Paraphyly and names
tdib at OCEANCONSERVANCY.ORG
Wed Jan 30 10:24:58 CST 2002
Skála Zdenek wrote:
Either we will name all clades as Thomas DiBenedetto apparently proposes or
we will select only some of them as named taxa .AND
Denis Brothers wrote:
... I've never managed to get a good
explanation as to how one then decides which should be named and which
not. I suspect that this is as subjective as how eclecticists decide on
the same issue (basically, "where are the 'significant' gaps?").
I did not ever propose to name all taxa. I specifically said that not all
taxa need be named - very much in line with what Denis heard at the Hennig
meeting. Denis's charge that the decision as to which taxa to name is
"subjective" or somehow similar to eclectic practice strikes me as very
strange. I am really at a loss to understand why this seems to be such a
difficult concept. Maybe I can try to lay this out very simply.
1- Life has evolved in a system of divergent lineages
2- As scientists who wish to understand the history of life, we try to
discover these lineages
3- When we discover a lineage, that is a scientific result, and this result
is communicated to the rest of the scientific community
4- Given the large number of such units of knowledge that are avilable for
discovery, we often choose to communicate our discoveries by simply
presenting a graphical diagram on which these results are plotted (a
5- A node on a cladogram points to a discovered clade, a taxon
6- If a particular taxon becomes the subject of discussion in the scientific
community, it becomes far more useful to refer to the taxon with a name,
rather than having to drag out the cladogram and point to the node
7- Thus the decision to name a taxon is a purely heuristic decision, but it
is in no way an example of a subjective scientific methodology, for naming a
taxon or not naming a taxon does not change anything about the scientific
result. The result is there in the cladogram - putting a name on it changes
nothing. It merely represents a substitution of a single word (e.g.
"Cladidae"), for the phrase "fifth node down from the node we refer to as
8- "Important" nodes, or what Denis refers to as "significant gaps", are no
different from anyother node. Their "importance" means nothing more than
that scientists find them to be interesting to discuss, for whatever reason.
Therefore they obviously fit into that group of nodes to which names are
applied, so that communication is facilitated. This is no different than
some other insignificant node, where there is not much of a "gap", but
which, for some reason, has become a topic of discussion - it too will have
a name so that that discussion can proceed easily.
9- For a general synoptic discussion of life's diversity, one might wish to
make frequent reference to particular well-known large taxa, such as
Mammalia, or Arthropoda. Fine - so long as they are monophyletic groups -
i.e. clades, one can do so - once again, for ease of comunication.
What is the problem folks?
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