Yet this subroutine could well be integrated into quite a different overall set of genes. Archaeopteryx has feathers. There exists absolutely no evidence for the evolution of feathers. The guess that DNA coding for scales 'must have' changed to produce feathers is entirely unsubastantiated. No intermediate scale-feather exists.
Feathers are aerodynamic beauties.
They are light, the shaft being hollow, and quite different from the scales which are coded on to the feet alone of birds. They grow from capsules called 'pin feathers' and become lifeless when full grown. A feather from wing or tail is composed of a shaft with branches, called barbs, arranged diagonally to the left and right. The barbs have branches to the right and left called barbules. These overlap neighboring barbules and are interlocked to eachother by little hooks and eyelets.