LAUSR

The star-nosed mole is aptly named. Its distinctive snout consists of 22 tendrils ringing a pair of nostrils and, from some angles, the entire setup resembles a misshapen star. The tendrils are fleshy and look a bit like fingers, and, like fingers, they have a certain dexterity. But why? Why does the mole have such a singular appendage as opposed to something more ordinary? What is the function or purpose of this bizarre structure? From the dedicated work of Ken Catania, of Vanderbilt University, and colleagues, it appears that the appendage facilitates rapid handling of small prey items, making it advantageous for an organism whose diet consists of tiny invertebrates. We might therefore hazard that this feature arose evolutionarily because it conferred this benefit. But the matter is difficult to resolve, because current utility does not permit a straightforward inference of a reason for existence. Problems of this sort have exercised students of living things for more than two millennia. Aristotle offered the first systematic account of why animals have the parts they do. He held that a key element to answering these questions was provided by an understanding of the telos, or purpose, of particular organs. But while the theme of purposiveness has been continuously salient from antiquity to the present day, two developments in biological theorizing have challenged its interpretation and significance. The first and most familiar was the advent of evolutionary thinking by Darwin and others during the nineteenth century. Prior to the nineteenth century, natural philosophers and theologians had formulated ways of using natural evidence to support arguments about the existence and attributes of a deity, a tradition that reached its zenith in the work of William Paley. Darwin argued that the design-like quality of organisms could be accounted for by different means. In particular, he argued that, if organisms vary in their characteristics and if some of these variations make a difference in the struggle for existence, then a process of natural selection will tend to fashion useful adaptations, provided favorable variations are reliably transmitted to offspring. For many biologists, Darwin’s achievement sounded a death knell for teleology, rendering obsolete all talk of purpose and purposiveness applied to nonconscious life. Despite this, however, closely related terms continued to be used, such as function and adaptation, which are ubiquitous in areas such as behavioral ecology and evolutionary genetics. Indeed, Darwin himself employed these terms liberally, which has led some to claim that Darwin—far from vanquishing teleology—in fact, reinvented it. Philosophical analyses demonstrate that teleological explanations involving natural selection can take several distinct forms that are fully amenable to contemporary scientific research. In fact, new conceptual work on these topics is a growth industry. For example, several distinct notions of function operate across biological disciplines and play diverse roles in ongoing investigation, leaving their interrelationships a pressing question, especially as interdisciplinary research becomes more common. Teleology, however, remains a term of poor repute, standing at once acquitted and condemned: acquitted as phenomenology but condemned as an explanatory strategy associated with final causes or intelligent designers. The second development that has shaped the interpretation and role of purposiveness in biological thought is the origin and elaboration of mechanistic conceptions of living phenomena. These conceptions have been on offer since antiquity but rose to prominence in the eighteenth and nineteenth centuries as scientists sought to identify new laws, principles, or forces operative in living beings. Mechanistic conceptions have traditionally been defined in opposition to a loose body of beliefs labeled vitalism. Vitalism argues, in one way or another, that life cannot be wholly understood in physicochemical terms—something additional (whatever that is) must be invoked. The attractiveness of these beliefs arose in part from genuine explanatory difficulties, such as the problem of accounting for the seemingly goal-directed phenomena of embryogenesis and, in part, from a view that organisms are intrinsically purposive entities. These motivations also animated early twentieth century organicism, which sought an alternative perspective that took the purposiveness of organisms seriously while avoiding “unscientific” metaphysical claims about vital forces and the like. Recent decades have seen a revival of interest in these nonvitalist alternatives to mechanism, both within biology and outside of it. In addition, cognate lines of thinking inspired by the study of far from equilibrium,