Striking a balance, weighting and Cladistics

[Ken Kinman]

    Thomas DiBenedetto wrote:
If a homology is a something "small" like a particular nucleotide or
something "big", like a feather, does not make any difference that I can
see.
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Tom,
    I don't how many nucleotide changes were involved in the evolution of
feathers, but it was a large number.  The above statement boggles my mind
and had my jaw dropping.
    Even individual nucleotides are of differential importance and will
someday be weighted routinely in some fashion.  But comparing nucleotides to
feathers----if there is no difference between them, then establishing
phylogenies must be a hopeless task.
    Not that I am in favor of the other extreme of overweighting certain
homologies at the expense of others, as has often been done in the
inordinate weight given to rRNA sequences even in the face of contradictory
evidence.  We can never achieve a perfect balance in weighting characters,
but that should not stop us from trying to at least approximate a reasonable
balance.
     Categorizing characters as either important or not important, useful or
useless, without any weight whatsoever, seems rather simplistic and
unrealistic.  Granted there is great difficulty in determining how some
characters may be related to one another, and incorrectly weighted trees can
sometimes be worse than unweighted trees, but we can't just throw up our
hands and give up on differential weighting just because it is a very
difficult task.  Both underweighting and overweighting need to be minimized,
but a failure to weight at all is just asking for trouble in my opinion.
                        ------Ken Kinman
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