[Taxacom] Read... and believe...
m.j.dallwitz at netspeed.com.au
Tue Sep 8 08:13:44 CDT 2009
Stephen Thorpe wrote:
"I certainly think you are correct inasmuch as lack of comparative
descriptions is a problem in taxonomy ... but I don't think it is strictly
relevant to the subjectivity/objectivity issue under discussion here."
A good description will help others to understand and reproduce an
author's concept of a taxon - i.e. to identify specimens as belonging or
not belonging to the taxon. This is the process that I am suggesting
should be made more reproducible/reliable/objective. This should provide
the infrastructure for the possibly subjective questions of whether new
taxa should be defined (or existing ones merged).
Bob Mesibov wrote:
"I'm having a little trouble understanding how you project your wish for
well-organised comparative data over time, i.e. over the many decades that
a particular group has been (and will be) studied. So, the comprehensive
organising of character data works fine at Time N, but at Time N+1:
a) Old methods give consistent and reliable character states, but with new
methods, you find that many of the states were incorrectly recorded.
b) Individual characters are shown to be more complex than previously
thought, and require reworking as multiple characters with new and
different states, and the Time N set needs to be chucked out.
c) Many new characters are discovered which have to be added to descriptions.
d) Some old characters really need to be discarded, e.g. they were
believed to be apomorphic but are now known to be plesiomorphic.
The paper you quote IMO confuses inadequate description with outmoded
description. I think those are two different things. One specialist I know
bravely created a matrix with many more characters than any one previous
description had ever included, then went back to types to fill in the
states for a *lot* of species. (This was for a phylogenetic analysis.) He
dealt with all 4 of the time-related issues above, but he isn't naive
enough to think that his matrix will be 100% correct, or even useful, in
100 years' time."
I don't see any reference to the time factor in the quote. The
descriptions won't improve with time, but the point is that they are
inadequate on the day they are published.
Your points (a)-(d) refer to characters. But the worst part of the problem
is that most descriptions don't use characters (sensu Colless, D.H. 1985.
On “character” and related terms. Syst. Zool. 34: 229–233). They just use
words strung together. I'm not implying that the descriptions have to be
in the form of a coded matrix. But the characters must be explicitly
defined, and must obey the rules, e.g. mutually exclusive states.
(a) and (b) imply that characters can change. A properly defined character
can't change. If, for example, a state is added, or the meaning of a word
is changed, that produces a different character. A data matrix based on
properly defined characters will be just as correct, and just as useful,
in 100 years time as it is today.
(c) Yes. Or at least they _may_ need to be added. Depending on the
circumstances, the old ones may be adequate indefinitely.
(d) No. A character can't be apomorphic or plesiomorphic; those terms
apply to character states. If you discarded all the characters that had
plesiomorphic states, you would have few if any characters left. You may
_choose_ to discard old characters, e.g. if ones that are better (in some
sense) are found, but the old ones retain their usefulness for
identification, and may conceivably be better for that purpose than the
"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. _Identification_ (or its equivalent) is the true test of
reproducibility. Reading a description and comparing it with a specimen is
_not_ equivalent to identification; it's too easy to agree with the
description (like a leading question).
People who produce general-purpose data matrices or keys are at least
trying to produce comparative and reproducible descriptions. But they
generally don't succeed very well - a failed identification means that the
key user couldn't reproduce the data (provided the specimen does belong to
one of the taxa in the matrix or key).
The method I proposed in an earlier posting
tries to nip reproducibility problems in the bud.
"I'd like to stress the importance of illustrations (drawings, photos,
SEMs) in taxonomic publications."
No argument about that. Most modern interactive-key programs allow for the
use of images - but some do it better than others. For example, Intkey
(typically) illustrates a character with a single image containing
illustrations and text of all the states, displays this image
automatically when the character is selected, allows state selection
directly from the image window, and closes the window automatically after
state selection. There are flexible options for the display of taxon
images. For example, if a few taxa remain in an identification, the user
can display, automatically tiled, all illustrations of a specified kind or
kinds for these taxa, e.g. the genitalia and/or wing images.
"the humans most likely to read my papers couldn't care less whether the
text descriptions were machine-readable and machine-analysable."
But if they use the descriptions (as opposed to the illustrations) at all,
they presumably like them to be human-understandable (i.e. reproducible).
"No, it isn't taboo, it's just more complicated than you seem to think."
Well, it seems to be hard to get a response on Taxacom to postings on the
subject. Are you suggesting that Taxacom subscribers don't like discussing
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