MECHANISM, BIOLOGICAL

Any application of the general principles of mechanism to the explanation of life and vital processes. The several varieties of biological mechanism that have appeared in the history of thought are first explained in this article and then subjected to philosophical analysis and critique.

Early Forms. Histories of biological mechanism commonly begin with the examination of Cartesian dualism. Both Aristotle and thomas aquinas, however, found themselves in opposition to a doctrine, similar to mechanism, elaborated as early as the 5th century b.c. This doctrine figures importantly in the objections raised by Simmias in Plato's Phaedo. Simmias, who had studied under a Pythagorean, Philolaus, argues in the Phaedo that life must be understood as flowing from a particular harmony of the body. This position may have arisen from a coalescence of the Pythagorean enthusiasm for explaining the whole of reality in terms of numerical proportions and of the Empedoclean thesis current in the Sicilian school of medicine, viz, that health consists in a balance of four basic qualities hot, cold, dry, and wet.

Aristotle and St. Thomas object to this position as if it were arguable on at least two levels, although they do not themselves explicitly distinguish these levels in their writings. The first sort of objection addresses itself to the inadequacy, for the explanation of vital phenomena, of certain special features of contemporary physics: vitality cannot be explained in terms of warmth, for fire tends to increase without limit; the explanation of nutrition and growth in terms of the tendency of the elements to move to their natural places ignores the unique function of roots and leaves in plants; the explanation of vital organization in terms of the ratio and spatial arrangement of physical elements accounts for special tissues or organs, but not for the organism as a whole.

The second sort of objection is more general, seeming to reject, principle, the possibility of any explanation of vital activity in terms of the concept of physical organization, regardless of the complication this concept might undergo with the advance of physical theories. For example, it is argued that the "harmony," or organization, of a living body cannot explain its spontaneous initiation of its own movements ("nor can harmony move a body…") and that any explanation in terms of structural or physically organizing principles ignores the fact that structure is inherently variable or modifiable without limit, whereas a thing is either living or it is not: "Substance has no contrary, and does not admit a variation of degree" (C. gent. 2.63–64; cf. In 1 anima. 9, In 2 anima. 8; Aristotle, anim. 407b 30–409a 30, 416a 1–15).

Modern Types. The controversy between Aristotle and St. Thomas, on the one hand, and the mechanists of their day, on the other hand, may be clarified in terms of a modern distinction of mechanism into three types, characterized roughly by the adjectives physical, biological, and philosophical.

Physical Mechanism. The first type holds that biological laws may be explained by deriving them from a postulate set including the basic laws of physics and chemistry and a small number of additional, compatible postulates. This definition is both flexible and vague: obviously the laws regarded as basic in physics and chemistry do not remain the same in succeeding epochs. In the history of thought, science has moved from Empedocles's earth, air, fire, and water, to the solid, uncutable, and elastic atom of the 17th and 18th centuries, to the present, nearly organic model of the atom as an ordered array of electrically charged particles, capable of varying degrees of stability or reactivity. The words "small" and "compatible" appearing in the definition of this type of mechanism are left deliberately vague to reflect the informal character of the conditions of scientific advance. The standards of economy and consistency proper to a scientific theory are dependent on such a great variety of cultural and scientific factors that is inappropriate to attempt to specify them in a formal way.

A current variant of this type of mechanism, proposed by J. J. C. Smart (1963), holds that the complication of physical and chemical laws in biological systems inevitably involves reference to the idiosyncratic history of evolution on earth, i.e., to organisms that have the properties they do, not for any generally statable theoretical reason, but because they happened to evolve at a particular time under particular circumstances. In this view, biology is a form of technology or engineering rather than a science proper; its concern with the application of the laws of physics and chemistry is comparable to that of the electrical engineer, who is not properly concerned with the discovery of universal laws of nature. The key assumption of Smart's mechanism, viz, that the complicating postulates enabling the application of the laws of physics and chemistry to biological phenomena are inevitably of limited, contingent significance, is too recent to have been subjected to thorough debate.

Biological Mechanism. A second type of mechanism vitalism. It rejects the introduction, into theoretical biology, of factors that either (1) fail to increase the simplicity and scope (fertility) of biological theory, (2) fail to increase the precision and facility with which biological theory may be empirically confirmed, or (3) are conceivable only by "anthropomorphic empathy," in terms of such concepts as will, desire, and urge.

This type of mechanism is compatible with the recognition, e.g., in genetics or physiology, of system laws that elude reduction to laws governing physical and chemical processes. It may admit the unpredictable course of evolutionary history and the irreducibility of the principal of natural selection. Mendel's laws and the principles of crossing-over are also seen as eluding derivation from the theoretical principles of physics and chemistry.

Biological mechanism seems to involve the positive requirement that biological phenomena lend themselves to explanation in terms that have the same logical form as those of physics and chemistry. Yet neither the concepts nor the basic laws of biology and physics are required to be identical or even similar, so long as biology and physics have a similar theoretical structure.

This type of mechanism might be said to have as its primary aim, the preservation and clarification of an autonomous scientific method of inquiry into biological phenomena. So understood, it is not necessarily incompatible with philosophies of nature that recognize the independent validity of nonphilosophical investigation of vital processes, or that speculate about the human or metaphysical significance of such scientific inquiry.

Philosophical Mechanism. Whereas biological mechanism is primarily methodological, and hopefully neutral in substantive philosophical debate, the third type of mechanism is thoroughly philosophical, both in its inception and in its ultimate claims. It is primarily associated with R. descartes, who may have been innocent of its more exaggerated aspects, but whose trenchant dicta do not always establish this innocence beyond question.

Descarte's mechanism shares all the strengths and weaknesses of his metaphysical system as a whole. Its foundations are the methodic doubt and the intuition of the existence of the thinking self. Its consequences are formulated as an absolute and exhaustive account of the nature of all reality below the level of human consciousness: inorganic objects, plants, animals, and the human body itself. Thus understood, the foundation of Cartesian mechanism are not tentative and subject to the pragmatic tests of scope and precision; they are indubitable, primitive truths: man cannot doubt his own act of thought in doubting, but he can doubt the existence of any physical object whatsoever, including his own body. This difference marks mind and body as distinct concepts; and in the Cartesian system, reinforced with proofs that God is omnipotent and benevolent, separate conceivability is the surest mark of separate existence. Mind and body are distinct substances, totally distinct types of reality, each with its own laws and essential characteristics.

Biological mechanism excludes evidence gathered by means of "anthropomorphic empathy" from biology because of the practical difficulty in getting general agreement as to the meaning and consequences of such evidence. Philosophical mechanism, on the other hand, insists on the same exclusion because of a prior philosophical decision to regard consciousness and life as irreducibly distinct realms of reality.

Descartes also appears to have been committed to an excessively rigid version of physical mechanism, insisting that all the laws of biology and animal behavior are explicable in terms of a physics whose single primitive term was extension and whose dominant explanatory model was simple, mechanical clock work. It is a simple fact of history that Harvey's revolutionary success in explaining the circulation of the blood in terms of a mechanical system of a pump and vessels or tubes fitted with valves was not duplicated in efforts to explain "animal heat" and embryological development in terms of the same sort of clockwork. The explanation of these latter phenomena waited for the development of biochemical theories employing a more complex explanatory apparatus than that suggested by such concepts as pump, friction, momentum, and so on.

It may be argued that Cartesian mechanism leads to such a parochial form of physical mechanism because of its insistence on the privileged, clear and distinct status of its basic concepts, which consequently are made to seem beyond the need of the gradual process of reform and modification characteristic of scientific concepts as understood in biological mechanism and in more open forms of physical mechanism.

Analysis and Critique. The inadequacy of Decartes's rigid physical mechanism seems to follow upon the self-reforming, progressive nature of scientific method. To reply to this sort of inadequacy by the construction of a similarly inflexible form of vitalism is to share the fallacious belief that scientific concepts must be so clear and distinct that they are unchangeable, closed to modification in terms of expanding contexts and altered relations among themselves. Hans Driesch seems to have made this sort of error in reacting to the limits and indequacies of simple preformationist theories in embryology, T. H. Morgan opened a new field of biological research in the related and extremely productive area of genetics. Morgan explicitly advocated biological mechanism.

The foregoing discussion should clarify the issues involved in the two-level criticism of mechanism made by Aristotle and St. Thomas. At the first level, in objecting to explanations of vital activity in terms of the natural movement of fire or of some harmonic balance of the tendencies of physical elements to move to their natural places, they point out the inevitable shortcomings of any rigid form of physical mechanism that assumes that inorganic theories of the moment are totally adequate for the explanation of vital processes.

At the second level, careful research on a variety of related topics is still necessary to determine their evaluation of the more recent forms of mechanism as used in biological theory. The weight of evidence concerning their positions on the irreducible variety of man's methods of approaching truth seems to exclude the possibility of their opposition to all mechanistic explanations. In fact, the flexibility and pragmatic fertility of such explanations count against any attempt to reject their scientific acceptability. The only appropriate criterion by which they can be judged is their actual success or failure in the organization and clarification of biological research. On the other hand, philosophical mechanism suggests that all knowledge of life below the level of human consciousness is to be gained through a single method and explained in terms of a single set of univocal concepts. This form of mechanism is invalidated by the observation that such terms as substantial unity, vitality, and even homeostasis exhibit an analogical variety of uses, and by the continued use of a variety of techniques—molecular, cellular, organic, ecological, and ethological—for the accumulation of biological data.

See Also: life; soul; matter and form.

Bibliography: l. von bertalanffy, Problems of Life (New York 1960), distinguishes types of mechanisms in a fashion similar to that presented here. r. schubert-soldern, Mechanism and Vitalism, tr. c. e. robin (Notre Dame, Indiana 1962), primarily a review of German literature, on this topic. e. nagel, The Structure of Science (New York 1961). m. beckner; The Biological Way of Thought (New York 1959). j. j. c. smart, Philosophy and Scientific Realism (London 1963). g. j. goodfield, The Growth of Scientific Physiology (London 1960). j. loeb, The Mechanistic Conception of Life (Chicago 1912). b. farrington, Greek Science (rev. Baltimore 1961). j. maritain Distinguish to Unite, or The Degrees of Knowledge, tr. g. b. phelan (New York 1959). t. h. morgan, "Relation of Physics to Biology," Vassar College Physics in its Relations: A Symposium (Poughkeepsie, New York 1927). p. weiss, "From Cell to Molecule," The Molecular Control of Cellular Activity, ed. j. m. allen (New York 1962). j. h. woodger, "Biology and Physics," British Journal for the Philosophy of Science 11 (1960) 89–100.

[a. e. manier]