A 09:48 09/09/2002 +0200, vous avez écrit :
> >For monophyletic taxa to be classes of equivalence, the matrix above should
> >be recoded :
>
> 1 1' 2 3 4 5
>A + + + + + +
>B + - + + + +
>C + - + + - -
>D + - - - - -
>
> >The recoding of columns 1 and 1' makes sense only because the
> >1' character state is considered a derived avatar of 1. The formal
> >recoding above highlights the class nature of clades.
>
>I do not believe that you can place a new property (that was not
>observable before) to the set of taxa *after* the analysis to make it class.
I don't believe that you can forbid anybody to base a classification of
living beings on the basis of the results of a previous phylogenetic
analysis. The process of phylogeny reconstruction should simply not be
confused with the process of classifying on that basis.
> Your definition "features interpreted as nested synapomorphies define
> classes" is in fact definition of clades, not of classes. In this
> respect, your argumentation is OK - as concern clades, but do not try to
> support it by a concept that does not know anything about unobservable
> properties.
I fear you have a rather naive notion of "observable" properties in biology
(and in natural sciences at large). There is no
"naturally-obvious-self-evident" properties. Any scientific "observation"
is an interpretation inside a theoretical framework. Synapomorphies are
just that, after the phylogenetic analysis, and can then play the role of
"observed properties" for classification. But "face value" similarities in
the data matrix are also interpretations (just think of the nightmare of
character state delineation for some morphological data).
> Funnily enough, from the point of view of the class theory, the only
> class in the above cladogram is the paraphyletic taxon BCD (supported by
> the +1). This can be a case also for other paraphyletic taxa, so it could
> be rather dangerous to operate with a class theory to support cladistic
> solutions ;-)
Not at all if you aknowledge the interpretative nature of "scientific
observations".
Earth circling around the sun is not "observable" by the lay people, who do
observe the sun rising and falling down every day. It is nevertheless an
interpreted "observation" for the scientist. Will you class the sun in the
category of "things rising and falling" (thus, logically, clustering with
the yoyo) in order to stick with "observable properties"? I guess not.
Phylogeneticians are bold people indeed. They do pretend to "observe" past
history of characters in taxa, in the well documented cases. They
scientifically argue their concepts and methods for such a historical
reconstruction. Other people prefer to stick to some "face value overall
similarity" and perform phenetic clustering on that basis ("safer" maybe
some way, but devoided of biological meaning).
>BTW, "to be in the euclidean distance less than 0.26 from the point (6;8)"
>is indeed "property", so even clusters can be considered classes if one
>really needs it. As you can see, the border between cladistics and
>phenetics will probably go in another direction :-)
Plenty features may be considered "properties". They will nevertheless be
either interpretations under some explanatory theory, or arbitrarily
defined features, or a mixture of both. The data for phenetics may be
interpreted biological similarities (= putative homologies of cladists) but
with no attempt to further interpret these similarities in a historically
consistent system (to the difference of cladist's confirmed homologies, or
secondary homologies, as inferred from a cladogram taken as the likely
phylogenetic structure of the group).
Best
Pierre