Systematics -Reply

John E. Silvius SILVIUSJ at CEDARNET.CEDARVILLE.EDU
Sat Mar 1 13:21:13 EST 1997


>>> Patrick Elvander concludes his 2/27/97, 02:59pm remarks by
saying:

The arguments over how far to take cladistic approaches in defining
higher taxonomic groupings are quite heated and often fascinating.
There are some potentially major revolutions afoot!
_____________________________________________________
	Patrick Elvander	Department of Biology
	Lecturer in Biology	Sinsheimer Labs
	408-459-3674		University of California
				1156 High St.
elvander at biology.ucsc.edu	Santa Cruz, CA  95064
-----------------------------------------------------------
In my view, Patrick's statements are quite accurate.  As an aid to
Lenore Durkee and others who attempt to include cladistics in botany
courses, may I further emphasize that we must be careful to
distinguish the cladistic from phylogenetic approaches to deciphering
evolutionary relationships.   The "heated arguments" attest to the
fact that there are differences, and the following quotes emphasize
this further:

"Cladistics, which is, of course, an anathema to new-Darwinians, is
favored by those who prefer not to transcend the observable data in
their theorizing to "speculate" about genealogical relationships". 
        -- D. Oldroyd (1986) Biology and Philosophy Vol. 1:133.

"Nearly all biologists must share, the species is the only taxonomic
category that has at least in more favorable examples a completely
objective basis.  Higher categories are all more or less a matter of
opinion.  -- O. Richards. 1970. Science 167: 1477.

Discussing the origin of anthocyanin and betalain pigments, Randy
Moore et al (Botany text, 1st ed. 1995, page 580, Column #1) state:
"This example (anthocyanin and betalain pigments) illustrates a
significant assumption of cladistics, and one that distinguishes
cladistics from other phylogenetic methods:  Only shared-dreived
character states indicate phylogenetic relationships;
shared-primitive character states do not.  This contrasts with the
assumption that overall similarity can be used to show evolutionary
relatedness--an assumption that remains common in most large-scale
phylogenetic classifications".

I would also recommend an article by Colin Patterson (1982.
Cladistics and classification.  New Scientist 93: 303-306) in which
he distinguishes cladograms from phylogenetic trees as follows:
"Branching diagrams can be seen not as evolutionary trees, but as
cladograms in which there is no time scale and the nodes imply shared
characters (synaptomorphies) rather than common ancestry.  This
distinction, between cladograms and trees, may seem like
hair-splitting, but it is important."

I need much more study of this subject, but I have read enough to
recognize that one should be knowledgeable of the differences between
the cladistic approach (indeed, there much diversity of approach
within this camp) and the phylogenetic approach as one would prepare
laboratory experiences and discussions.

John E. Silvius
Professor of Biology
Cedarville College
Cedarville, OH  45314

Phone 513-766-7948
silviusj at cedarville.edu



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