Teleological language is frequently used in biology in order to make statements about the functions of organs, about physiological processes, and about the behavior and actions of species and individuals. Such language is characterized by the use of the words 'function', 'purpose', and 'goal', as well as by statements that something exists or is done 'in order to'. Typical statements of this sort are 'It is one of the functions of the kidneys to eliminate the end products of protein metabolism', or 'Birds migrate to warm climates in order to escape the low temperatures and food shortages of winter'. In spite of the long-standing misgivings of physical scientists, philosophers, and logicians, many biologists have continued to insist not only that such teleological statements are objective and free of metaphysical content, but also that they express something important which is lost when teleological language is eliminated from such statements. Recent reviews of the problem in the philosophical literature (Nagel, 1961; Beckner, 1969; Hull, 1973; to cite only a few of a large selection of such publications), concede the legitimacy of some teleological statements but still display considerable divergence of opinion as to the actual meaning of the word 'teleological' and the relations between teleology and causality.
This confusion is nothing new and goes back at least as far as Aristotle, who invoked final causes not only for individual life processes (such as development from the egg to the adult) but also for the universe as a whole. To him, as a biologist, the form-giving of the specific life process was the primary paradigm of a finalistic process, but for his epigones the order of the universe and the trend toward its perfection became completely dominant. The existence of a form-giving, finalistic principle in the universe was rightly rejected by Bacon and Descartes, but this, they thought, necessitated the eradication of any and all teleological language, even for biological processes, such as growth and behavior, or in the discussion of adaptive structures.
The history of the biological sciences from the 17th to the 19th centuries is characterized by a constant battle between extreme mechanists, who explained everything purely in terms of movements and forces, and their opponents who often went to the opposite extreme of vitalism. After vitalism had been completely routed by the beginning of the 20th century, biologists could afford to be less self-conscious in their language and, as Pittendrigh (1958) has expressed it, were again willing to say 'a turtle came ashore to lay her eggs', instead of saying 'she came ashore and laid her eggs'. There is now complete consensus among biologists that the teleological phrasing of such a statement does not imply any conflict with physico-chemical causality.
Yet, the very fact that teleological statements have again become respectable has helped to bring out uncertainties. The vast literature on teleoloy is eloquent evidence for the unusual difficulties connected with this subject. This impression is reinforced when one finds how often various authors dealing with this subject have reached opposite conclusions (e.g. Braithwaite, 1954; Beckner, 1969; Canfield, 1966; Hull, 1973; Nagel, 1961). They differ from each other in multiple ways, but most importantly in answering the question: What kind of teleological statements are legitimate and what others are not? Or, what is the relation between Darwin and teleology? David Hull (1973) has recently stated "evolutionary theory did away with teleology and that is that", yet a few years earlier McLeod (1957) had pronounced "what is most challenging about Darwin, is his reintroduction of purpose into the natural world". Obviously, the two authors must mean very different things.
Purely logical analysis helped remarkably little to clear up the confusion. What finally produced a breakthrough in our thinking about teleology was the introduction of new concepts from the fields of cybernetics and new terminologies from the language of information theory. The result was the development of a new teleological language, which claims to be able to take advantage of the heuristic merits of teleological phraseology without being vulnerable to the traditional objections.
1. TRADITIONAL OBJECTIONS TO THE USE OF TELEOLOGICAL LANGUAGE Criticism of the use of teleological language is traditionally based on one or several of the following objections. In order to be acceptable, teleological language must be immune to these objections.
1. Teleological Statements and Explanations Imply the Endorsement of Unverifiable Theological or Metaphysical Doctrines in Science This criticism was indeed valid in former times, as for instance when natural theology operated extensively with a strictly metaphysical teleology. Physiological processes, adaptations to the environment, and all forms of seemingly purposive behavior tended to be interpreted as being due to non-material vital forces. This interpretation was widely accepted among Greek philosophers, including Aristotle, who discerned an active soul everywhere in nature. Bergson's (1910) élan vital and Driesch's (1909) Entelechie are relatively recent examples of such metaphysical teleology. Contemporary philosophers reject such teleology almost unanimously. Likewise, the employment of teleological language among modern biologists does not imply adoption of such metaphysical concepts (see below).
2. The Belief that Acceptance of Explanations for Biological Phenomena that Are not Equally Applicable to Inanimate Nature Constitutes Rejection of a Physico-Chemical Explanation Ever since the age of Galileo and Newton it has been the endeavor of the 'natural scientists' to explain everything in nature in terms of the laws of physics. To accept special explanations for teleological phenomena in living organisms implied for these critics a capitulation to mysticism and a belief in the supernatural. They ignored the fact that nothing exists in inanimate nature (except for man-made machines) which corresponds to DNA programs or to goal-directed activities. As a matter of fract, the acceptance of a teleonomic explanation (see below) is in no way in conflict with the laws of physics and chemistry. It is neither in opposition to a causal interpretation, nor does it imply an acceptance of supernatural forces in any way whatsoever.
3. The Assumption that Future Goals were the Cause of Current Events Seemed in Complete Conflict with any concept of Causality Braithwaite (1954) state the conflict as follows:
In a [normal] causal explanation the explicandum is explained in terms of a cause which either precedes it or is simultaneous with it; in a teleological explanation the explicandum is explained as being causally related either to a particular goal in the future or to a biological end which is as much future as present or past.
This is why some logicians up to the present distinguish between causal explanations and teleological explanations.
4. Teleological Language Seemed to Represent Objectionable Anthropomorphism The use of words like 'purposive' or 'goal-directed' seemed to imply the transfer of human qualities, such as intent, purpose, planning, deliberation, or consciousness to organic structures and to sub-human forms of life.
Intentional, purposeful human behavior is, almost by definition, teleological. Yet I shall exclude it from further discussion because the words 'intentional' or 'consciously premeditated', which are usually used in connection with such behavior, endanger us with getting involved in complex controversies over psychological theory, even though much of human behavior does not differ in kind from animal behavior. The latter, although usually described in terms of stimulus and response, is also highly 'intentional', as when a predator stalks his prey or when the prey flees from the pursuing predator. Yet, seemingly 'purposive', that is goal-directed behavior in animals can be discussed and analyzed in operationally definable terms, without recourse to anthropomorphic terms like 'intentional' or 'consciously'.
As a result of these and other objections teleological explanations were widely believed to be a form of obscurantism, an evasion of the need for a causal explanation. Indeed, some authors went so far as to make statements such as 'Teleological notions are among the main obstacles to theory formation in biology' (Lagerspetz, 1959: 65). Yet, biologists insisted in continuing to use teleological language.
The teleological dilemma, then consists in the fact that numerous and seemingly weighty objections against the use of teleological language have been raised by various critics, and yet biologists have insisted that they would lose a great deal, methodologically and heuristically, if they were prevent from using such language. It is my endeavor to resolve this dilemma by a new analysis, and particularly by a new classification of the various phenomena that have been traditionally designated as 'teleological'.
2. THE HETEROGENEITY OF TELEOLOGICAL PHENOMENA One of the greatest shortcomings of most recent discussions of the teleology problem has been the heterogeneity of the phenomena designated as 'teleological' by different authors. To me it would seem quite futile to arrive at rigorous definitions until the medley of phenomena, designated as 'teleological', is separated into more or less homogeneous classes. To accomplish this objective, will be my first task.
Furthermore, it only confuses the issue, when a discussion of teleology is mingled with that of such extraneous problems as vitalism, holism, or reductionism. Teleological statements and phenomena can be analyzed without reference to major philosophical systems.
By and large all the phenomena that have been designated in the literature as teleological, can be grouped into three classes:
(1) Unidirectional evolutionary sequences (progressionism, orthogenesis).
(2) Seemingly or genuinely goal-directed processes.
(3) Teleological systems.
The ensuing discussion will serve to bring out the great differences between these three classes of phenomena.
1. Unidirectional evolutionary sequences (progressionism, orthogenesis, etc.) Already with Aristotle and other Greek philosophers, but increasingly so in the 18th century, there was a belief in an upward or forward progression in the arrangement of natural objects. This was expressed most concretely in the concept of the scalanaturae, the scale of perfection (Lovejoy, 1936). Originally conceived as something static (or even descending owing to a process of degradation), the Ladder of Perfection was temporalized in the 18th century and merged almost unnoticeably into evolutionary theories such as that of Lamarck. Progressionist theories were proposed in two somewhat different forms. The steady advance toward perfection was either directed by a supernatural force (a wise creator) or, rather vaguely, by a built-in drive toward perfection. During the flowering of Natural Theology the 'interventionist' concept dominated, but after 1859 it was replaced by so-called orthogenetic theories widely held by biologists and philosophers (see Lagerspetz, 1959: 11-12 for a short survey). Simpson (1949) refuted the possibility of orthogenesis with particularly decisive arguments. Actually, as Weissmann had said long ago (1909), the principle of natural selection solves the origin of progressive adaptation without any recourse to goal-determining forces.
It is somewhat surprising how many philosophers, physical scientists, and occasionally even biologists, still flirt with the concept of teleological determination of evolution. Teilhard de Chardin's (1955) entire dogma is built on such a teleology and so are, as Monod (1971) has stressed quite rightly, almost all of the more important ideologies of the past and present. Even some serious evolutionists play, in my opinion rather dangerously, with teleological language. For instance Ayala (1970:11) says,
the overall process of evolution cannot be said to be teleological in the sense of directed towards the production of specified DNA codes of information, i.e. organisms. But it is my contention that it can be said to be teleological in the sense of being directed toward the production of DNA codes of information which improve the reproductive fitness of a population in the environments were it lives. The process of evolution can also be said to be teleological in that it has the potentiality of producing end-directed DNA codes of information, and has in fact resulted in teleologically oriented structures, patterns of behavior, and regulated mechanisms.
To me this seems a serious misinterpretation. If 'teleological' means anything it means 'goal-directed'. Yet, natural selection is strictly an a posteriori process which rewards current success but never sets up future goals. No one realized this better than Darwin who reminded himself "never to use the words higher or lower." Natural selection rewards past events, that is the production of successful recombinations of genes, but it does not plan for the future. This is, precisely, what gives evolution by natural selection its flexibility. With the environment changing incessantly, natural selection – in contradistinction to orthogenesis – never commits itself to a future goal. Natural selection is never goal oriented. It is misleading and quite inadmissible to designate such broadly generalized concepts as survival or reproductive success as definite and specified goals.
The same objection can be raised against similar arguments presented by Waddington (1968: 55-56). Like so many7 other developmental biologists, he is forever looking for analogies between ontogeny and evolution. "I have for some years been urging that quasi-finalistic types of explanations are called for in the theory of evolution as well as in that of development." Natural selection "in itself suffices to determine, to a certain degree, the nature of the end towards which evolution will proceed, it must result in an increase in the efficiency of the biosystem as a whole in finding ways of reproducing itself." He refers here to completely generalized processes, rather than to specific goals. It is rather easy to demonstrate how ludicrous the conclusions are which one reaches by over-extending the concept of goal-direction. For instance, one might say that it is the purpose of every individual to die because this is the end of every individual, or that it is the goal of every evolutionary line to become extinct because that is what has happened to 99.9% of all evolutionary lines that have ever existed. Indeed, one would be forced to consider as teleological even the second law of thermodynamics.
One of Darwin's greatest contributions was to have made it clear that teleonomic processes involving only a single individual are of an entirely different nature from evolutionary changes. The latter are controlled by the interplay of the production of variants (new genotypes) and their sorting out by natural selection, a process which is quite decidedly not directed toward a specified distant end. A discussion of legitimately teleological phenomena would be futile unless evolutionary processes are eliminated from consideration.
2. Seemingly or Genuinely Goal-Directed Processes Nature (organic and inanimate) abounds in processes and activities that lead to an end. Some authors seem to believe that all such terminating processes are of one kind and 'finalistic' in the same manner and to the same degree. Taylor (1950), for instance, if I understand him correctly, claims that all forms of active behavior are of the same kind and that there is no fundamental difference between one kind of movement or purposive action and any other. Waddington (1968) gives a definition of his term 'quadi-finalistic' as requiring "that the end state of the process is determined by its properties at the beginning."
Further study indicates, however, that the class of 'end-directed processes' is composed of two entirely different kinds of phenomena. These two types of phenomena may be characterized as follows:
A. Teleomatic processes in inanimate nature. Many movements of inanimate objects as well as physico-chemical processes are the simple consequences of natural laws. For instance, gravity provides the end state for a rock which I drop into a well. It will reach its end-state when it has come to rest on the bottom. A red-hot piece of iron reaches its 'end-state' when its temperature and that of its environment are equal. All objects of the physical world are endowed with the capacity to change their state and these changes follow natural laws. They are 'end-directed' only in a passive, automatic way, regulated by external forces or conditions. Since the end state of such inanimate objects is automatically achieved such changes might be designated as teleomatic. All teleomatic processes come to an end when the potential is used up (as in the cooling of a heated piece of iron) or when the process is topped by encountering an external impediment (as a falling stone hitting the ground). Teleomatic processes simply follow natural laws, i.e. lead to a result consequential to concomitant physical forces, and the reaching of their end state is not controlled by a built-in program. The law of gravity and the second law of thermodynamics are among the natural laws which most frequently govern teleomatic processes.
B. Teleonomic processes in living nature. Seemingly goal-directed behavior in organisms is of an entirely different nature from telomatic processes. Goal-directed 'behavior' (in the widest sense of this word) is extremely widespread in the organic world; for instance, most activity connected with migration, food-getting, courtship, ontogeny, and all phases of reproduction is characterized by such goal orientation. The occurrence of goal-directed processes is perhaps the most characteristic feature of the world of living organisms.
The definition of the term teleonomic. For the last 15 years or so the teleonomic has been used increasingly often for goal-directed processes in organisms. I proposed in 1961 the following definition for this term: "It would seem useful to restrict the term teleonomic rigidly to systems operating on the basis of a program, a code of information" (Mayr, 1961). Although I used the term 'system' in this definition, I have since become convinced that it permits a better operational definition to consider certain activities, processes (like growth) and active behaviors as the most characteristic illustrations of teleonomic phenomena. I therefore modify my definition, as follows: A teleonomic process or behavior is one which owes its goal-directedness to the operation of a program. The term teleonomic implies goal-direction. This, in turn, implies a dynamic process rather than a static condition, as represented by a system. The combination of 'teleonomic' with the term system is, thus, rather incongruent (see below).
All teleonomic behavior is characterized by two components. It is guided by a 'program' and it depends on the existence of some end point, goal, or terminus which is foreseen in the program that regulates the behavior. This endpoint might be a structure, a physiological function, the attainment of a new geographical position, or a 'consummatory' (Craig, 1918) act in behavior. Each particular program is the result of natural selection, constantly adjusted by the selective value of the achieved endpoint.
My definition of 'teleonomic' has been labeled by Hull (1973) as a 'historical definition'. Such a designation is rather misleading. Although the genetic program (as well as its individually acquired components) originated in the past, this history is completely irrelevant for the functional analysis of a given teleonomic process. Whether this program had originated through a lucky macromutation (as Richard Goldschmidt had conceived possible) or through a slow process of gradual selection, or even through individual learning or conditioning as in open programs, is quite immaterial for the class of a process as 'teleonomic'. On the other hand, a process that does not have a programmed end, does not qualify to be designated as teleonomic (see below for a discussion of the concept 'program').
All teleonomic processes are facilitated by specifically selected executive structures. The fleeing of a deer from a predatory carnivore is facilitated by the existence of superlative sense organs and the proper development of muscles and other components of the locomotory apparatus. The proper performing of teleonomic processes at the molecular level is made possible by highly specific properties of complex macromolecules. It would stultify the definition of 'teleonomic' if the appropriateness of these facilitating executive structures were made part of it. On the other had it is in the nature of a teleonomic program that it does not induce a simple unfolding of some completely preformed Gestalt, but that it always controls a more or less complex process which must allow for internal and external disturbances. Teleonomic processes during ontogenetic development, for instance, are constantly in danger of being derailed even if only temporarily. There exist innumerable feedback devices to prevent this or to correct it. Waddington (1957) has quite rightly called attention to the frequency and importance of such homeostatic devices which virtually guarantee the appropriate canalization of development.
We owe a great debt of gratitude to Rosenblueth et al. (1943) for their endeavor to find a new solution for the explanation of teleological phenomena in organisms. They correctly identified two aspects of such phenomena, (1) that they are seemingly purposeful being directed toward a goal, and (2) that they consist of active behavior. The background of these authors was in the newly developing field of cybernetics and it is only natural that they should have stressed the fact that goal directed behavior is characterized by mechanisms which correct errors committed during the goal-seeking. They considered the negative feedback loops of such behavior as its most characteristic aspect and stated "teleological behavior thus becomes synonymous with behavior controlled by negative feedback." This statement emphasizes important aspects of teleological behavior, yet it misses the crucial point: The truly characteristic aspect of goal-seeking behavior is not that mechanisms exist which improve the precision with which a goal is reached, but rather that mechanisms exist which initiate, i.e. 'cause' this goal-seeking behavior. It is not the thermostat that determines the temperature of a house, but the person who sets the thermostat. It is not the torpedo which determines toward what ship it will be shot and at what time, but the naval officer who releases the torpedo. Negative feebacks only improve the precision of goal-seeking, but do not determine it. Feedback devices are only executive mechanisms that operate during the translation of a program.
Therefore it places the emphasis on the wrong point to define teleonomic processes in terms of the presence of feedback devices. They are mediators of the program, but as far as the basic principle of goal achievement is concerned, they are of minor consequence.
3. Recent Usages of the Term Teleonomic The term 'teleonomic' was introduced into the literature by Pittendrigh (1958:394) in the following paragraph:
Today the concept of adaptation is beginning to enjoy an improved respectability for several reasons: it is seen as less than perfect; natural selection is better understood; and the engineer-physicist in building end-seeking automata has sanctified the use of teleological jargon. It seems unfortunate that the term 'teleology' should be resurrected and, as I think, abused in this way. The biologists' long-standing confusion would be more fully removed is all end-directed systems were described by some other term, like 'teleonomic', in order to emphasize that the recognition and description of end-directedness does not carry a commitment to Aristotelian teleology as an efficient [sic] casual principle.
It is evident that Pittendrigh had the same phenomena in mind as I do,1 even though his definition is rather vague and his placing the term 'teleonomic' in opposition to Aristotle's 'teleology' is unfortunate. As we shall see below, most of Aristotle's references to end-directed processes refer precisely to the same things which Pittendrigh and I would call teleonomic (see also Delbrück, 1971).
Other recent usages of the term that differ from my own definition are the following. B. Davis (1962), believing that the term denotes 'the development of valuable structures and mechanisms' as the result of natural selection, uses the term virtually as synonymous with adaptiveness. The same is largely true for Simpson (1958: 520-521) who sees in 'teleonomic' the description for a system or structure which is the product of evolution and of selective advantage:
The words 'finalistic' and 'teleological' have, however, had an unfortunate history in philosophy which makes them totally unsuitable for use in modern biology. They have too often been used to mean that evolution as a whole has a predetermined goal, or that the utility of organization in general is with respect to man or to some supernatural scheme of things. Thus these terms may implicitly negate rather than express the biological conclusion that organization in organisms is with respect to utility to each separate species at the time when it occurs, and not with respect to any other species or any future time. In emphasis of this point of view, Pittendrigh [above] suggests that the new coinage 'teleonomy' be substituted for the debased currency of teleology.
Monod (1971) likewise deals with teleonomy as if the word simply meant adaptation. It is not surprising therefore that Monod considers teleonomy "to be a profoundly ambiguous concept." Furthermore, says Monod, all functional adaptations are "so many aspects or fragments of a unique primary project which is the preservation and multiplication of the species." He finally completes the confusion by choosing "to define the essential teleonomic project as consisting in the transmission from generation to generation of the invariant content characteristic of the species. All these sturctures, all the performances, all the activities contributing to the success of the essential project will hence be called teleonomic."
What Monod calls 'teleonomic' I would designate as of 'selective value'. Under these circumstances it is not surprising when Ayala (1970) claims that the term 'teleonomy' had been introduced into the philosophical literature in order 'to explain adaptation in nature as the result of natural selection'. If this were indeed true, and it is true of Simpson's and Davis's cited definitions, the term would be quite unnecessary. Actually, there is nothing in my 1961 account which would support this interpretation, and I know of no other term that would define a goal-directed activity or behavior that is controlled by a program. Even though Pittendrigh's discussion of 'teleonomic' rather confused the issue and has led to the subsequent misinterpretations, he evidently had in mind the same processes and phenomena which I denoted as teleonomic. It would seem well worthwhile to retain the term in the more rigorous definition, which I have now given.