S.J. Gould and E. Vrba (1982, Paleobiology vol 8 pg 4-15) have suggested a different term: exaptation to stress the cooptedness of traits. Three examples: the evolution of bone tissue is believed to have proceeded under selection for a tissue that stores inorganic ions (e.g. phosphate ions). The ions need to be stored and released depending on the physiological demands of the body. The tissue best at doing this became rigid and could be coopted as a structural member. Thus organisms with "bone" as a structural tissue entered a new "adaptive zone" and adapted for various functions. Skull sutures in mammals appear as an adaptation for birth since they allow the skull to deform when passing through the birth canal (a tight squeeze). But reptiles and birds have them and they hatch out of eggs. Sutures evolved in one context (allow for growth of brain, head) but are an exaptation for birth in mammals (they do allow for the head to change shape during birth which is adaptive). Isolating mechanisms
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