Jon Shaw and David Wagner have cogent thoughts on nonmonophyly. I will
go a bit further.
Reciprocal monophyly after speciation (budding) of a daughter line or
splitting of one ancestral line is commonly considered inevitable by
those who cannot tolerate surviving ancestors of static phenotype, or
who insist on gradualistic evolution of expressed traits through
divergence of both resultant lineages after splitting. But there is
abundant evidence that taxa that derive from within a population or a
group of species or a group of genera do not eventually become a
sister-group of that ancestor (i.e. reciprocally monophyletic), but the
ancestral species, genus or family remains paraphyletic. Think cryptic
species, genera and families that are indistinguishable by robust traits
from other species, genera and families.
Given this evidence, insistence on phylogenetic monophyly is counter
reality. Phylogenetic monophyly is a "principle" of classification, and
is thus an axiom, maxim, or slogan, not necessarily representing a thing
in nature (as opposed to evolutionary monophyly, which allows
paraphyly). Regression to first principles and Aristotelian logic where
any deduction is necessarily true (a syllogism) is crippling
systematics. Remember when cladists asked "traditional" taxonomists to
examine the basis for their methods, and we all said, hey, wonderful,
yes we should analyze what we are doing? Actually, we were doing
science, which is rather free-form and involves induction. When we
examined our "principles," however, we found to our chagrin we had no
guiding "principles." Beyond doing science, I mean.
Yes, using first principles (e.g. species are named by phylogenetic
monophyly, some species are not phylogenetically monophyletic, therefore
these must be split or lumped with something else -- syllogism) makes
things simple, but such axioms are not simplifying. Binomial
nomenclature is simplifying, though exact long names are lost.
Phylogenetic monophyly is simplistic, because representation of
macroevolution in classification is lost.
One more point: If species, genera and families may occur in more than
one molecular lineage (as in paraphyly), then molecular analysis does
not necessarily determine the sequence of splitting of a lineage. This
is because extinct lines of different molecular lineage but same
phenotype may have come off earlier than what is given in the molecular
cladogram. Again, we have empty precision that is based on assumptions
that are, indeed, contradicted by scientific evidence. Thus, molecular
systematics is not "easy" as some have said because it is just lab work
(that's often quite difficult), but because recourse to axioms makes
conclusions about evolution simplistic.
I believe that the long foray of systematics into cladistics and
phylogenetics, using both morphological and molecular data, has been a
tremendous waste of time because of empty precision, reliance on the
"automatic classification" originating in phenetics (e.g. insistence on
all traits being equally weighted to eliminate inserting any "phyletic"
element, and regression to the authority of first principles. Much labor
in the years to come will be necessary to repair the damage.
Richard H. Zander
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
Web sites: http://www.mobot.org/plantscience/resbot/
Non-post deliveries to:
Missouri Botanical Garden, 4344 Shaw Blvd., St. Louis, MO 63110
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