[Taxacom] Phylogenetic classification?

[Richard Zander]

I agree with you, Ken, on most of this. I don't think good taxa should be lumped just because one is paraphyletic and the other merely appended distally rather than laterally as a sister-group. This is totally artificial.

*****************************
Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
richard.zander at mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Non-post deliveries to:
Missouri Botanical Garden, 4344 Shaw Blvd., St. Louis, MO 63110
*****************************


-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman
Sent: Friday, July 31, 2009 9:46 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Phylogenetic classification?

 Hi Richard,
       Such an expectation by some cladists that ancestor-daughter species "inexorably" become sister species seems to be largely wishful thinking. This might tend to occur in cases where the daughter species has a population that is not greatly smaller than the population of the mother species. However, such an expectation seems rather unlikely in frequent speciation where there some element of "founder effect", especially when the mother species is highly polytypic. This would be most evident in extreme cases where the founder is a single pregnant female (such as for metazoans) or even a single seed (for plants) which manages to survive in a new environment and is
reproductively isolated.          
      The paraphyly is even more evident when one adds the time dimension and considers the earlier history of the mother species (which would usually be broader both genetically and phenotypically) than it was at the later time when it gave rise to its daughter species.  If I was a strict cladist, I would find it VERY disturbing to conceive of one sister species having perhaps evolved a considerable period earlier than its sister species.  Given the lack or sparsity of a fossil record (along the stem between nodes) leading to most such species pairs,
having no good evidence of relative age makes it even more problematic.   
       Extinction and a poor fossil record is truly a double-edged sword that can make the recognition of clades both useful in the face of that lack of information, but often only temporarily useful and subject to destablizing challenges to that cladistic recognition when fossil intermediates are eventually discovered.  The trick is to occasionally use paraphyly where cladistic assumptions seem likely to be overturned by new information (fossil or otherwise).  Paraphyletic speciation (and paraphyly at higher taxonomic levels) is too common for strict cladism to continue hoping that it won't cause them any major problems (and classificatory unstability for us all).  Stability and usefulness require the occasional use of paraphyletic taxa at appropriate points in the Tree of Life.
      ---------Ken Kinman