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Re: courses




On Monday, December 9, 2002, at 03:57 AM, Daniel Bensen wrote:
(I wrote) I was talking about characters that would be used in a morphological
cladistic analysis (which presumably would have already undergone
selective pressure)... No direction, it's just that
characters - as pieces of morphology - must be functional, which
reduces the possible characters any organism can evolve (and pathways
too). <<

I disagree.  Just because a feature is present in an organism, does not
mean that feature performs a function.  There's a long list of useless
features in humans and in other organisms as well, and it is _these
useless features that are the best characters on which to base
classification_.

Which features? If you are talking about spandrels, then this is debatable. I don't think the list of useless features is as long as you imply. However, my use of the word "must" was too strong, and probably worked counter to my point.


So the best characters to use in cladistic analysis
are the ones subject to the _least_ selective pressure.  That way you
stay away from convergence.

Um, this was actually the point of my last two posts, but tracing this logic through popperian notions of parsimony. My secondary point is that it is, of course, extremely difficult to do, due to the fact that genetic and adaptive explanations are somewhat mutually exclusive.


I'll put my second point more clearly: the more successful adaptive (biomechanical and evolutionary scenarios) become, the less reliable cladistics becomes; due to the fact that both are attempting to explain morphology by different means.

And I actually have a quote to back this up:

" No one regards the external similarity of a mouse to a shrew, of a
dugong to a whale, of a whale to a fish, as of any importance. These
resemblances, though so intimately connected with the whole life of the
being, are ranked as merely `adaptive or analogical characters;' but to
the consideration of these resemblances we shall have to recur. It may
even be given as a general rule, that the less any part of the
organization is concerned with special habits, the more important it
becomes for classification."

(From Charles Darwin, the Origin of Species, Ch 13)

Dan


John Conway, Palaeoartist

"Do I contradict myself? Very well, then I contradict myself, I am large, I contain multitudes." - Walt Whitman

Systematic ramblings: http://homepage.mac.com/john_conway/
Palaeoart: http://homepage.mac.com/john_conway/_palaeoart.html
Skeletals: http://homepage.mac.com/john_conway/_skeletals/