Paraphyly: the continuing saga

[Curtis Clark]

Two points:

At 07:15 AM 1/15/02, Byron J. Adams wrote:
>I'm not yet convinced that there are *real* instances where evolution
>produced paraphyletic groups, or at least those that can be recovered
>objectively.  And I hesitate to enthusiastically endorse those that aren't.

I may not know mammals, but I know speciation. In annual plants for sure,
possibly in some perennial plants, and I have heard in annual insects, new
variant populations arise in modest frequency on the periphery of the range
of existing species. Most of these evidently come to nothing, but now and
again one will successfully reorganize its genome and expand its range
outside the range of the "parent" species. While I appreciate the
theoretical views of Byron and Tom, it seems extraordinarily likely that
the evolutionary fate of the "parent" species is affected no more by the
successful new species than by the failed ones.

This in no way can be a support for paraphyletic higher taxa, except to
people who believe that evolution works exactly the same at all levels. It
would be nice if species "behaved" and were always monophyletic, but in
fact the interest and importance of species is that they are the interface
between tokogenetic relationships and phylogenetic relationships.

At 08:51 AM 1/15/02, Richard Pyle wrote:
>Linnaeus
>probably had NO CLUE about the concept of natural descent.

In fact, Linnaeus (iirc) was explicit in his belief that all species had
been separately created. His entire research program in systematics was an
attempt to distinguish "essential variation" (between the originally
created species) from "accidental variation" (within a single species), and
thus determine what *should* be the central question for any creationist
biologist: what were the original species? I tell my students than in my
view, Linnaeus was among the last truly scientific creationists.

But if all species were created by God, He was not limited to a hierarchy.
Since Man was created in His image, and people like hierarchies, that might
be a reflection of God's nature, but in fact Linnaeus was never quite
comfortable with arranging taxa above the level of genus. Systema Naturae
and Species Plantarum were both explicitly artificial in their arrangement.
It remained for Linnaeus's successors to create the "Linnaean Hierarchy"
that we enjoy today. I always find it amusing that Linnaeus gets the rap
for something he didn't do (the formal hierarchy), and the thing he *did*
do that he is most known for (binomial nomenclature) wasn't his original
intent.

I point out to my students that chemists, for example, had to abandon the
early hierarchic classification of elements because it didn't work, and
Mendeleev, though the periodic table, provided a different and appropriate
classificatory framework. But because the natural pattern of descent with
modification is overwhelmingly hierarchic, biologists still use a system
that is two and a half centuries old, because for the most part it still
works passably well.


--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Biological Sciences Department             Voice: (909) 869-4062
California State Polytechnic University      FAX: (909) 869-4078
Pomona CA 91768-4032  USA                  jcclark at csupomona.edu