Function
Résumé
Function is omnipresent in every aspect of biological knowledge. From the 1970s, two major philosophical theories have been discussed: the « etiological » theory of function and the « systemic » or « causal role » theory of function. The most popular version of the etiological theory states that “The function of a trait is the effect for which that trait was selected” (Neander). The causal role theory considers that the issue of origin is not relevant: ascribing a function is no more no less than stating the causal role of a part in the system that contains it. Both conceptions claim to be in agreement with the standard use of causation in science, but they have quite a different taste in biology. The etiological theory fits well with evolutionary biology; the systemic theory is atemporal, mecanicist, and analytical. Consequently, the method of testing is different: convergent circumstantial evidence vs. experimental demonstration.
In the current practice of biology, function cannot operationally be treated as an abstraction, as philosophers currently do, but rather as a specific action, or interaction, as a concrete manifestation, here and now, of the particular properties of material objects or structures. “Structures without functions are corpses, functions without structures are ghosts.” (Wainwright). This aspect that has been neglected by mot contemporary philosophers.
In reality, the characteristics of any biological entity are controlled by not two, but by three kinds of causes, denoted historical, functional, and structural (Gould’s reformulation of Seilacher’s proposal). These categories are common in the field of morphology. The present chapter confronts them with the modern philosophical theories of function.