[Taxacom] Response to Dallwitz - part 2

[Don.Colless at csiro.au]

I try hard to stay away from philosophical challenges these days, but occasionally I can't resist! By my analysis, a character is a variable that takes an observed set of states. In a reasonable view, it IS a set of mutually exclusive states. So, I agree with Mike, that a character can't change, although it may be modified or amended by adding extra states or correcting mistakes in earlier analyses. On the other hand, Bob is correct, granted his view that a character is a structure (note his "states of the structure in question"). One can. e.g., by electron  microscopy, completely change the applicable set of states, which in this case are more like parts of an object than the more rarified values of a variable. I happen to agree with Mike; but as I pointed out long ago, there are signs here of a conceptual dimorphism in Homo sapiens taxonomicus.

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

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From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Bob Mesibov [mesibov at southcom.com.au]
Sent: 09 September 2009 10:16
To: m.j.dallwitz at netspeed.com.au
Cc: TAXACOM
Subject: [Taxacom] Response to Dallwitz - part 2

(Continuing)

Fourth minor point. You write ""This was for a phylogenetic analysis." Then it doesn't really matter whether the data are reproducible; the odds are no one will ever know or
care." Excuse me? The analysis was based on a published morphological data set laid out in a matrix. All the many characters were explicitly defined. All the states were explicitly defined. I and other taxonomists have referred to that structured data for information. In what way, exactly, doesn't it matter?

Fifth: "(a) and (b) imply that characters can change. A properly defined character can't change." This is hardline to the point of being nonsensical, but it's at the core of our disagreement. I know of explicitly definable characters that have changed when observers moved from fixed to fresh material, or (more often) from optical to electron microscopy. Sure, in a strictly logical sense the formerly understood character didn't change. You can still observe the old, incorrect or misleading states of the structure in question and report on them, if you want. But the taxonomy of those taxa has moved on from there, and so has the character, in the sense used by taxonomists.

We agree, I hope, on one thing. It is impossible to completely describe any specimen. A description *must* consist of a subset of all the possible, explicitly definable characters and their states. The selection of this subset is made by a taxonomist. It will be based on what that taxonomist and previous specialists regard as diagnostic characters, and will also include (this is important) observations similar to those made by earlier workers, no matter how non-diagnostic - not just to continue a silly tradition, but to make the contemporary and earlier descriptions comparable.

Some people see this selection process as 'arbitrary' and 'subjective'. They would prefer to select a different or more restricted subset of characters and states which is suited to machine analysis and presentation, as though this approach wasn't arbitrary and subjective as well (i.e., a matter of preference). Whether you see this difference as one of slackness vs rigour, or wetware vs software is less important than whether you think the difference matters. I use both approaches and find both of them useful. It's disappointing that you reject one of them.

I also second an earlier poster's comment (sorry, can't find it in the maze of recent Taxacom threads) about taxon concepts not dying with the conceiver. As a reviewer of taxonomic manuscripts, I judge overall quality by how well the author backs up their taxonomic decisions with evidence, and most papers pass that test easily.
--
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195
Website: http://www.qvmag.tas.gov.au/mesibov.html

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T