Compromise in the air? (was: Boolean games)

[Curtis Clark]

on 2005-03-11 19:17 Ken Kinman wrote:
> Curtis, You're right, I should be thankful some strict cladists (like
> yourself) have finally conceded that paraphyletic groups are natural.

Shit is natural, too, but I don't want it in my kitchen.

As I've said before, paraphyletic formal taxa don't play well with
others. Choosing the dividing line between a paraphyletic taxon and an
included clade is necessarily arbitrary ("anagenesis" notwithstanding).
Certainly, a lot of decisions of which clades to name are also
arbitrary. But because clades are nested, they can coexist (in a
rankless system such as Phylocode, they can coexist *easily*, but that's
another issue). Paraphyletic groups don't have that freedom; for
example, two different views of where reptiles stop and birds begin
cannot coexist. And so recognition of paraphyletic groups enforces a
sort of hegemony. The Kinman System notwithstanding, basic textbooks
that talk about Class Reptilia cannot simultaneously deal with
Archosauria as a formal taxon *at any rank*.

> And this may sound very strange coming from someone who has turned
> strongly against PhyloCode, BUT HERE GOES.  I would probably support
> a PhyloCode if it included provisions for occasional exceptions where
> major formal paraphyletic taxa (explicitly marked) would be allowed
> in order to foster stability and renewed harmony in the taxonomic
> community.  Especially exceptions such as Bryophyta and Pteridophyta
> in botany, Sarcopterygii and Amphibia in vertebrates, Prokaryota in
> microbiology, and invertebrate phylogeny is still too poorly known to
> determine what exceptions would be most important there.

Unfortunately, this only makes the problem worse. Because Phylocode is
unranked (and I agree with Norm Platnick that this is more of a
shortcoming than an advantage), even a single paraphyletic group
destroys the system (or, more specifically, destroys any
non-intersecting properties it has), because it has the potential to
intersect and thus preclude any other taxon (remember than in Phylocode
there is a fluidity in which today's "A is a subclade of B" can be
tomorrow's "B is a subclade of "A" when new evidence is presented).

Bryophyta and Pteridophyta are clades; including the liverworts in the
former and the lycophytes in the latter was always a mistake, and when a
solid traditional morphologist like Ernie Gifford became aware of the
lycophyte mistake, he corrected it. Systematics has advanced by
systematists correcting the mistakes of the past based on new evidence.
It's one thing to champion the usefulness of paraphyletic groups; it's
another thing to champion the usefulness of outmoded, unsupported
conclusions.

> And once a few PhyloCodists begin to compromise on this,

I hope I've made it clear that they can't, even if they wanted to. For a
system to be composed of groups that are simultaneously unranked and
non-intersecting, they have to be nested. I think another failing of
Phylocode is the insistence on non-intersecting groups (species of
hybrid origin are members of two different lineages, for example), but
that's another issue.

--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
Professor, Biological Sciences                   +1 909 869 4062