While it is simpler, this modified formula has the further advantage of being somewhat more comprehensive. To say that it includes not only those definite combinations of simul- taneous and successive changes in an organism, which cor- respond to co-existences and sequences in the environment, but also those structural arrangements which enable the or- ganism to adapt its actions to actions in the environment, may perhaps be going too far; for though these structural arrangements present internal relations adjusted to external relations, yet the contitiuous adjustme^it of relations can scarcely be held to include a fixed adjustment already made. Clearly, Life, which is made up of dynamical phenomena, cannot be defined in terms that shall at the same time define the apparatus manifesting it, which presents only statical phenomena. But while this antithesis serves to remind us that the fundamental distinction between the organism and * In further elucidatiou of this general doctrine, see First Principles, § 25.
^' CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. 81 its actions, is as wide as that between Matter and Motion, it at the same time draws attention to the fact, that if the structural arrangements of the adult are not properly in- cluded in the definition, yet the developmental processes by which those arrangements were established, are included. For that process of evolution during which the organs of the embr3^o are fitted to their prospective functions, is from be- ginning to end the gradual or continuous adjustment of in- ternal relations to external relations. Moreover, those struc- tural modifications of the adult organism, which, under change of climate, change of occupation, change of food, slowly bring about some re- arrangement in the organic balance, must simi- larly be regarded as continuous adjustments of internal re- lations to external relations. So that not only does the de- finition, 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 development 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 comprehen- siveness, so abstract a formula as this is scarcely fitted for our present purpose. Reserving its terms for such use as oc- casion may dictate, it will be best commonly to employ its more concrete equivalent — to consider the internal relations as " definite combinations of simultaneous and successive changes; " the external relations as " co- existences and se- quences; " and the connexion between them as a " corre- spondence."
CHAPTER YI.
THE DEGREE OF LIFE VARIES AS THE DEGREE OF CORRESPONDENCE.
§ 31. Already it has been shown respecting each other qualification 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 be- tween internal and external relations. It is manifest a priori, that since changes in the physical state of the environment, as also those mechanical actions and those variations of available food which occur in it, are liable to stop the processes going on in the organism; and since the adaptive changes in the organism have the efiects of directly or indirectly counter- balancing these changes in the environment; 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. Allow- ing 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 corre- spondence; and the life will be perfect only when the corre- spondence is perfect. Not to dwell in general statements, however, let us contemplate this truth under its concrete aspects.
§ 32. In life of the lowest order, we find that only the THE MKK VARIES AS THE CORRESPONDENCE. 83 most prevalent coexistences and sequences in the environ- ment, have any simultaneous and successive changes answer- ing to them in the organism. A plant's vital processes display adjustment solely to the continuous coexistence of certain elements and forces surrounding its roots and leaves; and vary only with the variations produced in these ele- ments and forces by the sun — are 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 pro- perties of adjacent things. All those visible and audible changes which happen near it, and are connected with other changes that may presently destroy it, pass unrecognized — produce in it no adapted changes: its only adjustment of in- ternal relations to external relations of this order, is seen when it escapes to the surface on feeling the vibrations pro- duced by an approaching mole. Adjusted as are the pro- ceedings of a bird, to a far greater 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 tem- perature and supply of food, consequent on the seasons. And when we see the plant eaten, the worm trodden on, 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 or- ganism made no answering change; and that thus, both in shortness and simplicity, the life was incomplete in propor- tion as the correspondence was incomplete. Progress towards more prolonged and higher life, evidently implies an ability to respond to less general coexistences and sequences. Each 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 84 THE DATA OF BIOLOGY.
greater correspondence thus established, must, other things equal, show itself both 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 increase of longevity and diminution of fertility which we meet with on ascending to creatures of higher and higher development.
It must, however, be remarked, that while length and com- plexity of life are, to a great extent, associated — while a more extended correspondence in the successive changes, commonly implies increased correspondence in the simul- taneous changes; yet it is not uniformly so. Between the two great divisions of life — animal and vegetal — this contrast by no means holds. A tree may live a thousand years, though the simultaneous changes going on in it answer only to the few chemical affinities in the air and the earth, and though its serial changes answer only to those of day and night, of the weather and the seasons. A tortoise, which exhibits in a given time nothing like the number of internal actions adjusted to 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 re- sponding 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 countless dynamical relations external to them. But notwithstanding the qualifications suggested by such cases, it needs but to compare a microscopic fungus with an oak, an animalcule with a shark, a mouse with a man, to recognize the fact that this increasing correspondence of its changes with those of the environment, which characterizes progressing life, ha- bitually shows itself at the same time in continuity and in complication.
Even were not the connexion between length of life and complexity of life thus conspicuous, it would still be true THE LIFE VARIES AS THE CORRESPONDENCE. 85 that the degree of life varies with the degree of correspond- ence. For if the lengthened existence of a tree bo looked upon as tantamount to a considerable degree of life; then it must be admitted that its lengthened display of correspond- ences is tantamount to a considerable degree of correspond- ence. 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 changes are more complex and more rapid — because the correspondence is greater. And since we regard as the high- est 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; the equivalence between deo:ree of life and de<2rree of corresoondence, is un- questionable.
§ 33. In further elucidation of this general truth, and especially in 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, literally, the environment means all surrounding space with the coexistences and sequences contained in it; yet, practi- cally, it often means but a small part of this. The environ- ment of an entozoon, can scarcely be said to extend beyond the body of the animal in which the entozoon lives. That of a fresh- water alga is, virtually, limited to the ditch inhab- ited by the alga. And understanding the term in this re- stricted sense, we shall see that the superior organisms inhabit the more complicated environments.
Thus, contrasted with that found on land, the lower life is that found in the sea; and it has the simpler environment. Marine creatures are affected by a smaller number of co- existences and sequences than terrestrial ones. Being very nearly of the same specific gravity as the surrounding medium, they have to contend with less various mechanical 86 THE DATA OF BIOLOGY.
actions. 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, the sea is liable to none of those extreme and rapid alterations of temperature which the air suffers. Night and day produce no appreciable modifications in it; and it is comparatively little affected by the seasons. Thus its contained fauna show no marked cor- respondences similar to those by which air-breathing crea- tures counterbalance thermal changes. Further, in respect to the supply of nutriment the conditions are 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 inte- grated, coexist under the simplest relation. 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 too with that liquid by the agency of which the vital processes are 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 made available only through those nervous changes constituting perception, and those muscular ones by which drinking is effected. Simi- larly, the contrast might be continued with respect to the electric and hygrometric variations; and the greater multi- plicity of optical and acoustic phenomena with which,ter- restrial life is surrounded. And tracing upwards from the amphibia the widening extent and complexity which the environment, as practically considered, assumes — observing further how increasing heterogeneity in the flora and fauna of the globe, itself progressively complicates the environment THE LIFE VAlllES AS THE CORRESrONDENCE. 87 of each species of organism — it miglit finally be shown that the same general truth is displayed in the history of mankind: 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 environ- ment a social environment that has been growing even more involved. Thus, speaking generally, it is clear that those re- lations in the environment to which relations in the organism must correspond, themselves increase in number and intricacy as the life assumes a higher form.
§ 34. To make yet more manifest the fact, that the degree of life varies as the degree of correspondence, I may here point out, that those other distinctions successively noted when contrasting vital changes with non-vital changes, are all implied in this last distinction — their correspondence with external coexistences and sequences. And to this may be added the supplementary fact, that the increasing fulfil- ment of those other distinctions which we found to accompany increasing life, is involved in the increasing fulfilment of this last distinction. To descend to particulars: — We saw that living organisms are characterized by successive changes; and that as the life becomes higher, the successive changes become more numerous. Well, the environment is full of successive changes, both positive and relative; and the greater the correspondence, the greater the number of suc- cessive changes an organism must display. We saw that life presents simultaneous changes; and that the more elevated it is, the more marked the multiplicity of them. Well, besides countless phenomena of coexistence in the environ- ment, there are often many changes occurring in it at the same moment; and hence increased correspondence with it, supposes an increased display of simultaneous changes in the 88 THE DATA OF BIOLOGY.
organism. Similarly with the heterogeneity of the changes. In the environment the relations are very varied in their kinds; and hence, as the organic actions come more and more into correspondence with them, they also must become very 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 meteorologic variations 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 surrounding changes with which each animal has to deal, are the definitely- combined changes exhibited by other animals, whether prey or enemies; 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. So that throughout, the correspondence of the internal relations with the external ones, is the essential thing; and all the special characteristics of the internal relations, are but the collateral results of this correspondence.
§ 35. As affording the simplest and most conclusive proof that the degree of life varies as the degree of correspondence, it remains 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 relations be- tween assimilation, oxidation, and genesis of force going on in the organism, gradually fall out of correspondence with the relations between oxygen and food and absorption of heat by THE LIFE VARIES AS THE CORRESPONDENCE. 89 the environment. 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 by accident, implies some neighbouring mechanical changes of which the causes are either unobserved from inattention, or are so intricate that their results cannot be foreseen; and consequently certain relations in the organism are not adjusted 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 nu- merous 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.
§ 36. Before closing the chapter, it will be useful to compare the definition of Life here set forth, with the defini- tion of Evolution set forth in First Trinciples. Living bodies being bodies which display in the highest degree the structural changes constituting Evolution; and Life being made up of the functional changes that accompany these structural changes; we ought to find a certain harmony between the definitions of Evolution and of Life. Such a harmony is not wanting.
The first distinction we noted between the kind of change shown in Life, and other kinds of change, was its serial character: we saw that vital change is substantially unlike non-vital change, in being made up of successive changes. Now since organic bodies display in so much higher a de- gree than inorganic bodies, those continuous difierentiations and integrations which constitute Evolution; and since the re- distributions of matter thus carried so far in a compara- tively short period, imply concomitant re -distributions of mo- tion; it is clear that in a given time, organic bodies must 90 THE DATA OF BIOLOGY.
undergo changes so comparatively numerous as to render the successiveness of their changes a marked characteristic. And it will follow a priori, as we found it to do a ^posteriorly that the organisms exhibiting Evolution in the highest degree, exhibit the longest or the most rapid successions of changes, or both. Again, it was shown that vital change is distinguished from non- vital change by being made up of many simultaneous changes; and also that creatures possess- ing high vitality are marked off from those possessing low vitality, by the far greater number of their simultaneous changes. Here too there is entire congruity. In First Principles, § 116, we reached the conclusion, that a force falling on any aggregate is divided into several forces; that when the aggregate consists of parts that are unlike, each part becomes a centre of unlike differentiations of the inci- dent force; and that thus the multiplicity of such differen- tiations must increase with the multiplicity of the unlike parts. It follows necessarily, therefore, that organic aggre- gates, which as a class are distinguished from inorganic aggregates by the greater number of their unlike parts, must be also distinguished from them by the greater number of simultaneous changes they display; and further that the higher organic aggregates, having more numerous unlike parts than the lower, must undergo more numerous simul- taneous changes. We next found that the changes occurring in living bodies, are contrasted with those occurring in other bodies, as being much more heterogeneous; and that the changes occurring in the superior living bodies, are similarly contrasted with those occurring in inferior ones. Well, heterogeneity of function is the correlate of hetero- geneity of structure; and heterogeneity of structure is the leading distinction between organic and inorganic aggre- gates, as well as between the more highly organized and the more lowly organized. By reaction, an incident force must be rendered multiform in proportion to the multiformity of the aggregate on which it falls; and hence those most mul- THE LIFE VATITES AS THE CORRESPONDENCE. 91 tiform aggregates which display in the highest degree the phenomena of Evolution structurally considered, must at the same time be aggregates which display in the highest de- gree the multiform actions which constitute Evolution functionally considered. These heterogeneous changes, exhibited simultaneously and in succession by a living or- ganism, prove, on further inquiry, to be distinguished by their combination from certain non-vital changes which simulate them. Here, too, the parallelism is maintained. It was shown in § 56 of First Princii^les, that an essential characteristic of Evolution is the integration of parts, which accompanies their differentiation — an integration that is shown both in the consolidation of each part, and in the consolidation of all the parts into a whole. Now, nianifestl}^ combination among the changes going on in different com- bined parts, must be proportionate to the degree of com- bination among these parts: the more mutually-dependent the parts, the more mutually- dependent must be their actions. Hence, animate bodies having greater co-ordin- ation of parts than inanimate ones, must exhibit greater co-ordination of changes. And this greater co-ordination of their changes must not only distinguish organic from inor- ganic aggregates; but must, for the same reason, distinguish higher organisms from lower ones, as we found that it did. Yet once more, it was pointed out that the changes constituting Life, differ from other changes in the dcfiniteness of their combination; and that a distinction like in kind, though less in degree, holds between the vital changes of superior creatures and those of inferior creatures. Thes9, also, are contrasts in harmony with the contrasts disclosed by the analysis of Evolution. We saw [First Principles^ §§ 54, 55) that during Evolution, there is an increase of definiteness as well as an increase of heterogeneity. We saw that the integration accompanying differentiation, has necessarily the effect of increasing the distinctness with which the parts are marked off from each other; and that so, out of the inco- 92 THE DATA OF BIOLOGY.