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Holy BCF



I'm sure that this is going to seem very mean of me, but I can't
resist noting that George Olshevsky has a penchant for applying
different rules to the arguments he makes versus the arguments he
criticises.  One of his hobby horses vis a vis cladistics is the
unprovability that evolutionary transitions occur parsimoniously.  To
wit he wrote:

Fri, 11 Oct 1996 14:58:48 -0500

> The data, such as they are, fit BCF far better than they do
> BADD. [...] Evolution is a random walk through a
> multimultidimensional morphospace; it almost never goes from point A
> to point B in a straight line.  That's just an approximation we make
> when we have no handle on the intermediate steps, an approximation
> that, as I noted previously, seldom holds.

It appears rather inconsistent to me that said approximation actually
forms the cornerstone of George's argument about the origin of
dinosaurs.  To wit he wrote:

Sun, 3 Dec 1995 17:22:21 -0500 

} If you consider the key lineage, the one that goes from the common
} ancestor of all the archosaurs, toward any particular modern
} bird--say, the robin--two facts hit you in the face: (1) The
} archosaurs started out small (say, 10-15 cm long snout-vent length),
} and the robin (and many, many other birds) is itself small. This
} suggests that _on that lineage_ the animals didn't get much bigger,
} because then they would have had to reverse and become small
} again. I'm not saying that they didn't evolve that way (by starting
} out small, getting big, and then becoming small again); I'm saying
} we should look at the more parsimonious alternative first. (2) The
} archosaurs started out with relatively large forelimbs, and the
} robin (and many, many other birds) still has relatively large
} forelimbs. Maybe the forelimbs shrank and then reversed and grew
} big--at the same time that the animals grew big and then became
} small again--but again, why not look at the more parsimonious
} alternative first: that the forelimbs _didn't_ shrink and re-expand
} during the evolution _of that lineage_?
}
}  If you continue in this manner with other features such as teeth,
} feathers, skull shape, hind limb anatomy, forelimb/wing anatomy, and
} so forth, trying the _most direct route of change_ first, then you
} eventually get the BCF phylogeny. 

Do the above two quotes seem rather inconsistent to everyone else or
is it just me?  George, if you have an explanation as to why you're
basing your main point on the occurence of something which you claim
"seldom" occurs, I'm sure we'd all like to hear it.  In any case, it
also appears to me that if what George is saying in the final
paragraph is true, then it should show up in a cladistic analysis.
So why doesn't it?

--
Mickey Rowe     (mrowe@indiana.edu)