holophyly (was: Ashlock was treated badly)
skala at INCOMA.CZ
Tue Jan 8 08:48:34 CST 2002
From: Curtis Clark
>Paraphyletic groups have a minimum of two origins: the origin of the
>inclusive clade and the origin(s) of the clades excluded from it.
Not exactly; we are discussing the oriented (rooted) cladogram I
believe, so each taxon has one origin only (you can speak of the "end"
of taxon if you want, indeed).
>They *are* incomplete. Their incompleteness is in every sense but the
>trivial a result of ad hoc human intervention, so they are unnatural.
The paraphyletic taxa are natural/unnatural in the same sense as are the
holophyletic: human always need to (1) either specify the limit(s) of
them (well, one for holophyletic, two for paraphyletic ones) (2) or
accept that each splitting on the cladogram will constitute (real, not
only possible!) taxa, which, I guess, is hardly used option.
>(By "trivial", I mean that *every* paraphyletic group is natural in the
>sense that it can be described by boolean operations on clades, but
>our classifications don't admit to a multitude of overlapping groups,
>choice of a *specific* paraphyletic group and the rejection of others
>overlap it is artificial.)
There can exist various sets of holophyletic taxa over a cladogram as
well as various sets of paraphyletic taxa. Why do you think that a
choice among different holophyletic solutions is less artificial than a
choice among the paraphyletic solutions? Yes, different para solutions
can overlap, but the *final* solutions of course does not include
overlaps, so where is the problem?
skala at incoma.cz
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