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Evolutionary theory lacks a term for a crucial concept—a feature, now useful to an organism, that did not arise as an adaptation for its present role, but was subsequently coopted for its current function. I call such features “exaptations” and show that they are neither rare nor arcane, but dominant features of evolution—though previously unappreciated in the context of the overly adaptationist neo-Darwinian theory. This article argues that exaptation overcomes the fallacy of human sociobiology, helps us to understand the major patterns of flexibility and contingency in life's history, revises the roles of structure and function in evolutionary theory, serves as a centerpiece for grasping the origin and meaning of brain size in human evolution, and thereby cries out for recognition as a key to evolutionary psychology. Historical origin and current utility are distinct concepts and must never be conflated.