An “exaptation” is just one example of a characteristic that evolved, but that isn’t considered an adaptation. Stephen Gould and Elizabeth Vrba1 proposed vocabulary to let biologists talk about features that are and are not adaptations:

  • Bat echolocationAdaptation—a feature produced by natural selection for its current function (such as echolocation in bats, right).

  • Exaptation—a feature that performs a function but that was not produced by natural selection for its current use. Perhaps the feature was produced by natural selection for a function other than the one it currently performs and was then co-opted for its current function. For example, feathers might have originally arisen in the context of selection for insulation, and only later were they co-opted for flight. In this case, the general form of feathers is an adaptation for insulation and an exaptation for flight.

Flight feather
Explore further
•  Not everything is an adaptation
•  Neutral theory
•  Qualifying as an adaptation

Teach this!
Lesson plans for teaching about exaptation

1 Gould, S.J., and E.S. Vrba. 1982. Exaptation: A missing term in the science of form. Paleobiology 8(1):4–15.

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Misconceptions about Natural Selection