Biological functions and natural selection: a reappraisal

The goal of this essay is to assess the Selected-Effects Etiological Theory of biological function, according to which a trait has a function F if and only if it has been selected for F. First, I argue that this approach should be understood as describing the paradigm case of functions, rather than as establishing necessary and sufficient conditions for function possession. I contend that, interpreted in this way, the selected-effects approach can explain two central properties of functions and can satisfactorily address some recent counterexamples. This reading, however, shows that there is only a partial overlap between biological functions and selected effects, so the former cannot be reduced to the latter. Finally, I maintain that this result is still compatible with a naturalistic theory of function that appeals to some evolutionary process.