Optimality Models and the Test of Adaptationism

Abstract

The use of optimality models in the investigation of adaptation remains controversial. Critics charge that advocates of the optimality approach assume that the traits they analyze are optimal. Advocates of the approach deny this but admit to assuming that the traits have adaptive explanations. This controversy is part of the ongoing debate about adaptationism. We believe that this controversy remains unresolved in part because of ambiguity in the definition of adaptationism. In this article, we clarify the thesis of adaptationism, show how the structure of optimality models relates to that thesis, and describe how the thesis of adaptationism is testable. In addition, we describe the types of analyses that are essential to a test of an optimality model if the optimality of the trait is to be assessed and if assessments of the success of specific models are to contribute to a test of adaptationism. These analyses allow one to distinguish between the hypothesis that natural selection has had some influence or an important influence on a trait and the hypothesis that the trait is optimal. At present, to our knowledge, there are only two sets of studies in evolutionary biology in which this critical distinction has been made.