The ultimate source of explanation in biology is the principle of natural selection. Natural selection means differential reproduction of genes and gene combinations. It is a mechanistic process which accounts for the existence in living organisms of end-directed structures and processes. It is argued that teleological explanations in biology are not only acceptable but indeed indispensable. There are at least three categories of biological phenomena where teleological explanations are appropriate.

Michael Ruse has offered an interesting and insightful analysis of function statements in biology. The analysis he gives of statements of the form ‘The function of x in z is to do y‘ is : z does y by using x.y is an adaptation.The first thing to notice about this formulation is the peculiarity of step. There are many cases in which we would naturally say that x was the adaptation, instead of y; or perhaps we might say that everything (...) asserted in step constituted the adaptation. For example, the function of the duck's webbed feet is to enable it to swim. But we would commonly and naturally say that the adaptation was the webbing, not the swimming. It seems to me that Ruse's insistence on the formulation in points to the major difficulty of his analysis : and understanding what drives him to this unnatural formulation suggests the way out of those difficulties. (shrink)

Michael Ruse [3] has criticized the distinction between biological function and evolutionary adaptation that I argued for in my article “Biological Adaptation” [2]. I shall show below that Ruse's criticisms are not, for the most part, well taken and that the distinction remains as I made it.

In this paper I attempt to show that adaptational sentences (i.e. sentences containing the terms "adaptive", "adapted", etc.) in evolutionary biology are best interpreted as equivalent to sentences about Darwinian or genetical selection. Thus, the use of adaptational languages does not introduce final purposes or other nonempirical notions into biology. I also try to demonstrate that adaptational sentences and functional sentences are not equivalent in an evolutionary context so that an analysis of function does not dispense with the need for (...) an analysis of adaptation. Finally, it is argued that, although some adaptational sentences might be construed as teleological explanations, given an empirical content, they do not serve as explanations. Rather, they express the outcome of selection, regarded in one way, and regarded in another, they express data for which a theory of evolution must account. (shrink)

In successive issues of this journal Ronald Munson [2] and I [4] have made, quite independently, conflicting claims about the relationship between biological adaptation and biological function. I state, admittedly without proof, that “a functional statement in biology draws attention to the fact that what is under consideration is an adaptation or something which confers an ‘adaptive advantage’ on its possessor”. This was an identity claim. Munson claims, with proof, that “adaptation and function are not identical”. In this discussion note (...) I want to examine the three arguments Munson gives in support of his claim, and I shall try to show that they do not hold. (shrink)