Points of reference (was Re: terms)

Charles J. O'Kelly okellyc at megasun.BCH.UMontreal.CA
Thu Jun 23 09:29:08 EST 1994


In article <CrtzEr.25s at zoo.toronto.edu>, mes at zoo.toronto.edu (Mark Siddall) writes:

[chop chop]

|> Patterson writes:
|> 
|> >my usage is:
|> >Monophyly - single origin included in group
|> >Holophyly - monophyly and all descendents
|> >Paraphyly - monophyly and not all descendents
|> >Polyphyly - not single origin

[damn - gotta sharpen the hatchet now]

|> ... since there IS a single common ancestor for
|> any set of taxa regardless of monophyly or paraphyly or polyphyly.

hmmm ... so any taxon being created or assessed can only be treated with respect
to a stated fixed point of reference (Wiley's "level of universality", if memory
serves).  this creates a couple of problems with respect to protist classification:

a) the only sensible starting point is the origin of life.  otherwise, for example, one could
create an "Empire Eukaryota" that is monophyletic (Hennigian definition) with respect to
the presumed urkaryote ancestor, but paraphyletic with respect to prokaryote origins - 
assuming one tries to recognize a prokaryote taxon of equal rank with eukaryotes, eg
an "Empire Prokaryota", and eukaryotes share a nearest common ancestor with archaebacteria
(ie they both belong to the same clade).

b) if, in a global classification (which is pretty close to what one ends up with if a
a phylogenetic classification of all protists is attempted), one allows
a starting point other than the origin of life, then what is there to stop a person
defining as many (paraphyletic with respect to the origin of eukaryotes - IMHO such
a specific statement should always be made when using the M, H or P words) taxa of equal
rank as is desired, based on multiple "floating" points of reference?  indeed this would 
seem to be necessary if one wishes to preserve the sanity of persons locked in to e.g. "Kingdom 
Plantae" and "Kingdom Animalia".

I wonder (and it seems I'm not alone on this) if this entire argument would be best
defused by abandoning Linnean categories in favor of a system based on direct (on-line?)
presentation of trees - the clades might then be given nonhierarchical names to help
text-based or verbal discussion.  could such a system be sold to "the outside world" ...?
 
|> Mark
|> 
|> -- 
|> Mark E. Siddall                "I don't mind a parasite...
|> mes at vims.edu                    I object to a cut-rate one" 
|> Virginia Inst. Marine Sci.                     - Rick
|> Gloucester Point, VA, 23062

Charley O'Kelly				Complex problems have simple,
Mad Protistologist			easy-to-understand wrong answers.
okellyc at bch.umontreal.ca



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