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Re: In Defense of Cladistics



>>I said: 
>> Actually, a clade is defined by a *node* and everything which descended from
>> it. 
>>  Clearly, this node was, in real-life, occupied by a singular species.....
>>  <snip>.

>Neil Clark responded:
>Perhaps.  Depends very much on how evolution is observed in the 
>living or fossil species ie. what form the mutations took.

(Extreme blush mode -on)  
Yes, you're right.  Cladistically, I suppose, more than one 
species could occupy a node, if parallelism
or convergence were taking place.  But if you consider it phylogenetically,
only one taxum is the TRUE ancestor of that group, because the
other taxa will either leave no descendents, or they will evolve into
different clades (in other words, evolve in other directions).  We would have 
to apply 20/20 hindsight in identifying the true node-species of that clade.
It's also a totally irrelevent triviality, if you think about it!  Why should
cladists waste their energy trying to find a single node-species??   :-)
 But you are right.  I hadn't thought about the direction(s) that evolution
could take near speciation points. 
Intersting places, those nodes.
<Extreme blush mode -off> 

>Neil Clark continues: 
>I like cladistics because it helps me see taxonomic groupings of 
>organisms in a more objective way (but not entirely objective) than 
>Linnaean classifications.  I see very little difference between the 
>two types of classification except one is more 'descriptive' and the 
>other more 'numerical'.

  Cladistics is appealing because it forces people to use diagnostic criteria
even-handedly between organisms.  Classical Linnaean systematics has always
struck me as being both very "Gestalt" and very arbitrary in regards to how its'
classification "rules" are applied. 

  And now, for those who prefer their dinosaurs served without cladistics, I
will bow out of this very dry discussion.