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Re: Cladistic Massive Retaliation
Jonathan R. Wagner wrote:
> As I said, this is clearly recognized, but if one is basing one's
> taxa on common decent, it is irrelevant. Common decent removes an element
> of human judgement from the systematic proceedure. *WHO* is making the
> determination that these advanced characters justify a new paraphyletic
> taxon? *YOU* are. Cladists do not assume this responsibility. They do not
> define taxa on the basis of their own oppinion of what constitutes a "HIGHLY
> modified" structure. They do use their own judgement on characters, but so
> does everyone else. Cladists end up with real groups. Paraphyletic groups
> are not real.
If cladistic groups are real, then how is it that all cladists do
not produce identical cladograms? Presumably because they made different
JUDGEMENTS about the traits, how many there were, and which were
relavant. Human judgement is a factor in all phylogenetic reconstructions,
and cladistics is not an inherently flawless method.
And what about intermediates? For a given trait, how fully
developed does that feature have to be to say that all memebers of that
clade possess it? If you start out with a nekkid theropod, and
start having scutes develop into funny scutes into feathers, at what
point do you say: "THIS is a feather, this species had FEATHERS, and so
this clade is defined by the possesison of feathers." Without arbitrary
decisions, this should be impossible, because there are ALWAYS
intermediates**(see below). However, cladists make the decision
and define a clade by that trait. That is an arbitrary decision. Finally,
this may seem like a nitpicky point but cladistics makes arbitrary judgements
in another way: it assigns NAME, which are for our convenience only.
Cladistics may be a hypothetically flawless method, but it can't operate
without human judgements.
I am not saying cladistics is bad, far from it, I am simply that a
fully comprehensive evolutionary phylogeny needs something MORE.
**The creation of a paraphyletic clade that is defined by the
loss of a trait is no more arbitrary than the creation of a
monophyletic clade that is defined by the development of a
trait**. In either case, an arbitrary decision must be made
about what constitutes the full development of a trait, and what
constitutes the loss of a trait, in light of intermediates.
Taxonomy should be based on descent, but it should ALSO help us to
understand interrelationships and similarites of organisms which were NOT
inherited. This was the idea behind "traditional" taxonomies, and **IF**
the morphological similarities and differences reflect on phylogney, why is
this bad? Why can't an undertanding of evolved morphological
differences of ALL kinds be laid over a simple cladistics framework of
common descent? Why can't a taxonomy cover as many phylogenetic bases as