Dangerous Topic: Taxonomy

Joe Shaw jshaw@opuntiads.com
Sat, 14 Oct 2006 09:44:11 PDT
Hi Gang,

A discussion on another list (cacti)  prompted me to look up the definition 
of a phylum, or merely a taxon.  I found the following wording and realized 
it is almost precisely what I learned in college in my plant taxonomy class. 
One key part of the definition is the word "arbitrary."


"A phylum is part of the hierarchy of classification of organisms. It is an 
arbitrary grouping; that is, it is developed from a combination of 
scientific observation, theorizing, and guesswork in an attempt to find 
order in the complexity of living and extinct life forms. The same is true 
of all classification levels above and below it except for species, which 
consist of organisms known to be capable, at least potentially, of 
interbreeding"  (FROM:  "Phylum," Microsoft® Encarta® Online Encyclopedia 
2000; http://encarta.msn.com/  © 1997-2000 Microsoft Corporation. All rights 

It occurred to me that much miscommunication (or misunderstanding) might 
derive from the arbitrariness of taxonomic decisions.   Such decisions as 
where to place a division (e.g., these plants belong to 2 different genera) 
are inherently tricky when there is no universal definition of "how far 
apart organisms must be in order to belong to different genera."  The 
decisions are not silly, or taken without great deliberation, but they do 
involve some educated guesswork and hypothesis-testing and hence, have an 
arbitrary element.

It is no wonder that people disagree about where to draw the boundaries. 
The boundaries are placed according to human decisions, but there is no 
higher authority that controls "where" to place a boundary.  Human-created 
rules (such as the ICBN) have no inherent mechanism to force anyone to agree 
with anyone else about where to place a split, or where to lump.

In 2003 the Angiospermy Phylogeny Group (AGP II report) lumped several 
monocot families "back" into the Alliaceae and the Asparagaceae.  If this 
arrangement catches on, such families as the Agapanthaceae and others will 
be footnotes in history.  The decision is arbitrary but well-thought-out and 
the rationale for such lumping is contained within the article (see pages 
403 and 404 for the discussion).  I've put the article online so interested 
parties can read it.  It was published in the Botanical Journal of the 
Linnean Society, 2003, 141:399-436.

LINK:  Angiosperm Phylogeny Group II Report, 2003



Conroe, TX

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