[Taxacom] Endless debate

[Don.Colless at csiro.au]

Richard mentions cluster methods, which employ a distance metric. We might note that parsimony algorithms, such as PAUP, when attaching an object to a candidate internode on a growing tree, employ a criterion that is a simple function of Manhattan Distance. Lengths on the tree are likewise measured in that metric. It is difficult to view these as anything but "cluster methods".  This is, I gather, anathema to many; but the alternative is strict Hennigian a priori characterisation of character states as primitive or derived. And (pace John Grehan) that has its own problems.
   
Donald H. Colless
CSIRO Div of Entomology
GPO Box 1700
Canberra 2601
don.colless at csiro.au
tuz li munz est miens envirun

________________________________________
From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Richard Zander [Richard.Zander at mobot.org]
Sent: 07 April 2009 23:54
To: Curtis Clark; taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Endless debate

Well, actually, now that this has come up, cladistics is just a way of approaching the "paraphyletic" Darwinian Tree of Life (p. 95 of Darwin's paperback) which has one taxon giving rise to another.

Saying cladistically that "these two taxa are more related to each other than either is to a third" is just a way of clustering the results of descent with modification of taxa (as opposed to traits, but that is a different problem). Descent with modification is evolution, not the bifurcating results of a cluster analysis, although the results of cluster analysis can help us understand evolution. If we had lots of information on descent with modification, which would be better, a sister-group classification or some kind of grade-based classification? Must we choose?

The Linnaean classification is what we have and is closest to a general-purpose classification if we mix all our interpretations of descent with modification, both sister-group and ancestor-descendant relationships into it, explaining our reasons, methods and data elsewhere.

_______________________
Richard H. Zander
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166 U.S.A.
richard.zander at mobot.org


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From: taxacom-bounces at mailman.nhm.ku.edu on behalf of Curtis Clark
Sent: Mon 4/6/2009 10:18 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Endless debate


 The "paraphylocode" I propose would consist of
nothing but grade taxa, delimited by key innovations. It would be to
grades as phylocode is to clades. I disagree with grade-based
classification, but I have suggested a way to make it rigorous, if
anyone were interested, which it seems no one is, because all of you who
support grade-based groups seem content to mix them willy-nilly with clades.

--
Curtis Clark

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