Feathers in birds appear to have first evolved for insulation but later conveyed a new advantage in helping create light aerodynamic surfaces. This switch in function is an example of .

Explanation:

Exaptation is the process by which the features acquire those functions for which they were not originally selected or adapted. Feather is an example of exaptation, it has appeared in various fossils of the flightless ancestors of modern birds, it later became important for flying, Once they molded for flying it adapted for that function, It is found in both behavior and anatomy.

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