§ 52. Were they needed, many further illustrations might be cited. Going back to the early time when the deeds of the god-king, chanted and mimetically represented in dances round his altar, were further narrated in picture-writings on the walls of temples and palaces, and so constituted a rude literature, we might trace the development of Literature through phases in which, as in the Hebrew Scriptures it presents in one work, theology, cosmogony, history, biography, civil law, ethics, poetry; through other phases in which, as in the Iliad, the religious, martial, historical, the epic, dramatic, and lyric elements are similarly commingled; down to its present heterogeneous development, in which its divisions and subdivisions are so numerous and varied as to defy complete classification. Or we might track the evolution of Science: beginning with the era in which it was not yet differentiated from Art, and was, in union with Art, the handmaid of Religion; passing through the era in which the sciences were so few and rudimentary, as to be simultaneously cultivated by the same philosophers; and ending with the era in which the genera and species are so numerous that few can enumerate them, and no one can adequately grasp even one genus. Or we might do the like with Architecture, with the Drama, with Dress. But doubtless the reader is already weary of illustrations; and my promise has been amply fulfilled. I believe it has been shown beyond question, that that which the German physiologists have found to be the law of organic development, is the law of all development. The advance from the simple to the complex, through a process of successive differentiations, is seen alike in the earliest changes of the Universe to which we can reason our way back, and in the earliest changes which we can inductively establish; it is seen in the geologic and climatic evolution of the Earth, and of every single organism on its surface; it is seen in the evolution of Humanity, whether contemplated in the civilized individual, or in the aggregation of races; it is seen in the evolution of Society, in respect alike of its political, its religious, and its economical organization; and it is seen in the evolution of all those endless concrete and abstract products of human activity, which constitute the environment of our daily life. From the remotest past which Science can fathom, up to the novelties of yesterday, that in which Evolution essentially consists, is the transformation of the homogeneous into the heterogeneous.
CHAPTER III.
THE LAW OF EVOLUTION, CONTINUED
§ 53. But now, does this generalization express the whole truth? Does it include all the phenomena of Evolution? and does it exclude all other phenomena? A careful consideration of the facts, will show that it does neither.
That there are changes from the less heterogeneous to the more heterogeneous, which do not come within what we call Evolution, is proved in every case of local disease. A portion of the body in which there arises a cancer, or other morbid growth, unquestionably displays a new differentiation. Whether this morbid growth be, or be not, more heterogeneous than the tissues in which it is seated, is not the question. The question is, whether the structure of the organism as a whole, is, or is not, rendered more heterogeneous by the addition of a part unlike every pre-existing part, both in form and composition. And to this question there can be none but an affirmative answer. Again, it might with apparent truth be contended, that the earlier stages of decomposition in a dead body, similarly involve an increase of heterogeneity. Supposing the chemical changes to commence in some parts of the body earlier than in other parts, as they commonly do; and to affect different tissues in different, ways, as they must; it seems to be a necessary admission that the entire body, made up of undecomposed parts and parts decomposed in different ways and degrees, has become more heterogeneous than it was. Though greater homogeneity will be the eventual result, the immediate result is the opposite. And yet this immediate result is certainly not evolution. But perhaps of all illustrations the least debatable are those furnished by social disorders and disasters. When in any nation there occurs a rebellion, which, while leaving some provinces undisturbed, developes itself here in secret societies, there in public demonstrations, and elsewhere in actual appeal to arms, leading probably to conflict and bloodshed; it must be admitted that the society, regarded as a whole, has so been rendered more heterogeneous. Or when a dearth causes commercial panic with its entailed bankruptcies, closed factories, discharged operatives, political agitations, food riots, incendiarisms; it is manifest that as, throughout the rest of society, there still exists the ordinary organization displaying the usual phenomena, these new phenomena must be regarded as adding to the complexity previously existing. Nevertheless, it is clear that such changes so far from constituting a further stage of evolution, are steps towards dissolution.
There is good reason to think then, that the definition arrived at in the last chapter, is an imperfect one. We may suspect, not that the process of evolution is different from the process there described; but that the description did not contain all that it should. The changes above instanced as coming within the formula as it now stands, are so obviously different from the rest, that the inclusion of them implies some oversight – some distinction hitherto overlooked. Such further distinction we shall find really exists.
§ 54. At the same time that all evolution is a change from the homogeneous to the heterogeneous, it is also a change from the indefinite to the definite. As well as an advance from simplicity to complexity, there is an advance from confusion to order – from undetermined arrangement to determined arrangement. In the process of development, no matter what sphere it is displayed in, there is not only a gradual multiplication of unlike parts; but there is a gradual increase in the distinctness with which these parts are marked off from each other. And so is that increase of heterogeneity which characterizes Evolution, distinguished from that increase of heterogeneity which does not. For proof of this, it needs only to reconsider the instances given above. The structural changes constituting a disease, have no such definiteness, either in locality, extent, or outline, as the structural changes constituting development. Though certain morbid growths arise much more commonly in some parts of the body than in others (as warts on the hands, cancer on the breasts, tubercle in the lungs), yet they are not confined to these parts; nor, when found on them, are they anything like so precise in their relative positions as are the normal parts around them. In size, again, they are extremely variable – they bear no such constant proportion to the body as organs do. Their forms, too, are far less specific than organic forms. And they are extremely irregular or confused in their internal structures. That is to say, they are in all respects comparatively indefinite. The like peculiarity may be traced in decomposition. That state of total indefiniteness to which a dead body is finally reduced, is a state towards which the putrefactive changes have tended from their commencement. Each step in the destruction of the organic compounds, is accompanied by a blurring of the minute structure – diminishes its distinctness. From the portions that have undergone most decomposition, there is a gradual transition to the less decomposed portions. And step by step the lines of organization, once so precise, disappear. Similarly with social changes of an abnormal kind. A political outbreak rising finally to a rebellion, tends from the very first to obliterate the specializations, governmental and industrial, which previously existed. The disaffection which originates such an outbreak, itself implies a loosening of those ties by which the citizens are bound up into distinct classes and sub-classes. Agitation, growing into revolutionary meetings, shows us a decided tendency towards the fusion of ranks that are usually separated. Acts of open insubordination exhibit a breaking through of those definite limits to individual conduct which were previously observed; and a disappearance of the lines previously existing between those in authority and those beneath them. At the same time, by the arrest of trade, artizans and others lose their occupations; and in so ceasing to be functionally distinguished, become fused into a mass from which the demarcations in great part vanish. And when at last there comes positive insurrection, all magisterial and official powers, all class distinctions, and all industrial differences, at once cease: organized society lapses into an unorganized aggregation of social units. How the like holds true of such social disasters as are entailed by famine, needs not be pointed out. On calling to mind that in cases of this kind the changes are from order towards disorder, it will at once be seen that like the foregoing they are changes from definite arrangements to indefinite arrangements.
Thus then is that increase of heterogeneity which constitutes Evolution, distinguished from that increase of heterogeneity which does not do so. Though in disease and death, individual or social, the earliest modifications may be construed as additions to the heterogeneity previously existing; yet they cannot be construed as additions to the definiteness previously existing. They begin from the very outset to destroy this definiteness; and so, gradually produce a heterogeneity that is indeterminate instead of determinate. Just in the same way that a city, already multiform in its variously arranged structures of various architecture, may be made more multiform by an earthquake, which leaves part of it standing and overthrows other parts in different ways and degrees, and yet is at the same time reduced from definite arrangement to indefinite arrangement; so may organized bodies be made for a time more multiform by changes which are nevertheless disorganizing changes. And in the one case as in the other, it is the absence of definiteness which distinguishes the multiformity of regression from the multiformity of progression.
If the advance from the indefinite to the definite is an essential characteristic of Evolution, we shall of course find it everywhere displayed; as in the last Chapter we found the advance from the homogeneous to the heterogeneous. With a view of showing that it is so, let us now briefly reconsider the same several classes of facts.
§ 55. Beginning as before with a hypothetical illustration, we have to note that each further stage in the evolution of the Solar System, supposing it to have originated from diffused matter, was an advance towards more definite forms, and times, and forces. At first irregular in shape and with indistinct margins, the attenuated substance, as it concentrated and acquired a rotatory motion, must have assumed the shape of an oblate spheroid; which, with every increase of density, became more specific in general outline, and had its surface more sharply marked off from the surrounding void. At the same time, the constituent portions of nebulous matter, instead of independently moving towards their common centre of gravity from all points, and tending to revolve round it in various planes, as they would at first do, must have had these planes more and more merged into a single plane; and this plane must have gained greater precision as the concentration progressed. To which add that in the gradual establishment of a common and determinate angular velocity, instead of the various and conflicting angular velocities of different parts, we have a further change of like nature. According to the hypothesis, change from indistinct characteristics to distinct ones, was repeated in the evolution of each planet and satellite; and may in them be traced to a much greater extent. A gaseous spheroid is less definitely marked off from the space around it than a fluid spheroid, since it is subject to larger and more rapid undulations of surface, and to much greater distortions of general form; and similarly a fluid spheroid, covered as it must be with waves of various magnitudes, is less definite than a solid spheroid. Nor is it only in greater fixity of surface that a planet in its last stage, is distinguished from a planet in its earlier stages. Its general form, too, is more precise. The sphere, to which in the end it very closely approximates, is a perfectly specific figure; while the spheroid, under which figure it previously existed, being infinitely variable in oblateness, is an imperfectly specific figure. And further, a planet having an axis inclined to the plane of its orbit, must, while its form is very oblate, have its plane of rotation greatly disturbed by the attraction of external bodies; whereas its approach to a spherical form, involving a less extreme precessional motion, implies less marked variations in the direction of its axis. Nor is it only in respect of space-relations that the Solar System in general and in detail has become more precise. The like is true of time-relations. During the process of concentration the various portions of the nebulous mass must not only differ more or less from each other in their angular velocities, but each of them must gradually change the period in which it moves round the general axis. In every detached ring however, and in the resulting planet, this progressive alteration ceases: there results a determinate period of revolution. And similarly the time of axial rotation, which, during the formation of each planet, is continually diminishing, becomes at last practically fixed: as in the case of the Earth, whose day is not a second less than it was 2000 years ago. It is scarcely needful to point out that the force-relations have simultaneously become more and more settled. The exact calculations of physical astronomy, show us how definite these force-relations now are; while the great indefiniteness which once characterized them, is implied in the extreme difficulty, if not impossibility, of subjecting the nebular hypothesis to mathematical treatment.
From that originally molten state of the Earth inferable from established geological data – a state in harmony with the nebular hypothesis but inexplicable on any other – the transition to its existing state has been through stages in which the characters became more determinate. Besides being, as above pointed out, comparatively unstable in surface and contour, a fluid spheroid is less definite than a solid spheroid in having no fixed distribution of parts. Currents of molten matter, though kept to certain general circuits by the conditions of equilibrium, cannot in the absence of solid boundaries be precise or permanent in direction: all parts must be in motion with respect to other parts. But a solidification of the surface, even though but partial, is manifestly a step towards the establishment of definite relations of position. In a thin crust however, frequently ruptured as it must be by disturbing forces, and moved by every tidal undulation, such fixity of relative position can be but temporary. Only as the crust slowly increases in thickness, can there arise distinct and settled geographical relations. Observe too that when, on a crust that has cooled to the requisite degree, there begins to precipitate the water floating above as vapour, the water which is precipitated cannot maintain any definiteness either of state or place. Falling on a surface not thick enough to preserve anything beyond slight variations of level, it must form small shallow deposits over areas sufficiently cool to permit condensation; which areas must not only pass insensibly into others that are too hot for this, but must themselves from time to time be so raised in temperature as to drive off the water lying on them. With progressive refrigeration, however, – with an increasing thickness of crust, a consequent formation of larger elevations and depressions, and the condensation of more atmospheric water, there comes an arrangement of parts that is comparatively fixed in both time and space; and the definiteness of state and position increases, until there results such a distribution of continents and oceans as we now see – a distribution that is not only topographically precise, but also in its cliff-marked coast-lines presents a more definite division of land from water than could have existed during the period when islands of low elevation had shelving beaches up which the tide ebbed and flowed to great distances. Respecting the characteristics technically classed as geological, we may draw parallel inferences. While the Earth’s crust was thin, mountain-chains were impossibilities: there could not have been long and well-defined axes of elevation, with distinct water-sheds and areas of drainage. Moreover, from small islands admitting of but small rivers, and tidal streams both feeble and narrow, there would result no clearly-marked sedimentary strata. Confused and varying masses of detritus, such as those now found at the mouths of brooks, must have been the prevailing formations. And these could give place to distinct strata, only as there arose continents and oceans, with their great rivers, long coast-lines, and wide-spreading marine currents. How there must simultaneously have resulted more definite meteorological characters, need not be pointed out in detail. That differences of climates and seasons must have grown relatively decided as the heat of the Sun became distinguishable from the proper heat of the Earth; that the establishment through this cause of comparatively constant atmospheric currents, must have similarly produced more specific conditions in each locality; and that these effects must have been aided by increasing permanence in the distribution of land and sea and of ocean currents; are conclusions which are sufficiently obvious.
Let us turn now to the evidence furnished by organic bodies. In place of deductive illustrations like the foregoing, we shall here find numerous illustrations which, as being inductively established, are less open to criticism. The process of mammalian development, for example, will supply us with numerous proofs ready-described by embryologists. The first change which the ovum of a mammal undergoes, after continued segmentation has reduced its yelk to a mulberry-like mass, is the appearance of a greater definiteness in the peripheral cells of this mass: each of which acquires a distinct enveloping membrane. These peripheral cells, vaguely distinguished from the internal ones both by their greater completeness and by their minuter subdivision, coalesce to form the blastoderm or germinal membrane. One portion of the blastoderm presently becomes contrasted with the rest, through the accumulation of cells still more subdivided, which, together, form an opaque roundish spot. This area germinativa, as it is called, is not sharply delineated, but shades off gradually into the surrounding parts of the blastoderm; and the area pellucida, subsequently formed in the midst of this germinal area, is similarly without any precise margin. The “primitive trace,” which makes its appearance in the centre of the area pellucida, and is the rudiment of that vertebrate axis which is to be the fundamental characteristic of the mature animal, is shown by its name to be at first indefinite – a mere trace. Beginning as a shallow groove, this becomes slowly more pronounced: its sides grow higher, their summits overlap, and at last unite; and so the indefinite groove passes into a definite tube, forming the vertebral canal. In this vertebral canal the leading divisions of the brain are at first discernible only as slight bulgings; while the vertebræ commence as indistinct modifications of the tissue bounding the canal. Simultaneously, the outer portion of the blastoderm has been undergoing separation from the inner portion: there has been a division into the serous and mucous layers – a division at the outset indistinct, and traceable only about the germinal area, but which insensibly spreads throughout nearly the whole germinal membrane, and becomes definite. From the mucous layer, the development of the alimentary canal proceeds as that of the vertebral canal does from the serous layer. Originally a simple channel along the under surface of the embryonic mass, the intestine is rendered step by step more distinct by the bending down, on each side, of ridges which finally join to form a tube – the permanent absorbing surface is by degrees clearly cut off from that temporary absorbing surface of which it was at first a part like all the rest. And in an analogous manner the entire embryo, which at first lies outspread upon the surface of the yelk-sack, gradually rises up from it, and, by the infolding of its ventral surface, becomes a separate mass, connected with the yelk-sack only by a narrow duct. These changes through which the general structure of the embryo is marked out with slowly-increasing precision, are paralleled in the evolution of each organ. The heart is at first a mere aggregation of cells, of which the inner liquify to form the cavity, while the outer are transformed into the walls; and when thus sketched out, the heart is indefinite not only as being unlined by limiting membrane, but also as being but vaguely distinguishable from the great blood-vessels: of which it is little more than a dilatation. By and by the receiving portion of the cavity becomes distinct from the propelling portion. Afterwards there begins to be formed across the ventricle, a septum, which, however, is some time before it completely shuts off the two halves from each other; while the later-formed septum of the auricle remains incomplete during the whole of fœtal life. Again, the liver commences as a multiplication of certain cells in the wall of the intestine. The thickening produced by this multiplication “increases so as to form a projection upon the exterior of the canal;” and at the same time that the organ grows and becomes distinct from the intestine, the channels which permeate it are transformed into ducts having clearly-marked walls. Similarly, by the increase of certain cells of the external coat of the alimentary canal at its upper portion, are produced buds from which the lungs are developed; and these, in their general outlines and detailed structure, acquire distinctness step by step. Changes of this order continue long after birth; and, in the human being, are some of them not completed till middle life. During youth, most of the articular surfaces of the bones remain rough and fissured – the calcareous deposit ending irregularly in the surrounding cartilage. But between puberty and the age of thirty, the articular surfaces are finished off by the addition of smooth, hard, sharply-cut “epiphyses.” Thus we may say that during Evolution, an increase of definiteness continues long after there ceases to be any appreciable increase of heterogeneity. And, indeed, there is reason to think that those structural modifications which take place after maturity, ending in old age and death, are modifications of this nature; since they result in a growing rigidity of structure, a consequent restriction of movement and of functional pliability, a gradual narrowing of the limits within which the vital processes go on, ending at length in an organic adjustment too precise – too narrow in its margin of possible variation to permit the requisite adaptation to external changes of condition.
To demonstrate that the Earth’s Flora and Fauna, regarded either as wholes or in their separate species, have progressed in definiteness, is of course no more possible than it was to demonstrate that they have progressed in heterogeneity: lack of facts being an obstacle to the one conclusion as to the other. If, however, we allow ourselves to reason from the hypothesis, now daily rendered more probable, that every species of organic form up to the most complex, has arisen out of the simplest through the accumulation of modifications upon modifications, just as every individual organic form arises; we shall see that in such case there must have been a progress from the indeterminate to the determinate, both in the particular forms and in the groups of forms. We may set out with the significant fact that many of the lowest living organisms (which are analogous in structure to the germs of all higher ones) are so indefinite in character that it is difficult, if not impossible, to decide whether they are plants or animals. Respecting sundry of them there are unsettled disputes between zoologists and botanists; and it has even been proposed to group them into a separate kingdom, forming a common basis to the animal and vegetal kingdoms. Note next that among the Protozoa, extreme indefiniteness of shape is very general. In the shell-less Rhizopods and their allies, not only is the form so irregular as to admit of no description, but it is neither alike in any two individuals nor in the same individual at successive moments. By the aggregation of such creatures, are produced, among other indefinite bodies, the sponges – bodies that are indefinite in size, in contour, in internal arrangement, and in the absence of an external limiting membrane. As further showing the relatively indeterminate character of the simplest organisms, it may be mentioned that their structures vary very greatly with surrounding conditions: so much so that, among the Protozoa and Protophyta, many forms which were once classed as distinct species, and even as distinct genera, are found to be merely varieties of one species. If now we call to mind how precise in their attributes are the highest organisms – how sharply cut their outlines, how invariable their proportions, and how comparatively constant their structures under changed conditions, we cannot deny that greater definiteness is one of their characteristics; and that if they have been evolved out of lower organisms, an increase of definiteness has been an accompaniment of their evolution. That in course of time, species have become more sharply marked off from other species, genera from genera, and orders from orders, is a conclusion not admitting of a more positive establishment than the foregoing; and must, indeed, stand or fall with it. If, however, species and genera and orders have resulted from the process of “natural selection,” then, as Mr. Darwin shows, there must have been a tendency to divergence, causing the contrasts between groups to become more and more pronounced. By the disappearance of intermediate forms, less fitted for special spheres of existence than the extreme forms they connected, the differences between the extreme forms must be rendered more decided; and so, from indistinct and unstable varieties, must slowly be produced distinct and stable species. Of which inference it may be remarked, not only that it follows from a process to which the organic creation is of necessity ever subject, but also that it is in harmony with what we know respecting races of men and races of domestic animals.
Evidence that in the course of psychial development, there is a change from the vague to the distinct, may be seen in every nursery. The confusion of the infant’s perceptions is shown by its inability to distinguish persons. The dimness of its ideas of direction and distance, may be inferred from the ill-guided movements of its hands, and from its endeavours to grasp objects far out of reach. Only by degrees does the sense of equilibrium, needful for safe standing and moving, gain the requisite precision. Through the insensible steps that end in comprehensible speech, we may trace an increase in the accuracy with which sounds are discriminated and in the nicety with which they are imitated. And similarly during education, the change is towards the establishment of internal relations more perfectly corresponding to external ones – to exactness in calculations, to a better representation of objects drawn, to a more correct spelling, to a completer conformity to the rules of speech, to clearer ideas respecting the affairs of life. How in the further progress to maturity the law still holds, needs not here be pointed out; more especially as it will presently be shown in treating of the evolution of intelligence during the advance of civilization. The only further fact calling for remark, is, that this increase of mental definiteness is, in some ways, manifested even during the advance from maturity to old age. The habits of life grow more and more fixed; the character becomes less capable of change; the quantity of knowledge previously acquired ceases to have its limits alterable by additions; and the opinions upon every point admit of no modification.
Still more manifestly do the successive phases through which societies pass, display the progress from indeterminate arrangement to determinate arrangement. A wandering tribe of savages, as being fixed neither in its locality nor in the relative positions of its parts, is far less definite than a nation, covering a territory clearly marked out, and formed of individuals grouped together in towns and villages. In such a tribe the social relations are similarly confused and unsettled. Political authority is neither well established nor precise. Distinctions of rank are neither clearly marked nor impassable. “Medicine-men” and “rain-makers” form a class by no means as distinct from the rest of the community as eventually becomes the priesthood they foreshadow. And save in the different occupations of men and women, there are no complete industrial divisions. Only in tribes of considerable size, which have enslaved other tribes, is the economical differentiation decided. Any one of these primitive societies however that developes, becomes step by step more specific. Increasing in size, consequently ceasing to be so nomadic, and restricted in its range by neighbouring tribes, it acquires, after prolonged border warfare, a more settled territorial boundary. The distinction between the royal race and the people, grows so extreme as to amount in the popular apprehension to a difference of nature. The warrior-class attains a perfect separation from classes devoted to the cultivation of the soil or other occupations regarded as servile. And there arises a priesthood that is defined in its rank, its functions, its privileges. This sharpness of definition, growing both greater and more variously exemplified as societies advance to maturity, is extremest in those that have reached their full development or are declining. Of ancient Egypt we read that its social divisions were strongly-marked and its customs rigid. Recent investigations make it more than ever clear, that among the Assyrians and surrounding peoples, not only were the laws unalterable, but even the minor habits, down to those of domestic routine, possessed a sacredness which insured their permanence. In India at the present day, the unchangeable distinctions of caste, not less than the constancy in modes of dress, industrial processes, and religious observances, show us how fixed are the arrangements where the antiquity is great. Nor does China with its long-settled political organization, its elaborate and precise conventions, and its unprogressive literature, fail to exemplify the same truth. The successive phases of our own and neighbouring societies, furnish facts somewhat different in kind but similar in meaning. After our leading class-divisions had become tolerably well-established, it was long before they acquired their full precision. Originally, monarchical authority was more baronial, and baronial authority more monarchical, than they afterwards became. Between modern priests and the priests of old times, who while officially teachers of religion were also warriors, judges, architects, there is a marked difference in definiteness of function. And among the people engaged in productive occupations, the like contrast would be found to hold: the industrial office has become more distinct from the military; and its various divisions from each other. A history of our constitution, reminding us how, after prolonged struggles, the powers of King, Lords, and Commons, have been gradually settled, would clearly exhibit analogous changes. Countless facts bearing the like construction would meet us, were we to trace the development of legislation: in the successive stages of which, we should find statutes made more precise in their provisions – more specific in their applications to particular cases. Even at the present time we see that each new law, beginning as a vague proposition, is, in the course of enactment, elaborated into specific clauses; and further that only after its interpretation has been established by judges’ decisions in courts of justice, does it reach its final definiteness. From the history of minor institutions like evidence may be gathered. Religious, charitable, literary, and all other societies, beginning with ends and methods roughly sketched out and easily modifiable, show us how, by the accumulation of rules and precedents, the purposes become more distinct and the modes of action more restricted; until at last death often results from a fixity which admits of no adaptation to new conditions. Should it be objected that among civilized nations there are examples of decreasing definiteness, (instance the breaking down of limits between ranks,) the reply is, that such apparent exceptions are the accompaniments of a social metamorphosis – a change from the military or predatory type of social structure, to the industrial or mercantile type, during which the old lines of organization are disappearing and the new ones becoming more marked.