[Taxacom] categorical systematics

John Grehan calabar.john at gmail.com
Fri Jan 24 12:26:10 CST 2014


Sure - as long as it is represented as a "minimal estimate"

The pheneticist goal (of overall simiarlity) might have foundered, but I am
not a pheneticist. Interestingly, it is molecular reconstructions that seem
to be more phenetic than cladistic.

John Grehan


On Sat, Jan 25, 2014 at 7:10 AM, Fred Schueler <bckcdb at istar.ca> wrote:

> Quoting John Grehan <calabar.john at gmail.com>:
>
> >> Fred said "Surely we're at the state now where we can characterize at
> >> least these higher taxa by their estimated age of divergence, and the
> >> genomic difference between their surviving descendents."
> >
> > 'Surely' it depends. What constitutes an 'estimate' of age of divergence
> > when all estimates are minimal?
>
> * well, as in all things, an estimate is a best estimate on the basis
> of available evidence. But you can argue about an age of divergence in
> a rational way that's not available in arguing whether a taxon is a
> genus or a subfamily.
>
> > And we might have 'genomic difference' but we have always had that (in
> its
> > morphogenetic aspect).
>
> * that's the third measure of divergence which ought to be tabulated,
> as a measure of ecological difference, but the pheneticists goal of
> measuring overall morphological similarity seems to have foundered.
>
> Ken Kinman wrote:
>
> > I think Linnaean categories are (and always have been) a good,
> > useful tool.  The human brain organizes things by using categories,
> > and Linnaean categories give classifications a much needed structure.
>
> * but the Linnaean categories are "merely conventional signs" as the
> Bellman's crew affirmed - geological ages are also named entities,
> which are tied to something that can be measured, and which relate to
> evolution, and both genomic and morphological divergence are numbers.
> Evolved taxa are naturally categorical classifications, but Linnaean
> categories are a partitioning of a continuum into segments, and I
> suppose I'm just biased against this practice.
>
> In our autobiographical whinge - http://pinicola.ca/transition.ca - we
> write "Fred also realized, during the composition of his thesis, that
> in every case where he'd classified a phenomenon into categories, the
> situation was better explained as an ordination or regression – a
> response to continuous variables, rather than a chopping-into-parts.
> This doubtless had roots in taking plant ecology from Bob Whittakker
> (who had explained plant distribution as species independently arrayed
> along environmental gradients, rather than as co-adapted
> phyto-societies), and infra-specific systematics from Bill Brown (who
> had debunked the classical subspecies as spurious partitions of clinal
> variation). He was also immersed in the 1970's culture of multivariate
> analysis at the University of Toronto Department of Zoology, and
> further back, had read Peter Freuchen's 'Book of the Eskimos,' with
> its exposition of seasonal, as opposed to calendric, time. This leads
> us to suspect all classifications, boundaries, and partitions, and
> prefer explanations based on combinations of continuous causal
> factors. We're then struck with the often-surprising discovery that
> categorical partitions are acceptably congenial to many who employ
> them, and who don't feel that they need to replace them by relational,
> regression-like, explanations. Our loathing of categorical
> classifications is probably associated with our skittishness of
> national borders, parks, and all other arbitrary geographical
> partitions."
>
> fred.
> ------------------------------------------------------------
>           Frederick W. Schueler & Aleta Karstad
> Bishops Mills Natural History Centre - http://pinicola.ca/bmnhc.htm
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>           http://pinicola.ca/books/SNR_book.htm
>      RR#2 Bishops Mills, Ontario, Canada K0G 1T0
>    on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
>     (613)258-3107 <bckcdb at istar.ca> http://pinicola.ca/
> ------------------------------------------------------------
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>
>
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