Predictivity vs Useful

Richard.Zander at MOBOT.ORG Richard.Zander at MOBOT.ORG
Thu Feb 17 11:42:04 CST 2005

Consider the following example of the optimal branch arrangement
((AB)C)D)with morphological data:

Taxon A shares 10 advanced morphological traits with B.
Taxon B shares 5 advanced morphological traits with C.
Taxon A shared 5 advanced morphological traits with C.

Then, compare with the optimal branch arrangement ((AC)B)D) with mol. data:
Taxon A shares 10 advanced molecular traits with C.
Taxon B shares 5 advanced molecular traits with A.
Taxon A shared 5 advanced molecular traits with B.

Why choose the second arrangement? Why choose any of the two?

Even if the arrangments agreed, one can discuss or try to discuss the
relative worth of the morphological traits vs the molecular traits (even in
the likelihood case where unchanging traits are to some extent informative).

If morphological traits vary in evolutionary speed and fashion, so do
molecular traits. There has been an interesting study recently on
heterogeneity of models among DNA sites (e.g. Kolaczkowski, B. & J. W.
Thornton. 2004. Performance of maximum parsimony and likelihood
phylogenetics when evolution is heterogeneous. Nature 431: 980-984), which
is perhaps parallel with the problems of morphological traits. I wonder if
there might be some way of standardizing morphological traits, or formally
assigning probabilities (other than intuitive weighting)?

Richard H. Zander
Bryology Group, Missouri Botanical Garden
PO Box 299, St. Louis, MO 63166-0299 USA
richard.zander at <mailto:richard.zander at>
Voice: 314-577-5180;  Fax: 314-577-9595
Bryophyte Volumes of Flora of North America:
Res Botanica:
Shipping address for UPS, etc.:
Missouri Botanical Garden
4344 Shaw Blvd.
St. Louis, MO 63110 USA

-----Original Message-----
From: Barry Roth [mailto:barry_roth at YAHOO.COM]
Sent: Thursday, February 17, 2005 10:39 AM
Subject: Re: [TAXACOM] Predictivity vs Useful

Yes, this is basically a restatement of the fundamental fact underlying the
endeavour of taxonomy:  characters do not all evolve in lock step.  (If they
did, most of our debates would disappear, and a lot of us would have to find
other lines of work!)

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