Paraphyly is real (+ "strict cladist" defined)

Thomas DiBenedetto tdib at OCEANCONSERVANCY.ORG
Tue Jan 15 10:40:35 CST 2002

Lets start with this:
From: Ken Kinman
   DEFINITION:  A "strict" cladist is one who never recognizes formal
paraphyletic taxa (apparently due to the strange notion that they are unreal
"mistakes" that must always be done away with).  In my opinion, they are the
ones who got it wrong, and universities should be giving students both sides
of the story.  Maybe with the Internet, both sides of the story will
eventually get out and discussed.
Your definition is of a cladist, not a strict cladist. The principle of
classifying with reference to the real descent history of taxa is
fundamental to cladistics. If you think paraphyly is real, or if you think
paraphyletic groups should be recognized even though they are obviously
artificial (and y'all seem to go back and forth between the two
justifications based on which argument you are losing at the moment), then
you are not a cladist. As to your whining about not getting a fair hearing,
I might point our that Darwinian systematics was the paradigm for one
hundred years, and is a system that has been rejected. It is ludicrous to
claim that the arguments have not had a fair hearing. Cladistic arguments
had to be advanced in the face of an "establishment" position that claimed
that "evolutionary systematics" was fundamental to the entire Darwinian
revolution, and this was argued by such brilliant biologists as Ernst Mayr.
The argumentative burden was massivly on the shoulders of cladistics, and
yet it proved to be convincing. Your efforts to "strike a balance" or find a
compromise between an obsolete set of concepts and their replacement is, I
fear, somewhat misguided.
....what *really* happens.  There is one mother and
only one daughter in a cladogenic event.  The daughter species has at least
one synapomorphy that the mother species lacks (otherwise they would still
be the same species).
     The paraphyletic mother species persists,.....
Once again Ken, you are trapped by your own concepts. "Species" is a rank
applied to a taxon. Let's use some neutral terms to get at the underlying
reality (which we probably agree on). A lineage branch (what you and I would
agree to call a species) divides. The original species was recognized by
apomorphies but is inferred to have coherence because information, through
genes are passed from parent to offspring throughout the species. This is
the process of descent, and is what causes the lineage to have (to
paraphrase Simpson) its own unique evolutionary fate. This system of descent
is a natural phenomenon which distinguishes the grouping from other
groupings and lies at the heart of our concept of the reality of taxa, or
species. As I pointed out yesterday, this natural process of descent is
ended only when there are no more descendants - i.e. when the lineage goes
extinct. A natural system of classification recognizes real natural
phenomena such as these lineage systems. They originate when a novel descent
system arises (a new division between two parts of a previously coherent
descent system), and they end with extinction. To recognize, with a name,
only part of a descent system, to cut off some of the descendants, is to
impose an artificial, non-natural criterion, and it leads to an artifical
classification system.
 You say the mother persists as a "higher taxon",
No, I say the grouping of the mother AND the descendants persist as a
"higher taxon". That taxon originated when it took on its own unique
evolutionary fate. And it will persist until all descendants are dead. There
is absolutely NO difference between the descent relationships of individuals
in one daugher to the mother, or the other daugher to the mother. Even if
the original species had a million individuals, and all but two persist
unchanged, whereas the two aquire a radical apomorphy and go off to start a
new "species" on the other side of the mountain, the descent relationships
are the same, and unbroken from the mother taxon to the new individuals on
either side of the mountain. The lineage branch that started when the
maternal species originated persists. It is now a higher taxon. After the
division there are now two separate lineage branches. But BOTH are connected
in the exact same way to the previously coherent "mother". To say that one
should be identified with the mother, but not the other is to abandon the
notion of descent as your critierion for taxon recognition. The two new
groups on either side of the mountain remain part of the maternal (now
higher) taxon, and they both go off into the future with their own unique
evolutionary fate, and so they are recognized as two new species level taxa.
Perhaps I am wasting my time with long arguments when a simple obvious point
would suffice. A concept (paraphyly), which is explicitly a grouping that
excludes some descendants, is obviously artificial in a classification
system based on the principle of recognizing natural descent systems. It can
only be "real" in a system in which descent is not the crucial criterion. As
I pointed out in my first posting in this round, the basic issue that
divides us is whether or not you think scientific classification should
reflect the real history of taxic divergence or not. Clearly you don't.
I accept that the diversity of life is inherently structured by a history of
descent thorugh lineage branches that have diverged, and that only a
classification that reflects that, can claim to be natural. Cladistics is,
yours aint.

Tom DiBenedetto

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