Cladistics and "Eclecticism"
tdib at OCEANCONSERVANCY.ORG
Thu Feb 7 09:58:07 CST 2002
From: SKÁLA Zdenek
the current paraphyly/holophyly discussion seems to point constantly to one
Is the amount of character change (better of character state difference in
an operational context) a core subject of systematics?
I think that "character change" or character-state transformations are very
much the core subject of systematics. The _amount_ of such changes is an
interesting, but not crucial factor.
Cladistics involves an inherent tension in this respect:
(1) On one side, cladists are trying to make their monophyly concept purely
topological. This is also behind the disagreement about the "paraphyletic
speciation". For those that use solely the topology of phylogenetic
relationships paraphyletic species obviously cannot exist. For those that
want to include character information in the systematics paraphyletic
species do exist well.
Let us be precise. Cladistics uses character information. Cladistics is
based entirely on character information. How can anyone claim that
cladistics doesn't include character information? What else is there to
cladistics except the extraction of pattern from the character information?
Those who use paraphyletic groups use character information in a very
bizarre manner. Their classifications are much LESS based on character
information. How is it possible to look at character information and
classify birds anyplace other than up within the Dinosauria?
The purposeful recognition of a paraphyletic group means that one
disresepcts the evidence from characters, and substitutes a subjective
judgement, ususally based on a crude sense of the number of changes, rather
than the changes themselves.
(2) On the other side, cladists would like to have also a
character-informative taxa; topology itself, however, does not provide
criteria of how to split a cladogram into a set of taxa.
Of course it does. The cladogram IS the organization of taxa.
I completely disagree with your notion that monophyletic and paraphyletic
taxa are somehow equally arbitrary. Monophyly is the recognition of real
lineage branches. When a lineage began, when those organisms began to be
isolated from the rest of life (in terms of inheritence), something new and
worthy of naming and recognition happened, and we name it and recognize it
as a taxon. So long as that nexus of inheritence continues, the taxon
continues, either as a simple singular entity (an unbranched lineage - a
species) or perhaps as a divergent lineage, a higher taxon. So long as the
taxon persists, we continue to recognize its existence. When it goes extinct
we recognize that. In short, we try to recognize what happens in "Nature".
That is why it is a natural system.
If you recognize a newly isolated lineage branch, but then withdraw that
recognition at a later time, or pretend that it is a new taxon, even though
the critters are still out there reproducing, passing on their inheritence,
evolving, then you are introducing non-natural criterea to your
More information about the Taxacom