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Re: synapomorphies



In a message dated 96-02-13 13:40:39 EST, Robert.J.Meyerson@uwrf.edu (Rob
Meyerson) writes:

>And yet...
>
>Most cladigrams I have seen tend to be constructed in the speciation model,=
> where the cladigram gets broader as one goes up the "tree" (like a maple).
=
> Since Gould's punk eq has shown quite convincingly that the tree of life
is=
> actually shaped like a pine, is it possible that most cladigrams portrays=
> an old fashioned view of evolution?

This is an artifact of the process of speciation by cladogenesis. In
vertebrates certainly, and probably in most animals, species diversify by
branching apart, not by coming together. So a cladogram will always resemble
a tree, with more branches at the top than lower down. But the cladogram
doesn't tell you which branches became extinct and which survived, and it
doesn't tell you which of the groups of organisms whose evolution it diagrams
were contemporaries.