Teleology and Teleological Explanations

Explanation by design, or teleology, is "the use of design, purpose, or utility as an explanation of any natural phenomenon" (Webster's Third New International Dictionary, 1966). An object or a behavior is said to be teleological when it gives evidence of design or appears to be directed toward certain ends. For example, the behavior of human beings is often teleological. A person who buys an airplane ticket, reads a book, or cultivates the earth is trying to achieve a certain end: getting to a given city, acquiring knowledge, or getting food. Objects and machines made by people also are usually teleological: a knife is made for cutting, a clock is made for telling time, a thermostat is made to regulate temperature. Similarly features of organisms are teleological as well: a bird's wings are for flying, eyes are for seeing, kidneys are constituted for regulating the composition of the blood. The features of organisms that may be said to be teleological are those that can be identified as adaptations, whether they are structures like a wing or a hand, or organs like a kidney, or behaviors like the courtship displays of a peacock. Adaptations are features of organisms that have come about by natural selection because they serve certain functions and thus increase the reproductive success of their carriers.

Inanimate objects and processes (other than those created by people) are not teleological in the sense just explained because we gain no additional scientific understanding by perceiving them as directed toward specific ends or for serving certain purposes. The configuration of a sodium chloride molecule (common salt) depends on the structure of sodium and chlorine, but it makes no sense to say that that structure is made up so as to serve a certain purpose, such as tasting salty. Similarly, the shape of a mountain is the result of certain geological processes, but it did not come about so as to serve a certain purpose, such as providing slopes suitable for skiing. The motion of the earth around the sun results from the laws of gravity, but it does not exist in order that the seasons may occur. We may use sodium chloride as food, a mountain for skiing, and take advantage of the seasons, but the use that we make of these objects or phenomena is not the reason why they came into existence or why they have certain configurations. On the other hand, a knife and a car exist and have particular configurations precisely in order to serve the purposes of cutting and transportation. Similarly, the wings of birds came about precisely because they permitted flying, which was reproductively advantageous. The mating display of peacocks came about because it increased the chances of mating and thus of leaving progeny.

The previous comments point out the essential characteristics of teleological phenomena, which may be encompassed in the following definition: "Teleological explanations account for the existence of a certain feature in a system by demonstrating the feature's contribution to a specific property or state of the system." Teleological explanations require that the feature or behavior contribute to the persistence of a certain state or property of the system: wings serve for flying; the sharpness of a knife serves for cutting. Moreover, and this is the essential component of the concept, this contribution must be the reason why the feature or behavior exists at all: the reason why wings came to be is because they serve for flying; the reason why a knife is sharp is that it is intended for cutting.

The configuration of a molecule of sodium chloride contributes to its property of tasting salty and therefore to its use as food, not vice versa; the potential use of sodium chloride for food is not the reason why it has a particular molecular configuration or tastes salty. The motion of the earth around the sun is the reason why seasons exist; the existence of the seasons is not the reason why the earth moves about the sun. On the other hand, the sharpness of a knife can be explained teleologically because the knife has been created precisely to serve the purpose of cutting. Motorcars and their particular configurations exist because they serve transportation, and thus can be explained teleologically. Many features and behaviors of organisms meet the requirements of teleological explanation. The hand of man, the wings of birds, the structure and behavior of kidneys, the mating displays of peacocks are examples already given.

It is useful to distinguish different kinds of design or teleological phenomena. Actions or objects are purposeful when the end-state or goal is consciously intended by an agent. Thus, a man mowing his lawn is acting teleologically in the purposeful sense; a lion hunting deer and a bird building a nest have at least the appearance of purposeful behavior. Objects resulting from purposeful behavior exhibit artificial (or external) teleology. A knife, a table, a car, and a thermostat are examples of systems exhibiting artificial teleology: their teleological features were consciously intended by some agent.

Systems with teleological features that are not due to the purposeful action of an agent but result from some natural process exhibit natural (or internal) teleology. The wings of birds have a natural teleology; they serve an end, flying, but their configuration is not due to the conscious design of any agent. We may distinguish two kinds of natural teleology: bounded, or determinate or necessary, and unbounded or indeterminate or contingent.

Bounded natural teleology exists when specific end-state is reached in spite of environmental fluctuations. The development of an egg into a chicken is an example of bounded natural teleological process. The regulation of body temperature in a mammal is another example. In general, the homeostatic processes of organisms are instances of bounded natural teleology.

Unbounded design or contingent teleology occurs when the end-state is not specifically predetermined, but rather is the result of selection of one from among several available alternatives. The adaptations of organisms are designed, or teleological, in this indeterminate sense. The wings of birds call for teleological explanation: the genetic constitutions responsible for their configuration came about because wings serve to fly and flying contributes to the reproductive success of birds. But there was nothing in the constitution of the remote ancestors of birds that would necessitate the appearance of wings in their descendants. Wings came about as the consequence of a long sequence of events, where at each stage the most advantageous alternative was selected among those that happened to be available; but what alternatives were available at any one time depended, at least in part, on chance events.

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