Re: Origin of feathers

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-04-10 03:04:47 EDT, jjackson@interalpha.co.uk writes:

<< A need is never an initial cause in evolution.  And every body surface has
 drag of some kind, and there will always be some variation of it within the
 population.  There is not however always some background element of
 solid-form sulphur excretion through the skin, and no variability to drive
 any selection for it. >>

"Need" of course cannot provoke the evolution of a structure that fills the
need; this is elementary. But "need" provides the background against which
selection can act. An animal that lives in high places "needs" protection from
falls. Thus structures that may appear spontaneously by mutation will be
selected for if they meet this "need." We all know that there is basically no
>cause< of the appearance of any structure, since the mutations responsible
for the structure occur randomly (i.e., the real cause might be cosmic
radiation, weird biochemistry, or something equally tangential). So when we
ask for a "cause" for the appearance of a structure, we are really asking for
a description of the "need" for that structure--that is, for a reason why that
structure would be selected for. I submit that the need comes before the
structure; a structure for which there is no need won't spread throughout a
population and will likely vanish. An animal may need to display to attract a
mate, but would it need feathers for this? Clearly not. The paper on feathers
for sulfur excretion implies there is a need for animals to excrete excess
sulfur, and suggests that pre-feathers could serve as a mechanism for this.
The desired immediacy of "cause" is present in this hypothesis, whereas it is
almost always absent in other hypotheses for the appearance of pre-feathers,
so I like it. Meanwhile, we're nowhere near proving any of this, of course,
and I'm quite sure we never will be.