Hawks, Doves, and Perissodus microlepis. Undermining the selected effects theory of function

The selected effects theory is supposed to provide a fully naturalistic basis for statements about what biological traits or processes are for without appeal to final causes or intelligent design. On the selected effects theory, biologists are allowed to say, for instance, that hindwing eyespots on butterfly wings serve to deflect predators' attacks away from vital organs because a similar fitness-enhancing effect explains why eyespots themselves were favoured by natural selection and persisted in the population. This is known as the explanatory dimension of the selected effects theory. According to it, appealing to the fitness-enhancing effect of a certain trait or process is sufficient to explain its current presence in a population, namely, why it persisted and still exists in that population. In this paper, however, I will call such a claim into question, and I will do so by discussing a mathematical Hawk-Dove example and a real case scenario taken from evolutionary biology, that of Perissodus microlepis. These are scenarios in which the selective filter does not allow variants with the highest fitness at a certain moment to prevail over their available alternatives. In similar cases, I will argue, citing fitness-enhancing effects does not represent an adequate explanation of what happens in the population, undermining the explanatory dimension of the selected effects theory.