• Natural Selection
• Natural selection at work
  • A case study: Tegula
• What about fitness?
• Sexual selection
  • Runaway selection
• Artificial selection
• Adaptation
  • Not everything is an adaptation
  • Neutral theory
  • Exaptations
  • Qualifying as an adaptation
• Misconceptions about natural selection
  • Survival of the “fit enough”
  • Deleterious genes

Exaptations

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:

• Adaptation—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.

	•	Not everything is an adaptation
	•	Neutral theory
	•	Qualifying as an adaptation

	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.