holophyly (was: Ashlock was treated badly)
skala at INCOMA.CZ
Tue Jan 8 17:09:25 CST 2002
From: Curtis Clark
>>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).
>A paraphyletic taxon "ends" when an excluded clade originates. If
>an birds had never evolved, reptiles would be monophyletic.
I agree; it was only against the notion of "two origins" of a para taxa.
>>The paraphyletic taxa are natural/unnatural in the same sense as are
>>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 branching on the cladogram will constitute (real, not
>>only possible!) taxa, which, I guess, is hardly used option.
>The clade of all flowering plants (if in fact they originated from a
>species) exists without human intervention--in fact, it had existed for
>over 100 million years before there were any humans at all.
Well, clades, lineages, individuals etc. do exist (at least in some
sense) as well as sets of descendants of a given species do exist;
however we are speaking about taxa or - even better - of a *system* of
My main point is that not each clade (and not each set of descendants of
given ancestor) form taxon - in splitting the cladogram into system of
taxa we simply *must* make arbitrary decisions. The paraphyletic and
holophyletic taxa are quite comparable as concerns their arbitrariness.
>... Rather, paraphyletic
>groups and clades have a different biological meaning. A classification
>overlapping paraphyletic groups could be as "natural" as one of clades,
>perhaps, but mixing them is like selling apples and claiming they are
Perhaps here is the key: why do you think so? Given a cladogram is
already constructed, we need to split it into taxa. Why should be
apomorphic character states considered different/better set of
descriptors than their respective plesiomorphic states for this specific
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