Positivism vs Realism

Tom DiBenedetto tdib at UMICH.EDU
Sun Dec 14 18:19:30 CST 1997

 James Francis Lyons-Weiler wrote:

>> gee, like maybe we should assume more modification even when we dont
>> see it, eh?

>       Depends on how you "see it". If you "see" modification as those
>       positioned on the parsimony tree, you are sure to underestimate
>       the degree of modification sometimes.

so,,,,lets make up some more....give me your criterion by which to
declare that certain specific character matches are not homologs.....

>> The hypothesis tested is that the distributions coded in the matrix
>> are the result of descent. Logical violations of that are revealed as
>> homoplasy.

>       But isn't the backbone of the background knowlegde that
>       characters are inherited?  What does this do to c?

not in any particular way.I should have been a bit more precise. The
hypothesis tested is that the distributions in the matrix are the
result of descent in the specific pattern tested.

>> What gives
>> you the predictive power to claim that parsimony is underestimating
>> homoplasy, or that  a particular synapomorphy is really an artifact
>> of something?

>       I can't imagine a world where processes of evolution
>       and taxon sampling and chaarcter sampling don't cause
>       parsimony to (sometimes) underestimate homoplasy.  How
>       do the principles of evolutionary biology lead to the
>       ridiculous conclusion that the processes of evolution will
>       not render misleading data in specific cases???

Whoa,,,homoplasy IS misleading data,.We are not denying it, we are
finding it.

>       A major limitation of cladistics is the insistence that
>       a synapomorphy is something that we get from a tree.
>       It's not: they existed before humans evolved - before
>       the term was coined.  Hence, _apparent_ synapomorphy...

What silliness. That is like saying that a major limitation of modern
chemistry is the insistence that an element is something found in a
periodic table,,,in fact they are found in the real world.  Trust me
on this James, all cladists understand that synapomorphies refer to
things that happened in the real world, often a long time ago.

>> How exactly do you propose to derive trees?

>       With informative data that have survived critical tests.

Well cool, welcome to the club.

Tom DiBenedetto                 http://www-personal.umich.edu/~tdib/
Fish Division                                   tdib at umich.edu
University of Michigan Museum of Zoology

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