2014 11:51 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Knocking Hennig off his pedestal

Or, phrased in a manner that seems more straightforward to me:

Polyphyletic groups are based on homoplastic character states. Both
monophyletic and paraphyletic groups are based homologous character
states. For monophyletic groups the homologous character states are
apomorphic, while for paraphyletic groups they are plesiomorphic.

However, this is just shoehorning phylogenetic terms into typology. It
assumes that you start with an ahistorical, similarity-based
classification and then examine how that classification maps onto
descent. A grouping of species is, on its own, only monophyletic or not.

Paraphyly and polyphyly are not characteristics of groups of species,
they are characteristics of a typological classification of those
species. They are only distinguishable if you accept a priori that
typology is the appropriate approach to defining groups of
species--which, of course, is diametrically opposed to the goals and
concepts of phylogenetic classification, which defines groups of species
by descent. From the viewpoint of phylogenetic classification, they are
equally bad because they are indistinguishable.

Patrick





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