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Re: feathers

In a message dated 97-07-18 14:09:54 EDT, jbois@umd5.umd.edu (John Bois)

<< 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. >>

Feathers also serve as an important method of excreting excess sulfated amino
acids, because they are regularly moulted. See

Reichholf, J. H., 1996. "Die Feder, die Mauser und der Ursprung der Voegel,"
Archaeopteryx 14: 27-38.

Feathers owe much of their elasticity to the disulfide bridges between the
sulfated amino acids (e.g., cysteine) in their structural proteins. But if
the animal cannot get rid of such amino acids, it risks being poisoned by
hydrogen sulfide, a product of sulfated-amino-acid metabolism. So feathers
may have originated to excrete these substances and became exapted for
display, insulation, and flight.