How did feathers originally evolve from reptilian scales, and what was their initial function before becoming adapted for flight?

• A. Feathers evolved from scales as a defense mechanism against predators before being used for flight.
• B. Feathers evolved from scales to improve swimming ability and subsequently were adapted for flight.
• C. Feathers evolved from scales for decorative purposes, and then became essential for flight.
• D. Feathers evolved from scales primarily for insulation, and later were adapted for flight through exaptation.

Answer: (D)