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Per Ahlberg wrote:
> Well, unless you believe in multiple parallel origins of life, followed by
> either 1) entirely linear, non-branching, ancestor-descendant sequences
> down to the present day, or; 2) a reticulate mode of evolution were
> new species always arise from hybridisation, there will be SOME clades out
> there somewhere!
Yes, clades exist, as defined by branching points, but the questions are:
(1) Are they the *only* 'natural' taxonomic units, as cladists have
insisted for decades?
(2) Are they even the most meaningful units for the various purposes we
want to use them for?
I would answer 'no' to both questions. Paraphyletic taxa may possess a
greater biological coherence (morphologically, genetically, everything)
than the strictly monophyletic taxa required by cladist philosophy. They
may thus represent more meaningful categories in ecological,
biogeographical, etc. studies, in no way less 'natural' than the clades.
The reason why cladists shun them seems to be that they cannot be easily
defined by reference to a single criterion, but that doesn't make them
less 'natural'. If ease of definition were the only criterion for
'naturalness', then life itself is not 'natural'. (Then again, maybe it
isn't!!) If we want to study how various kinds of organisms behave in
nature it seems misdirected to use a strict monophyly criterion to define
these kinds, forcing us to utter such howlers as 'The first eukaryote was
a prokaryote', 'Dinosaurs are alive and well and going "Chirp!" in my
garden', 'Reptiles don't exist', or 'We are all fish'.
> Merry Christmas and a Happy New Year to you all!
I second that!
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Stefan Bengtson
Institute of Earth Sciences
(Historical Geology & Palaeontology)
Norbyvagen 22
S-752 36 Uppsala
Sweden
tel. +46-18 18 27 62 (work)
+46-18 54 99 06 (home)
+46-18 18 27 49 (fax)
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