Paraphyly and names
tdib at OCEANCONSERVANCY.ORG
Tue Jan 29 15:35:35 CST 2002
From: SKÁLA Zdenek
>Your statement is your statement, purposely designed to sound circular. My
>statement is that monophyletic taxa are best becaue they are based on
>synapomorphy, and synapomorphies are the preferred basis for classification
>because they represent character states considered at their true historical
>level of generality- and thus indicate complete groupings of species that
>share descent from a common ancestor.
It's puzzling. Here are you repeating your circularity even more explicitly
- you write:
"...monophyletic taxa are best because ... based on synapomorphy, and
preferred...because...indicate complete groupings of species...". Where I am
reading you wrong?
Interesting that you cut out the phrase after "because", and substituted a
later phrase that represents a consequence of the reason rather than the
reason itself. Are you making an effort to make it sound circular? Why not
simply consider the statement as written? If you wish to cut something, cut
out the phrase after "- and thus" - I agree that for the purpose of a strict
logical analysis, it is superfluous.
>Feathers are not an apomorphy of Aves,
>although they once were considered to be so. For a cladist this means
>that the character moves up a node or two,...
Well, your argument was that to have an apomorphy in two taxa of the same
rank is to indicate that this apomorphy evolved twice. My response is that
this necessarily occurs whenever you do not use some basal apomorphy for the
delimitation of a taxon (and, obviously, not all apomorphies can be used so
unless we have as many taxa as clades). Evidently this is not dependent on
which monophyly concept you prefer and hence fail to be a plausible argument
in this discussion.
I dont understand much of this at all. First of all, the decision to use
basal apomorphies to delimit taxa is intimately tied to the question of
which monophyly concept you prefer. Use apomorphies, and you end up with
mono(holo)phyletic taxa. Dont use apomorphies, and you allow for paraphyly.
Secondly, all apomorphies _are_ to be used so that we _do_ end up with as
many taxa as clades, That is the whole point. A recognized clade is a taxon
- that is why we call it cladistics. Thirdly, as to your response to my
argument, I agree. It necessarily occurs that you will present results that
confuse the issue of character evolution unless you define taxa with basal
apomorphies. Given that I do not wish to obscure the history of characters,
I take this as a reason to use apomorphies - and hence to subscribe to a
"strict" view of monophyly.
Are we all clear on this now?
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