3TA (correction)

David Williams dmw at NHM.AC.UK
Mon Apr 14 12:13:32 CDT 2003

I confess some puzzlement over the recent three-item posts.

Richard Zander see the problem of AB(CD) + AC(BD) as 'nonsense'. He
recommends some figures, some probabilities. He evidently has access to
knowledge I do not have. Perhaps he might still feel the same if the
problem was different. There are one thousand AB(CD) characters and one
thousand AC(BD) characters.

Don Colless understands 'character' to have "a pretty widespread usage (a
set of mutually exclusive attributes - or, if you wish, a Hennigian
transformation series)." Mutually exclusive attributes. So when, in the
past, fins 'transformed' into limbs, because the 'fins' vanished from view
the limbs must be considered something new altogether (exclusive); limbs
are usually considered to be modified fins. They are modified. In that
sense the fin is still present; fin and limb are inclusive. The notion of
'exclusive attributes' seems to demonstrate (or promote) the
non-evolutionary nature of binary data. Don Colless noted in his paper
(Syst. Zool. 34: 229-233, 1985) "Problems in the term 'character' seem to
have surfaced first in the field of numerical taxonomy" (from p. 229).
Indeed. And there they reside.

Peter Hovercamp suggests that the A(BCD) answer requires justification, and
asks "why do you prefer the outcome (BCD) over the outcome (ABCD)." Peter
neglects to add that ABCD is not a solution at all; it represents no
solution. But, of course, standard parsimony analysis of AB(CD) + AC(BD)
finds two solutions, identical to the original characters: AB(CD) and
AC(BD), which is also not an answer. One might imagine some poor taxonomist
who has diligently studied his organisms and finds one thousand AB(CD)
characters and one thousand AC(BD) characters, and still nothing may be
said of those data.

Kirk Fitzhugh recommends the reading of thousands of pages of philosophy.
Of which all I can say is 'thank you for the references.' I wonder if
delving into the metaphysics behind 'things', will explain to me why AB(CD)
+ AC(BD) [all x 1000] appears to have no answer. Philosophy, after all, can
be quite rewarding.


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