[Taxacom] Defining polyphyly

[Richard Zander]

Students should note that definitions by cladists are ALWAYS in terms of patterns of nested exemplars, never in terms of process-based theory of descent-with-modification with informed guesses on which was the progenitor and which the descendant. Thus paraphyly and phylogenetic polyphyly can be anything represented by these simple patterns that turn up in patterns of evidence. Evolutionary polyphyly is when the same taxon is generated by an ancestor taxonomically different from the ancestor of a different but similar line. Phylogenetic polyphyly could be this, or it could signal what Ken Kinman refers to as paraphyly with multiple exgroups.
 
_______________________
Richard H. Zander
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166 U.S.A.
richard.zander at mobot.org
 

________________________________

From: taxacom-bounces at mailman.nhm.ku.edu on behalf of Kenneth Kinman
Sent: Tue 12/14/2010 5:55 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Defining polyphyly



Dear All,
         As I said in my last post, I agreed with how
Chris defined a paraphyletic group (specifically, a singly paraphyletic
group). However, I think that he misspoke in defining a polyphyletic
group as "clade A minus clades B. C., etc." Actually that defines a
paraphyletic group with multiple exgroups (doubly paraphyletic, etc.).
But if you then combine those exgroups together, you do get a
polyphyletic group. Creating a paraphyletic group is a subtractive
process, while creating a polyphyletic group is an unnatural additive
process.            
            For instance, Class Reptilia is a
doubly paraphyletic group: Clade A (Amniota) minus Clades B and C
(exgroups Aves and Mammalia). However, if you combine the two exgroups
(B plus C), you do get a polyphyletic taxon (namely Haemothermia).
Polyphyletic taxa are unnatural, while paraphyletic and holophyletic
taxa are natural.
                    ----------Ken           
----------------------------------------------
Chris Thompson wrote:
      Not exactly as a paraphyletic group is merely clade A
minus clade B. A polyphletic group is merely clade A minus clades B, C,
etc. So, it is not argument by authority.


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