Re: In Defense of Cladistics

[Neil Clark <NCLARK@museum.gla.ac.uk>]

>   I'll go a step further and say that it is *impossible* to say
> with certainty that one fossil species evolved from another fossil 
species.

No theory in Science is 100 per cent provable, but enough evidence 
can be amassed to allow a fair degree of confidence.

> Actually, a clade is defined by a *node* and everything which descended from
> it. 

Sounds more like a phylogenetic analysis than cladistics?

>  Clearly, this node was, in real-life, occupied by a singular species.

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

> But from a cladistic point of view, we don't have to have fossil evidence of
> that species to define the node. ....[edit]...
>   For instance, cladists have *never* claimed that Archaeopteryx is a *direct*
> ancestor of modern birds. 

This is presumably because cladistics is not an evolutionary tool for 
phylogenetics 
but a classificatory tool for taxonomy.  There is no harm in trying 
to use taxonomy to help us understand how similar organisms are to 
each other, but it doesn't always work to impose cladistic analyses 
on the geological time scale to understand how organisms evolved.

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'.

My thoughts for the day anyway.  Please feel free to discuss this 
further;-)

Neil