Aetiological Naturalism in the Philosophy of Medicine: A Shaky Project

Abstract Griffiths and Matthewson (2018) employ the selected effects theory to contend that disease involves the impairment of the normal functioning of biological items. Since the selected effects theory focuses on the past effects of those items, I refer to their proposal as “aetiological naturalism”. In this paper, I argue that aetiological naturalism cannot constitute an adequate theory of disease. This is due to the fact that the selected effects theory, which lies at the heart of aetiological naturalism, is flawed. One promise of the selected effects theory is indeed that it is able to account for our normative intuitions about dysfunctional biological items by grounding them on the concept of natural selection incorporated in the selected effects theory itself, where this promise rests upon its claim that appealing to the fitness-enhancing effect of biological items can always explain why they persisted in a population. However, I contend that the naturalisation of normativity cannot be cashed out in terms of biological items’ past effects by discussing two biological phenomena: phenotypic plasticity and negative frequency-dependent selection. I illustrate that in both cases the selected effects theory cannot recognise adaptive items as having a selected effects function, therefore preventing the possibility to assign them any dysfunction. The normative force of the selected effects theory is consequently much diminished, leading in turn to a weakening of aetiological naturalism, given that such project actually relies on the assumed normative force of the selected effects theory itself.