[Taxacom] save Prokaryota!!! (was: Knocking Hennig off his pedestal

John Grehan calabar.john at gmail.com
Mon Jan 27 05:39:43 CST 2014


Ken states "classifications which include paraphyletic taxa are more
informative because they include both plesiomorphic and apomorphic
character information (not just apomorphic, which thus renders
"cladifications" less informative, less useful, and often less stable)."

Of course a non-paraphyletic taxa do not 'contain' information on
plesiomorphic features as they are defined on apomorphic characters.
However, the phylogeny analysis will provide that information. Similarly, a
paraphyletic taxon does not contain information on apomorphic features
present in some members and the excluded taxa unless one goes back to the
analysis.

To my understanding, paraphyletic 'taxa' are not taxa at all. They may
constitute a grouping of taxa, but as the group does not represent an
inclusive representation of all descendants of a unique common ancestor, it
is not a taxon in the sense of a complete genealogical assemblage. I might
refer to 'great apes', for example, but that is not a taxon in this sense
as the great apes may only be defined as such by leaving out the hominids.
If a paraphyletic group such as 'great apes' is more 'useful' it is
interesting that this appears not to have been adopted by primate
phylogeneticists who might use the descriptive term 'great ape' but do not
treat it as a taxon, but rather divide the great apes into one or other
monophyletic groups (either Orang, Gorilla, chimp/human or African apes,
orang/human).

John Grehan


On Sun, Jan 26, 2014 at 8:44 PM, Ken Kinman <kinman at hotmail.com> wrote:

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> Hi Patrick,
>      Seems to me what is most important here is to emphasize that
> paraphyletic taxa are based on homologous character states as well (not
> those which are homoplastic/convergent. which we agree make polyphyletic
> taxa unnatural).  Furthermore, classifications which include paraphyletic
> taxa are more informative because they include both plesiomorphic and
> apomorphic character information (not just apomorphic, which thus renders
> "cladifications" less informative, less useful, and often less stable).
>        "Cladifications" are also often very asymmetric and thus unbalanced
> (which can add to instability), making them even harder to remember (and
> often harder for the general user to even understand).  This has resulted
> in an explosion of new clade names (many of which eventually turn out to be
> invalid) as well as a proliferation of categories that is so extreme that
> calls for the elimination of Linnaean categories naturally followed (but
> one shouldn't abuse a useful tool like that and then complain when problems
> arise).
>        And it seems to me that Prokaryota (a paraphyletic group of
> species) is just as valid and important as Eukaryota (a holophyletic group
> of species).  Add the two together and you get all cellular life on Earth.
>  The symplesiomorphies shared by Prokaryota and Eukaryota are extremely
> important, while a cladification of cellular life is unfortunately overly
> fixated on just a single synapomorphic character state for Eukaryota
> (possession of a nucleus).  In fact, cladifications are often regarded as
> just one character classifications (and that is definitely not a good thing
> to rely on).
>      And FINALLY, and to my mind MOST IMPORTANTLY, we can all actually in
> an important way "have our cake and eat it too", by simply adding my
> {{place-markers}} within a paraphyletic "mother" group showing the
> cladistic placement of the removed "daughter" exgroup.  For example, you
> simply place a {{Eukaryota}} place-marker within the Prokaryota
> classification showing its relationship to Archaebacteria.  That alone
> would invalidate many of the excuses that are made for not using
> paraphyletic taxa and bashing them as being bad (which is only true for the
> really BAD paraphyletic taxa, not for ALL paraphyletic taxa).  Again I
> implore strict cladists, don't throw the baby out with the bath water!!!
>         ----------------Ken Kinman
>
> -----------------------------------------------------------------------------------------------------
> > Date: Sat, 25 Jan 2014 22:51:08 -0700
> > From: paalexan at polyploid.net
> > To: taxacom at mailman.nhm.ku.edu
> > Subject: Re: [Taxacom] Knocking Hennig off his pedestal
> >
> > Or, phrased in a manner that seems more straightforward to me:
> >
> > Polyphyletic groups are based on homoplastic character states. Both
> > monophyletic and paraphyletic groups are based homologous character
> > states. For monophyletic groups the homologous character states are
> > apomorphic, while for paraphyletic groups they are plesiomorphic.
> >
> > However, this is just shoehorning phylogenetic terms into typology. It
> > assumes that you start with an ahistorical, similarity-based
> > classification and then examine how that classification maps onto
> > descent. A grouping of species is, on its own, only monophyletic or not.
> > Paraphyly and polyphyly are not characteristics of groups of species,
> > they are characteristics of a typological classification of those
> > species. They are only distinguishable if you accept a priori that
> > typology is the appropriate approach to defining groups of
> > species--which, of course, is diametrically opposed to the goals and
> > concepts of phylogenetic classification, which defines groups of species
> > by descent. From the viewpoint of phylogenetic classification, they are
> > equally bad because they are indistinguishable.
> >
> > Patrick
> >
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