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Re: Why insulation = endothermy



 From: Joe Daniel <jdaniel@aristotle.net>
 > He didn't actually say anything 
 > complicated.  It seems to me that he said that feathers could have
 > developed for insulation, then been adapted for flight.  Afterwards,
 > selection pressure for this adaptation governed the current shape
 > of the body feathers.

If I understood him correctly, there is a subtle difference in
what we suggested.

I pointed out that the post-flight selection may have been on the
*wings*, and the body feathers may have been affected mainly by
indirect, pleiotropic effect.  He suggested that there may have
been direct selection on body feathers to be streamlined for flight.
In other words, we differ on the *mode* of selection, indirect versus
direct.

Now, these two style of selection are not entirely mutually exclusive.
Both could have occurred in some combination.  Indeed, at some level
both probably *did* occur (pleiotropy is common, but few external
physical features are ever free of direct selection as well).

The only way to actually answer such questions is to do research on
birds to see which combination of factors best explains the form of
the feathers.  This could involve studies of the genetics involved
in feather devlopment (my suggestion predicts a common program among
all types of feathers).  It could also involve studies of changes
in aerodynamic quality with changes in feather form.  I am sure other
experiments could be devised to investigate this matter.

 >  You added the bit about them degenerating in flightless birds but
 > this is by no  means exclusive to Stan's comment and in fact fits
 > in nicely with it. ...

Indeed. In the absence of selection for flight feathers, the pleiotropic
drive would vanish, and selection for insulation would dominate.

This certainly does not really distinguish the two modes of selection.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.