[Taxacom] (endless subject)

Sun Apr 5 04:30:38 CDT 2009

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

Originally I wanted to only respond personally and not to the whole list,
no need to run in circles, but this needs clarification. I never declared
anything of the kind. I asked if there is a universally applicable
_criterion_ apart from monophyly to test which of two circumscriptions of
a group of organisms is to be preferred. If I say that the (fantasy)
genera Plantella and Arboriopsis should be in Plantellaceae, Fruticiodes
not, and another scientist says that Plantella and Fruticioides should be
in Plantellaceae, but Arboriopsis not, by what criterion would you, as a
third and previously uninvolved person decide who makes the more
convincing case? You are a scientist, so it should neither be gut feeling
nor the personal authority of one of the two. DHC seems to indicate that
similarity and difference are good criteria. But if you demonstrate that
the inflorescences and corollas of P and A are more similar than both are
to F, maybe a colleague will come and say that this is all very well, but
wood structure and secondary metabolites are more similar in F and P, and
that is obviously more important than your puny characters. (How does he
demonstrate this importance against the assumed importance of other
characters - if not by showing his to be apomorphies and others to be
plesiomorphies?)

Alexander

> 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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