[Taxacom] (endless subject)

[Don.Colless at csiro.au]

Alexander Schmidt declared that there is no "metric for measuring difference".

As it happens, there is a perfectly good one, often used. The idea is simple enough, but has been plagued by quasi-philosophers.  They correctly point out that raw similarity cannot be measured, because of the indefinite, perhaps infinite, number of available characters. That does not apply to difference,  because we only count the characters that are observed to differ over our study group. The result will be corrigible, but so what? An account of all this can be found in my 2006 paper - Biol. & Philosophy 21:353-367.

Donald H. Colless
CSIRO Div of Entomology
GPO Box 1700
Canberra 2601
don.colless at csiro.au
tuz li munz est miens envirun

________________________________________
From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Frederick W Schueler [bckcdb at istar.ca]
Sent: 04 April 2009 03:29
To: TAXACOM
Subject: Re: [Taxacom] (endless subject)

Alexander.Schmidt-Lebuhn at biologie.uni-goettingen.de wrote:

> Similarity lies in the eye of the beholder.

* well, maybe that's the root of this unending thread, as I commented
(below) at an earlier stage. If "overall phenotypic similarity" could be
recognized as a stand-in for "ecological similarity," and could be
measured on this basis, then there'd be some way of meaningfully
measuring and discussing the phenomena that are now obliquely discussed
under the heading of paraphyly.

Linnean ranks could serve to express the chronological age of
holophyletic groups or to express "degree of difference," but if there's
no metric for measuring "difference" there's no way to discuss it.

Forty years ago it would have been considered hopeless to express the
phyletic connection between, say, an Elephant and a Bacterium, but we
can do that now, so we've got a grip on the "vertical" time dimension of
biotic diversity. What's needed as the next step in understanding is to
come to grips with the conceptually more complex "horizontal," or
ecological dimension(s).

imho,

fred.
------------------------------------------------------------
             Bishops Mills Natural History Centre
           Frederick W. Schueler & Aleta Karstad
        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
------------------------------------------------------------
Frederick W Schueler wrote:
 >  I think the problem is, to cast it in Hegelian terms,
 > that when the thesis of cladistics was struggling
 > with the antithesis of phenetics in the 1960s and 1970s, there wasn't
 > ever a synthesis that incorporated phenetics' "overall similarity" into
 > new systematic procedures. "Holophyly" was such an engaging idea, and
 > "overall similarity" was so complex, and so dependent on the character
 > set analysed, and then so mixed up between phenotypic and genetic data
 > sets, that "overall phenotypic similarity" wasn't widely recognized as
 > a stand-in for "ecological similarity" in the same way that
"synapomorphy"
 > was recognized as a stand-in for "propinquity of descent." Just saying
 > "evolutionary systematics" & continuing in the old New Synthesis ways
 > didn't count as a new synthesis.
 >
 > I'm not sure what such a synthesis would look like, & maybe old-
 > fashioned phenetics requires too much caliper work to be attractive,
 > but I think that ecological similarity would be somehow incorporated in
 > a systematics that reflected our best understanding of organisms. --
 >
 > fred
 > ========================================================
 >

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