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In Defense of Cladistics

>>Peter wrote: 
>>    I am also not to enthusiastic about cladistics (if you haven't noticed)
>>because, as I have said before, they tend to split up ancestor-descendant
>>lineages into sister groups with an as-of-yet-undiscovered common ancester to
>>both as the node at which they both appear; leave out animals that are very
>>close to the ultimate ancestor of a stock with the phrase "The most recent
>>common ancestor of both this and that;" and place too much of an emphasis on
>>the most evolved by bestowing upon it the most titles (I believe this is
>>refered to as nesting).

>James Shields reponded: 
>As I understand it, a clade is supposed be represented by a particular
>species and everything which descended from it. The problem is that it is
>very hard to prove that one species evolved from another degree of certainty.

  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.
But I fail to see why this should be considered a weakness in cladistics.  

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.
But from a cladistic point of view, we don't have to have fossil evidence of
that species to define the node.  It is unfair to criticize the cladistic
method by pointing out that we don't have fossil species that ARE those
nodes, just as it is unfair for creationists to claim that evolution has no
true "missing-links".  It is the same faulty logic. 

  For instance, cladists have *never* claimed that Archaeopteryx is a *direct*
ancestor of modern birds.  Some are claiming that Archaeopteryx belongs to a
clade that had as one of its members an unknown species that is a direct
ancestor to modern birds.  We don't have to have fossil evidence of that
species.  In fact, that is a *minor* detail.  What is really important is that
we know what clade is ancestral.
  Having a known species at an exact clade-node is actually a THEORETICAL
concept, not a real-life concept.  Cladists don't sweat-it down to that
level of detail!  :-)