[Taxacom] Evolutionary info from non-monophyly

Richard Zander Richard.Zander at mobot.org
Fri Nov 21 14:11:36 CST 2008


As an alternative view on monophyly as a classification method in
molecular phylogenetics, I submit that there are considerable
evolutionary data to be had from the apparent splitting of morphological
taxa on molecular trees. 

 

Basically, phenomena like "massive homoplasy" and cryptic species (and
genera and families) can be explained by morphological stasis of
isolated populations of one taxon, with continued DNA changes in
non-coding sequences, and survival of at least two of such populations.
These imply a shared ancestor of the same name deep in the evolutionary
tree, a "virtual fossil." This requires the at least tentative
acceptance that at least some taxa are affected by punctuated
equilibrium, and that splits in molecular cladograms may represent
isolation events but not necessarily speciation events that affect both
products of the split.

 

The alternative explanation of parallelism or convergence is less
plausible because at least well-known traditional taxa based on
expressed traits have been diagnosed only after examination of many,
sometimes thousands of specimens over 250 years by multiple taxonomists
to try to establish that total parallelism or total convergence is fully
minimized in these taxa.

 

The application of phylogenetic monophyly as a classification tool when
dealing with molecular cladograms may organize relationships of genetic
lines of descent and isolation but, by ignoring any other evolutionary
features, such as new taxa of higher rank (signaling new evolutionary
developments) arising from paraphyletic taxa, limits greatly our aim at
developing a classification with the largest evolutionary component
possible. It also requires acceptance that only the pure form of
gradualist evolution and the biological species concept are operant in
classification.

 

A copy of this newly published paper is at

http://tinyurl.com/6frd9l 

while a vigorous exchange of personal views by bryological
phylogeneticists and evolutionary taxonomists on paraphyly and other
controversial subjects has been archived in a blog:

http://internationalassociationofbryologists.blogspot.com/ 

You'll have to (if interested) winkle out the relevant posts as they
have been scattered among several topic threads, like classification,
monophyly, morphology, paraphyly and species concepts. What is nice is
that a debate like this is long overdue.

*****************************
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
*****************************

 




More information about the Taxacom mailing list