Function and Fitness

Abstract

This chapter focuses on the fitness-contribution theory of function, which holds, roughly, that the function of a trait consists in its typical contribution to the fitness of the organisms that possess it. I begin by surveying several different theories within this family, and I show why any plausible version must include a statistical element. I then pose three questions that any proponent of the fitness-contribution theory must answer. First, is fitness a relative notion? When one says a trait “contributes to fitness,” is one saying it contributes to fitness better than some alternative? If so, when we attribute a function to a trait, how do we specify the relevant alternatives? Second, is fitness relative to specific environments? If so, then when we attribute a function to a trait, how do we specify the relevant environments? Third, what precisely must a trait contribute to in order to have a function? Is it survival, reproduction, inclusive fitness, or something else? I then critically assess a major argument in its favor, namely, that it coheres well with the way biologists actually use the term. I consider three different interpretations of this claim and I argue that it does not, in fact, provide an advantage over the selected effects theory in this regard. I close by considering how well it satisfies the adequacy conditions set out in Chap. 1. Theorists disagree about whether the fitness-contribution theory can make sense of the explanatory and normative aspects of function and I survey those disagreements.