[Taxacom] burn out (was: classification of Class Rosopsida)
Richard.Zander at mobot.org
Wed Apr 22 09:23:15 CDT 2009
I'll reply to the comments of Alexander Schmidt-Lebuhn dissected thus;
ASL: The ancestors as individuals are dead anyway. Quite logically, extant
reptiles are not the ancestors of birds. Extant apes are not the ancestors
of humans. Etc.
ASL: As a group, and that is what we are interested in, the
ancestors did not survive as a paraphyletic (and completely static,
unevolving) taxon, while somehow a new group appeared out of the blue of
which they are nevertheless the ancestors.
Reply: Yes they did. The paraphyletic taxon is a classification item that describes the extant exemplars, and because these branch off a molecular tree sequentially, then the inference is that a species or population or individual of that taxon existed as an ancestor somewhere along the line, probably basally, and that ancestor is the ancestor of all lineages terminal to the paraphyletic group even if they are unique in major evolutionary but parsimoniously uninformative traits..
ASL: Instead, the ancestors who were
reptiles survived as both reptiles and birds, and the ancestors who were
apes survived as both apes and humans. Seen this way, it is the only
logical consequence to place birds in the group reptiles and humans in the
group apes. Seen this way, monophyly describes best what happened in the
course of evolution.
Reply "Seen this way...." The way this is seen is a tree. No diagnosable ancestors, maybe just a node. The logic is circular because you are describing a branching tree as evolution. Evolution is descent with modification of something into another thing. Cladistics by itself does not and cannot deal with the something.
ASL: It is really important that people think this through.
evolution with paraphyletic groups actually leads to a lot of
misconceptions especially for laypersons, starting with "we are descended
from monkeys" (no: we ARE monkeys)
Reply: There is no force in nature called holophyly (justifying naming groups to include all descendants). The name of a phylogenetically monophyletic group is generated in an artificial classification based only on sister-group information, and ignores other information that may be available on the evolution of the lineage. A tree is the result of a method investigating evolutionary sister-group relationships and is only that. It is not evolution itself. "Monkeys"? I don't think it is yet clear what we are descended from in the hominiod line (unless it is a node). Maybe we are all descended from nodes. Of course if we could identify a paraphyletic group somewhere in the hominoid line, then we might have an idea of what at least one of the ancestors of humans might look like : )
ASL: and ending with "is it not amazing that
there are more species of genus X than of genus Y?" (no: you can only
compare sister groups or maybe clades of exactly the same age, but genus
is simply an arbitrarily assigned rank).
Reply: No, no. If judgement is involved and genus represents either an important sister lineage or an evolutionarily unique autophyletic group, then genus is not an arbitrarily assigned rank. Even in the realm of automatic classification and judgment-free taxonomy there are no arbitrary ranks, since there is a reason, no matter how it is derived, for the assignment.
Richard H. Zander
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166 U.S.A.
richard.zander at mobot.org
From: taxacom-bounces at mailman.nhm.ku.edu on behalf of Alexander.Schmidt-Lebuhn at biologie.uni-goettingen.de
Sent: Wed 4/22/2009 5:02 AM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] burn out (was: classification of Class Rosopsida)
Richard Zander wrote:
> The reason some of us insist on paraphyletic taxa is because evolution,
> if defined as descent with modification, is described only by
> paraphyletic-autophyletic series, where the paraphyletic taxon is the
> descendee (ancestor), and the autophyletic taxon is the descender.
already wrote something about this off-list, but once again:
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