Jeremy Wideman (Dalhousie University)
There are two broad views of how to define biological functions. The selected effects (SE) view of function requires that functions be grounded in “the historical features of natural selection” (Perlman 2012), whereas the causal role (CR) view does not (Cummins and Roth 2012). SE functions are separated from mere effects by reference to events in evolutionary/selective history (e.g., Garson 2017). Therefore, SE functions are real things/processes, which thereby explain how traits originated and why they persist. CR functions are ascribed by “functional analysis” (Cummins and Roth 2012) which involves defining a containing system (which can be anything from a metabolic pathway to a medical diagnosis) and describing the role that the trait in question plays in the system of interest. CR functions are thus subjectively defined, and dependent upon the interests of the investigator.
It has been suggested by CR proponents that biologists like molecular and cell biologists are do not need evolution to understand the functions that they are interested in. However, molecular and cell biologists are driven to determine ‘the function’ of organismal components, secondary effects are not so interesting. What then is meant by the function if not selected effect? Furthermore, comparative evolutionary biologists make inferences about conserved functions based on functions identified by molecular and cell biologists. An analysis of biological function at this level is lacking from the philosophical literature.
In order to determine if an SE view of function can accommodate actual biological usage I have turned away from abstract examples like the heart, to a concrete case study from molecular cell biology, the multicomponent molecular machines called ATP synthases. ATP synthases are extremely well studied protein complexes present in all domains of life (Cross and Müller 2004). As their name suggests, their generally agreed upon function is to synthesize (or hydrolyze) ATP. My analysis demonstrates that SE views of function that require positive selection for an effect (e.g., Gould and Vrba 1982) do not accommodate contemporary usage. Instead biological usage requires that function be defined to include effects arising from solely purifying selection, constructive neutral evolution, or exaptation, in addition to positive selection. Thus, the SE view of function must be construed more broadly in order to accommodate all facets of biological usage. A consequence of an expanded view of SE function is that while all adaptations have functions not all functions result from adaptations. Therefore, this view is not panadaptationist.
