Exaptation

Exaptation (Stephen Jay Gould and Elisabeth Vrba's proposed replacement for what he considered the teleologically-loaded term 'pre-adaptation') and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour. Bird feathers are a classic example: initially they may have evolved for temperature regulation, but later were adapted for flight. Interest in exaptation relates to both the process and products of evolution: the process that creates complex traits and the products (functions, anatomical structures, biochemicals, etc.) that may be imperfectly developed.(1) A character, previously shaped by natural selection for a particular function (an adaptation), is coopted for a new use—cooptation.(2) A character whose origin cannot be ascribed to the direct action of natural selection (a nonaptation), is coopted for a current use—cooptation. (Gould and Vrba 1982, Table 1) Exaptation (Stephen Jay Gould and Elisabeth Vrba's proposed replacement for what he considered the teleologically-loaded term 'pre-adaptation') and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour. Bird feathers are a classic example: initially they may have evolved for temperature regulation, but later were adapted for flight. Interest in exaptation relates to both the process and products of evolution: the process that creates complex traits and the products (functions, anatomical structures, biochemicals, etc.) that may be imperfectly developed. The idea that the function of a trait might shift during its evolutionary history originated with Charles Darwin (Darwin 1859). For many years the phenomenon was labeled 'preadaptation', but since this term suggests teleology in biology, appearing to conflict with natural selection, it has been replaced by the term exaptation. The idea had been explored by several scholars when in 1982 Stephen Jay Gould and Elisabeth Vrba introduced the term 'exaptation'. However, this definition had two categories with different implications for the role of adaptation.