Function and Selection

Abstract

This chapter focuses on the selected effects theory of function. According to this view, a function of a trait is whatever it was selected for by natural selection or some natural process of selection. I show how the theory plausibly accounts for the explanatory and normative aspects of function. First, if a function of a trait is whatever it was selected for by natural selection, then when one attributes a function to a trait one provides a causal explanation for why the trait currently exists. Second, since the function of a trait is determined by its history rather than current performance, it is easy to see how a trait can have a function that it cannot perform (“dysfunction”). I sketch the somewhat complex historical background of this theory. The theory was actually developed by biologists throughout the twentieth century, and in the 1970s philosophers began to explore it systematically. I survey the major criticisms of the theory and show why they are not compelling. Critics say that it does not really account for the explanatory and normative features of function; that it is inconsistent with the way biologists actually use the term; that there are (real or imaginary) counterexamples; and that it is committed to adaptationism. I close by presenting a new version of the theory, the generalized selected effects theory, which shows how brain structures (such as synapses) can acquire new functions during an individual’s lifetime through a process that is analogous in some ways to natural selection itself.