Paraphyly=mistakes? (There's the rub)
dyanega at POP.UCR.EDU
Mon Jan 14 11:28:08 CST 2002
I rarely diasgree with Richard Pyle, but he wrote:
>No, not really. The "Definition" of a Phylocode name remains constant: it
>is, and always will be, the most recent common ancestor shared by at least
>two different species (or specimens, or nodes, depending on how the name was
>originally defined). In other words, the "definition" remains constant over
>time (even though the complete scope of its contents may change over time as
>phylogenetic interpretations change). When phylogenies are eventually
>solidified, the names (by their definitions) also solidify.
>In contrast, Linnaean names are anchored to only a single point (the
>holotype of the type species, etc...). Thus, they can slide up and down the
>phylogenetic lineage, superceding or resurrecting other names of like-ranked
>taxa, at the whim of any splitter or lumper looking to add a publication to
>his or her CV -- all without a single branch change in the hypothesized
>phylogeny. Their true "definitions" (taxonomic scope) are subjective, even
>with a "known" phylogeny.
>That is the key distinction between a name defined by a single point, versus
>a name defined by more than one point. The exact position of Phylocode names
>may move about as different phylogenetic hypotheses are asserted, but they
>will always represent a "real" node -- independently of our ability to
>accurately map where that node fits in the larger evolutionary context.
>Single-point Linnaean names, on the other hand, aren't defined in any
>evolutionary context, and thus are subject to change both with changes in
>the intrpreted phylogeny, *and* in the absense of phylogenetic
>I hope that clears up the point I was trying to make, but I fear I've only
>made things more confusing....
We've been here before, and I've said this before: Which do you
prefer - a system in which the definitions of names can change when
the hypotheses of relationships are altered, or a system in which the
definitions never change, but require creation of new names when the
hypotheses of relationships are altered?
I'll give a hypothetical example: Rhipicerid beetles are presently
placed in the superfamily Dascilloidea. Suppose someone then
discovers that they are actually a branch within the family
Artematopodidae, in the superfamily Elateroidea. Under the present
system, this is handled simply by redefining what we mean by
Dascilloidea, Elateroidea, Rhipiceridae, and Artematopodidae. Things
like this do happen frequently in insects, where taxa jump from one
superfamily to another. It's a MAJOR shift cladistically, but causes
very few problems. Under the Phylocode approach, however, the
definitions and constituencies of those taxa are FIXED, which creates
a nightmare when branches jump that far. For example, since
"Dascilloidea" would be defined as "the most recent common ancestor
of Dascillidae, Karumiidae, and Rhipiceridae" we are faced with a
substantial dilemma: we must make a new name for the new resulting
"quasi-Dascilloidea" (now Dascillidae + Karumiidae), and the name
"Dascilloidea" (if one decides to retain it) jumps up the cladogram
to occupy a new position, since the most recent common ancestor is
now a lot farther back than had been originally supposed. [I'll note
that my recollection of the Phylocode principles is that each name's
definition explicitly lists all subtending names, and any change
therein necessitates the creation of a new name, so "Dascilloidea"
would have to be scrapped - you imply otherwise, so I'll go with your
concept for the moment] The name "Elateroidea" might have to be
trashed, depending on whether the inclusion of Rhipiceridae violates
its definition (how could it not?), and similarly for
"Artematopodidae". Confusing, huh?
Exactly in what way do you see this as an improvement in stability?
To me, it's six of one, half dozen of the other: there are
practically the same number of changes necessitated in BOTH systems,
they're just different *kinds* of changes. For my money, I think it's
easier to use old names and keep track of changes in definitions.
Otherwise, the frequent occurrence of rearrangements such as the
above will ultimately and *inevitably* create a "ratchet" effect
where all the old, familiar names fall by the wayside, one by one, as
their original definitions are violated and they need to be replaced.
Maybe this wouldn't happen to fish, mammals, etc., but it sure as
heck would happen with insects.
Doug Yanega Dept. of Entomology Entomology Research Museum
Univ. of California - Riverside, Riverside, CA 92521
phone: (909) 787-4315 (standard disclaimer: opinions are mine, not UCR's)
"There are some enterprises in which a careful disorderliness
is the true method" - Herman Melville, Moby Dick, Chap. 82
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