Paraphyly is real (and inevitable)
kinman at HOTMAIL.COM
Sat Jan 12 11:27:57 CST 2002
Discussions of Linnean ranks really miss (and obscure) the much deeper
conceptual issues. If you think about it long enough, it seems clear to me
that paraphyly is not only real, natural, and "scientific"----even more than
that, paraphyly is INEVITABLE for evolution to continue.
If mother species didn't paraphyletically give rise to daughter
species, the evolutionary process would CEASE to continue. Sister species
and higher sister groups are a very useful Hennigian "convention", but it is
the unfounded belief that they are real and natural which has generated this
absurd schism in biological systematics.
Read My Lips: Clades are real, but "sister clades" are a convention.
Having said that, this does not mean I think classifications should be
nothing but a nested series of formal paraphyletic groups. It is the
massive extinction rate and scant fossil record which makes both cladistic
analysis and heavily cladified classifications so useful and necessary.
Contrary to what is usually argued, it is paraphyly that is natural,
and it is the "cladification" of classifications that must be defended in
terms of practicality and usefulness. Purely cladistic classifications are
excessive, unnatural, impractical, and unstable. The only logical solution
is a cladisto-eclectic system that combines paraphyly and holophyly in a way
that maximizes the utility of classifications. With both extreme
paraphyletic classifications and extreme holophyletic classifications, the
utility and naturalness approach zero on both sides of a "utility"
bell-curve. A balance is essential.
I certainly think that paraphyly can be overused, and deeply regret the
continued use of paraphyletic groups that are not explicitly labelled as
such. But the attempted total elimination of formal paraphyletic groups
from classifications is perhaps the most absurd, harmful, and unscientific
development in the history of biological systematics. Why should it be
surprising that this is still so controversial?
--------- Ken Kinman
P.S. From this perspective, ranked classifications make perfect sense (even
if they are human constructs). Ranks provide a balance between holophyly
and paraphyly, and this is just a true today as it was in Darwin's time.
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