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Re: book reviews, parsimony and some loose ends



George Olshevsky writes:

>What is more difficult for me to imagine is for bipedal animals with
>grasping forelimbs to lose their manual digits. I can't imagine a
>grasping hand that would be helped by having >fewer<
>digits. Shucks--pandas even evolved an extra digit(!).

This may be (as I have suggested before) because you are assuming that
grasping would have been done the way we do it (or pandas) - by evolving
opposable digits (or, in the panda's case, a digit substitute) on the same
hand.  Some reptiles do this, of course (chamaeleons are the best example I
can think of), but there is another way - especially if the thing grasped
is a living prey object.  That is to use both hands as opposite tines of a
pair of tongs, operating towards the midline (or together, like the arms of
a mantis).  In that case I would expect the lines of force to be directed
along the anterior (internal) digits as these reach farthest forward, with
the lateral digits being much less useful.  Such a function would explain
how the outermost digits came to be lost.