exaptation

The use of a biological structure or function for a purpose other than that for which it initially evolved.

Birds initially developed wings and feathers as a means of heat regulation. The use of wings for flight is an example of exaptation.

I believe that Stephen Gould and Elizabeth Vrba were correct in proposing exaptation as a missing term in evolutionary biology. I want to make a distinction between adaptation and exaptation here. Again it is about mechanistic differences. An exaptation can be viewed as the acquisition of a new and useful function once the novelty has spread and once the environment has changed.

The promotion of meaningless or redundant material so that it does new grammatical (morphosyntactic or phonological) or semantic work.

The process Haiman focuses on is exaptation, which he defines as "the promotion of meaningless or redundant material so that it does new grammatical (morphosyntactic or phonological) or semantic work" (p52).