Front Page Titles (by Subject) CHAPTER XIX.: THE INSTABILITY OF THE HOMOGENEOUS. ∗ - First Principles
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CHAPTER XIX.: THE INSTABILITY OF THE HOMOGENEOUS. ∗ - Herbert Spencer, First Principles 
First Principles, 2nd ed. (London: Williams and Norgate, 1867).
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THE INSTABILITY OF THE HOMOGENEOUS.∗
§ 149. The difficulty of dealing with transformations so many-sided as those which all existences have undergone, or are undergoing, is such as to make a definite or complete deductive interpretation seem almost hopeless. So to grasp the total process of re-distribution of matter and motion, as to see simultaneously its several necessary results in their actual inter-dependence, is scarcely possible. There is, however, a mode of rendering the process as a whole tolerably comprehensible. Though the genesis of the re-arrangement undergone by every evolving aggregate, is in itself one, it presents to our intelligence several factors; and after interpreting the effects of each separately, we may, by synthesis of the interpretations, form an adequate conception.
On setting out, the proposition which comes first in logical order, is, that some re-arrangement must result; and this proposition may be best dealt with under the more specific shape, that the condition of homogeneity is a condition of unstable equilibrium.
First, as to the meaning of the terms; respecting which some readers may need explanation. The phrase unstable equilibrium is one used in mechanics to express a balance of forces of such kind, that the interference of any further force, however minute, will destroy the arrangement previously subsisting; and bring about a totally different arrangement. Thus, a stick poised on its lower end is in unstable equilibrium: however exactly it may be placed in a perpendicular position, as soon as it is left to itself it begins, at first imperceptibly, to lean on one side, and with increasing rapidity falls into another attitude. Conversely, a stick suspended from its upper end is in stable equilibrium: however much disturbed, it will return to the same position. The proposition is, then, that the state of homogeneity, like the state of the stick poised on its lower end, is one that cannot be maintained. Let us take a few illustrations.
Of mechanical ones the most familiar is that of the scales If they be accurately made, and not clogged by dirt or rust, it is impossible to keep a pair of scales perfectly balanced: eventually one scale will descend and the other ascend—they will assume a heterogeneous relation. Again, if we sprinkle over the surface of a fluid a number of equal-sized particles, having an attraction for each other, they will, no matter how uniformly distributed, by and by concentrate irregularly into one or more groups. Were it possible to bring a mass of water into a state of perfect homogeneity—a state of complete quiescence, and exactly equal density throughout—yet the radiation of heat from neighbouring bodies, by affecting differently its different parts, would inevitably produce inequalities of density and consequent currents; and would so render it to that extent heterogeneous. Take a piece of redhot matter, and however evenly heated it may at first be, it will quickly cease to be so: the exterior, cooling faster than the interior, will become different in temperature from it. And the lapse into heterogeneity of temperature, so obvious in this extreme case, takes place more or less in all cases. The action of chemical forces supplies other illustrations. Expose a fragment of metal to air or water, and in course of time it will be coated with a film of oxide, carbonate, or other compound: that is—its outer parts will become unlike its inner parts. Usually the heterogeneity produced by the action of chemical forces on the surfaces of masses, is not striking; because the changed portions are soon washed away, or otherwise removed. But if this is prevented, comparatively complex structures result. Quarries of trap-rock contain some striking examples. Not un-frequently a piece of trap may be found reduced, by the action of the weather, to a number of loosely-adherent coats, like those of an onion. Where the block has been quite undisturbed, we may trace the whole series of these, from the angular, irregular outer one, through successively included ones in which the shape becomes gradually rounded, ending finally in a spherical nucleus. On comparing the original mass of stone with this group of concentric coats, each of which differs from the rest in form, and probably in the state of decomposition at which it has arrived, we get a marked illustration of the multiformity to which, in lapse of time, a uniform body may be brought by external chemical action. The instability of the homogeneous is equally seen in the changes set up throughout the interior of a mass, when it consists of units that are not rigidly bound together. The atoms of a precipitate never remain separate, and equably distributed through the fluid in which they make their appearance. They aggregate either into crystalline grains, each containing an immense number of atoms, or they aggregate into flocculi, each containing a yet larger number; and where the mass of fluid is great, and the process prolonged, these flocculi do not continue equi-distant, but break up into groups. That is to say, there is a destruction of the balance at first subsisting among the diffused particles, and also of the balance at first subsisting among the groups into which these particles unite. Certain solutions of non crystalline substances in highly volatile liquids, exhibit in the course of half an hour a whole series of changes that are set up in the alleged way. If for example a little shell-lac-varnish (made by dissolving shell-lac in coal-naptha until it is of the consistence of cream) be poured on a piece of paper, the surface of the varnish will shortly become marked by polygonal divisions, which, first appearing round the edge of the mass, spread towards its centre. Under a lense these irregular polygons of five or more sides, are seen to be severally bounded by dark lines, on each side of which there are light-coloured borders. By the addition of matter to their inner edges, the borders slowly broaden, and thus encroach on the areas of the polygons; until at length there remains nothing but a dark spot in the centre of each. At the same time the boundaries of the polygons become curved; and they end by appearing like spherical sacs pressed together; strangely simulating (but only simulating) a group of nucleated cells. Here a rapid loss of homogeneity is exhibited in three ways:—First, in the formation of the film, which is the seat of these changes; second, in the formation of the polygonal sections into which this film divides; and third, in the contrast that arises between the polygonal sections round the edge, where they are small and early formed, and those in the centre which are larger and formed later.
The instability thus variously illustrated is obviously consequent on the fact, that the several parts of any homogeneous aggregation are necessarily exposed to different forces—forces that differ either in kind or amount; and being exposed to different forces they are of necessity differently modified. The relations of outside and inside, and of comparative nearness to neighbouring sources of influence, imply the reception of influences that are unlike in quantity or quality, or both; and it follows that unlike changes will be produced in the parts thus dissimilarly acted upon.
For like reasons it is manifest that the process must repeat itself in each of the subordinate groups of units that are differentiated by the modifying forces. Each of these subordinate groups, like the original group, must gradually, in obedience to the influences acting upon it, lose its balance of parts—pass from a uniform into a multiform state. And so on continuously. Whence indeed it is clear that not only must the homogeneous lapse into the non-homogeneous, but that the more homogeneous must tend ever to become less homogeneous. If any given whole, instead of being absolutely uniform throughout, consist of parts distinguishable from each other—if each of these parts, while somewhat unlike other parts, is uniform within itself; then, each of them being in unstable equilibrium, it follows that while the changes set up within it must render it multiform, they must at the same time render the whole more multiform than before. The general principle, now to be followed out in its applications, is thus somewhat more comprehensive than the title of the chapter implies. No demurrer to the conclusions drawn, can be based on the ground that perfect homogeneity nowhere exists; since, whether that state with which we commence be or be not one of perfect homogeneity, the process must equally be towards a relative heterogeneity.
§ 150. The stars are distributed with a three-fold irregularity. There is first the marked contrast between the plane of the milky way and other parts of the heavens, in respect of the quantities of stars within given visual areas. There are secondary contrasts of like kind in the milky way itself, which has its thick and thin places; as well as throughout the celestial spaces in general, which are much more closely strown in some regions than in others. And there is a third order of contrasts produced by the aggregation of stars into small clusters. Besides this heterogeneity of distribution of the stars in general, considered without distinction of kinds, a further such heterogeneity is disclosed when they are classified by their differences of colour, which doubtless answer to differences of physical constitution. While the yellow stars are found in all parts of the heavens, the red and blue stars are not so: there are wide regions in which both red and blue stars are rare; there are regions in which the blue occur in considerable numbers, and there are other regions in which the red are comparatively abundant. Yet one more irregularity of like significance is presented by the nebulæ—aggregations of matter which, whatever be their nature, most certainly belong to our sidereal system. For the nebulæ are not dispersed with anything like uniformity; but are abundant around the poles of the galactic circle and rare in the neighbourhood of its plane. No one will expect that anything like a definite interpretation of this structure can be given on the hypothesis of Evolution, or any other hypothesis. The most that can be looked for is some reason for thinking that irregularities, not improbably of these kinds, would occur in the course of Evolution, supposing it to have taken place. Any one called on to assign such reason might argue, that if the matter of which stars and all other celestial bodies consist, be assumed to have originally existed in a diffused form throughout a space far more vast even than that which our sidereal system now occupies, the instability of the homogeneous would negative its continuance in that state. In default of an absolute balance among the forces with which the dispersed particles acted on each other (which could not exist in any aggregation having limits) he might show that motion and consequent changes of distribution would necessarily result. The next step in the argument would be that in matter of such extreme tenuity and feeble cohesion there would be motion towards local centres of gravity, as well as towards the general centre of gravity; just as, to use a humble illustration, the particles of a precipitate aggregate into flocculi at the same time that they sink towards the earth. He might urge that in the one case as in the other, these smallest and earliest local aggregations must gradually divide into groups, each concentrating to its own centre of gravity,—a process which must repeat itself on a larger and larger scale. In conformity with the law that motion once set up in any direction becomes itself a cause of subsequent motion in that direction, he might further infer that the heterogeneities thus set up would tend ever to become more pronounced. Established mechanical principles would justify him in the conclusion that the motions of these irregular masses of slightly aggregated nebular matter towards their common centre of gravity must be severally rendered curvelinear, by the resistance of the medium from which they were precipitated; and that in consequence of the irregularities of distribution already set up, such conflicting curvelinear motions must, by composition of forces, end in a rotation of the incipient sidereal system. He might without difficulty show that the resulting centrifugal force must so far modify the process of general aggregation, as to prevent anything like uniform distribution of the stars eventually formed—that there must arise a contrast such as we see between the galactic circle and the rest of the heavens. He might draw the further not unwarrantable inference, that differences in the process of local concentration would probably result from the unlikeness between the physical conditions existing around the general axis of rotation and those existing elsewhere. To which he might add, that after the formation of distinct stars, the ever-increasing irregularities of distribution due to continuance of the same causes would produce that patchiness which distinguishes the heavens in both its larger and smaller areas. We need not here however commit ourselves to such far-reaching speculations. For the purposes of the general argument it is needful only to show, that any finite mass of diffused matter, even though vast enough to form our whole sidereal system, could not be in stable equilibrium; that in default of absolute sphericity, absolute uniformity of composition, and absolute symmetry of relation to all forces external to it, its concentration must go on with an ever-increasing irregularity; and that thus the present aspect of the heavens is not, so far as we can judge, incongruous with the hypothesis of a general evolution consequent on the instability of the homogeneous.
Descending to that more limited form of the nebular hypothesis which regards the solar system as having resulted by gradual concentration; and assuming this concentration to have advanced so far as to produce a rotating spheroid of nebulous matter; let us consider what further consequence the instability of the homogeneous necessitates. Having become oblate in figure, unlike in the densities of its centre and surface, unlike in their temperatures, and unlike in the velocities with which its parts move round their common axis, such a mass can no longer be called homogeneous; and therefore any further changes exhibited by it as a whole, can illustrate the general law, only as being changes from a more homogeneous to a less homogeneous state. Changes of this kind are to be found in the transformations of such of its parts as are still homogeneous within themselves. If we accept the conclusion of Laplace, that the equatorial portion of this rotating and contracting spheroid will at successive stages acquire a centrifugal force great enough to prevent any nearer approach to the centre round which it rotates, and will so be left behind by the inner parts of the spheroid in its still-continued contraction; we shall find, in the fate of the detached ring, a fresh exemplification of the principle we are following out. Consisting of gaseous matter, such a ring, even if absolutely uniform at the time of its detachment, cannot continue so. To maintain its equilibrium there must be an almost perfect uniformity in the action of all external forces upon it (almost, we must say, because the cohesion, even of extremely attenuated matter, might suffice to neutralize very minute disturbances); and against this the probabilities are immense. In the absence of equality among the forces, internal and external, acting on such a ring, there must be a point or points at which the cohesion of its parts is less than elsewhere—a point or points at which rupture will therefore take place. Laplace assumed that the ring would rupture at one place only; and would then collapse on itself. But this is a more than questionable assumption—such at least I know to be the opinion of an authority second to none among those now living. So vast a ring, consisting of matter having such feeble cohesion, must break up into many parts. Nevertheless, it is still inferrable from the instability of the homogeneous, that the ultimate result which Laplace predicted would take place. For even supposing the masses of nebulous matter into which such a ring separated, were so equal in their sizes and distances as to attract each other with exactly equal forces (which is infinitely improbable); yet the unequal action of external disturbing forces would inevitably destroy their equilibrium—there would be one or more points at which adjacent masses would begin to part company. Separation once commenced, would with ever-accelerating speed lead to a grouping of the masses. And obviously a like result would eventually take place with the groups thus formed; until they at length aggregated into a single mass.
Leaving the region of speculative astronomy, let us consider the Solar System as it at present exists. And here it will be well, in the first place, to note a fact which may be thought at variance with the foregoing argument—namely, the still-continued existence of Saturn’s rings; and especially of the internal nebulous ring lately discovered. To the objection that the outer rings maintain their equilibrium, the reply is that the comparatively great cohesion of liquid or solid substance would suffice to prevent any slight tendency to rupture from taking effect. And that a nebulous ring here still preserves its continuity, does not really negative the foregoing conclusion; since it happens under the quite exceptional influence of those symmetrically disposed forces which the external rings exercise on it. Here indeed it deserves to be noted, that though at first sight the Saturnian system appears at, variance with the doctrine that a state of homogeneity is one of unstable equilibrium, it does in reality furnish a carious confirmation of this doctrine. For Saturn is not quite concentric with his rings; and it has been proved mathematically that were he and his rings concentrically situated, they could not remain so: the homogeneous relation being unstable, would gravitate into a heterogeneous one. And this fact serves to remind us of the allied one presented throughout the whole Solar System. All orbits, whether of planets or satellites, are more or less excentric—none of them are perfect circles; and were they perfect circles they would soon become ellipses. Mutual perturbations would inevitably generate excentricities. That is to say, the homogeneous relations would lapse into heterogeneous ones.
§ 151. Already so many references have been made to the gradual formation of a crust over the originally incandescent Earth, that it may be thought superfluous again to name it. It has not, however, been before considered in connexion with the general principle under discussion. Here then it must be noted as a necessary consequence of the instability of the homogeneous. In this cooling down and solidification of the Earth’s surface, we have one of the simplest, as well as one of the most important, instances, of that change from a uniform to a multiform state which occurs in any mass through exposure of its different parts to different conditions. To the differentiation of the Earth’s exterior from its interior thus brought about, we must add one of the most conspicuous differentiations which the exterior itself afterwards undergoes, as being similarly brought about. Were the conditions to which the surface of the Earth is exposed, alike in all directions, there would be no obvious reason why certain of its parts should become permanently unlike the rest. But being unequally exposed to the chief external centre of force—the Sun—its main divisions become unequally modified: as the crust thickens and cools, there arises that contrast, now so decided, between the polar and equatorial regions.
Along with these most marked physical differentiations of the Earth, which are manifestly consequent on the instability of the homogeneous, there have been going on numerous chemical differentiations, admitting of similar interpretation. Without raising the question whether, as some think, the so-called simple substances are themselves compounded of unknown elements (elements which we cannot separate by artificial heat, but which existed separately when the heat of the Earth was greater than any which we can produce),—without raising this question, it will suffice the present purpose to show how, in place of that comparative homogeneity of the Earth’s crust, chemically considered, which must have existed when its temperature was high, there has arisen, during its cooling, an increasing chemical heterogeneity: each element or compound, being unable to maintain its homogeneity in presence of various surrounding affinities, having fallen into heterogeneous combinations. Let us contemplate this change somewhat in detail. There is every reason to believe that at an extreme heat, the bodies we call elements cannot combine. Even under such heat as can be generated artificially, some very strong affinities yield; and the great majority of chemical compounds are decomposed at much lower temperatures. Whence it seems not improbable that, when the Earth was in its first state of incandescence, there were no chemical combinations at all. But without drawing this inference, let us set out with the unquestionable fact that the compounds which can exist at the highest temperatures, and which must therefore have been the first formed as the Earth cooled, are those of the simplest constitutions. The protoxides—including under that head the alkalies, earths, &c.—are, as a class, the most fixed compounds known: the majority of them resisting decomposition by any heat we can generate. These, consisting severally of one atom of each component element, are combinations of the simplest order—are but one degree less homogeneous than the elements themselves. More heterogeneous than these, more decomposable by heat, and therefore later in the Earth’s history, are the deutoxides, tritoxides, peroxides, &c.; in which two, three, four, or more atoms of oxygen are united with one atom of metal or other base. Still less able to resist heat, are the salts; which present us with compound atoms each made up of five, six, seven, eight, ten, twelve, or more atoms, of three, if not more, kinds. Then there are the hydrated salts, of a yet greater heterogeneity, which undergo partial decomposition at much lower temperatures. After them come the further-complicated supersalts and double salts, having a stability again decreased; and so throughout. After making a few unimportant qualifications demanded by peculiar affinities, I believe no chemist will deny it to be a general law of these inorganic combinations that, other things equal, the stability decreases as the complexity increases. And then when we pass to the compounds that make up organic bodies, we find this general law still further exemplified: we find much greater complexity and much less stability. An atom of albumen, for instance, consists of 482 ultimate atoms of five different kinds. Fibrine, still more intricate in constitution, contains in each atom, 298 atoms of carbon, 49 of nitrogen, 2 of sulphur, 228 of hydrogen, and 92 of oxygen—in all, 660 atoms; or, more strictly speaking—equivalents. And these two substances are so unstable as to decompose at quite moderate temperatures; as that to which the outside of a joint of roast meat is exposed. Possibly it will be objected that some inorganic compounds, as phosphuretted hydrogen and chloride of nitrogen, are more decomposable than most organic compounds. This is true. But the admission may be made without damage to the argument. The proposition is not that all simple combinations are more fixed than all complex ones. To establish our inference it is necessary only to show that, as an average fact, the simple combinations can exist at a higher temperature than the complex ones. And this is wholly beyond question. Thus it is manifest that the present chemical heterogeneity of the Earth’s surface has arisen by degrees as the decrease of heat has permitted; and that it has shown itself in three forms—first, in the multiplication of chemical compounds; second, in the greater number of different elements contained in the more modern of these compounds; and third, in the higher and more varied multiples in which these more numerous elements combine.
Without specifying them, it will suffice just to name the meteorologic processes eventually set up in the Earth’s atmosphere, as further illustrating the alleged law. They equally display that destruction of a homogeneous state which results from unequal exposure to incident forces.
§ 152. Take a mass of unorganized but organizable matter—either the body of one of the lowest living forms, or the germ of one of the higher. Consider its circumstances. Either it is immersed in water or air, or it is contained with-in a parent organism. Wherever placed, however, its outer and inner parts stand differently related to surrounding agencies—nutriment, oxygen, and the various stimuli. But this is not all. Whether it lies quiescent at the bottom of the water or on the leaf of a plant; whether it moves through the water preserving some definite attitude; or whether it is in the inside of an adult; it equally results that certain parts of its surface are more exposed to surrounding agencies than other parts—in some cases more exposed to light, heat, or oxygen, and in others to the maternal tissues and their contents. Hence must follow the destruction of its original equilibrium. This may take place in one of two ways. Either the disturbing forces may be such as to overbalance the affinities of the organic elements, in which case there result those changes which are known as decomposition; or, as is ordinarily the case, such changes are induced as do not destroy the organic compounds, but only modify them: the parts most exposed to the modifying forces being most modified. To elucidate this, suppose we take a few cases.
Note first what appear to be exceptions. Certain minute animal forms present us either with no appreciable differentiations or with differentiations so obscure as to be made out with great difficulty. In the Rhizopods, the substance of the jelly-like body remains throughout life unorganized, even to the extent of having no limiting membrane; as is proved by the fact that the thread-like processes protruded by the mass coalesce on touching each other. Whether or not the nearly allied Amœba, of which the less numerous and more bulky processes do not coalesce, has, as lately alleged, something like a cell-wall and a nucleus, it is clear that the distinction of parts is very slight; since particles of food pass bodily into the inside through any part of the periphery, and since when the creature is crushed to pieces, each piece behaves as the whole did. Now these cases, in which there is either no contrast of structure between exterior and interior or very little, though seemingly opposed to the above inference, are really very significant evidences of its truth. For what is the peculiarity of this division of the Protozoa? Its members undergo perpetual and irregular changes of form—they show no persistent relation of parts. What lately formed a portion of the interior is now protruded, and, as a temporary limb, is attached to some object it happens to touch. What is now a part of the surface will presently be drawn, along with the atom of nutriment sticking to it, into the centre of the mass. Either the relations of inner and outer have no permanent existence, or they are very slightly marked. But by the hypothesis, it is only because of their unlike positions with respect to modifying forces, that the originally like units of a living mass become unlike. We must therefore expect no established differentiation of parts in creatures which exhibit no established differences of position in their parts; and we must expect extremely little differentiation of parts where the differences of position are but little determined—which is just what we find. This negative evidence is borne out by positive evidence. When we turn from these proteiform specks of living jelly to organisms having an unchanging distribution of substance, we find differences of tissue corresponding to differences of relative position. In all the higher Protozoa, as also in the Protophyta, we meet with a fundamental differentiation into cell-membrane and cell-contents; answering to that fundamental contrast of conditions implied by the terms outside and inside. On passing from what are roughly classed as unicellular organisms, to the lowest of those which consist of aggregated cells, we equally observe the connection between structural differences and differences of circumstance. Negatively, we see that in the sponge, permeated throughout by currents of sea-water, the indefiniteness of organization corresponds with the absence of definite unlikeness of conditions: the peripheral and central portions are as little contrasted in structure as in exposure to surrounding agencies. While positively, we see that in a form like the Thalassicolla, which, though equally humble, maintains its outer and inner parts in permanently unlike circumstances, there is displayed a rude structure obviously subordinated to the primary relations of centre and surface: in all its many and important varieties, the parts exhibit a more or less concentric arrangement.
After this primary modification, by which the outer tissues are differentiated from the inner, the next in order of constancy and importance is that by which some part of the outer tissues is differentiated from the rest; and this corresponds with the almost universal fact that some part of the outer tissues is more exposed to certain environing influences than the rest. Here, as before, the apparent exceptions are extremely significant. Some of the lowest vegetal organisms, as the Hematococci and Protococci, evenly imbedded in a mass of mucus, or dispersed through the Arctic snow, display no differentiations of surface; the several parts of their surfaces being subjected to no definite contrasts of conditions. Ciliated spheres such as the Volvox have no parts of their periphery unlike other parts; and it is not to be expected that they should have; since, as they revolve in all directions, they do not, in traversing the water, permanently expose any part to special conditions. But when we come to organisms that are either fixed, or while moving preserve definite attitudes, we no longer find uniformity of surface. The most general fact which can be asserted with respect to the structures of plants and animals, is, that however much alike in shape and texture the various parts of the exterior may at first be, they acquire unlikenesses corresponding to the unlikenesses of their relations to surrounding agencies. The ciliated germ of a Zoophyte, which, during its locomotive stage, is distinguishable only into outer and inner tissues, no sooner becomes fixed, than its upper end begins to assume a different structure from its lower. The disc-shaped gemmœ of the Marchantia, originally alike on both surfaces, and falling at random with either side uppermost, immediately begin to develop rootlets on the under side, and stomata on the upper side: a fact proving beyond question, that this primary differentiation is determined by this fundamental contrast of conditions.
Of course in the germs of higher organisms, the metamorphoses immediately due to the instability of the homogeneous, are soon masked by those due to the assumption of the hereditary type. Such early changes, however, as are common to all classes of organisms, and so cannot be ascribed to heredity, entirely conform to the hypothesis. A germ which has undergone no developmental modifications, consists of a spheroidal group of homogeneous cells. Universally, the first step in its evolution is the establishment of a difference between some of the peripheral cells and the cells which form the interior—some of the peripheral cells, after repeated spontaneous fissions, coalesce into a membrane; and by continuance of the process this membrane spreads until it speedily invests the entire mass, as in mammals, or, as in birds, stops short of that for some time. Here we have two significant facts. The first is, that the primary unlikeness arises between the exterior and the interior. The second is, that the change which thus initiates development, does not take place simultaneously over the whole exterior; but commences at one place, and gradually involves the rest. Now these facts are just those which might be inferred from the instability of the homogeneous. The surface must, more than any other part, become unlike the centre, because it is most dissimilarly conditioned; and all parts of the surface cannot simultaneously exhibit this differentiation, because they cannot be exposed to the incident forces with absolute uniformity. One other general fact of like implication remains. Whatever be the extent of this peripheral layer of cells, or blastoderm as it is called, it presently divides into two layers—the serous and mucous; or, as they have been otherwise called, the ectoderm and the endoderm. The first of these is formed from that portion of the layer which lies in contact with surrounding agents; and the second of them is formed from that portion of the layer which lies in contact with the contained mass of yelk. That is to say, after the primary differentiation, more or less extensive, of surface from centre, the resulting superficial portion undergoes a secondary differentiation into inner and outer parts—a differentiation which is clearly of the same order with the preceding, and answers to the next most marked contrast of conditions.
But, as already hinted, this principle, understood in the simple form here presented, supplies no key to the detailed phenomena of organic development. It fails entirely to explain generic and specific peculiarities; and indeed leaves us equally in the dark respecting those more important distinctions by which families and orders are marked out. Why two ova, similarly exposed in the same pool, should become the one a fish, and the other a reptile, it cannot tell us. That from two different eggs placed under the same hen, should respectively come forth a duckling and a chicken, is a fact not to be accounted for on the hypothesis above developed. We have here no alternative but to fall back upon the unexplained principle of hereditary transmission. The capacity possessed by an unorganized germ of unfolding into a complex adult, which repeats ancestral traits in the minutest details, and that even when it has been placed in conditions unlike those of its ancestors, is a capacity we cannot at present understand. That a microscopic portion of seemingly structureless matter should embody an influence of such kind, that the resulting man will in fifty years after become gouty or insane, is a truth which would be incredible were it not daily illustrated. Should it however turn out, as we shall hereafter find reason for suspecting, that these complex differentiations which adults exhibit, are themselves the slowly accumulated and transmitted results of a process like that seen in the first changes of the germ; it will follow that even those embryonic changes due to hereditary influence, are remote consequences of the alleged law. Should it be shown that the slight modifications wrought during life on each adult, and bequeathed to offspring along with all like preceding modifications, are themselves unlikenesses of parts that are produced by unlikenesses of conditions; then it will follow that the modifications displayed in the course of embryonic development, are partly direct consequences of the instability of the homogeneous, and partly indirect consequences of it. To give reasons for entertaining this hypothesis, however, is not needful for the justification of the position here taken. It is enough that the most conspicuous differentiations which incipient organisms universally display, correspond to the most marked differences of conditions to which their parts are subject. It is enough that the habitual contrast between outside and inside, which we know is produced in inorganic masses by unlikeness of exposure to incident forces, is strictly paralleled by the first contrast that makes its appearance in all organic masses.
It remains to point out that in the assemblage of organisms constituting a species, the principle enunciated is equally traceable. We have abundant materials for the induction that each species will not remain uniform, but is ever becoming to some extent multiform; and there is ground for the deduction that this lapse from homogeneity to heterogeneity is caused by the subjection of its members to unlike sets of circumstances. The fact that in every species, animal and vegetal, the individuals are never quite alike; joined with the fact that there is in every species a tendency to the production of differences marked enough to constitute varieties; form a sufficiently wide basis for the induction. While the deduction is confirmed by the familiar experience that varieties are most numerous and decided where, as among cultivated plants and domestic animals, the conditions of life depart from the original ones, most widely and in the most numerous ways. Whether we regard “natural selection” as wholly, or only in part, the agency through which varieties are established, matters not to the general conclusion. For as the survival of any variety proves its constitution to be in harmony with a certain aggregate of surrounding forces—as the multiplication of a variety and the usurpation by it of an area previously occupied by some other part of the species, implies different effects produced by such aggregate of forces on the two, it is clear that this aggregate of forces is the real cause of the differentiation—it is clear that if the variety supplants the original species in some localities but not in others, it does so because the aggregate of forces in the one locality is unlike that in the other—it is clear that the lapse of the species from a state of homogeneity to a state of heterogeneity arises from the exposure of its different parts to different aggregates of forces.
§ 153. Among mental phenomena it is difficult to establish the alleged law without an analysis too extensive for the occasion. To show satisfactorily how states of consciousness, originally homogeneous, become heterogeneous through differences in the changes wrought by different forces, would require us carefully to trace out the organization of early experiences. Were this done it would become manifest that the development of intelligence, is, under one of its chief aspects, a dividing into separate classes, the unlike things previously confounded together in one class—a formation of sub-classes and sub-sub-classes, until the once confused aggregate of objects known, is resolved into an aggregate which unites extreme heterogeneity among its multiplied groups, with complete homogeneity among the members of each group. If, for example, we followed, through ascending grades of creatures, the genesis of that vast structure of knowledge acquired by sight, we should find that in the first stage, where eyes suffice for nothing beyond the discrimination of light from darkness, the only possible classifications of objects seen, must be those based on the manner in which light is obstructed, and the degree in which it is obstructed. We should find that by such undeveloped visual organs, the shadows traversing the rudimentary retina would be merely distinguished into those of the stationary objects which the creature passed during its own movements, and those of the moving objects which came near the creature while it was at rest; and that so the extremely general classification of visible things into stationary and moving, would be the earliest formed. We should find that whereas the simplest eyes are not fitted to distinguish between an obstruction of light caused by a small object close to, and an obstruction caused by a large object at some distance, eyes a little more developed must be competent to such a distinction; whence must result a vague differentiation of the class of moving objects, into the nearer and the more remote. We should find that such further improvements in vision as those which make possible a better estimation of distances by adjustment of the optic axes, and those which, through enlargement and subdivision of the retina, make possible the discrimination of shapes, must have the effects of giving greater definiteness to the classes already formed, and of sub-dividing these into smaller classes, consisting of objects less unlike. And we should find that each additional refinement of the perceptive organs, must similarly lead to a multiplication of divisions and a sharpening of the limits of each division. In every infant might be traced the analogous transformation of a confused aggregate of impressions of surrounding objects, not recognized as differing in their distances, sizes, and shapes, into separate classes of objects unlike each other in these and various other respects. And in the one case as in the other, it might be shown that the change from this first indefinite, incoherent and comparatively homogeneous consciousness, to a definite, coherent, and heterogeneous one, is due to diffrences in the actions of incident forces on the organism. These brief indications of what might be shown, did space permit, must here suffice. Probably they will give adequate clue to an argument by which each reader may satisfy himself that the course of mental evolution offers no exception to the general law. In further aid of such an argument, I will here add an illustration that is comprehensible apart from the process of mental evolution as a whole.
It has been remarked (I am told by Coleridge, though I have been unable to find the passage) that with the advance of language, words which were originally alike in their meanings acquire unlike meanings—a change which he expresses by the formidable word “desynonymization.” Among indigenous words this loss of equivalence cannot be clearly shown; because in them the divergencies of meaning began before the dawn of literature. But among words that have been coined, or adopted from other languages, since the writing of books commenced, it is demonstrable. In the old divines, miscreant is used in its etymological sense of unbeliever; but in modern speech it has entirely lost this sense. Similarly with evil-doer and malefactor: exactly synonymous as these are by derivation, they are no longer synonymous by usage: by a malefactor we now understand a convicted criminal, which is far from being the acceptation of evil-doer. The verb produce, bears in Euclid its primary meaning—to prolong, or draw out; but the now largely developed meanings of produce have little in common with the meanings of prolong, or draw out. In the Church of England liturgy, an odd effect results from the occurrence of prevent in its original sense—to come before, instead of its modern specialized sense—to come before with the effect of arresting. But the most conclusive cases are those in which the contrasted words consist of the same parts differently combined; as in go under and undergo. We go under a tree, and we undergo a pain. But though, if analytically considered, the meanings of these expressions would be the same were the words transposed, habit has so far modified their meanings that we could not without absurdity speak of undergoing a tree and going under a pain. Countless such instances might be brought to show that between two words which are originally of like force, an equilibrium cannot be maintained. Unless they are daily used in exactly equal degrees, in exactly similar relations (against which there are infinite probabilities), there necessarily arises a habit of associating one rather than the other with particular acts, or objects. Such a habit, once commenced, becomes confirmed; and gradually their homogeneity of meaning disappears. In each individual we may see the tendency which inevitably leads to this result. A certain vocabulary and a certain set of phrases, distinguish the speech of each person: each person habitually uses certain words in places where other words are habitually used by other persons; and there is a continual recurrence of favourite expressions. This inability to maintain a balance in the use of verbal symbols, which characterizes every man, characterizes, by consequence, aggregates of men; and the desynonymization of words is the ultimate effect.
Should any difficulty be felt in understanding how these mental changes exemplify a law of physical transformations that are wrought by physical forces, it will disappear on contemplating acts of mind as nervous functions. It will be seen that each loss of equilibrium above instanced, is a loss of functional equality between some two elements of the nervous system. And it will be seen that, as in other cases, this loss of functional equality is due to differences in the incidence of forces.
§ 154. Masses of men, in common with all other masses, show a like proclivity similarly caused. Small combinations and large societies equally manifest it; and in the one, as in the other, both governmental and industrial differentiations are initiated by it. Let us glance at the facts under these two heads.
A business partnership, balanced as the authorities of its members may theoretically be, practically becomes a union in which the authority of one partner is tacitly recognized as greater than that of the other or others. Though the share-holders have given equal powers to the directors of their company, inequalities of power soon arise among them; and usually the supremacy of some one director grows so marked, that his decisions determine the course which the board takes. Nor in associations for political, charitable, literary, or other purposes, do we fail to find a like process of division into dominant and subordinate parties; each having its leader, its members of less influence, and its mass of uninfluential members. These minor instances in which unorganized groups of men, standing in homogeneous relations, may be watched gradually passing into organized groups of men standing in heterogeneous relations, give us the key to social inequalities. Barbarous and civilized communities are alike characterized by separation into classes, as well as by separation of each class into more important and less important units; and this structure is manifestly the gradually-consolidated result of a process like that daily exemplified in trading and other combinations. So long as men are constituted to act on one another, either by physical force or by force of character, the struggles for supremacy must finally be decided in favour of some one; and the difference once commenced must tend to become ever more marked. Its unstable equilibrium being destroyed, the uniform must gravitate with increasing rapidity into the multiform. And so supremacy and subordination must establish themselves, as we see they do, throughout the whole structure of a society, from the great class-divisions pervading its entire body, down to village cliques, and even down to every posse of school-boys. Probably it will be objected that such changes result, not from the homogeneity of the original aggregations, but from their non-homogeneity—from certain slight differences existing among their units at the outset. This is doubtless the proximate cause. In strictness, such changes must be regarded as transformations of the relatively homogeneous into the relatively heterogeneous. But it is abundantly clear that an aggregation of men, absolutely alike in their endowments, would eventually undergo a similar transformation. For in the absence of perfect uniformity in the lives severally led by them—in their occupations, physical conditions, domestic relations, and trains of thought and feeling—there must arise differences among them; and these must finally initiate social differentiations. Even inequalities of health caused by accidents, must, by entailing inequalities of physical and mental power, disturb the exact balance of mutual influences among the units; and the balance once disturbed, must inevitably be lost. Whence, indeed, besides seeing that a body of men absolutely homogeneous in their governmental relations, must, like all other homogeneous bodies, become heterogeneous, we also see that it must do this from the same ultimate cause—unequal exposure of its parts to incident forces.
The first industrial divisions of societies are much more obviously due to unlikenesses of external circumstances. Such divisions are absent until such unlikenesses are established. Nomadic tribes do not permanently expose any groups of their members to special local conditions; nor does a stationary tribe, when occupying only a small area, maintain from generation to generation marked contrasts in the local conditions of its members; and in such tribes there are no decided economical differentiations. But a community which, growing populous, has overspread a large tract, and has become so far settled that its members live and die in their respective districts, keeps its several sections in different physical circumstances; and then they no longer remain alike in their occupations. Those who live dispersed continue to hunt or cultivate the earth; those who spread to the sea-shore fall into maritime occupations; while the inhabitants of some spot chosen, perhaps for its centrality, as one of periodical assemblage, become traders, and a town springs up. Each of these classes undergoes a modification of character consequent on its function, and better fitting it to its function. Later in the process of social evolution these local adaptations are greatly multiplied. A result of differences in soil and climate, is that the rural inhabitants in different parts of the kingdom have their occupations partially specialized; and become respectively distinguished as chiefly producing cattle, or sheep, or wheat, or oats, or hops, or cyder. People living where coal-fields are discovered are transformed into colliers; Cornishmen take to mining because Cornwall is metalliferous; and the iron-manufacture is the dominant industry where iron-stone is plentiful. Liverpool has assumed the office of importing cotton, in consequence of its proximity to the district where cotton goods are made; and for analogous reasons, Hull has become the chief port at which foreign wools are brought in. Even in the establishment of breweries, of dye-works, of slate-quarries, of brickyards, we may see the same truth. So that both in general and in detail, the specializations of the social organism which characterize separate districts, primarily depend on local circumstances. Those divisions of labour which under another aspect were interpreted as due to the setting up of motion in the directions of least resistance (§ 80), are here interpreted as due to differences in the incident forces; and the two interpretations are quite consistent with each other. For that which in each case determines the direction of least resistance, is the distribution of the forces to be overcome; and hence unlikenesses of distribution in separate localities, entails unlikenesses in the course of human action in those localities—entails industrial differentiations.
§ 155. It has still to be shown that this general truth is demonstrable à priori. We have to prove specifically that the instability of the homogeneous is a corollary from the persistence of force. Already this has been tacitly implied by assigning unlikeness in the exposure of its parts to surrounding agencies, as the reason why a uniform mass loses its uniformity. But here it will be proper to expand this tacit implication into definite proof.
On striking a mass of matter with such force as either to indent it or make it fly to pieces, we see both that the blow affects differently its different parts, and that the differences are consequent on the unlike relations of its parts to the force impressed. The part with which the striking body comes in contact, receiving the whole of the communicated momentum, is driven in towards the centre of the mass. It thus compresses and tends to displace the more centrally situated portions of the mass. These, however, cannot be compressed or thrust out of their places without pressing on all surrounding portions. And when the blow is violent enough to fracture the mass, we see, in the radial dispersion of its fragments, that the original momentum, in being distributed throughout it, has been divided into numerous minor momenta, unlike in their directions. We see that these directions are determined by the positions of the parts with respect to each other, and with respect to the point of impact. We see that the parts are differently affected by the disruptive force, because they are differently related to it in their directions and attachments—that the effects being the joint products of the cause and the conditions, cannot be alike in parts which are differently conditioned. A body on which radiant heat is falling, exemplifies this truth still more clearly. Taking the simplest case (that of a sphere) we see that while the part nearest to the radiating centre receives the rays at right angles, the rays strike the other parts of the exposed side at all angles from 90° down to 0°. Again, the molecular vibrations propagated through the mass from the surface which receives the heat, must proceed inwards at angles differing for each point. Further, the interior parts of the sphere affected by the vibrations proceeding from all points of the heated side, must be dissimilarly affected in proportion as their positions are dissimilar. So that whether they be on the recipient area, in the middle, or at the remote side, the constituent atoms are all thrown into states of vibration more or less unlike each other.
But now, what is the ultimate meaning of the conclusion that a uniform force produces different changes throughout a uniform mass, because the parts of the mass stand in different relations to the force? Fully to understand this, we must contemplate each part as simultaneously subject to other forces—those of gravitation, of cohesion, of molecular motion, &c. The effect wrought by an additional force, must be a resultant of it and the forces already in action. If the forces already in action on two parts of any aggregate, are different in their directions, the effects produced on these two parts by like forces must be different in their directions. Why must they be different? They must be different because such unlikeness as exists between the two sets of factors, is made by the presence in the one of some specially-directed force that is not present in the other; and that this force will produce an effect, rendering the total result in the one case unlike that in the other, is a necessary corollary from the persistence of force. Still more manifest does it become that the dissimilarly-placed parts of any aggregate must be dissimilarly modified by an incident force, when we remember that the quantities of the incident force to which they are severally subject, are not equal, as above supposed; but are nearly always very unequal. The outer parts of masses are usually alone exposed to chemical actions; and not only are their inner parts shielded from the affinities of external elements, but such affinities are brought to bear unequally on their surfaces; since chemical action sets up currents through the medium in which it takes place, and so brings to the various parts of the surface unequal quantities of the active agent. Again, the amounts of any external radiant force which the different parts of an aggregate receive, are widely contrasted: we have the contrast between the quantity falling on the side next the radiating centre, and the quantity, or rather no quantity, falling on the opposite side; we have contrasts in the quantities received by differently-placed areas on the exposed side; and we have endless contrasts between the quantities received by the various parts of the interior. Similarly when mechanical force is expended on any aggregate, either by collision, continued pressure, or tension, the amounts of strain distributed throughout the mass are manifestly unlike for unlike positions. But to say the different parts of an aggregate receive different quantities of any incident force, is to say that their states are modified by it in different degrees—is to say that if they were before homogeneous in their relations they must be rendered to a proportionate extent heterogeneous; since, force being persistent, the different quantities of it falling on the different parts, must work in them different quantities of effect—different changes. Yet one more kindred deduction is required to complete the argument. We may, by parallel reasoning, reach the conclusion that, even apart from the action of any external force, the equilibrium of a homogeneous aggregate must be destroyed by the unequal actions of its parts on each other. That mutual influence which produces aggregation (not to mention other mutual influences) must work different effects on the different parts; since they are severally exposed to it in unlike amounts and directions. This will be clearly seen on remembering that the portions of which the whole is made up, may be severally regarded as minor wholes; that on each of these minor wholes, the action of the entire aggregate then becomes an external incident force; that such external incident force must, as above shown, work unlike changes in the parts of any such minor whole; and that if the minor wholes are severally thus rendered heterogeneous, the entire aggregate is rendered heterogeneous.
The instability of the homogeneous is thus deducible from that primordial truth which underlies our intelligence. One stable homogeneity only, is hypothetically possible. If centres of force, absolutely uniform in their powers, were diffused with absolute uniformity through unlimited space, they would remain in equilibrium. This however, though a verbally intelligible supposition, is one that cannot be represented in thought; since unlimited space is inconceivable. But all finite forms of the homogeneous—all forms of it which we can know or conceive, must inevitably lapse into heterogeneity. In three several ways does the persistence of force necessitate this. Setting external agencies aside, each unit of a homogeneous whole must be differently affected from any of the rest by the aggregate action of the rest upon it. The resultant force exercised by the aggregate on each unit, being in no two cases alike in both amount and direction, and usually not in either, any incident force, even if uniform in amount and direction, cannot produce like effects on the units. And the various positions of the parts in relation to any incident force, preventing them from receiving it in uniform amounts and directions, a further difference in the effects wrought on them is inevitably produced.
One further remark is needed. To the conclusion that the changes with which Evolution commences, are thus necessitated, remains to be added the conclusion that these changes must continue. The absolutely homogeneous must lose its equilibrium; and the relatively homogeneous must lapse into the relatively less homogeneous. That which is true of any total mass, is true of the parts into which it segregates. The uniformity of each such part must as inevitably be lost in multiformity, as was that of the original whole; and for like reasons. And thus the continued changes which characterize Evolution, in so far as they are constituted by the lapse of the homogeneous into the heterogeneous, and of the less heterogeneous into the more heterogeneous, are necessary consequences of the persistence of force.
[∗]The idea developed in this chapter originally formed part of an article on “Transcendental Physiology,” published in 1857. See Essays, pp.279–290.