FACTORS OF ORGANIC EVOLUTION
Variation—Selection—Isolation—Spencer's Contribution—External Factors—Internal Factors—Direct Equilibration—Indirect Equilibration
Darwin rendered three great services to evolution-doctrine, (1) By his marshalling of the evidences which suggest the doctrine of descent, he won the conviction of the biological world. (2) He applied the evolution-idea to various sets of facts, not only to the origin of species in general, but to the difficult case of Man; not only to the origin of the countless adaptations with which organic nature is filled, but to particular problems such as the expression of the emotions; and in so doing he corroborated the evolution-formula by showing what a powerful organon it is. (3) Along with Alfred Russel Wallace, he elaborated the theory of natural selection, which disclosed one of the factors in the evolution-process.
As we have seen, Herbert Spencer preceded Darwin in his championing of the doctrine of descent, to which the natural mood of his mind, and the influences of Lamarck and von Baer had led him to give his adhesion. He also applied the evolution-formula to an even wider series of facts than Darwin ventured to touch, viz., to the inorganic world and to psychological and sociological facts. It remains to be seen what his position was in regard to the Factors of Organic Evolution.
Spencer's position may be more clearly defined if we first sketch the answer which most biologists would at present give to the question—What are the factors of Organic Evolution?
Variation.—Postulating the powers of growing and reproducing, of acting on and reacting to the environment, postulating also heredity without which no organic evolution is possible, biologists distinguish two sets of factors in the evolution process. On the one hand there are originative factors which produce those changes in living creatures which make them different from their fellows. These changes or observed differences are of two kinds—(a) they may have their origin in the arcana of the germ and be inborn variations (germinal, constitutional, endogenous, etc.), or (b) they may be acquired modifications wrought on the body of the individual by environmental influences or by use and disuse (somatic, acquired, exogenous, etc.). Thus "modifications" or "acquired characters" may be defined as structural changes in the body of the individual organism, directly induced by changes in the environment or in the function, and such that they transcend the limit of organic elasticity and persist after the inducing causes have ceased to operate. Merely transient changes which disappear soon after their cause has ceased to operate may be conveniently called "adjustments." Now when we subtract from the total of observed differences between individuals of the same stock, all the modifications and adjustments which we can distinguish as such by their being causally related to some alteration in function or environment, we have a remainder which we call "variations." We cannot causally relate them to differences in habit or surroundings, they are often hinted at even before birth, and they are not alike even among forms whose conditions of life seem absolutely uniform. This distinction between modifications and variations, though clear in theory, is not always readily drawn in practice, but it is of great importance, for while all innate variations, except complete sterility, are transmissible, and thus may form the raw materials of progress, there is no secure evidence that acquired characters or somatic modifications are transmissible. Therefore, the latter, though very important for the individual, and indirectly important for the race, cannot be assumed (without further proof) as directly important in the transmutation of species.
As to the nature and frequency of inborn variations, Biology has recently begun to accumulate precise observations, and has renounced the bad habit of simply postulating variability without statistically or otherwise defining it. Life is so abundant and so Protean that biologists have tended to draw cheques upon Nature as if they had unlimited credit, scarce waiting in their impetuosity to see whether these are honoured, but the very title—Biometrika—of a new journal shows that the science is emerging from the slough of vagueness in which, to the physicists' contempt, it has so long floundered. All science begins with measurement, and one of the great steps that have been made of recent years is in the tedious, but necessary task of recording the variations which do actually occur. From these we can argue with a clear intellectual conscience back to what may have been. One result is plain, that variation is a very general fact of life; whenever we settle down to measure we find that specific diagnoses are averages, that specific characters require a curve of frequency for their expression, that a living organism is usually like a Proteus. There are no doubt long-lived, non-plastic, conservative types, such as Lingula, where no visible variability can be detected (even in untold ages if we consider the hard parts preservable as fossils), but to judge from these as to the rate of evolutionary change is like estimating the rush of a river from the eddies of a sheltered pool. Another result is that it becomes possible to distinguish between continuous variations, which are just like stages in continuous growth, in which the descendant has a little more or a little less of a given character than its parents had, and discontinuous variations in which a new combination appears suddenly without gradational stages, and with no small degree of perfection. Although there is truth in Lamarck's dictum that "Nature is never brusque," although Jack-in-the-box phenomena are rare, the evidence, e.g. of Bateson and De Vries, as to the frequent occurrence of discontinuous variations appears conclusive. Such words as "freaks" and "sports" express a truth, suggested by Mr Galton's phrase "transilient variations," that organisms may pass with seeming abruptness from one form of equilibrium to another. There is evidence that these sudden and discontinuous variations—"mutations" many of them are called—are often very heritable, that when they appear they come to stay; and it seems likely, especially from facts of breeding and cultivation, that these mutations, rather than the minute "fluctuating" variations, have supplied the raw material on which selection has chiefly operated in the evolution of species.
It also becomes more and more evident that the living creature may vary as a unity, so that if there is more of one character there is less of another, and so that one change brings another in its train. It seems as if the organism as a whole—through its germinal organisation, of course—may suddenly pass from one position of organic equilibrium to another. Thus we are not shut up to the assumption of the piecemeal variation of minute parts; there is greater definiteness and less fortuitousness in variation than was previously supposed. We begin, from actual data, to see the truth of the view which Goethe and Nägeli suggested, that the evolution of organisms is pre-eminently a story of self-differentiating and self-integrating growth,—cumulative, selective, definite, and harmonious—like crystallisation. As to the origin of variations, it must be admitted that until we know the actual facts better, we cannot expect to know much in regard to their antecedents. Many suggestions have been made, some of which may be summarised.
There is something comparable to the First Law of Motion to be read out of the persistence of characteristics from generation to generation. Like tends to beget like. But while the relation of genetic continuity which links generation to generation tends to ensure this persistence, it presents no more than a curb to the occurrence of variation. While complete and perfect inheritance and complete and perfect expression of that inheritance in development would mean the absence of variation, there are many reasons why this completeness of hereditary resemblance is rare. For the inheritance seems to consist of sets of hereditary qualities not in duplicate merely but in multiplicate; they are not all of equal strength or of equal stability; there may be a struggle amongst them; and they are subject to changes induced by the changes in the complex nutritive supply which the parental body—their bearer—affords.
A variation, which makes its possessor different from the parents, is often interpretable as due to some incompleteness of inheritance or in the expression of the inheritance. It seems as if the entail were sometimes broken in regard to a particular characteristic. Oftener, perhaps, as the third generation shows, the inheritance has been complete enough potentially, but the young creature has been prevented from realising its entire legacy. Contrariwise, it may be that the novelty of the newborn is seen in an intensifying of the inheritance, for the contributions from the two parents may, as it were, corroborate one another.
But in many cases a variation turns up which we must call novel, some peculiar mental pattern, it may be, which spells originality, some structural change which suggests a new departure. We tentatively interpret this as due to some fresh permutation or combination of the complex substances which form the material basis of inheritance, and are mingled from two sources at the outset of every life sexually reproduced. It is not merely in an intermingling of maternal and paternal contributions that a life begins, but of legacies through the parents from remoter ancestors. The permutations and combinations may be due to a struggle between the elements which are the bearers of the heritable qualities, or they may be due to fluctuations in the nutritive stream which the body supplies to its germ-cells. It must be remembered that the hereditary material is very complex, and that it has a complex environment within the parental body. In spite of its essential architectural stability, it may have a tendency to instability as regards minor details, and we may perhaps find the change-exciting stimuli in the ceaseless nutritive oscillations within the body, while the mode of restoring a disturbed equilibrium may be through a germinal struggle among the different sets of minute elements which we may call the heritage-bearers. The idea of germinal selection has been elaborated with great subtlety by Prof. Weismann.
Nor does it seem to us legitimate to exclude the possibility that the germ-cell, or the germ-plasm as the essential part of it, may grow into a slightly more differentiated and integrated unity before it begins its task of development. For the power of growth is characteristic of everything living. Enough has been said, however, to indicate how uncertain is the voice of biology in answering the fundamental questions as to the nature and origin of variations.
Selection.—The first and most important of the directive factors is natural selection, and the most distinctive contribution which Darwin and Wallace made to ætiology was to show how selection works and what it can effect. The process admits of brief statement.
Variability is a fact of life, the members of a family or species are not born alike; some may have qualities which give an advantage both as to hunger and love; others are relatively handicapped. But a struggle for existence, as Malthus called it, is also a fact of life, necessitated especially by two facts—first, that two parent organisms usually produce many more than two children organisms, and that population thus tends to outrun the means of subsistence; and, secondly, that organisms are at the best only relatively well-adapted to the complex and changeful conditions of their life. This struggle expresses itself not merely as an elbowing and jostling around the platter of subsistence, but at every point where the effectiveness of the response which the living creature makes to the stimuli playing upon it, is of critical moment. As Darwin said, though many seem to have forgotten, the phrase "struggle for existence" must be used "in a wide and metaphorical sense." It includes much more than an internecine scramble for the necessities of life; it includes all endeavours for and all changes that make towards preservation and welfare, not only of the individual, but of the offspring as well. In many cases, indeed, the struggle for existence both among men and beasts is fairly described as an endeavour after well-being, and what may have been primarily self-regarding impulses become replaced by others which are distinctively species-maintaining, the self failing to find full realisation apart from its kin and society.
Now, in this struggle for existence, which has so many expressions, the relatively less fit to the present conditions tend to be eliminated. Though the process may work out progress, as measured by degree of differentiation and integration, by increasing freedom and fullness of life, and has doubtless done so, yet until we come to its highest forms in subjective and finally rational selection, it works not towards an ideal but towards a relative fitness to present conditions. And this may spell degeneration, as in parasites, when an extrinsic standard is used. Tapeworms may be just as fit to survive as golden eagles. Again, the process of elimination does not necessarily mean that the handicapped variants come at once to a violent end, as when rat devours rat, or the cold decimates a flock of birds in a single night; it often simply means that the less fit die before the average time, and are less successful than their neighbours as regards pairing and having offspring. Moreover, although the selective process is primarily eliminative or destructive, like thinning turnips or pruning fruit-trees, we cannot separate its positive and negative aspects. That nothing succeeds like success is continually verifiable in nature, the fit variant gets a start just as surely as the unfit variant is handicapped; there is favouring and fostering just because there is sifting and singling.
Given variations and given some mode of selection in the manifold struggle for existence, the argument continues, then the result will be in Spencer's phrase "the survival of the fittest." And since many variations are transmitted from generation to generation, and may, through the pairing of similar or suitable mates, be gradually increased in amount and stability, the eliminative or selective process works towards the establishment of new adaptations and the origin of new species.
Darwin thought chiefly of the struggle between individuals—either between fellows of the same kin or between fellow-kin and foreign foes—and of the struggle between organisms and the inanimate environment. He also emphasised the sexual selection which occurs (a) when rival males fight or otherwise compete for the possession of a desired mate or mates, and in so doing reduce the leet, and (b) when the females appear to choose their mates from amid a crowd of suitors. While many now doubt if the range and effectiveness of preferential mating is so great as Darwin believed, there seems no reason to doubt that this mode of selection has been a factor in evolution. There are facts which warrant us in saying that das ewig weibliche plays a part in the upward march of life, that Cupid's darts as well as Death's arrows have evolutionary significance.
Even more important, however, are other extensions of the selection-idea. There may be struggle between groups as well as between individuals, as when one ant-colony goes to war with another, and there may be struggle of the parts within the organism just as there is struggle between organisms. There is struggle when one ovum survives in an ovary by devouring all its sister-cells, as in the case of Hydra and Tubularia, and, after allowing a wide margin for chance, there may be some form of selection among the crowd of spermatozoa encompassing the egg which only one will fertilise, just as there is some form of selection among the many drones which pursue the queen-bee in her nuptial flight. Weismann has carried the selection-idea to a logical finesse in his theory that there may be a struggle between the different sets of hereditary qualities in the germ-cell, or that there is a process of "germinal selection" at the very beginning of the individual life. There are, we admit, great differences between the struggle of hereditary items and the struggle of large parts within the organism; between intra-organismal and inter-organismal struggle; between the competition of individuals and the struggle against physical nature; between personal selection and the conflict of races; between objective and subjective selection; but, as it seems to us, they may be all expressed in the same formula if it is useful so to do.
Isolation.—In organic evolution variation supplies the materials which some form of selection sifts. But besides selection another directive factor has been indicated in what is called the theory of isolation. A formidable objection to the Darwinian doctrine, first clearly stated by Professor Fleeming Jenkin, is that variations of small amount and sparse occurrence would tend to be swamped out by inter-crossing before they had time to accumulate and gain stability. In artificial selection, the breeder takes measures to prevent this swamping-out by deliberately pairing similar or suitable forms together, or by deliberately removing unsuitable mateable forms; but what in Nature corresponds to the breeder?
It may be that similar variations occur in many individuals at once and many times over; it may be that many variations are not at first small in amount, but express big steps in organisation, as in Bateson's instances of Discontinuous Variation or in De Vries's instances of Mutation; it may be that many variations are not from the first unstable, but express changes of organic equilibrium which have come to stay if they get a chance at all; and it may be that the supposed swamping effects of inter-crossing are in part illusory, as is strongly suggested by some of the facts summed up in Mendel's Law; but there seems to be still room and need for the theory of Isolation worked out by Romanes, Gulick, and others.
They point out the great variety of ways in which, in the course of nature, the range of inter-crossing is restricted—e.g. by geographical barriers, by differences in habit, by psychical likes and dislikes, by reproductive variation causing mutual sterility between two sections of a species living on a common area, and so on. According to Romanes, "without isolation, or the prevention of free inter-crossing, organic evolution is in no case possible." The supporting body of illustrative facts is still unsatisfactorily small, but there seems sound sense in the idea.
An interesting corollary has been recently indicated by Professor Cossar Ewart. Breeding within a narrow range often occurs in nature, and often in human kind, being necessitated by geographical and other barriers. In artificial conditions, this in-breeding often results in the development of what is called prepotency. This means that certain forms have an unusual power of transmitting their peculiarities, even when mated with dissimilar forms, or, in other words, that some variations have a strong power of persistence. Therefore, wherever through in-breeding (which implies some form of isolation) prepotency has developed, there is no difficulty in understanding how even a small idiosyncrasy may come to stay, even although the bridegroom does not meet a bride endowed with a peculiarity like his own. Similarly, Dr A. Reibmayr has argued that the establishment of a successful human tribe or race involves periods of in-breeding (i.e., marriage within a limited range of relationship), with the effect of "fixing" constitutional characteristics, and periods of cross-breeding (i.e. marriage between members of distinct stocks), with the effect of promoting a new crop of variations or initiatives.
Spencer's contribution.—Spencer was led to become an evolutionist by the workings of his own mind, influenced by Laplace's Nebular Hypothesis, by the transformist theory of Lamarck, by von Baer's law of individual development, and by Malthus's recognition of the struggle for existence in mankind. On the whole, it may be said that he came to the theory of organic evolution from above, rather than from below, from his studies on the intellectual and social evolution of man rather than from acquaintance with the biological data. Not unnaturally, therefore, he was to begin with a Lamarckian, believing in the cumulative transmission of the transforming results of use and disuse and of environmental influences.
In the essay on "a theory of Population" (1852) Spencer was within sight of one of the great doctrines of Darwinism. "From the beginning," he said, "pressure of population has been the proximate cause of progress." "The effect of pressure of population, in increasing the ability to maintain life, and decreasing the ability to multiply, is not a uniform effect, but an average one.... All mankind in turn subject themselves more or less to the discipline described; they either may or may not advance under it; but, in the nature of things, only those who do advance under it eventually survive.... For as those prematurely carried off must, in the average of cases, be those in whom the power of self-preservation is the least, it unavoidably follows that those left behind to continue the race, are those in whom the power of self-preservation is the greatest—are the select of their generation."
Here Spencer recognised the eliminative and selective effect of struggle in mankind. Why was he "blind to the fact," as he afterwards said, "that here was a universally-operative factor in the development of species"? In his Autobiography he gives two reasons for his oversight, one was his Lamarckian preconception that the inheritance of functionally-produced modifications sufficed to explain the facts of evolution. The other was, that he "knew little or nothing about the phenomena of variation," that "he had failed to recognise the universal tendency to vary."
Similarly, in his essay on "Progress: its Law and Cause" (1857), he still "ascribed all modifications to direct adaptations to changing conditions; and was unconscious that in the absence of that indirect adaptation effected by the natural selection of favourable variations, the explanation left the larger part of the facts unaccounted for" (Autobiography, i. p. 502).
In his article "Transcendental Physiology" (1857), Spencer advanced a step beyond the position occupied in his essay on "Progress." He showed that with advance in the forms of life there is an increasing differentiation of them from their environments, that integration as well as differentiation is part of the developmental process, but the leading conception of the essay was "the instability of the homogeneous." This was recognised, like "the multiplication of effects," as a cause of progress, as "a principle holding not among organic phenomena only, but among inorganic and super-organic phenomena." It was in this essay also that he began to use the word "evolution" in place of the more teleological word "progress."
In the same year (1857) Spencer again approached the idea of selection as a directive factor in evolution. In an essay on "State Tamperings with Money and Banks" he gave among other reasons for reprobating grandmotherly legislation, that "such a policy interferes with that normal process which brings benefit to the sagacious and disaster to the stupid." "The ultimate result of shielding men from the effects of folly, is to fill the world with fools." "This was a tacit assertion, recalling like assertions previously made, that the survival of the fittest operates beneficially in society."
Darwin's Origin of Species appeared in 1859, and marked another step in Spencer's evolutionism. Hitherto, though he had several times approached the idea of Natural Selection, he had "held that the sole cause of organic evolution is the inheritance of functionally-produced modifications"; now it became clear to him that he was wrong, and that the larger part of the facts cannot be due to any such cause (Autobiography, ii. 50).
In 1864 Spencer definitely sought to assimilate the Darwinian idea of Natural Selection into his system. He had become convinced that the hereditary accumulation of functional modifications could not be the sole factor in organic evolution; he had recognised the importance and efficacy of Natural Selection as a directive agency thinning and "singling" the crop of variations which is always abundant; but he had not seen how to absorb "Natural Selection" into his general physical theory of evolution. It seemed "to stand apart as an unrelated process."
"The search for congruity led first of all to perception of the fact that what Mr Darwin called 'natural selection,' might more literally be called survival of the fittest. But what is survival of the fittest, considered as an outcome of physical actions?"
Spencer's answer was that the changes constituting evolution tend ever towards a state of equilibrium; on the way to this there are stages of "moving equilibrium"; some organisms have their moving equilibrium less easily overthrown than others; these are the fittest which survive; they are, in Darwin's language, the select which nature preserves; and thus "the survival and multiplication of the select becomes conceivable in purely physical terms, as an indirect outcome of a complex form of the universal redistribution of matter and motion" (Autobiography, ii. pp. 100-1). In short, natural selection is part of the universal process towards more stable equilibrium.
When formulating his views on the classification of the sciences and his reasons for dissenting from the philosophy of Comte, Spencer pointed out that all the concrete sciences under their most general aspects give accounts of the redistributions of matter and motion; and he asked the question, What is the universal trait of all such redistributions? His answer was that "increasing integration of matter necessitates a concomitant dissipation of motion, and that increasing amount of motion implies a concomitant disintegration of matter." Thus Evolution and Dissolution appeared "under their primordial aspects," and differentiations, with resulting increase of heterogeneity, were seen to be secondary not primary traits of evolution. So he arrived at his famous definition of evolution:—"Evolution is an integration of matter and concomitant dissipation of motion, during which the matter passes from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity; and during which the retained motion undergoes a parallel transformation" (First Principles, p. 396).
Having illustrated the evolution of the evolution-theory in Spencer's mind, we pass to his final statement of the factors of organic evolution.
(1) External Factors.—He begins by pointing out that living creatures are in the grip of a complex environment, which acts on them and to which they react. And whether we think of the seasons or the climate, the soil or the sea, we find that this environment is intricately variable. Every kind of plant and animal may be regarded as for ever passing into a new environment, and with increasing fullness of life there is additional complexity in the incidence of external forces. Every increase of locomotive power, for instance, increases the multiplicity and multiformity of action and reaction between organism and environment. There are chemical, mechanical, dynamic, and animate influences which modify organisms, and as the actions of these several orders of factors are compounded, there is produced a geometric progression of changes increasing with immense rapidity. All through the ages living creatures have as it were been passing over a series of anvils on which the hammers of external forces play, with tunes of ever-increasing complexity.
(2) Internal Factors.—Passing to internal factors, Spencer started from the fact that organic matter is built up of very unstable complex molecules. "But a substance which is beyond all others changeable by the actions and reactions of the forces liberated from instant to instant within its own mass, must be a substance which is beyond all others changeable by the forces acting on it from without." In any aggregate "the relations of outside and inside, and of comparative nearness to neighbouring sources of influences, 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 on." Thus arise differentiations of structure, a transition from a uniform to a multiform state, a passage from homogeneity to heterogeneity, and this must go on cumulatively. For "the more strongly contrasted the parts of an aggregate become, the more different must be their reactions on incident forces, and the more unlike must be the secondary effects which these initiate. This multiplication of effects conspires, with the instability of the homogeneous, to work an increasing multiformity of structure in an organism." Thus, if the head of a bison becomes much heavier, what a multiplication of effects—mechanical and physiological—must ensue on muscles and bones and blood-vessels. One modification brings another in its train; there are secondary and tertiary effects. And as the increasing assemblage of individuals arising from a common stock is thus liable to lose its original uniformity and to grow more pronounced in its multiformity, indirect effects follow from inter-crossing and from altered competitive conditions. Moreover, as times and seasons and ages pass, the environment goes on changing, and on previous complications wrought by incident forces, new complications are continually superimposed by new incident forces. Thus there is an almost continuous movement towards heterogeneity. But how is that kind of heterogeneity insured which is required to carry on life? How is the evolution directed?
(3) Direct Equilibration.—How is it that action and reaction between the organism and its environment bring about effective adaptations? Spencer's answer is that every change is towards a balance of forces, and can never cease until a balance of forces is reached. "Any unequilibrated force to which an aggregate is subject, if not of a kind to overthrow it altogether, must continue modifying its state until an equilibrium is brought about." Thus "there go on in all organisms, certain changes of function and structure that are directly consequent on changes in the incident forces—inner changes by which the outer changes are balanced, and the equilibrium restored." "That a new external action may be met by a new internal action, it is needful that it shall either continuously or frequently be borne by the individuals of the species, without killing or seriously injuring them; and shall act in such a way as to affect their functions." But as many of the environing agencies to which organisms have to be adjusted, either do not immediately affect the functions at all, or else affect them in ways that prove fatal, there must be at work some other process which equilibrates the actions of organisms with the actions they are exposed to.
(4) Indirect Equilibration.—There are many very precise adaptations, e.g. in the not-living hard parts of many animals, which no ingenuity can interpret as the directly equilibrated results of incident forces. To interpret mimicry as due to direct equilibration is hopeless. Therefore, Spencer passed to what he called "indirect equilibration."
"Besides those perturbations produced in any organism by special disturbing forces there are ever going on many others—the reverberating effects of disturbing forces previously experienced by the individual, or by ancestors; and the multiplied deviations of function so caused implied multiplied deviations of structure." A directly induced modification induces correlated secondary and tertiary perturbations, and when two differently endowed parents are mated they will bequeath to their joint offspring "compound perturbations of function and compound deviations of structure, endlessly varied in their kinds and amounts." In short, Spencer postulated variations as indirect results of the action of incident forces.
As the individuals of a species are thus necessarily made unlike in countless ways and degrees, then amongst them "some will be less liable than others to have their equilibria overthrown by a particular incident force previously unexperienced... Inevitably, some will be more stable than others when exposed to this new or altered factor. That is to say, those individuals whose functions are most out of equilibrium with the modified aggregate of external forces, will be those to die; and those will survive whose functions happen to be most nearly in equilibrium with the modified aggregate of external forces. But this survival of the fittest implies the multiplication of the fittest. Out of the fittest thus multiplied there will, as before, be an overthrowing of the moving equilibrium wherever it presents the least opposing force to the new incident force. And by the continual destruction of the individuals least capable of maintaining their equilibria in presence of this new incident force, there must eventually be reached an altered type completely in equilibrium with the altered conditions." In short, Spencer incorporated the characteristic Darwinian idea of Natural Selection operating upon a crop of variations, and thus securing by the survival of the fittest an indirect equilibration.
In an ingenious way, to which we have already alluded, Spencer assimilated the theory of Natural Selection with his own formula of evolution. Let us recapitulate his argument. All the processes by which organisms are refitted to their ever-changing environments must be equilibrations of one kind or another, for change of every order is towards equilibrium, and life itself is a moving equilibrium between inner and outer actions—a continual adjustment of internal relations to external relations. The process called Natural Selection is literally a survival of the fittest; and "that is a maintenance of the moving equilibrium of the functions in presence of outer actions; implying the possession of an equilibrium which is relatively stable in contrast with the unstable equilibria of those which do not survive." ... "The conception of Natural Selection is manifestly one not known to physical science: its terms are not of a kind physical science can take cognisance of. But here we have found in what manner it may be brought within the realm of physical science."
It is to be feared that Spencer deluded himself as to the success of his tour de force. For he did not show that there is in inanimate nature anything corresponding to the struggle for existence, nor did he give any instances where the degree of effectiveness of response is of critical value in determining the survival of competing inanimate systems.
After pointing out that the various factors in organic evolution must be thought of as co-operating, Spencer considered their respective shares in producing the total result. Briefly stated, his conclusions were the following:—
At first, the direct action of the physical environment was the only cause of change. "But as, through the diffusion of organisms and consequent differential actions of inorganic forces, there arose unlikenesses among them, producing varieties, species, genera, orders, classes, the actions of organisms on one another became new sources of organic modifications." The mutual actions of organisms became more and more influential, and eventually became the chief factors.
"Always there must have been, and always there must continue to be, a survival of the fittest: natural selection must have been in operation at the outset, and can never cease to operate! While organisms had small abilities of co-ordinating their actions and actively adjusting themselves, natural selection worked almost alone in moulding and remoulding organisms into fitness for their changing environments, but as activity increased and brains grew, the power of varying actions to fit varying requirements became considerable." "As fast as essential faculties multiply, and as fast as the number of organs which co-operate in any given function increases, indirect equilibration through natural selection becomes less and less capable of producing specific adaptations; and remains capable only of maintaining the general fitness of constitution to conditions. The production of adaptations by direct equilibration then takes the first place: indirect equilibration serving to facilitate it. Until at length, among the civilised human races, the equilibration becomes mainly direct: the action of natural selection being limited to the destruction of those who are too feeble to live, even with external aid."
Returning to our scheme of Originative and Directive Factors, let us inquire into Spencer's views regarding Variation and Selection.
Spencer recognised three causes of variation. First there is heterogeneity among progenitors which "generates new deviations by composition of forces"; in other words new patterns arise from the mingling of diverse hereditary contributions in fertilisation. Secondly, functional variation in the parents produces unlikeness in the offspring; those begotten under different constitutional states are different. In other words, fluctuations of nutrition in the parental body may cause variations in the germ-plasm. [In mammals there are also modifications produced during the pre-natal life of the offspring which are congenital in the sense that they are present at birth in latent or patent form, which do not, however, really affect the germ-plasm since they disappear in the third generation.] Thirdly, an organism exposed to a marked change of external conditions, may have its equilibrium altered, and the offspring may be influenced. "The larger functional variations produced by greater external changes, are the initiators of those structural variations which, when once commenced in a species, lead by their combinations and antagonisms to multiform results. Whether they are or are not the direct initiators, they must still be the indirect initiators."
But Spencer admitted that there were numerous minor so-called "spontaneous" variations, which could not be referred to the causes noticed above. He attributed these to the fact that no two ova, no two spermatozoa, can be identical, since the process of nutrition cannot be absolutely alike. Minute initial differences in the proportions of the physiological units will lead, during development, to a continual multiplication of differences. "The insensible divergence at the outset will generate sensible divergences at the conclusion." This is not different from the general idea that nutritive fluctuations in the body provoke variations in the complex germ-plasm, "still it may be fairly objected that however the attributes of the two parents are variously mingled in their offspring, they must in all of them fall between the extremes displayed in the parents. In no characteristic could one of the young exceed both parents, were there no cause of "spontaneous variation" but the one alleged. Evidently, then, there is a cause yet unfound."
Spencer's further answer was that the sperm-cells or egg-cells which any organism produces will differ from each other not quantitatively only but qualitatively, because inheritance is multiple. In some the paternal units, in another the maternal units, in another the grand-paternal or the grand-maternal units will give the impress. "Here, then, we have a clue to the multiplied variations, and sometimes extreme variations, that arise in races which have once begun to vary. Amid countless different combinations of units derived from parents, and through them from ancestors, immediate and remote—and the various conflicts in their slightly different organic polarities, opposing and conspiring with one another in all ways and degrees, there will from time to time arise special proportions causing special deviations. From the general law of probabilities it may be concluded that while these involved influences, derived from many progenitors, must, on the average of cases, obscure and partially neutralise one another; there must occasionally result such combinations of them as will produce considerable divergences from average structures; and at rare intervals, such combinations as will produce very marked divergences. There is thus a correspondence between the inferable results and the results as habitually witnessed."
In conclusion, after his wonted manner, Spencer pointed out that Variation, like everything else, is necessitated by the Persistence of Force. "The members of a species inhabiting any area cannot be subject to like sets of forces over the whole of that area. And if, in different parts of the area, different kinds or amounts or combinations of forces act on them, they cannot but become different in themselves and in their progeny. To say otherwise, is to say that differences in the forces will not produce differences in the effects; which is to deny the persistence of force."
Selection.—As we have seen, Spencer incorporated into his scheme the Darwinian concept of Selection, and sought to show that it could be included under the general concept of Evolution as "a continuous redistribution of matter and motion." "That natural selection is, and always has been, operative is incontestable.... The survival of the fittest is a necessity, its negation is incontestable."
That he did not take a narrow view of the process of Selection, which has so many forms and operates at so many levels, will be admitted; and we may illustrate this by showing that he had a prevision of what Roux called "intra-individual selection" or "intra-selection."
In his essay on "The Social Organism" (1860), he wrote:—
"The different parts of a social organism, like the different parts of an individual organism, compete for nutriment; and severally obtain more or less of it according as they are discharging more or less duty." (See also Essays, i. 290.) And, again, in 1876, in his Principles of Sociology, he amplified his statement thus: "All other organs, therefore, jointly and individually, compete for blood with each organ,... local tissue formation (which under normal conditions measures the waste of tissue in discharging function) is itself a cause of increased supply of materials... the resulting competition, not between units simply, but between organs, causes in a society, as in a living body, high nutrition and growth of parts called into the greatest activity by the requirements of the rest." And once more: "For clearly, if the survival of the fittest among organisms is a process of equilibration between actions in the environment and actions in the organism; so must the local modifications of their parts, external and internal, be regarded as survivals of structures, the reactions of which are in equilibrium with the actions they are subject to." Clearly Spencer had a prevision of what Roux calls "Der Kampf der Theile im Organismus" (The struggle of parts within the organism), and we have here another example of his biological insight. That Spencer was not far from the idea of a struggle between hereditary units, we see from the following passage: "In the fertilised germ we have two groups of physiological units, slightly different in their structures. These slightly different units severally multiply at the expense of the nutriment supplied to the unfolding germ—each kind moulding this nutriment into units of its own type. Throughout the process of development the two kinds of units, mainly agreeing in their proclivities and in the form which they tend to build themselves into, but having minor differences, work in unison to produce an organism of the species from which they were derived, but work in antagonism to produce copies of their respective parent-organisms. And hence ultimately results an organism in which traits of the one are mixed with traits of the other; and in which, according to the predominance of one or other group of units, one or other sex with all its concomitants is produced" (Principles of Biology, vol. i., revised ed., p. 315).
While Spencer had this wide appreciation of the scope of selection, he firmly held that biologists burdened it unjustifiably by disbelieving in the transmission of acquired characters, and, as we have seen, he gave a number of examples of phenomena which he believed the Darwinian theory minus the Lamarckian factor was quite inadequate to interpret. He went the length of saying: "Either there has been inheritance of acquired characters or there has been no evolution." Spencer indicated three general difficulties or limitations besetting the theory of Natural Selection.
(1) "The general argument proceeds upon the analogy between natural selection and artificial selection. Yet all know that the first cannot do what the last does. Natural Selection can do nothing more than preserve those of which the aggregate characters are most favourable to life. It cannot pick out those possessed of one particular favourable character, unless this is of extreme importance."
[It is admitted that we cannot prove that Natural Selection effected this or that result in the distant past, but we know that a process of discriminate elimination is a fact of life, and we argue from the present to the past. Given variations enough and time enough, it is difficult to put limits to the efficacy of selection. If in a race of birds fairly well adapted to the conditions of their life, variations occur in the length of wing, there is no theoretical difficulty in supposing that if a longer wing is advantageous, this particular favourable character may in the course of time become through selection the property of the whole race.]
(2) "In many cases a structure is of no service until it has reached a certain development; and it remains to account for that increase of it by natural selection which must be supposed to take place before it reaches the stage of usefulness."
[One variation is often correlated with another, and the stronger variation may afford point d'appui for the action of natural selection, and thus act as a cover for the incipient variation until that reaches the stage of usefulness and becomes itself of selection-value. What Spencer himself says in regard to the selection of aggregates rather than items, seems half the answer to his difficulty.
It has also been suggested that adaptive modifications may act as fostering nurses of germinal variations in the same direction. Let us suppose a country in which a change of climate made it year by year of the utmost importance that the inhabitants should become swarthy. Some individuals with a strong innate tendency in this direction would doubtless exist, and on them and their similarly endowed progeny, the success of the race would primarily, and might wholly depend. At the same time, there might be many individuals in whom the constitutional tendency in the direction of swarthiness was too weak and incipient to be of use. If these, or some of them, made up for their lack of natural swarthiness by a great susceptibility to acquired swarthiness, to becoming tanned by the sun, it is conceivable that this modification, though never taking organic root, might serve as a life-saving screen until coincident congenital variations in the direction of swarthiness had time to grow strong and become of selection value. We can also imagine that a stock without great mental ability might succeed, in conditions where a premium was put on brains, by their application and docility, till eventually innate variations in the direction of real cleverness became established in the stock. Similarly, many animals by increased 'will-power' or intelligence may survive until bodily variations of an adaptive kind arise to economise the higher energies. Here and everywhere we venture to say that the more anthropomorphic we can reasonably make our conception of organic evolution the truer it is likely to be.
A third answer to Spencer's second difficulty is afforded by Weismann's subtle theory of Germinal Selection.]
(3) "Advantageous variations, not preserved in nature as they are by the breeder, are liable to be swamped by crossing or to disappear by atavism."
[We have already referred to various answers to this difficulty—in terms of Isolation, Prepotency, and other conceptions. But the answer which will occur to everyone at the present time is in terms of "Mendelism," into a discussion of which we cannot enter. Suffice it to say, that for the cases with which he dealt, Mendel has given evidence that variations which arise suddenly and are discontinuous—mutations, as De Vries calls them—are not likely to be swamped by in-breeding with the normal form, and that he has given a reason why this swamping does not occur.]
In regard to the second directive factor—Isolation, Spencer had no criticism to offer. It seemed to him that "in whatever way effected, the isolation of a group subject to new conditions and in course of being changed, is requisite as a means to permanent differentiation."
But after allowing full play to variation and modification, selection and isolation, Spencer felt that "though all phenomena of organic evolution must fall within the lines indicated, there remain many unsolved problems." "We can only suppose that as there are devised by human beings many puzzles apparently unanswerable till the answer is given, and many necromantic tricks which seem impossible till the mode of performance is shown; so there are apparently incomprehensible results which are really achieved by natural processes. Or, otherwise, we must conclude that since Life itself proves to be in its ultimate nature inconceivable, there is probably an inconceivable element in its ultimate workings."