Exaptation 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... many structures that initially took on a function as exaptations, once molded for that new function they become adapted for that function. https://en.wikipedia.org/wiki/Exaptation

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