What is "exaptation"

n. (context biology English) The use of a biological structure or function for a purpose other than that for which it initially evolved.

Exaptation (a replacement for the teleologically-loaded term "pre-adaptation") and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour. Bird feathers are a classic example: initially they may have evolved for temperature regulation, but later were adapted for flight. Interest in exaptation relates to both the process and products of evolution: the process that creates complex traits and the products (functions, anatomical structures, biochemicals, etc.) that may be imperfectly developed.