BioConcepts

exaptationexaptation (fr.); Exaptation (ger.)

• A character or feature which evolved by a process other than selective adaptation for the function it subsequently acquired; the process by which features acquire functions for which they were not originally adapted or selected. Also in extended use. (OED 2012)
  category adaptation

  1982

  We suggest that such characters, evolved for other usages (or for no function at all), and later ›coopted‹ for their current role, be called exaptations. […] They are fit for their current role, hence aptus, but they were not designed for it, and are therefore not ad aptus, or pushed toward fitness. They owe their fitness to features present for other reasons, and are therefore fit (aptus) by reason of (ex) their form, or ex aptus. Mammalian sutures are an exaptation for parturition. Adaptations have functions, exaptations have effects. The general, static phenomenon of being fit should be called aptation, not adaptation. (The set of aptations existing at any one time consists of two partially overlapping subsets: the subset of adaptations and the subset of exaptations […])

  Gould, S.J. & Vrba, E.S. (1982). Exaptation – a missing term in the science of form. Paleobiol. 8, 4-15: 5.

  1992

  Gould and Vrba’s first category, adaptation, is just a special case of their third category, the exaptation of a trait that has arisen for non-adaptive reasons. Every trait arises by random mutation, and exists in the population at some low frequency waiting for selection to increase its frequency

  Griffiths, P. (1992). Adaptive explanation and the concept of a vestige. In: Griffiths, P. (ed.). Trees of Life, 111-131: 117.

  1995

  according to orthodox Darwinism, every adaptation is one sort of exaptation or the other – this is trivial, since no function is eternal; if you go back far enough, you will find that every adaptation has developed out of predecessor structures each of which either had some other use or no use at all

  Dennett, D.C. (1995). Darwin’s Dangerous Idea: 281.