Paraphyly: A "Real" Saga (thought experiment)
tdib at OCEANCONSERVANCY.ORG
Thu Jan 17 11:23:51 CST 2002
From: Ken Kinman
While *any* cut on the tree of life is going to be an
arbitrary human decision, these two particular cuts appear to minimize the
degree of arbitrariness.
Therefore, although even this particular delimitation of Amphibia
inevitably has some degree of arbitrariness, it is still a "REAL" section of
the tree life.
I am tempted to agree with you that "any" cut on the tree of life is
arbitrary (if I fully understand what you mean by that). Which is why I
support a system that _does not make any cuts_ in the natural processes of
descent. All of life is a taxon. Subtaxa are recognized to originate when
the flow of descent becomes divergent. This is a real-world natural event
that is not arbitrary. These new taxa are add-ons, on top of the
pre-existing "higher" taxa. That is what I mean when I say humans are
animals, they continue to be part of the taxon Animalia, while they also are
part of all the other taxa that are older and younger than Animalia and that
our ancestors were part of. Taxa should never be cut - that is why they do
not end until they naturally end in the real world- when they go extinct. An
end to a taxon through extinction is a real-world natural event, not
arbitrary. And these two principles - taxa origination at divergence, taxa
demise at extinction, are the two principles that underlie cladistic
classification - which is why it is NOT arbitrary, and IS natural.
I totally agree that your cutting to form a Class Amphibia is arbitrary. I
still dont see how you can claim this grouping is REAL, except for the
trivial point that it contains real organisms and real species, and is not a
random patchwork of distantly related groups. Fine - it has slightly more
historical reason than a group of "flying things". But still it represents
the imposition of human-defined limits to a natural process, whereas in
cladistics we accept the process - descent- on its own terms, and recognize
only real descent chains in their entirety.
Therefore, I have never understood the notion that species are real,
but higher taxa (bigger pieces of the tree of life) are not real (this makes
no sense to me at all).
Hey, I totally agree with you Ken!!! (ever think you would here me say
And FINALLY, and most importantly. The tree of life has an origin, so
any cutting of the tree of life above the origin automatically creates a
real paraphyletic group. Therefore, although it can certainly be
cladistically argued that we should *minimize* formal paraphyly (given the
incredible lack of data from extinction and scant fossil preservation), I
believe that it is logically impossible to justify the complete elimination
of all formal paraphyletic groups.
Just put away your knives Ken, and accept life as it is.
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