● Two types of adaptationism are distinguished – ontological and methodological. The ontological thesis asserts that natural selection is the only important cause of the evolution of the vast majority of phenotypic traits; the methodological thesis tells scientists to construct idealized models of the evolution of phenotypic traits that ignore genetics and assume that organisms reproduce asexually. ● The ontological thesis fails to be true of a trait’s evolution if the genetic system prevents the fittest of the available traits from evolving to fixation and if the character states of present organisms are strongly influenced by the character states of their ancestors. ● An optimality model for a trait is important in evolutionary biology, even if the individuals in the population do not have the optimal trait value. ● Since science often progresses when different investigators adopt different approaches to the same problem, evolutionary biology may benefit by having some investigators be methodological adaptationists even if it would be bad for the science if all investigators did so.