Front Page Titles (by Subject) CHAPTER IV.: THE CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. - The Principles of Psychology
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CHAPTER IV.: THE CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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THE CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES.
§ 117. On considering after what manner we habitually distinguish between a live object and a dead one, we shall find that we do so by observing whether a change which we make in the surrounding conditions, or one which Nature makes in them, is or is not followed by some perceptible change in the object. By discovering that certain things shrink when touched, or fly away when approached, or start when a noise is made, the child first roughly discriminates between the living and the not living; and the man when in doubt whether an animal he is looking at is dead or not, stirs it with his stick; or if it be at a distance, shouts, or throws a stone at it. Vegetable and animal life are alike primarily recognized by this process. The tree that puts out leaves when the spring brings a change of temperature; the flower which opens and closes with the rising and setting of the sun; the plant that droops when the soil is dry, and re-erects itself when watered; are considered alive in virtue of these induced changes: in common with the zoophyte which contracts on the passing of a cloud over the sun; the worm that comes out on to the surface when the ground is continuously shaken; and the hedgehog that rolls itself up when attacked.
Not only, however, do we habitually look for some response when an external stimulus is applied to a living organism, but we recognize a certain fitness in the response. Dead as well as living things display changes under certain changes of condition: as a lump of carbonate of soda that effervesces when dropped into sulphuric acid; as a cord that contracts when wetted; as a piece of wood that turns brown when held to the fire. But in these cases, we do not perceive any connection between the changes undergone, and the preservation of the things that undergo them; or, to avoid any teleological implication—the changes have no apparent relation to future external events which are sure or likely to take place. In vital changes, however, such a relation is clearly visible. Light being a necessary of vegetable life, we see in the action of a plant which, when much shaded, grows towards the unshaded side, an appropriateness which we should not see did it grow otherwise. The proceedings of a spider which rushes out when its web is gently shaken, and stays within when the shaking is violent, manifestly conduce better to the obtainment of food, and the avoidance of danger, than were they reversed. And without multiplying familiar illustrations, the fact that we feel surprise when, as in the case of a bird fascinated by a snake, we see actions tending towards self-destruction, at once shows how generally we have observed a harmony between living changes and changes in surrounding circumstances.
Yet further, there remains to notice the hackneyed truth—the truth rendered so common by infinite repetition that we almost forget its significance—that there is invariably, and necessarily, a certain conformity between the vital functions of any organism, and the conditions in which it is placed—between the processes going on inside of it, and the processes going on outside of it. We know that a fish cannot live in air, or a man in water. An oak growing in the ocean, and a seaweed on the top of a mountain, are incredible combinations of ideas. We find that each animal is limited to a certain range of climate; each plant to certain zones of latitude and elevation. Of the marine flora and fauna, each species is found only between such and such depths. Certain blind creatures can flourish only in dark caves; the limpet only where it is alternately covered and uncovered by the tide; the red-snow fungus only in the arctic regions, or among alpine peaks.
Grouping together these two classes of cases—the cases first named, in which a particular change in the circumstances of an organism is followed by a particular change in it, and the case last named, in which the constant actions going on inside of an organism are dependent upon some constant actions going on outside of it,—we see that in both, the changes or processes displayed by a living body, are specially related to the changes or processes in its environment. And in this truth we find the needful supplement to our definition. By the addition of this all-important characteristic, Life is defined as—The definite combination of heterogeneous changes, both simultaneous and successive, in correspondence with external coexistences and sequences. That the full significance of this addition may be seen, it will be necessary to glance at the correspondence under some of its leading aspects.
§ 118. If we study the actions going on in a plant, with the view of ascertaining what they presuppose, we find that, neglecting minor requirements, there needs a surrounding medium containing at least carbonic acid and water, together with a due supply of light and a certain temperature. Within the leaves, carbon is being assimilated and oxygen given off: without them, is the gas from which the carbon is abstracted, and the imponderable agents by whose aid the abstraction is effected. Be the particular character of the process what it may, it is certain that there are external elements prone to undergo special combination under special conditions: it is certain that the plant presents these conditions and so effects these combinations: and thus it is certain that the several cotemporaneous changes which constitute the plant's life, are in correspondence with coexistences in its environment.
If, again, we ask ourselves respecting the lowest animal cell, what are the changes in virtue of which it continues to live; the answer is, that whilst on the one hand its substance is constantly undergoing oxidation, it is on the other hand constantly absorbing new material from the surrounding medium: and that this organic monad may continue to exist, it is needful that on the average the absorption should go on as fast as, or faster than, the oxidation. If further we ask under what circumstances these combined changes are possible; there is the obvious reply, that the medium in which the monad is placed, must contain oxygen and assimilable matter in a certain ratio. The integrating and disintegrating actions, of which, so far as we can ascertain, the life of the cell consists, necessarily presuppose oxygen and food around the cell—the oxygen in such quantity as to produce some disintegration; the food in such quantity as to permit that disintegration to be made good. Or in other words:—the two antagonistic processes taking place internally, must be in correspondence with the two antagonistic elements present externally.
If, again, leaving those lowest animal forms revealed by the microscope, which simply take in through their external surfaces the nutriment and oxygen coming in contact with them, we pass to those somewhat higher and larger forms which possess a digestive cavity—which have their tissue partially specialized into assimilative and respiratory, in adaptation to these two fundamental processes of integration and disintegration—we see in them, a correspondence between certain actions in the digestive sac, and the properties of certain surrounding bodies. That a creature of this order may continue to live, it is, on the one hand, necessary, that there be available substances in the environment capable of transformation into its own tissue; and on the other hand it is necessary that the introduction of these substances into the digestive sac, shall be followed by the secretion of a solvent fluid capable of reducing them into a fit state for absorption.
When, from the process by which food is digested, we turn to the processes by which it is seized, we perceive the same general truth. The stinging and contractile power of a medusa's tentacle, correspond to the sensitiveness and strength of the living creatures serving for prey, amidst which it floats. Unless that external change which ends in bringing a living body in contact with the tentacle, were instantly followed by those internal changes which result in the coiling and drawing up of the tentacle, the medusa would die of inanition: that is, the fundamental processes of integration and disintegration within it, would get out of correspondence with the agencies and processes without it, and the life would cease.
Similarly, it might be shown that when the mass of tissue of which the creature consists, becomes so large that it cannot be efficiently supplied with nutriment by mere absorption through its limiting membranes, or duly aërated by the action of the surrounding fluid upon its surface, there arises a necessity for a circulatory system by which nutriment and oxygen may be distributed throughout the mass—a system whose actions, as subsidiary to the two primary actions, form links in the correspondence between internal and external changes. And the like is obviously true of all those subordinate functions, secretory and excretory, by which oxidation and assimilation are facilitated—functions which exhibit not only various cotemporaneous changes in mediate correspondence with coexistences in the environment; but which further exhibit successive changes, corresponding to those changes of composition, of temperature, of light, of moisture, of pressure, which the environment undergoes.
Ascending from the visceral actions constituting what physiologists term vegetative life, to the muscular and nervous actions of which animal life is made up, we find the correspondence displayed in a manner still more obvious. The successful performance of any act of locomotion, implies the expenditure of certain internal mechanical forces, adapted in amount and direction to overcome certain external ones. The recognition of an object, implies a harmony between the changes constituting perception, and the particular colours, size, and form, coexisting in the environment. Escape from enemies, presupposes motions within the organism, related in kind and rapidity to motions without it. Destruction of prey, requires a particular combination of subjective changes fitted in amount and succession to counterbalance a group of objective ones. And so with that infinity of adapted actions exemplified at length in works on animal instincts.
In the highest order of vital processes, the same fact is equally manifest. The empirical generalization that guides the farmer in his rotation of crops, serves to bring his actions into concord with certain of the actions going on around him. The rational deductions by which the educated navigator calculates his position at sea, imply a series of mental acts by which his proceedings are conformed to surrounding circumstances. Alike in the simplest inferences of the child, and the most refined ones of the man of science, we may recognize this same fundamental correspondence between the simultaneous and successive changes in the organism, and the coexistences and sequences in its environment.
§ 119. Before proceeding to develope this general formula, which, as we have seen, comprehends equally the lowest processes of plant-life and the highest manifestations of human intelligence, I must dispose of a few unimportant objections that may be urged against it.
In the first place, there are still a few inorganic actions apparently included within the definition; as for example that displayed by the storm-glass. The feathery crystallization, which, on the approach of atmospheric disturbance, takes place in the solution contained in this instrument—a crystallization said to assume this or that character according to the nature of the impending change, and which afterwards dissolves to reappear in new forms under new conditions—may be held to present simultaneous and successive changes that are to some extent heterogeneous, that occur with some definiteness of combination, and, above all, occur in correspondence with external changes. It must be admitted that in this case vegetable life is simulated to a considerable extent; but it is merely simulated. Were there no more conclusive mode of meeting the objection, it might be needful to dwell on the fact, that the simultaneous and successive changes here exhibited, consisting solely of modifications of form and atomic arrangement, are neither so numerous nor so heterogeneous as those going on in a plant, which is ever undergoing not only structural modifications, but also those modifications constituting assimilation, circulation, and respiration. It might be needful to dwell on the further fact, that though the changes occur with a certain definiteness of combination, yet that the combination is not so definite as in the plant, either in respect to the form produced, the time occupied in its production, or the time during which it lasts. And once more it might be requisite to urge, that as, though fulfilling the definition in this imperfect manner, these changes so far resemble vital ones that were it not for the great difference in chemical and other conditions we might confound the two, the definition must not be blamed for seeming to include what seems very much like life. But the proper and conclusive reply is, that the relation between the phenomena occurring in the storm-glass and in the atmosphere respectively, is really not a correspondence at all, in the proper sense of the word. Outside there is a certain change; inside there is a change of atomic arrangement: outside there is another certain change; inside there is another change of atomic arrangement. But subtle as is the dependence of each internal upon each external change, the relation between them does not, in the abstract, differ from the relation between the motion of a straw and the motion of the wind that disturbs it. In either case a change produces a change, and there it ends. As with every inanimate object whose state has been altered by an alteration in the environment, the alteration undergone by the object does not tend to produce in it a secondary alteration, in anticipation of some secondary alteration in the environment. But in every living body there is a tendency towards secondary alterations of this nature: and it is in their production that the correspondence consists. To express the difference by means of symbols:—Let A be a change in the environment; and B some resulting change in an inorganic mass. Then A having produced B, the action ceases. Though the change A in the environment, is followed by some consequent change a in it, no parallel sequence in the inorganic mass simultaneously generates in it some change b. But if we take a living organism, and let the change A impress on it some change C; then, whilst in the environment, A is occasioning a, in the organism C will be occasioning c: of which a and c will show a certain concord in time, place, or intensity. And whilst on the one hand, it is in the continuous production of such concords or correspondences that the life consists; it is on the other, by the continuous production of them that the life is made possible.
The further criticisms that may be expected, refer to certain verbal imperfections in the definition, which it seems impossible to avoid. It may be said with truth, that the word correspondence, will not include, without straining, the various relations to be expressed by it. It may be asked:—How can the continuous processes of assimilation and respiration, correspond with the coexistence of food and oxygen in the environment? or again:—How can the act of secreting some defensive fluid, correspond with some external danger which may never occur? or again:—How can the dynamical phenomena constituting perception, correspond with the statical phenomena of the solid body perceived? The only reply to these questions, is, that we have no word sufficiently general to comprehend all forms of this relation between the organism and its medium, and yet sufficiently specific to convey an adequate idea of the relation; and that the word correspondence seems the least objectionable. The fact to be expressed in all cases, is, that certain changes, continuous or discontinuous, in the organism, are connected after such a manner that, in their relative amounts, or variations, or periods of occurrence, or modes of succession, they have a manifest reference to external actions, constant or serial, actual or potential—a reference such that a definite relation amongst any members of the one group, implies a definite relation amongst certain members of the other group; and the word correspondence appears the best fitted to express this fact.
§ 120. And here this presentation of the phenomena under the general form of relations, suggests that before closing the chapter, it will be well to point out how this definition of life may be reduced to its most abstract shape, and its perhaps most perfect shape. By regarding the respective elements of the definition as relations, we may avoid both the circumlocution and the verbal inaccuracy; and that we may so regard them with propriety is obvious. If a creature's rate of respiration is increased in consequence of a decrease of temperature in its environment; it is that the modified relation between the quantity of heat and the quantity of oxygen in the environment, is met by a modified relation between the amount of oxygen absorbed and heat retained, by the creature. If a sound or a scent wafted to it on the breeze, prompts the stag to dart away from the deer-stalker; it is that there exists in its neighbourhood, a relation between a certain sensible property and certain actions dangerous to the stag, while in its organism there exists an adapted relation between the impression that this sensible property produces, and the actions by which danger is escaped. If a long course of inquiry has led the chemist to a law, enabling him to tell how much of any one element will combine with so much of another; it is that the course of inquiry has established in him specific mental relations, which accord with specific chemical relations in the things around. Hence then, as in all cases we may consider the external phenomena as simply in relation, and the internal phenomena also as simply in relation; the broadest and most complete definition of life will be—The continuous adjustment of internal relations to external relations.
At the same time that it is simpler and briefer, this modified formula has the further advantage of being somewhat more comprehensive. To say that it includes not only those simultaneous and sucessive changes in an organism which correspond to coexistences and sequences in the environment, but also those structural arrangements which enable the organism to adapt its actions to those in the environment, may perhaps be going too far; for though these structural arrangements present internal relations adjusted to external relations, yet the continuous adjustment of relations can scarcely be held to include a fixed adjustment already made. But while this antithesis serves to keep in view the distinction between the organism and its actions, it at the same time draws attention to the fact, that if the structural arrangements of the adult organism are not properly included, yet the developmental processes by which those arrangements were established, are included. For it needs but to contemplate that evolution of the embryo during which the organs are fitted to their prospective functions, to at once see, that from beginning to end it is the gradual, that is, continuous, adjustment of internal relations to external relations. Add to which fact the allied fact, that those structural modifications by which the adult organism becomes better adapted to its conditions—those structural modifications which, under change of climate, change of occupation, change of food, slowly bring about some rearrangement in the organic balance—must similarly be regarded as continuous adjustments of internal relations to external relations. So that not only does the definition, as thus expressed, comprehend all those activities, bodily and mental, which constitute our ordinary idea of life; but it also comprehends, both those processes of growth by which the organism is brought into general fitness for these activities, and those after-processes of adaptation by which it is specially fitted to its special activities.
Nevertheless, superior as it is in simplicity and comprehensiveness, so highly abstract a formula as this, is scarcely fitted for our present purpose. Reserving its terms for such use as occasion may dictate, it will be best commonly to employ its more concrete equivalent—to consider the internal relations as “simultaneous and successive changes;” the external relations as “coexistences and sequences;” and the connection between them as a “correspondence.”