An "exaptation" is just one example of a characteristic
that evolved, but that isn't
considered an adaptation. Evolutionary biologists Stephen Gould and Elizabeth Vrba proposed
vocabulary to let biologists talk about features that are and are
Adaptation a feature produced by natural selection for its current function (such as echolocation in bats, right).
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.