Front Page Titles (by Subject) CHAPTER V.: THE DEGREE OF LIFE VARIES AS THE DEGREE OF CORRESPONDENCE. - The Principles of Psychology
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CHAPTER V.: THE DEGREE OF LIFE VARIES AS THE DEGREE OF CORRESPONDENCE. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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THE DEGREE OF LIFE VARIES AS THE DEGREE OF CORRESPONDENCE.
§ 121. Already it has been shown respecting each of the other qualifications included in the foregoing definition, that the life is high in proportion as that qualification is well fulfilled; and it is now to be remarked, that the same thing is especially true respecting this last qualification—the correspondence between internal and external relations. It needs only to consider for a moment, the meaning of the correspondence, to render this fact certain, à priori. For if, as is manifest, the state of an organism is constantly affected by the state of its environment—if, as we know to be the fact, the changes of temperature, of composition, of hygrometric state, in the environment, as also those mechanical actions, and those variations of available nutriment which occur in it, are liable to stop the processes going on in the organism; and if, as is seen in the instances hourly afforded, the changes that take place in the organism have the effect of directly or indirectly counter-balancing these changes in the environment; then, it follows that the life of the organism will be short or long, low or high, according to the extent to which changes in the environment, are met by corresponding changes in the organism. Allowing a margin for perturbations, the life will continue only while the correspondence continues; the completeness of the life will be proportionate to the completeness of the correspondence; and the life will be perfect only when the correspondence is perfect. Not to dwell in general statements however, let us contemplate this law under its more concrete aspects.
§ 122. Looking at life in its lowest developments, we find that only the most prevalent coexistences and sequences in the environment, have any simultaneous and successive changes corresponding to them in the organism. The vital processes going on in a plant, display adjustment solely to the continuous coexistence of certain elements surrounding its roots and leaves; and vary only with the variations produced in these elements by the sun—are wholly unaffected by the countless mechanical and other changes occurring around; save when accidentally arrested by these. The life of a worm is made up of actions referring almost exclusively to the tangible properties of surrounding things: all those visible and audible changes which happen near it, and are connected with other changes that may presently destroy it, pass unrecognised—produce in it no adapted changes: its only adjustment of internal relations to external relations of this order, is seen when it escapes to the surface on feeling the vibrations produced by an approaching mole. Answering as do the proceedings of a bird to an immense number of coexistences and sequences in the environment, cognizable by sight, hearing, scent, and their combinations; and numerous as are the dangers it shuns, and the needs it fulfils, in virtue of this extensive correspondence; it exhibits no such actions as those by which a human being counterbalances variations in temperature and supply of food, consequent on the seasons—no actions such as those by which a human being entraps the prey he cannot run down. And when we see the plant eaten, the worm trodden upon, the bird dead from starvation; we see alike that the death is an arrest of such correspondence as existed; that it occurred when there was some change in the environment to which the organism made no answering change; and that thus, both in shortness and simplicity, the life was incomplete in proportion as the correspondence was incomplete. Evidently, if, as in those lowest organisms classed as protophyta and protozoa, the simultaneous and successive changes show an adjustment only to the most general coexistences and sequences in the surrounding medium; destruction will ensue when there occurs one of those less general coexistences or sequences to which no action in the organism responds. And evidently the progress towards more prolonged and higher life, will be seen in the ability to respond to such less general coexistences and sequences. Every step upwards must consist in adding to the previously-adjusted relations which the organism exhibits, some further relation parallel to a further relation in the environment. And the greater correspondence thus established, must, other things equal, show itself alike in greater complexity of life, and greater length of life—a truth which will be duly realized on remembering that enormous mortality which prevails among lowly-organized creatures, and that gradual lengthening of individual life and diminution of fertility which we meet with on ascending to creatures of higher and higher development.
To avoid misconstruction, it may be well here to remark, that though length of life and complexity of life, are, to a great extent, associated—though a more extended correspondence in the successive changes commonly implies increased correspondence in the simultaneous changes; yet it is not uniformly so. If we contrast the two great divisions of life—animal and vegetable—we find that this relation by no means holds. A tree may live a thousand years, though the simultaneous changes going on in it correspond only to the few chemical affinities in the air and the earth, and though its serial changes correspond only to those of day and night, of the weather, and of the seasons. A tortoise, though exhibiting in a given time nothing like the number of internal actions corresponding with external ones, that are exhibited by a dog, yet lives far longer. The tree by its massive trunk, and the tortoise by its hard carapace, are saved the necessity of responding to those many surrounding mechanical actions which organisms not thus protected must respond to or die; or rather—the tree and the tortoise display in their structures, certain simple statical relations adapted to meet an infinity of dynamical relations external to them. Notwithstanding, however, the sundry qualifications which these two cases will suggest, it needs but to compare a microscopic fungus with an oak, an animalcule with a shark, a mouse with a man, to recognize the general truth of the position, that this increasing correspondence of its changes with those of the environment, which characterizes progressing life, shows itself at the same time in continuity and in complication.
But it is, after all, unnecessary to insist upon this connection between length of life and complexity of life; seeing that, even were it not as conspicuous as it is, it would still be true that the degree of life varies with the degree of correspondence. For if the lengthened existence of a tree, be looked upon as tantamount to a considerable degree of life; then it must be admitted that its lengthened display of correspondences is tantamount to a considerable degree of correspondence. If otherwise it be held, that notwithstanding its much shorter existence, a dog must rank above a tortoise in degree of life because of its superior activity; then it is implied that its life is higher, because its simultaneous and successive correspondences are more complex and more rapid—because the correspondence is greater. And if, lastly, it be remembered, that we regard as the highest life, that which, like our own, shows great complexity in the correspondences, great rapidity in the succession of them, and great length in the series of them; we shall see it to be rigorously true that the degree of life varies as the degree of correspondence.
§ 123. For the further elucidation of this general truth, and especially for the explanation of the irregularities just referred to, it requires to be observed, that as the life becomes higher the environment itself becomes more complex. Though, in its largest acceptation, the environment must be held to mean all surrounding space with the coexistences and sequences contained in it; yet, practically, it often means but a small part of this. The environment of an entozoon can scarcely be said to extend beyond the body of the animal in which it lives: that of a freshwater alga is, virtually, limited to the ditch it floats in. And understanding the term in this restricted sense, we shall see that the superior organisms inhabit the more variable environments.
Thus, regarding it in the mass, the lowest life is that found in the sea; and it has the simplest environment. Marine creatures are affected by no such multiplicity of coexistences and sequences as terrestrial ones. Being very nearly of the same specific gravity as the surrounding medium, they have not to contend with those various mechanical actions which mammals and birds are subject to in their motions on the earth and through the air. The zoophyte rooted to a stone, and the acalephe passively borne along in the current, need to undergo no internal changes such as those by which the caterpillar meets the varying effects of gravitation while creeping over and under the leaves. Again, this aboriginal environment—this environment to which all the earliest forms of life known to geologists belong—is liable to none of those marked alterations of temperature which the air suffers. Night and day produce no appreciable modifications in it; and it is but little affected by the seasons. Thus its contained fauna show no marked correspondences similar to those by which air-breathing creatures counterbalance thermal changes. Again, in respect to the supply of nutriment the conditions are far more simple. The lower tribes of animals inhabiting the water, like the plants inhabiting the air, have their food brought to them. The same current which brings oxygen to the oyster, also brings it the microscopic organisms on which it lives: the disintegrating matter and the matter to be integrated, coexist under the simplest relation. But it is otherwise with land animals. The oxygen is everywhere; but that which is needed to neutralize its action is not everywhere; it has to be sought; and the conditions under which it is to be obtained are more or less complex. So again with the fluid by whose agency only, the vital processes can be carried on. To marine creatures, water is ever present; and by the lowest is passively absorbed: but to most creatures living on the earth and in the air, it is available only after they have undergone those nervous changes constituting perception, and those muscular ones by which drinking is effected. Similarly, the contrast might be continued with respect to the electric and hygrometric variations, and the greater multiplicity of optical and acoustic phenomena with which terrestrial life is surrounded. And tracing upwards from the amphibia the widening extent and complexity which the environment, as practically considered, assumes—observing further how that gradually-increasing heterogeneity in the flora and fauna of the globe, which time has produced, has itself progressively complicated the environment of each species of organism—it might finally be shown that the same general truth is displayed in the history of the human race: whose advance in civilization has been simultaneous with their advance from the less varied requirements of the torrid zone to the more varied requirements of the temperate zone; whose chief steps have been made in regions presenting a complicated physical geography; and who, in the course of their progress, have been adding to their physical environment a social environment that has been growing even more involved. Thus, neglecting details, it is clear that as an average fact, those relations in the environment to which the relations in the organism must correspond, themselves increase in number and intricacy as the life assumes a higher form.
§ 124. As tending to bring into yet clearer view the fact that the degree of life varies as the degree of correspondence, I may here point out, that those other qualifications which were successively introduced when seeking to distinguish vital changes from non-vital changes, are all implied in this last qualification—their correspondence with external coexistences and sequences; and further, that the peculiarity seen in each of those qualifications—namely, that the higher the life the more it is fulfilled—is involved in the analogous peculiarity of this last qualification—namely that the life is high in proportion as the correspondence is great. To descend to particulars:—We saw that living organisms are characterized by successive changes; and that as the life becomes greater, the successive changes become more numerous. Well, the environment is full of successive changes, both positive and relative; and the more complete the correspondence, the greater the number of successive changes an organism must display. We saw that life presents simultaneous changes; and that the more elevated it is, the greater the multiplicity of them. Well, besides the countless phenomena of coexistence, there are often many changes occurring at the same moment in the environment; and hence increased correspondence with it, presupposes an increased display of simultaneous changes in the organism. So, too, is it, with the heterogeneity of the changes. In the environment the relations are extremely varied in their kinds; and hence, as the organic actions come more and more into correspondence with them, they also must become extremely varied in their kinds. So again is it, even with definiteness of combination. For though the inorganic bodies of which the environment mainly consists, do not present definitely-combined changes, yet they present definitely-combined properties; and though the minor meteorological changes of the environment do not show much definiteness of combination, yet those resulting from day and night and the seasons do. Add to which, that as the environment of each organism comprehends all those other organisms existing within its sphere of life; as the most important and most numerous changes in the environment, with which each creature has to deal, are the changes exhibited by other creatures, whether prey or enemies; and as these changes are in more or less definite combination; it results that definiteness of combination is a general characteristic of the external changes with which internal ones have to correspond. Hence, increase of correspondence involves increased definiteness of combination. And thus it is manifest that throughout, the correspondence of the internal relations with the external ones is the essential thing; and that all the special characteristics of the internal relations, are but the collateral results of this correspondence.
§ 125. As affording perhaps the simplest and most conclusive proof that the degree of life varies as the degree of correspondence, it remains but to point out that perfect correspondence would be perfect life. Were there no changes in the environment but such as the organism had adapted changes to meet; and were it never to fail in the efficiency with which it met them; there would be eternal existence and universal knowledge. Death by natural decay, occurs because in old age the relation between the integrating and disintegrating processes going on in the organism, gradually falls out of correspondence with the relation between oxygen and food in the environment; and eventually the disintegrating process gets so far in advance, that the organism becomes unfit to act. Death from disease, arises either when the organism is congenitally defective in its power to balance the ordinary external actions by the ordinary internal actions, or when there has taken place some unusual external action to which there was no answering internal action. Death from accident, implies some neighbouring mechanical changes whose antecedents are either unobserved from lack of attention, or are so intricate in their dependencies that their consequences cannot be foreseen. In each of these cases the relations in the organism fail in their adjustment to the relations in the environment. Manifestly, if, to every outer coexistence and sequence by which it was ever in any degree affected, the organism presented an answering process or act; the simultaneous changes would be indefinitely numerous and complex, and the successive ones endless—the correspondence would be the greatest conceivable, and the life the highest conceivable, both in degree and in length.
§ 126. And now we may fitly proceed to study the gradual evolution of this correspondence, as seen in progressing from low to high types of life. Those more complex forms of internal change which constitute the subject matter of Psychology, cannot be adequately comprehended without a previous comprehension of those simple forms of it which constitute life in its unintelligent phases. Fundamentally determined, as both these classes of vital relations are, by relations in the environment; and insensibly developed as we shall find the one class to be out of the other; we must take a general view of the entire series of facts, before attempting to interpret the latter part of the series.
Even in the prosecution of this preparatory inquiry, we shall find it needful to arrange the phenomena into groups. Indivisible as they really are, their multiplicity, variety, and complication, is such, that they cannot be truly seen from any one point of view; but must be contemplated under a succession of different aspects.
I may further premise that some of the illustrations and subordinate statements, by which the general argument is elucidated, must be taken with a certain latitude. The phenomena of Life are so complicated, and the modifications of them that occur under modifications of conditions, so various, that duly to substantiate each example of the application of any universal principle, requires preliminaries and qualifications specially referring to the peculiarities of the case; and to give these in every instance would inconveniently encumber the argument. Rather than do this, I prefer leaving those who have a critical knowledge of the facts, to recognize for themselves the occasional imperfections of statement; and to perceive, as I think they will, that these do not militate against the substantial truth of the proposition to be established. I will add, that while there are sundry instances in which, rather than confuse the argument, I have purposely omitted qualifications that might readily be supplied; there are possibly others in which I have unwittingly fallen into error. My acquaintance with physiology is simply that of an amateur; and in a science so extensive, and now undergoing such rapid development, only those who devote their whole time to it can be sure of all their statements. The truth of the doctrines enunciated, however, will be found quite independent of errors in detail, if such there be.