[Taxacom] Paraphyletic groups as natural units of biological classification

[John Grehan]

Curits said



“Let's face it, a large proportion of the systematics/taxonomic community
clings to monophyly like a baby to its mother's breast! It is so ingrained
that it is probably impossible to shift.”

Hmm. Maybe we could just as equally turn that around to say ““Let's face
it, a large [large, small, I don’t know] proportion of the
systematics/taxonomic community clings to paraphyly like a baby to its
mother's breast! It is so ingrained that it is probably impossible to
shift.”


I say this to point out the absurdity of just labeling the ‘other side’ as
somehow irrational. Everyone is in the same boat when it comes to science.


If stability is the goal then it may be relatively easy to achieve. I can,
for example, designate the group of ‘all things that have chlorophyll. Of
course for any definition there will always be something to argue about.


What is the objective criterion for recognizing that there are “too many
monophyletic groups”



John Grehan

On Fri, Sep 26, 2014 at 6:31 PM, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
wrote:

> Ken (and list):
> Let's face it, a large proportion of the systematics/taxonomic community
> clings to monophyly like a baby to its mother's breast! It is so ingrained
> that it is probably impossible to shift. As with everything, the idea of a
> strictly monophyletic classification has its pros and cons. The main cons
> seem to be (1) instability of classification, resulting from the fact that
> determining monophyletic groups is evidence based science, subject both to
> changes resulting from additional data, and from subjective differences in
> the evaluation of evidence; and (2) one tends to be left with a
> paraphyletic residue which is just too hard to crack. There are only two
> options for forcing these residues to be monophyletic. Either (1) just
> recognise the wider monophyletic group and don't recognise any of the
> included monophyletic groups (e.g. recognise reptiles, but not birds); or
> (2) split up the residue into trivially monophyletic groups (maybe down to
> single species).
>  The problem with (1) is obvious. The problem with (2) is that you end up
> with far too many monotypic higher groups which don't really differ
> diagnostically from each other except in as much as the species can be
> distinguished. In my experience, scientists in our broad area are not so
> good at weighing up pros and cons and coming to a sensible and rational
> decision about what to do. They just cling to ideals ...
> Stephen
>
> --------------------------------------------
> On Fri, 26/9/14, Kenneth Kinman <kinman at hotmail.com> wrote:
>
>  Subject: [Taxacom] Paraphyletic groups as natural units of biological
> classification
>  To: "taxacom at mailman.nhm.ku.edu" <taxacom at mailman.nhm.ku.edu>
>  Received: Friday, 26 September, 2014, 12:52 PM
>
>
>
>
>  Dear All,
>             I was just
>  rereading a 2010 paper by Horandl and Stuessy (published in
>  the journal Taxon).  It should be required reading in
>  any systematics course.  Below is the abstract.
>
>      --------------------Ken
>
>
>
>
>
>  Hörandl, E. & Stuessy, T.F.  2010.
>  Paraphyletic groups as natural units ofbiological
>  classification.  Taxon 59: 1641-1653.
>
>  ABSTRACT:
>  Despite the broad acceptance of phylogenetic principles in
>  biologicalclassification, a fundamental question still
>  exists on how to classifyparaphyletic groups. Much of the
>  controversy appears due to (1) historicalshifts in
>  terminology and definitions, (2) neglect of focusing on
>  evolutionaryprocesses for understanding origins of natural
>  taxa, (3) a narrow perspective ondimensions involved with
>  reconstructing phylogeny, and (4) acceptance of lowerlevels
>  of information content and practicability as a trade-off for
>  ease ofarriving at formal classifications. Monophyly in
>  evolutionary biology originallyhad a broader definition,
>  that of describing a group with common ancestry.
>  Thisdefinition thus includes both paraphyletic and
>  monophyletic groups in the senseof Hennig. We advocate
>  returning to a broader definition, supporting use
>  ofAshlock's term holophyly as replacement for monophyly
>  s.str. By reviewingprocesses involved in the production of
>  phylogenetic patterns (budding, merging,and splitting), we
>  demonstrate that paraphyly is a natural transitional stage
>  inthe evolution of taxa, and that it occurs regularly along
>  with holophyly.
>  When a new holophyletic group arises, it usually coexists
>  for some time with itsparaphyletic stem group. Paraphyly and
>  holophyly, therefore, representrelational and temporal
>  evolutionary stages. Paraphyletic groups exist at alllevels
>  of diversification in all kingdoms of eukaryotes, and they
>  havetraditionally been recognized because of their
>  descent-based similarity. Wereview different methodological
>  approaches for recognition of monophyleticgroups s.l. (i.e.,
>  both holophyletic and paraphyletic), which are essential
>  fordiscriminating from polyphyly that is unacceptable in
>  classification. Forarriving at taxonomic decisions, natural
>  processes, information content, andpracticability are
>  essential criteria. We stress using shared descent as
>  aprimary grouping principle, but also emphasize the
>  importance of degrees ofdivergence plus similarity
>  (cohesiveness of evolutionary features) as
>  additionalcriteria for classification.
>
>
>
>
>
>
>
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