[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Cladists versus non-cladists



        I have tried very not to keep this posting off the front lines of
the clade wars...

E. Summer wrote (quoting Stan Friesen):
>Would you (or someone) be kind enough to give just one example of the
>identical nomenclature?
        Pseudosuchia in phylogenetic taxonomy (which is not to be confused
with "cladistics", as I think Stan pointed out) means all animals more
closely related to crocodiles than to birds (roughly). This includes
aetosaurs, rauisuchians, phytosaurs, and crocodilians. This is a
monophyletic taxon, ie it consists of an ancestral population and all of its
descendants, a clade.
        Pseudosuchia in Linean taxonomy, consists of some of the above named
groups, but does not include the crocodilians, and is not monophyletic.
        (I left out poposaurs. Only so many hours in the day... :)

>In the following which I've quoted so you know I read it, [...]
        That's kind of funny.  :)

Stan wrote:
>> This is not, in fact, the case.  Phylogenetic classification (that is the
>> "cladistic" sort) serves to provide a terminology for discussing
>> phylogenies, and also a simple textual way to represent phylogenies.  Taxa
>> based on cladistic principles proved a way to uniquely and unambiguously
>> speak of relationships and lineages.
        I should point out that, although Stan provides an excellent (IMHO)
account of the fundamental differences between PT and neo-Linnean
("Evolutionary") taxonomy, he is simplifying just a bit. PT emphasizes that
phylogeny must be the central feature of taxonomy, but it is *not* merely
for discussing phylogeny. It uses phylogeny as a convient (and appropriate,
so the idea goes) way of systematizing organisms, and as a proper
evolutionary context for discussing their adaptations and diversity as well.

E. Summer said he doesn't understand this paragraph of Stan's:
>> Evolutionary taxonomy, on the other hand, provides a way to summarize and
>> index general information about organisms.  It seeks to optimize both
>> overall information content and convenience of access (this last is partly
>> accomplished by keeping the number of names and categories to be remembered
>> limited).
        What he means is, Evolutionary Taxonomy includes a great deal of
information about "grade", similarity in morphology within a group. Thus, if
A is more closely related to B than it is to C, it may still be grouped with
C is it looks more like C than it does like B. This may be due to
convergence, reversal, etc. (collectively homoplaisy), or simply due to a
lack of subjectively significant morphological similarity linking A and B.
ET workers judge this to be more useful than phylogenetic information.
        By convenience of access, Stan means that, since in ET animals are
pidgeonholed into groups based on diagnostic characters, one can easily and
quickly find what group the animal belongs to. He also notes elsewhere that
the hierarchical nature of a Linnean structure, combined with the broad
equivalence of (subjective) morphological difference in a Linnean tree makes
it easier to rapidly catagorize organisms. He notes that these features make
ET a better information retrieval structure.
        I should point out that the last sentence quoted above is a bit
unfair. While I can imagine Stan can quote some sort of figures to say that
cladists use more names, he seems to be proceeding from the common
misconception that every phylogenetic divergence must be named. I believe it
is more fair to say that ET is easier to use in part because names mean
something more similar to their pre-1980s meanings in evolutionary
taxonomies, which certainly facilitates access to the literature.
----------------------------------------------------------------------------
      Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock TX 79409
      "The cost of living hasn't affected its popularity." - Unknown