Two different concepts of monophyly: diachronic and synchronic

-------- Original Message --------
Subject: RE: BRYONET: Pottiaceae and new classification
Date: Mon, 3 Nov 2008 16:00:51 -0800
From: Brent Mishler <BMishler@calmail.berkeley.edu>
To: bryonet-l@mtu.edu

BRYONET

Hi Richard,

Interesting discussion, getting to some really important issues for
bryology. Here is a quick comment on your note:

There have been two different concepts of monophyly out there in the
literature since Hennig; the first a diachronic definition that
includes the ancestor in the group, worded succinctly like this: "a
common ancestor and all of its descendants." You correctly point out
that this definition leads to logical paradoxes, especially with
ranked classifications. Others have pointed this out in the
literature as well, including me.

But the second view of monophyly, Hennig's own, is a synchronic
definition, worded succinctly like this: "all and only descendants of
a common ancestor." I.e., the ancestor (if known) is not classified
with its descendants; it has a special status. This definition is
not subject to the problems you outline. There is further discussion
in the chapters I co-authored in the book "Species Concepts and
Phylogenetic Theory: A Debate" edited by Wheeler & Meier, 2000.

Best,

Brent

--

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Brent D. Mishler
Professor, Department of Integrative Biology
Director, University and Jepson Herbaria
Associate Director, California Biodiversity Center
Mailing address:
UNIVERSITY OF CALIFORNIA, BERKELEY
UNIVERSITY AND JEPSON HERBARIA
1001 VALLEY LIFE SCIENCES BLDG # 2465
BERKELEY, CA 94720-2465 USA
Phone: (510) 642-6810
FAX: (510) 643-5390
E-mail: bmishler@calmail.berkeley.edu
WWW: http://ucjeps.berkeley.edu/people/mishler.html
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