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Re: my piece on clades
> Secondly, they encourage the right trains of thought.
> For example, if I'd never heard of cladism and you asked me what the
> integument of Dimetrodon was like, I'd have said something like:
> "Dimetrodon is a mammal-like reptile. And one of the features of all
> reptiles is a scaly, dry skin. It didn't have hair or sweat glands"
> But with the benefit of the cladistic approach, I'd say:
> "Dimetrodon is a synapsid. Living synapsids (mammals) all have hairy,
> glandular skin. The closest outgroup we know enough about is the Diapsida,
> with scales (sometimes feathers too) and no glands. The next outgroups are
> amphibians and lungfish, both of which have glandular skin. Amphibians
> have no scales, I don't know about lungfish. So from what I know, it's
> most likely that secretory skin is the primitive condition, retained in
> Dimetrodon. There is no phylogenetic evidence either way on the hair."
Wait a minute; both these viewpoints are based on evidence
regarding the type of skin present in Dimetrodon's ancestor; the
viewpoint you call "cladistic" is simply based on a more recent
evaluation of the evidence. If an evolutionary taxonomist considered the
evidence in favor of glandular skin in Dimetrodon to be compelling but
still wanted to include pelycosaurs and therapsids with the reptiles, he
would simply state that scaley skin is not a universal feature of
reptiles. Evoltionary and cladistic taxonomy both stick on labels AFTER
interrelationships (and the distribution of morphological characteristics)
has been established. Evolutionary taxonomy can modify the
definition as new evidence comes in. It doesn't let the tail wag the dog
any more then cladistics, it simply recognizes that the retention of
primitve charcters affects and is as effected by the fate of a
group (including evolution and/or exticntion) as much as derived
Are you saying that before cladistic taxonomy no one
understood the inheritance, or that evolutionary taxonomists undertand
evolution less then a cladist? Using similar logic you could say
that because an evolutionary taxonomist mightt not call a bird a dinosaur,
he doesn't realize where the avian antorbital fenestrae came from. This
is nonsense. Keep in mind that taxa only are labels, or reference points.
You could base taxonomy entirely on POLYphyletic groups and still understand why
Dimetrodon may have had glandular rather then scaley skin; neither
evolutionary or cladistic taxonomists do this because we CARE more about
common descent then convergence.
Don't confuse cladistic analysis with cladistic taxonomy. The
first, which evolutionary taxonomy is happy to use, infers evolutionary
relationships USING morphology. The second, like all taxonomy, just
sticks on labels AFTER this has been done.
> What this is assuming is simply that there is a 'tree of life', in which all
> organisms are united by common descent, and that once brances separate they
> never rejoin.
But there IS no tree. The tree is a conceptual aid to help
undertand descent and interrelationship. As I stated before, to picture a
tree, all the branches have to exist simultaneously. This never happened
in reality; the bald eagle never coexisted with _Archaeopteryx_.
connecting them with branches on a piece of paper simply helps
undertsand how they are related.
> Then one single cut with the pruning hook always grabs a
> monophyletic group. A paraphyletic group requires several cuts, and a
> polyphyletic one requires both cutting and grafting.
....which may have to do with SIMPLICITY, but not REALITY.
> Any set of organisms from the planet Earth is a subset of a monphyletic group.
Yes, but both are still imaginary. Great people are a subset of
good people, but how you define such people is still arbitrary, even
though the people themselves, the acts they commit, and the thoughts they
think, are nonarbitrarily real.
> So which did come first? The domestication of the jungle fowl _Gallus_, or
> anisogamy? :)
Let me know what anisogamy is and I'll tell you.
> If you see a capital letter,
> you know the term is expressing a theory about evolutionary history and not
> about any other aspect of the creature's biology.
Part of the evolutionary history of "thecodonts" is the last ones
went extinct at the end of the Triassic, while thier descendants did not,
probably due to some aspect of thier biology. (although not neccessarily
the same aspects for all groups, although if if they DID, it would make
"thecodont" a considerably more useful term).