follow up on paraphyly / polyphyly

SKÁLA Zdeněk skala at INCOMA.CZ
Thu Nov 11 09:24:53 CST 2004


Going back to the original question, the paraphyly / polyphyly distinction is quite straightforward:

1 - any "-phyly" is a result of splitting up a cladogram (i.e. an oriented graph, technically) and can be well described as a formal process

2 - the pieces of the cladogram can be either internally contected (= paraphyletic or mono/holophyletic) or discrete (= polyphyletic)
[hence the difference between the paraphyletic and polyphyletic taxa is a substantial one, perhaps greater than between the paraphyletic / monophyletic]

3 - given the graph orientation, the subgraph (a taxon) can either include all descendant nodes (in the graph-theory sense) of the basal node or only some of them - here is the difference between the mono/holo- and paraphyly

4 - any rating of different types of taxa as "natural" or "complete" is always a matter of taste and criteria; there were several (long) threads even here in Taxacom about the utility/naturalness of paraphyletic taxa - I would suggest to teach this field as a formal issue leaving the evaluation of different types of taxa as a separate lesson.

Best regards!
Zdenek Skala


-----Original Message-----
From: Derek Sikes [mailto:dsikes at UCALGARY.CA]
Sent: Wednesday, November 10, 2004 9:12 PM
To: TAXACOM at LISTSERV.NHM.KU.EDU
Subject: follow up on paraphyly / polyphyly


Dear Taxacomers,

Thanks to those who have replied already. I thought I might add one
additional bit on this issue:

I have also explained these terms informally (although I expect the
students to understand them formally as well) as follows:

Monophyly: a natural group

Paraphyly: a natural but incomplete group

Polyphyly: an unnatural group

I don't know where exactly I learned these informal definitions but
they're not mine. The problem with these is students memorize them but
often don't understand them!

Yours,
Derek
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Derek S. Sikes, Assistant Professor
Division of Zoology
Department of Biological Sciences
University of Calgary
2500 University Drive NW
Calgary, Alberta, Canada, T2N 1N4

dsikes at ucalgary.ca
http://homepages.ucalgary.ca/~dsikes/sikes_lab.htm

phone: 403-210-9819
FAX:  403-289-9311

"Remember that Truth alone is the matter you are in Search after; and
if you have been mistaken, let no Vanity reduce you to persist in your
mistake." Henry Baker, London, 1785

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http://www.biology.ualberta.ca/courses.hp/esa/esa.htm
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