Clades are not classes

SKÁLA Zdeněk skala at INCOMA.CZ
Mon Aug 5 11:17:47 CDT 2002

to summarize a bit:

pierre deleporte on clades=classes:
>My class theory accepts any kind of "equivalent
>properties of individals" for classifying into classes of equivalence (by
>difference with similarity clustering). A "character of an object" may thus
>be historically defined (why not ?).

Yes, why not. The problem is still the same; in the case of matrix:
  1 2 3 4 5
A - + + + +
B + + + + +
C + + + - -
D + - - - -
... and resulting cladogram:

... you simple have no "equivalent property" shared by all individuals. You can recode the homoplasy (-1) in (A) into something like (-1)' arguing that the (-1) in "A" is different from the (-1) in the outgroup. Even in this case you have no property shared by all individuals; you have only one new character state (-1)' which is, of course, also different from (+1). Arguing that this (-1)' "is a plain historical avatar of (+1)" (pierre d.) does not make any sense - sorry. In the same manner you can say that +2 or +5 is a historical avatar of -2 or -5 and thus deny all the structure of character matrix and the resulting cladogram.
Hence: clades are not classes but similarity-based objects like in the cluster analysis.
Best regards!

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