Clades are classes

pierre deleporte pierre.deleporte at UNIV-RENNES1.FR
Mon Sep 9 11:11:50 CDT 2002

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 

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).


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