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re:feathers




On Thu, 17 Jul 1997, brush wrote:
>    The problem again is one of langauge. We cannot ask if "the branching
>  of feathers evolved for aerodymanics, not insulation...". Evolution does not
>  entertain goals of this sort, no matter how attractive may be the adaptation
>  of the structure for its function. It is, however, informative to ask what
>  the common ancestor of feathers might have looked like, or how it evolved
>  (eg what changes were necessary to move from structure A to  subsequent
>  strcutures B,C, and D.). Certainly there were functional differences that
>   emerge from developmental sequence changes, incorporation of new
>  regulatory or structural genes, etc.

But in a casual conversation between scientists it is unproductive to
constantly have to include every level of complexity that might have
gone into the evolution of some morphology.  When we say something evolved
"for" something, we recognize that we are just using shorthand.  For
example, "feathers evolved for flight" means "feathers evolved when some
gene which may or may not have had anything to do with its subsequent
function made a protein which caused a branching structure which because
of the particular environment the organism was in gave it some selective
advantage remembering that the advantage may not have accrued immediately
and that its success was contingent upon the influence of the stochastic
forces of its day."
        Look at how much more mileage I can get if, assuming all of the
above for "for", I say: Feathers may have evolved for flying, insulation,
or for some unknown adaptive function.  Whatever their initial value, I
argue they now serve a seldom recognized function: transporting bird's
eggs further down a predator density gradient than they otherwise could. 
        I hasten to add that none of this takes away from the value of
discussing the deeper levels of causation, only that they, in this
instance, belong in a different conversation.