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In a message dated 95-12-08 13:45:45 EST, ornstn@inforamp.net (Ronald
Orenstein) writes:

>Again - I am not at all averse to the notion that the retroverted hallux
>evolved for perching.  I was merely countering your statement that no other
>function could possibly have been responsible for its evolution.  Prey
>capture may be less likely but it is certainly possible.

We all can imagine numerous functions for the many adaptations observed in
dinosaurs. The big problem is to select one of them as the most compelling
cause. Of course, the _primal_ cause for any adaptation is the random
mutation(s) that bring(s) the feature into existence in the first place. This
is the unpredictable part. Once the feature appears, it must confer an
immediate selective advantage on the organism that allows the organism to
produce more survivable offspring. It's this "immediate selective advantage"
that I would consider the "compelling" cause or the "proximate" cause of the
feature. There could well be more than one such advantage--and indeed, the
more immediate advantages, the more likely the feature is to persist in the
lineage. Still other advantages may show up later, after the feature becomes
incorporated into the lineage and begins undergoing modifications and
evolutionary improvements of its own. These advantages would not be
"proximate," however.