[Taxacom] Species monophyly!

[Stephen Thorpe]

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?

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From: Richard Zander [Richard.Zander at mobot.org]
Sent: Monday, 8 February 2010 9:37 a.m.
To: Stephen Thorpe; J. Kirk Fitzhugh; TAXACOM
Subject: RE: [Taxacom] Species monophyly!

Ah, but they are not sister species after your particular scenario
leading to reciprocal phylogenetic monophyly. One is the ancestor of the
other and they do not have a common shared ancestor other than
individuals assignable to one or the other of the two "sister" species.
We can SAY they do, but the mapping of traits suffers from this, as does
ongoing search for truth.

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

-----Original Message-----
From: Stephen Thorpe [mailto:s.thorpe at auckland.ac.nz]
Sent: Saturday, February 06, 2010 7:23 PM
To: Richard Zander; J. Kirk Fitzhugh; TAXACOM
Subject: RE: [Taxacom] Species monophyly!

It seems odd that the species status of one population could depend on
what happens in other populations. So, if one population of a
multi-population species quickly evolves into something
morphologically/genetically very different, its status as a species
depends on what happens to the other populations. If they remain in
stasis, evolving little, then we have persistent paraphyly, don't we?
But if, say, one of the other populations rapidly evolves into something
else novel, and the remaining static populations go extinct, then we are
left with two perfectly good monophyletic sister species ...