[Taxacom] Species monophyly!

[Richard Zander]

A sister species pair reflects ole timey new synthesis Darwinian thought
that evolution progressed gradually through accumulation of traits.
These could be selective and change with changing environments, or
neutral and changing with stochastic drift depending on population size.
Thus, with the gradualist viewpoint, any two closely related species
probably differ significantly from their closest shared ancestor because
of gradual change in expressed traits. 

Nowadays, both gradualist and punctuationalist evolution of expressed
traits has been inferred for different species, and both scenarios can
be expected such that some putative cladogram sister groups doubtless
have a different shared ancestor, and some are ancestor-descendant in
relationships, these usually not distinguishable, in my opinion, in
cladograms because ancestor-descendant relationships are heartlessly
hammered by holophyly. Ancestor-descendant relationships are clear,
however, if paraphyly is preserved as evolutionarily informative though
phylogenetically uninformative.

Molecular changes associated with tracking genetic continuity and
isolation events is, however, largely gradualist.

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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
Modern Evolutionary Systematics Web site:
http://www.mobot.org/plantscience/resbot/21EvSy.htm
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-----Original Message-----
From: Stephen Thorpe [mailto:s.thorpe at auckland.ac.nz] 
Sent: Sunday, February 07, 2010 2:43 PM
To: Richard Zander; J. Kirk Fitzhugh; TAXACOM
Subject: RE: [Taxacom] Species monophyly!

But surely, if you take into account to totality of all extant and
extinct taxa, every species has another species as its ancestor, does it
not? That ancestral species either (1) remains in stasis, or (2) evolves
independently of its daughter species. So what are sister species?