Platnick's view of Phylocode
Pierre.Deleporte at UNIV-RENNES1.FR
Tue Mar 12 16:08:27 CST 2002
At 09:21 12/03/2002 +0100, Zdenek Skala wrote:
>All questions you are asking were raised and answered in a recent thread
>on paraphyly. You need not accept the logic of "eclecticists" but you will
>learn more by reading the mail archives than by asking the same questions
Possibly, so let's apply this to everybody, for instance ;-) :
>From: Thomas Pape [mailto:thomas.pape at NRM.SE]
> >Why cannot a 'minor gap' be just as scientifically exciting as a 'major
>Z. Skala: Minor gaps can receive lower ranking in the system while the
>major gaps receive higher ranking - quite similarly to the hierarchy of
>small/large clade hierarchy in the holophyletic system.
It seemed to me that a common agreement had been reached concerning the
fact that a "significant" or "relevant" gap or novelty could be either
quantitative or qualitative and depend one one's interest. We can avoid
chewing this same question again and again.
There seemed also to be large agreement that the notion of "significant
gaps" was involved in eclectic as well as in (incomplete) cladistic naming.
I think that a real lasting debate concerns the possible "added
arbitrariness" linked to the definition of paraphyletic groups, in addition
to monophyletic ones (complete clades), all things beeing equal concerning
Or in other words, possibly viewing the delineation of paraphyletic groups
as requiring additional criteria relatively to the unique definition of
It seems to me that deciding when a paraphyletic group "should stop" is an
additional decision relatively to the definition of clades. And an
additional decision logically requires additional criteria.
More precisely: we must decide when does a "gap" will be sufficient to
terminate a paraphyletic taxon worth being named, and not only to begin a
monophyletic one worth being named.
A side (but in my view related) question concerns the hierarchy of groups
in an eclectic classification:
"vertebrates" include birds
"reptiles" exclude birds
Thus not only the current eclecticist must decide "when reptiles stop", but
he has also to decide that this significant gap is not significant when
considering "vertebrates" as a whole. Maybe feathers are getting more and
more important the closer you look at them when climbing the tree of
life... But I can't help viewing this as logically requiring additional
criteria and general rules for combing them.
So, isn't there some inconsistency in the way eclecticists apply their own
criteria? Why shouldn't vertebrates exclude birds because of the
significant gap called "feathers"?
Birds are vertebrates are reptiles seems more coherent to me, and I think
that this is because one applies one criterion throughout (monophyly,
indicated by synapomorphy). Possibly being "more natural" is another point.
If internal coherence is an issue at all... For me it seems at least
relevant to the possibility of reaching common agreement between scientists.
Also relevant to our recent debates on this list is the point by Platnick
about considering species (diagnosable) as different from clades at higher
levels (obligatorily defined by synapomorphies), and the development of the
very "budding species" example we recently discussed on this list. Platnick
suggests that, to be useful to biologists interested in evolutionary
processes, classification should not discard some possible modes of
speciation, and that a "species (population?) remaining the same" with a
side budding is worth being indentified as such. Isn't this a form of
eclecticism after all? But it does not interfere with higher levels oin the
classification, and concerns only the terminal units.
For Ken: I'd like that you label paraphyletic groups as such in your system
(rather than labeeling only "excluded monophyletic groups"). The fact that
you use a conventional "family" terminal for naming both paraphyletic and
monophyletic groups without warning seems potentially confusing, don't you
As for Kinman codes and avoiding a "cornucopia of ranks", Platnick
(referring to Papavero et al. 2001) suggests a very similar system:
signalling ranks "+1", +2", or "-1", "-2" above or under a given rank.
best and cheers
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