 Ford (1940) further distinguished two types of selective polymorphism, transient polymorphism and balanced polymorphism. Transient polymorphism, caused by a new favorable mutation in the process of displacing its ancestral allele by natural selection, was considered unlikely, because “…advantageous genes will usually have been already incorporated into the genetic constitution of the species” (Ford 1975: 110). This and statements like it reflect the viewpoint that organisms in nature are exquisitely adapted to their environments by the long-acting process of Fisherian gradualistic natural selection (see the entry on  natural selection).  It is a prelude to the more explicitly adaptationist views found in the current behavioral literature (see review in Shuster &amp; Wade 2003). This view of the evolutionary process as primarily one of refinement of existing organismal adaptation is an essential part of the Fisherian theory of evolutionary genetics (Wade &amp; Goodnight 1998).