cladism (final words)

[Tom DiBenedetto]

Ken Kinman wrote:

>  I never said clades are
>arbritrary or not real.  What is arbitrary about cladism is the refusal to
>recognize that paraphyly is ALSO real, as is cladism's insistence that
>paraphyletic groups are unnatural.

But they are unnatural, and it is not arbitrary to say so. Given an
evolutionary perspective on the history of life, we recognize that
biological diversity is the result of a process of character
transformation within a context of lineage branching. If you accept
that factual nature of evolution, I dont see how you can deny the
reality of monophyletic (holophyletic to you, I guess) historical
groups. Paraphyletic groups are simply partial monophyletic groups;
they do not encompass the totality of the reality that we are trying to
describe (the lineages of life's history).
We accept that our solar system is real, and we accept the reality of
Mercury, Venus, Earth, Mars etc. But a conception of a solar system
with all of the planets and asteroids etc. but without including Earth
would be considered artificial and unreal. It may be a heuristic notion
for some people, but I dont think that anyone would consider it real,
in the sense of being an accurate approximation of reality. I do not
consider the acceptance of the concept of the (complete) solar system
as being real, to be an arbitrary decision. It is an empirical finding,
as are monophyletic groups. Paraphyletic groups are not.

>It is arbitrary to assume that the
>"mother" species becomes extinct at the moment of cladogenesis, and
>misleading to then argue that we should never recognize paraphyletic groups.

I dont know of anyone who assumes that ancestral species go extinct.
Hennig toyed with that idea, but I havent met anyone who accepts it.