THEORIES OF LIFE
We find that the theories of the nature of life divide themselves into two varieties: the mechanistic and the vitalistic. The former kind of theory states that all living phenomena are to be explained solely by the ordinary physical laws, and that life differs from other phenomena only on account of its complexity, or in some other incidental manner. On the other hand, the vitalistic theories are to the effect that living phenomena are characterized by some mysterious sort of "vital force" which would seem to have the power to suspend or alter the operation of the physical laws that govern the rest of the universe. In the course of the history of science, much has been said both for the vitalistic and the mechanistic theories, and, as yet, no agreement has actually been reached on that subject.
In the attempt to solve our paradox of the second law of thermodynamics, we have incidentally reached a suggestion of the nature of life. According to the conclusions we have reached, there are in the universe what we have called positive tendencies, neutral tendencies, and negative tendencies, all of which are possible results of the reversible physical laws governing the motion of particles of matter. The neutral tendency being an extremely improbable result, very few cases of it are likely to take place; but, in any given case, unless further special circumstances alter the probabilities, the positive or the negative tendency has a 50% probability, and will therefore result from the reversible laws in about half of the cases occurring in the universe. In our section of the universe the positive tendency, however, preponderates, though, inasmuch as it would be extremely improbable that any section of the universe is entirely without instances of the negative tendency, it follows that there must be phenomena of the negative tendency within our observation. The phenomena of the negative tendency are the living phenomena; while the phenomena of the positive tendency are the non-living phenomena.
This theory of life is strictly mechanistic in so far as life is assumed to operate solely under the physical laws applying to the motion of particles, which laws are sufficient to determine a complete chain of causation. On the contrary, physicists, confining their observation entirely to inanimate matter, have reached the conclusion that there is a further physical law, the so-called second law of thermodynamics, which is suspended by living phenomena. There is according to our theory, this essential difference between living and non-living phenomena; and this difference would supply the basis for the idea of "vital force." Thus the two theories of life can be reconciled.
On the matter of the difference between living and non-living bodies, there is still less agreement. For instance, it is stated that lifeless substances, in so far as they form definite shapes, form only geometrical shapes, while living substances form irregular shapes. Outside of the fact that this does not distinguish living bodies from bodies which were once alive but which have lost the property of life, and outside of the fact that not all inorganic substances but only certain solid substances form geometrically shaped crystals, we may refute the statement that living bodies always have irregular shapes by simply adducing the example of the egg. This distinction is therefore on all sides untenable.
Again, it has been said that the difference between living and lifeless substances is the question of the presence of organs. But will that alone distinguish the average organism from a machine? The same objection can be urged against the proposed distinction on the ground that living bodies have a complex organization. However, either of these proposed distinctions may mean that a living body is so organized that everything has its teleological function; and this leads us to a proposed distinction between living and non-living bodies, namely, that living phenomena are essentially teleological. In the case of a machine we have the organization, but the teleology must be sought for in the living being that assembled the machine. Apparently, teleology is a characteristic of life; but yet every thing is explicable on a physico-chemical basis; therefore we have in life the property of apparent teleology as a distinguishing characteristic. Only in this form can the proposed differentiation on the basis of "organization" be tenable. But, as we have seen, apparent teleology is one of the characteristics by which a reversal of the second law of thermodynamics can be recognized. It therefore follows that, in all probability, our distinction on the basis of the second law of thermodynamics is really the fundamental point of difference between living and non-living bodies.
Another suggested method of differentiation is in the capability of reproduction. But, when we come down to the ultimate living units, the cells, this reproduction consists merely of constriction and division; in which it is hardly to be differentiated from the breaking up into smaller drops of a drop of oil in water or a drop of mercury on a glass surface under slight shock. As we have seen, while under ordinary circumstances a shock is necessary to accomplish this division in these cases, yet, under the reversal of the second law of thermodynamics, this form of division is a normal phenomenon.
A further suggestion as to a method of differentiation is that life always derived from other life, while inanimate matter may be derived from either living or non-living bodies. This distinction is a general one, simply stating a fact, but cannot serve as a definition or as a means of differentiation, because it would not show whether any individual case was one of living or lifeless substance. Should we try to apply the test, we should have to ask whether it could only have been derived from other living matter. What it could have been derived from we cannot experimentally find out; the actual causes might be discovered, and then we are reduced to the question whether life is to be found among those causes, and we are now no better off than at first. It is like trying in an unknown region to find the east by the directions in Schedrin's story: Face the north, and the east is on your right. Such directions obviously are useless where the north is as unknown as the east. The basis of fact behind this proposed distinction between living and lifeless bodies, however, we will examine more in detail later on.
The suggestion that organic bodies grow by absorbing particles, while growth, where it is found among inorganic bodies, is always by accretion of matter on the outside, turns out, when analysed, to be rather a distinction between solids and liquids than one between living and lifeless substance. The absorption of particles can be duplicated in the laboratory under circumstances by liquids enclosed in membranes, and a living cell consists of a membrane containing liquids.
Finally, we come to the dynamical distinctions. The most obvious of these is, to say that life is distinguished by movement. This is obviously an incorrect distinction, since all objects are in motion. But there is obviously something peculiar about living movement that seems to make it seem more mobile than other movement. It is thus, for instance, alleged, that living movement comes from internal causes, or else that living bodies work of themselves, while other objects need to be supplied with energy. Even that is not descriptive, for there are always "external" causes for all movements, and life does not create energy; if it uses up energy, it must obtain that energy from somewhere. Similarly with the distinction between static equilibrium of lifeless bodies and the so-called "dynamic" equilibrium of life, often more accurately defined as the metabolic process; such a dynamic equilibrium exists (as molar energy) in the case of almost all machines, and chemically in the case of any catalytic agent, which is also being constantly decomposed and recomposed.
But there are more accurate definitions of this mobility which is so peculiarly characteristic of life. We may notice, for instance, the theory advanced by the late Prof. William James, the theory of the existence of a "reserve energy" in the case of biological, and especially in psychological, activities, which is absent in the case of lifeless activities. According to this, while the living organism can normally use a certain amount of its energy; yet in some mysterious way it can, under special circumstances, draw on an immense surplus fund of "reserve energy." This property being absent in physical bodies, we may draw a distinction on that basis between living and lifeless bodies, and this would seem to be an absolute distinction. Now, it has long been known that physical bodies contain an immense amount of energy which is unavailable for conversion into any thing else; and the physical law that limits the amount of energy which it is possible for a physical body to utilize is precisely this second law of thermodynamics that has given us so much trouble. We must therefore come to the conclusion that, since life does not create energy, and this "reserve energy" is evidently real physical energy, that the peculiarity of life is its ability to draw on more energy than the second law of thermodynamics would allow; that is, its ability, in some circumstances at least, to reverse that second law. And again, we have seen that reversals of the second law are characterized by ability to use a fund of reserve energy that physical bodies cannot use. Let us say that the mechanical efficiency of a set of bodies is 85%; the reciprocal, or 118%, is that of the same set in the reverse universe. But as, under some circumstances, producing special results in the way of heat, etc., not quite 85% of the energy will be used, but, let us say, only 50%, then under those special cases in the reverse universe requiring more energy, the mechanical efficiency will be not 118%, but 200%, thus using over five times the amount of reserve energy normally used. This excess constitutes James's "reserve energy."
Another definition of the mobility of life is what is called "irritability," that is to say, the ability to make a large response to small stimuli. This, it is alleged, is possessed only by life, so that life may be defined by irritability. Against this Verworn objects that such inanimate substances as nitroglycerine also possess this property, that substance producing a powerful explosion under the influence of a slight shock. But in the case of nitroglycerine, we have an unstable equilibrium, and a slight shock simply lets loose the difference of level necessary to reduce to a stable equilibrium; while in the case of life, irritability is part of the so-called "dynamic equilibrium" and does not disturb that equilibrium. Irritability, as it is found in biological phenomena, is the ability to produce normally a large effect from a small stimulus without an irreparable leveling down of energy; in other words, the irritability that distinguishes life consists of the ability to build up higher differences, of energy-level from lower ones, in exactly the inverse order to that required by the second law of thermodynamics. In other words, irritability is identical with the "negative tendency" or, in other words, with the reversal of the second law of thermodynamics. Thus we are again reduced to our form of distinction between living and non-living bodies, namely, that between the negative and the positive tendency.
Verworn proposed the distinction on the basis of chemical constituency namely, that living bodies consist of complicated carbon compounds, such as albumen, protein, etc., which cannot be produced outside of life. But in what way would this definition distinguish a living body from, let us say, a corpse? Or, according to the definition by chemical composition, every wooden object is alive. It is obvious, therefore, that this distinction is untenable.
On the contrary, we have the extreme mechanistic view, represented by Dr. Jacques Loeb, that such a distinction cannot be drawn. The actual existence of a hard and fast distinction of this sort is, indeed difficult to prove, but there is certainly a difference in appearance, which must be based on something, however flimsy that something might be. Dr. Loeb calls a living body "a chemical machine," and states as the only base of differentiation "the power of automatic development, self-preservation, and reproduction." It is not quite clear whether or not all three properties are essential; and not all living bodies possess at all times all these three properties; while, on the contrary, these properties separately are possessed under certain circumstances by certain non-living bodies; so that, to say the least, this attempted distinction must be cleared up somewhat before it can be of any service at all.
Thus, of all the distinguishing characteristics that may be used to define life, we have left simply these three: apparent teleology, reserve energy, and irritability. The latter property (irritability) is, as we have seen, a condensed statement of the reverse of the second law of thermodynamics; while we have seen before that the other two properties, apparent teleology and reserve energy, are the outstanding characteristics by which a reversal of the second law of thermodynamics can be recognized. It follows, therefore, that the fundamental definition behind all these is: Life is a reversal of the second law of thermodynamics. Or, to put it in other terms, since we have seen that mechanical efficiency under positive tendency is less than 100%, under neutral tendency just 100%, and under the negative tendency more than 100%, we may define: Life consists of bodies with a mechanical efficiency of over 100%.