Evolution. Upon every developing mind, whether infantile or consciously philosophic, there presses at times the question of the origin of things. The attempt to answer this is to construct a cosmogony; and is alike the earliest and the latest extension of our common-sense account of things into complete and more orderly form as science. In seeking to do this the greater and more permanent phenomena at first impress us; and our speculative restlessness, if not lulled altogether, may seek to satisfy itself by postulating the existence of the universe substantially unchanged during an infinite past. But this philosophy of things is not only incapable of being really grasped by the highest effort of the intellect, but is incessantly contradicted by experience; it has hence never gained any real acceptance from the simplest common sense, much less any confirmation from science. The alternative then arises of drawing an explanation of the origin of things from our experience not of permanence, but of change. Here it is naturally the most changeful phenomena, the most marked and sudden contrasts, which first and most deeply arouse our attention, and this not only in nature, but still more in human life and affairs. The conception of uniformity among superficially different phenomena has hardly arisen, and the demand for explanations in terms of cause and effect, other than in terms of personal volition, is proportionately weak. The hypothesis of a sudden and unexplained, of a mysterious appearance or creation of things, thus next presents itself; and the subsequent explanation of this as an act of external will is rendered easy by our personal consciousness. As our practical and industrial powers develop, and the perception of phenomenal order deepens and extends, the original simple association of a simultaneous appearance of all phenomena with a flash of volition is modified. Phenomena are becoming classified and interconnected in larger and larger groups, with which a higher anthropomorphism can henceforth associate a conception of detailed design. The older view only remains provisionally so far as order is not yet apparent; such later creationist theories become increasingly supplemented by a recognition of the changes in progress around us. The importance of these is found steadily to increase, and the conception of evolution, nascent since the crudest view of creation had given place to a more gradual and causal explanation, now becomes independently formulated in each order of phenomena. Human affairs become more and more obviously interpretable than of old, and there arises in their place the characteristically modern idea of progress. Natural science meanwhile has become more active, the very astronomical and geological phenomena from which our ideas of permanence were most derived are seen to be in process of change. Changes which seemed to be catastrophic in their vastness are proved to be only the cumulative product of natural agencies in daily operation; and the idea of the present as the product of the past also becomes extended to the world of organic life. The details, the general mechanism and direction of the processes of change, thus become inquiries of paramount interest to each body of scientific specialists and still more to the philosopher. It is at this period that we find ourselves, and to the brief discussion of these questions therefore that we must pass; but it is useful from the outset to recognise that instead of having well-defined and sharply-opposed theories of creation and evolution, these are but phases of an incomplete evolution. Hence the controversies so active during the middle half of the present century have practically ceased; it is admitted on all hands that the evolution theory only supersedes those cruder anthropomorphisms of arbitrary creation and of mechanical contrivance which presented the universe as a mere aggregate of finished products, without excluding that higher and more unified teleology which interprets it as the orderly unfolding of a cosmic drama. And as we see the evolution theory to be an orderly development beyond its predecessors, mere destructive criticism of these becomes no longer necessary.
Mode of Treatment.—The student of theology or philosophy, or the man of general education, is usually inclined at once to plunge amid the conflicting currents, the perplexing eddies of past cosmogonic speculations. He hence sets out by reviewing the oriental theories of the universe, and comparing these with Hellenic ones; he develops mingled types of both through early Christian thought into the elaborate compromise of the scholastic world; and finally endeavours to trace the modifications and survivals of these in contact with the thought-streams of the Renaissance and the Revolution before reaching the theories of modern times. But it would be a grave mistake to suppose that these last are the product of any continuous development from the preceding course of speculation. They have arisen independently and upon a distinct line, and present themselves as the most generalised result and expression of our concrete studies of natural science. Hence such historic inquiries, in all cases difficult, if not actually misleading, would be in any case premature; whereas, when we have grappled with the scientific theories of evolution, we may then profitably note the analogies or parallelisms, the survivals of, or reversions to, earlier modes of thought which these present.
Scientific conceptions of evolution may themselves be approached from various sides. Minds of the more abstract type or training tend to begin with such a highly generalised analysis and exposition of the subject as that with which the labours of Herbert Spencer have been so prominently concerned. After accepting or modifying this dynamic view of the universe as a whole, we should then seek to satisfy ourselves as to the applicability of our principles to the genesis of the physical world, and thence pass to the phenomena of life, mind, and society. We should then be accustomed to regard the universe no longer as a mere phantasmagoria, nor even merely as an orderly succession of events, but as a process of becoming. And, since this orderly flux of evolution is still in progress, scientific prevision thus becomes possible, and with it a corresponding degree of practical prevision as well. We thus reach a transition from the cosmist to the humanist attitude; the essential step from an evolutionary system of science towards an evolutionary system of ethics would then be made. These general conceptions reached, and an evolutionary philosophy in its broadest outlines being thus settled, we are in a position to review the earlier systems of different historic periods, and rationally criticise and interpret them in the light of our own conceptions; it may be even to recognise defects or deficiencies in these, and to obtain suggestions how to correct or supply them.
A less arduous and more popular method, concrete and inductive moreover, and consequently more in harmony with the modern spirit, is to begin as a scientific specialist, artificially isolating in thought one order of phenomena at a time from the complex unity of nature. Reviewing in this way the physical sciences, next the biological, and finally the mental and social, we shall be able to trace the parallel rise of evolutionary interpretations in each order of phenomena. And, after adequate detailed study of physical and organic processes, we may not only discuss the broader generalisations with fuller grasp and certitude, but proceed to inquire into the evolutionary process in higher sciences with ampler preparation; and thus ultimately approach the philosophic ideal of clearest and completest general view.
In this way we should have again completed the same cycle of thought as that sketched in the preceding section, but this time inductively instead of deductively: we have, as it were, worked our way upwards from our scientific primers instead of down from Mr Spencer's First Principles or the like. In short, then, the most simple, safe, and fruitful scientific method of studying the problem of evolution we find to be to reverse the order of the three distinct methods above outlined; to commence with the concrete study of evolution as manifested in the universe as a whole, in the earth's crust, and among plants and animals; gradually to rise toward more abstract expression and more deductive grasp, then to pass to mental and social evolution. Within the present compass the utmost that can be attempted is to sketch out a few of the leading lines of thought and still more briefly indicate others.
Evolution in the Physical Sciences—Astronomy.—Here, as in other sciences, early conceptions of the universe agree in viewing it as being, as far as possible, in permanence and at rest, and not in change and motion. Such static views may be only tacitly implied, but are more usually directly avowed: thus the earth was long viewed as a plane stably supported, and till very recently the stars were viewed as fixed. But as the static universe of the ancient astronomer passes into that of Copernicus and Kepler, Galileo and Newton, Herschel and Leverrier, dynamic, or more accurately kinetic, conceptions have henceforward an assured prominence in at least one science, and that the one most obviously concerned with the universe as a whole. For although evolutionary speculations of more or less vagueness seem to have arisen once and again in almost every science, the first well-developed theory of evolution which has attempted to cope with the observed facts of any science must be credited to astronomy (if not to the professed astronomer) in the famous Nebular Hypothesis (q.v.), of which the suggestiveness to all other departments of science must be freely admitted. For the mind which has once fairly grasped the conception of stellar and planetary evolution cannot readily stop there.
Evolution in Chemistry.—In chemistry kinetic conceptions must naturally have been rife from the earliest times. The records of ancient chemistry are indeed largely those of the speculative exaggerations of kinetic hypotheses by the alchemists; as its history in more modern times bears the trace of a strong, and in some respects excessive reaction from these, albeit to occupy the more certain ground afforded by the conception of the permanence of matter. But the analytic researches, the studies of atoms and elements, of valencies and molecular constitutions viewed as absolutely definite, are again being used only as starting-points for new dynamic departures, such as those of thermo-chemistry; while new speculations, essentially evolutionist, such as those of Crookes and others, are arising on various hands around the well-known periodic law (see CHEMISTRY). The similarity in composition of our planet with that of sun and stars, and the intimate relation between organic and inorganic compounds, are also suggestive; while the actually observed genesis of many species of minerals by the action of natural causes, and the frequent transmutation of one species into another when some definite change takes place in the surrounding conditions, are not without evolutionary interest.
The recent movement in chemistry above alluded to is indeed only the counterpart of what has been taking place earlier and more fully in physics, thanks largely to astronomy and to the mechanical arts, not to speak of other influences. The laws of motion, the conception of gravitation, the abandonment of the theories of the material nature of light, heat, and electricity, are all steps of the same progress, as are also the positive demonstration of the existence of the imponderable ether, and finally the sublime conceptions of the conservation and dissipation of the evolution and dissolution of energy throughout the universe. And as the analytic task of the chemist and physicist rises from that of weighing and grasping at the atom to that of watching and measuring the wave, our general conceptions are inevitably changing also. The idea of a static universe, essentially constructed once for all of so many different masses and kinds of matter, upon which man of science, philosopher, and theologian alike formerly agreed, is on all hands fully giving place to that of a dynamic unity which owes its manifold and unceasing differentiation to the varying modes or moods of the universal energy.
Evolution in Geology.—That the last-century mineralogist was here and there already widening his interest to the rocks and even meditating as to their nature and origin is well evidenced by the penetrating speculation of Linnæus: 'It may be that the solid rocks are not primeval, but the daughters of time.' As subsequent generations of research have shown us, this solid rock is the product of igneous and that of aqueous action, here reaching back to an incalculable antiquity, or there evolved within the period of human occupancy; while others consist in great part, or even completely, of the remains of extinct animals or plants. These are conceptions now so familiar that it is difficult to realise their once revolutionary appearance and effect. But when we take into account the transition from the cataclysmal and essentially creationist theories which at first prevailed to the uniformitarian, or evolutionist, interpretation of geological phenomena which centres round the work of Lyell, we cannot wonder that such a revolution in geological doctrine should have exercised an influence upon general thought only second to that of the Copernican astronomy itself. More detailed studies, too, would be of no little service to our general theories; note, for instance, how the geologist takes from the astronomer, now a stellar evolutionist, the cooling planet, and outlines its primeval Sunderings of land and sea, its wrinkling hills and vales, how he proves that the pulse of ocean is but the dying ripple of a once fiftyfold mightier tidal wave, or how the glacial period is the inexorably recurrent winter of a year of ages. The mineralogist no longer merely measures and analyses, but deciphers the origin and transmutation of mineral species, and of the rocks they form under the forces of the environment (see MINERALOGY); and the typically changeful phenomena of climate and atmosphere are rendered the subject of a typically dynamic sub-science (see METEOROLOGY).
Modal Explanation of Physical Evolution.—We must sooner or later inquire whether any general principle can be found to verify and rationalise the process of evolution in the physical world, and to this the answer has been specially elaborated by Mr Herbert Spencer. His essential principle or Law of Evolution must be stated in his own words: '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.' The deductive and inductive establishment of this principle, and its comprehensive verification and fruitful application throughout the fields of the higher sciences as well, are necessarily left for fuller separate exposition (see SPENCER). And although the student who seeks to follow Mr Spencer in grappling with the riddle of evolution in higher orders of phenomena may not admit that his uncompromising application of the principles of physical evolution to higher categories is so exhaustive and satisfactory as he claims, there can be no doubt that this general treatment has been on the whole amply justified so far as it goes, alike in unifying the sciences, and in the separate organisation of these.
Evolution in Biology.—This portion of the subject demands special attention and fullest outline for many reasons. Not only is the transition from static to evolutionary conceptions of comparatively recent, indeed almost contemporary interest; but the progress of the doctrine of evolution as a general theory of the universe has been most closely connected with progress in biology. And while we can at best merely speculate as to the direct continuity of evolution from the inorganic to the organic world (see BIOLOGY, SPONTANEOUS GENERATION), we are constantly impressed by the fundamental unity of the process in the simplest and most complex forms of life, and by the thoroughness with which the same principles may be traced into the highest 'superorganic' phenomena of mind and society.
At the outset we require some such conception of the actual historic progress of our concrete knowledge of plants and animals as is outlined in the articles BOTANY and ZOOLOGY, and also of that rise of our more abstract kinetic and static (physiological and morphological) interpretations of the phenomena of life as is given under BIOLOGY and BOTANY. The general argument for evolution appended by Darwin to the classic statement of his theory of Natural Selection in the Origin of Species has been already summarised under DARWINIAN THEORY, and its separate heads are also to be found under separate articles; only the briefest reference to these need here be made. We must keep, for instance, in view the conceptions of the actual evolution of the individual which have become systematised in the sub-science of embryology (see EMBRYOLOGY). Suffice it, however, here to recall that, although it is in this connection that the term evolution first makes its appearance, it is used along with development, in a sense diametrically opposed to its present significance, as the mere enlargement and unfolding (evolutio, evolution, Entwicklung) of a form and structure in all essential respects a perfect miniature of that of the adult.
Without recording or analysing the various conceptions of species (see SPECIES) it is sufficient again to note how the belief in their objective constancy and practical definableness is shaken by such facts as (1) that pre-evolutionary systematists differ hopelessly upon the number and limits of the species of all the more variable groups of plants and animals; (2) that the mere numerical increase of the number of specimens in our museums is constantly compelling us to recognise that great numbers, sometimes even scores or hundreds, of 'type-specimens' of irreproachably described 'species' are but so many individual members of a series linked by the most infinitesimal gradations, yet of which the extremes differ by characters of specific, it may be even generic rank. And when (3) the assumption of the general sterility of hybrids is proved experimentally (see HYBRID) to be an exaggeration, it becomes, to say the least, increasingly difficult seriously to support the dogma of the constancy of species.
Leaving the general external form with which the species-maker is mainly concerned, we must accompany the anatomist through each level of his deepening analyses and comparisons, through organ-systems and organs, tissues and cells, to the ultimate protoplasm itself (see BIOLOGY, MORPHOLOGY). To realise how fully this analysis results in the demonstration of an unsuspected unity of structure not only between species and genera, but far larger groups, some actual study of the concrete facts is indispensable; as also to appreciate the same beautiful unity of type in individual structures so differentiated as the appendages of a lobster (see CRUSTACEA) or the parts of a flower (see FLOWER). Yet here again we have an instance of the tenacity of static conceptions; for although it could not be actually denied that the hypothesis of descent from common ancestors at least might explain the structural unity observable under classification, as from a simpler ancestor, that observable under the individual structure, the conception of conformity to a purely ideal 'archetype,' was long maintained. Rudimentary organs, such as the teeth of foetal whales, were thus explained not as reduced survivals of structures ancestrally useful, but as purely intellectual necessities of this arbitrary 'conformity to type.' This ingenious revival of Platonic ideas in conjunction with scholastic nominalism could not, however, very long survive the demonstration of the frequent absence of rudiments necessary for archetypal purposes; and the alternative evolution- ary explanation has thus inevitably succeeded to its place.
It is much to learn from the taxonomist that his classification of species and genera, even the whole world of plants or animals, assumes the form of a vast genealogical tree; and it is no small confirmation of the evolutionary view to note how every new fossil-trove throws some fresh light upon the order in which the branches or branchlets of this tree have historically developed. With all the missing links we can imagine or desire between the modern horse and his simple five-toed ancestor (see PALÆONTOLOGY, FOOT, HORSE), not to speak of other examples, we have indeed evidence which may well satisfy us of the historic fact of evolution; but this brings us no nearer comprehending the rationale of the process. Leaving the morphological sciences, we must pass with Darwin to the study of what we may call the higher physiology. Assuming what is known of the functions of the individual, we must note not only the relations of the species unit (in higher forms usually of course the pair), and so familiarise ourselves with the phenomena of reproduction and sex, of heredity and variation, breeding and relation to offspring, the results of intercrossing, the modification by environment, &c.; we must also consider the wider relations among the members of the same species, between allied species, and finally between practically unrelated ones, whether here of struggle or there of adaptation. He thus introduces us to this vast and practically new field, and gives us a glimpse of the living, whole nature in that magistral series of volumes, which we may as it were group into a Vita Naturæ, complementary to the static Systema Naturæ, and no less epoch-making for our day than was that of Linnæus for his.
We see how natural it is that the student of biology who thus becomes an evolutionist so largely by help of Darwin, should accept the lucid and comprehensive modal explanation so vitally associated with his whole evolutionary attitude, and thus also become a thoroughly convinced Darwinian, a natural selectionist without more ado: and we can readily understand that the assent of the majority of the intelligent public should have gradually followed the same course during the generation after the publication of the Origin of Species.
It is necessary, however, to refer more precisely to the history of opinion both as regards the fact of evolution and the factors in the process. The history of the two questions—of the empirical fact, and of the actual mechanism of evolution—can hardly be separated, though it is of course well known that the former was virtually settled by the demonstrations of Spencer, Darwin, Wallace, Haeckel, and others soon after the middle of this century, while we are still in the midst of keen debate as to the relative importance of the diverse factors. The history of the theory of evolution, so far as the organic world is concerned, is essentially modern, for in spite of vague hints and a priori speculations from Empedocles onwards, it was not till the 18th century that evolution began to be very definitely suggested as a modal explanation of the origin of our fauna and flora, or that inquiry began to be seriously directed to what we now call the etiology of organisms.
What was for so long only a germ-idea at length took shape in the mind of Buffon (1749), who not only urged the general conception with diplomatic skill and covert irony, but sought to show how new conditions evoked new functions, how these in turn reacted upon the structure of the organism, and how, most directly of all, altered climate, food, and other elements of the environment might be the external conditions of internal change, whether for progress or the reverse. Erasmus Darwin (1794), with a truly living conception of nature, emphasised the organism's inherent power of self-improvement, the moulding influence of new needs, desires, and exertions, and the indirect action of the environment in evoking these. To Treviranus (1802-31) organisms appeared almost indefinitely plastic, especially, however, under the direct influence of external forces, nor did his analysis of possible factors fail to recognise what Brooks, Weismann, and others have recently elaborated, that the union of diverse sexual elements in fertilisation was in itself a fountain of change. His contemporary Lamarck (1801-9) is well known to have emphasised the importance of changed conditions in evoking new needs, desires, and activities, while urging also the perfection wrought by practice and the degeneration which follows as the nemesis of disuse. Evolution seemed to him the interaction of two fates—an internal progressive power of life, and the external force of circumstances in the two-fold struggle with the environment and with competitors. Among the philosophers also, especially in the minds of those who had been disciplined in physical or historical investigations, the speculations of the ancients were ever taking fresh form, gaining moreover in concreteness; witness the contributions of Kant and Herder. In Goethe's epic of evolution the adaptive influence of the environment is clearly recognised, while the misty theories of his contemporary Oken chiefly interpret the organic progress in terms of action and reaction between the organism and its surroundings. Wells in 1813 and Patrick Matthew in 1831 forestalled Darwin in suggesting the importance of natural selection, but their buried doctrines were of much less practical importance than those of Robert Chambers, the long unknown author of the Vestiges of Creation (1844-53). His hypothesis of evolution emphasised the growing or evolving powers of the organisms themselves, which developed in rhythmic impulses through ascending grades of organisation, modified at the same time by external circumstances acting with most effect on the generative system. In France, Geoffroy and Isidore St Hilaire, father and son, supported the thesis of definite variation under direct environmental influence. And before reaching even the contemporaries of Darwin a complete history would have to take account of the conclusions of many naturalists, such as Von Buch, Von Baer, Schleiden, Naudin, and Wagner. The environmental factor was subsequently recognised with greater clearness and with less exclusiveness by Spencer; while Darwin and Wallace, recognising some truth in most of the above positions, but believing them wholly insufficient, left the problem of the origin of variations alone, and devoted their strength to establishing the theory of the origin of species by means of natural selection, a view which emphasises the destructive or eliminating and the conservative or selective action of the animate and inanimate environment in the struggle for existence.
Even from the above brief sketch of representative conclusions, it will be seen that successive authors accent diverse factors in the evolutionary process: in the view of one the organism has a motor power of variation inherent in its very constitution, or gained by the intermingling of sex-elements from which the individual life starts; to another the moulding power of changed function, the perfecting influence of exercise, the degenerating nemesis of disuse are all important; while to a third organisms seem to have been hammered from one shape into another by the action of that complex series of external influences which we briefly term the environment. Among modern naturalists we find champions of each of these three positions respectively emphasising (a) the organism itself, (b) its function, and (c) its environment; a few remain more or less exclusive Natural Selectionists, with or without theories of the origin of the variations which they postulate; while the majority more and more incline to an eclectic but not yet synthetic view, differing chiefly in regard to the relative importance of the various factors recognised.
The difficulty will be obvious of even briefly discussing so many positions, many of which are better dealt with under the separate articles ENVIRONMENT, HEREDITY, REPRODUCTION, SEX, VARIATION; and it is undesirable here to stereotype any one position as final during an unended controversy. That criticism will be certainly more temperate, and probably not less fruitful, which for a time seems to withdraw from the actual field of battle; which, instead of joining issue on this point or upon that, seeks rather to recognise all the leading points of view from which the subject may be approached, and thence to clear up the various lines on which a modal explanation is or may be offered, or to which it must at any rate be capable of satisfactory application. We should thus even be able to do more justice to the older naturalists' positions.
Evolution in Psychology.—The psychologist admits the same inability to derive psychical processes and states from the nutritive and reproductive functions and structures which form the subject-matter of biology that the biologist does to derive these from inorganic processes. This fact does not of course interfere with the investigation of the parallelism of each of these higher orders of phenomena (see BIOLOGY), still less with the detailed study of evolution in mind, for which, as Mr Spencer has especially demonstrated, evolution in the preliminary sciences of biology and physics is so suggestive. What most concerns us here is to note how largely the science of psychology, or what stood for it, was wont to be a matter of deduction from that time-honoured axiom that human nature is for practical purposes always and everywhere the same; which, as evolutionists, we now see to have been an erroneous postulate. The older psychology was concerned especially with less or more scientific analyses of the adult mind, and this usually of the isolated 'typical' one (usually of the psychologist himself), but in a form too generalised to admit of much practical application. The modern school recognises the necessity of unravelling the vast complexity of the actual details of psychical processes, and not only eagerly investigates the development of the infantile mind, but scrutinises the kindred though humbler phenomena of animal cerebration. Psychology is drawing new light from the long discredited study of hypnotic states (see ANIMAL MAGNETISM); since here psychical functions can be analysed at various levels, and this apart from the perturbing action of the will. Again, it finds a rich source of knowledge in those morbid variations towards excessive or deficient cerebration and neuration which we group under the complex term Insanity (q.v.). Yet that it reaches also the most complex concrete products of evolution is evidenced by the rise and progress of criticism in literature and art. That we have here the closest parallelism to biology and its progress is manifest, as our current phrases of comparative psychology, of mental physiology, pathology, variation, and the like clearly show. We see, indeed, that the science of psychology is now more biological, more evolutionary, and more unified than biology itself, which is still so largely limited by the numerous and confused dispersive and analytic specialisms from which it has arisen, and which it is still so far from having reorganised. The transition from the static to the kinetic attitude is thus more nearly complete. The debt of science to practice is here obvious in the gain from education and mental hygiene; while the return of the science into practice, as yet only incipient, promises results of the vastest kind. Education would at length have to be viewed and practised in an evolutionary sense, as the process of assisting the entire development of the individual into, it may be beyond, the actual living powers, into the stature and beauty, of the race; instead of smothering the development under the mere accumulation of its dead results in certain fields of detail. Nor is the parallelism of psychical and physiological processes, which enables us to modify more and more mind through body, failing to open up subtler possibilities of modifying body through mind.
Evolution in the Social Sciences.—Leaving fuller treatment to the article SOCIOLOGY, and such special articles (POLITICAL ECONOMY, &c.) as are therewith connected, we may note that the social science of the pre-evolutionary period, although represented on its concrete side by history, and its abstract side especially by political economy, was essentially static. History was necessarily a record of occurrences at specified dates, which, although sometimes set forth in their minor relations of cause and effect, did not admit of any large co-ordination in scientific terms; though the continual attempt by theologians and metaphysicians to construct a philosophy of history indicated at least the need of this. Upon the abstract side we have those attempts to formulate a purely deductive 'science of political economy,' which still so largely survives; although its pretended laws, deduced from postulates of the archaic psychology, such as that of action exclusively arising from self-interest, or from metaphysical abstractions such as utility, are now being replaced by generalisations drawn from the inductive study of social phenomena, actual and historic, and by principles firmly established in the preliminary sciences. The derivation of our whole body of social knowledge from social practice is here of course absolute, all the phenomena being human ones; and the reaction of theory upon practice can only at first sight seem disproportionately small when we lose sight of the importance of the past thought systematised in legal and religious systems. In the world of material interests static views have as yet essentially prevailed: witness the incomparable antiquity of law as compared with that of the modern process of law-making and unmaking which we call internal politics—a form of activity which, however disappointing in its practical results, has at least had something to do with the even more recent emergence and popularisation of the idea of social progress. This characteristically modern idea became increasingly systematised, on the one hand through special studies, and on the other through the unparalleled progress of the mechanical arts. We must note also that the very recent foundation of sociology as a distinct and unified science depended upon the attainment of a synthetic interpretation of the history of western Europe both material and intellectual as the central process of the general evolution of humanity; while no subsequent labours on behalf of the nascent science have been greater than those of that later thinker who has been far more concerned than any other with the general philosophy of evolution.
That the idea of evolution has originally been projected from the social plane into that of the other sciences, is a proposition which can only be doubted by the specialist who has not inquired into the history of his ideas; evolution in social affairs has not only suggested our ideas of evolution in the other sciences, but has deeply coloured them in accordance with the particular phase of social evolution current at the time. The hermit not unnaturally supposes his cosmist meditations to be wholly unspotted by the world he has left behind, but this cannot prevent the historian from rigorously viewing his whole thought and conduct as a product of that world. Nor is absolute demonstration difficult even from the strictest biological specialist's own postulate—that life is interpretable merely as a biological phenomenon. Be it so: then science is the summed (phylogenetic) experience of the race, and the investigator's contribution to it is of course measured by his own development (ontogeny). But the development of an organism, functional and cerebral, is so far pari passu with its adaptation to the world around it, but still more in relation to its own species. In other words, the measure of individuation attained by the individual of any species as compared with its fellows is dependent in the first place upon sexual maturity, (2) upon the relations to offspring towards which this tends to develop, and (3) upon the measure of sociality which in so many species arises through the widening of this direct reproductive relation into that of a larger aggregate. This is a proposition which the biologist should be the last to dispute; hence, while arguing for the evolution of the human species by the same agencies which have shaped the lower ones, it is impracticable permanently to retain the absurd assumption, inherited from pre-evolutionary psychology, that mental development goes on as it were in vacuo, without reference to the expansion of the organic functions of self-maintaining and species-maintaining. But as this survival becomes outgrown the pure biologist will of course be the first to emphasise and elaborate the proposition that all human developments, like those of any other species, are in terms of these.
Modal Explanation of Organic Evolution.—The conception thus reached of the measure of evolution of a species being expressible in terms of the progress of its (1) self-maintaining and (2) species-maintaining functions is equally capable of statement in biological, psychological, sociological, or indeed also, as moralists are now agreeing (see ETHICS), in ethical terms; what are termed egoistic or altruistic actions being respectively self-maintaining or species-maintaining ones, of course at different levels of evolution. Here, then, we have a basis for the required inquiry as to the mechanism of the evolutionary processes. The evolutionist at any rate will not dispute this parallelism between the non-ethical aspects of organic evolution, nor deny that the results and processes of evolution in their highest manifestations may be of service in elucidating or criticising the similar ones which must be supposed to exist in less developed forms. Hence he would be in some respects even better justified in tracing the evolutionary process down from the highest aspects to the more simple ones, and from the human species to humbler ones, than conversely: thus the limitations of the doctrine of natural selection may be better understood, and this on two or three distinct sides. It is not altogether easy to meet the criticism sometimes urged by the economist that the process which kills off the weakest of the race weakens and deteriorates those which survive, and that, while some struggle for existence is needful for individuation, human progress is yet observably associated with an advance of the subsistence fund over the requirements of maintenance. Without insisting upon the difficulties urged by Wallace, Mivart, and other evolutionists as to the descent of man (see MAN, DESCENT OF), the ethical difficulty so common to all inquiries respecting evolution and natural selection in general, but human evolution in particular, cannot be escaped. For we have as yet little beyond the cheerful optimism which sets off the cumulative gain to the species against the incessant sacrifice of the weak to the strong which is in constant progress alike in nature and in human society. And if this be indeed the spring of human progress, how can we resist the logic which calls upon us to remove those adjustments for the mitigation of the struggle for existence for the protection of the weaker, with which, however, not only our feelings and what we have been accustomed to call our higher instincts, but our whole civilisation, material and moral, are inextricably bound up? A classical statement of the central difficulty, of which the Darwinism and the morals are alike unexceptionable, and the resultant dualism therefore clearly set forth, may be quoted from Huxley: 'From the point of view of the naturalist the world is on about the same level as a gladiator's show. . . . We must say that its governing principle is intellectual, and not moral, that it is a materialised logical process accompanied by pleasures and pains. . . . Society differs from nature in having a definite moral object. . . . The ethical man tries to escape from his place in the animal world founded on the free development of the principle of non-moral evolution, and to found a Kingdom of Man, governed upon the principle of moral evolution. For society not only has a moral end, but, in its perfection, social life is embodied morality. But the effort of the ethical man to work to a moral end, by no means abolished, perhaps has hardly modified the deep-seated organic impulses which impel the natural man to follow his non-moral course.'
The natural selectionist sometimes seeks (as Mr Darwin has indeed himself done) to escape this frank return to a pre-evolutionary ethical dualism by reminding us that, since on his view 'nature trusts to the chapter of accidents for variation,' favourable ethical variations may spontaneously have arisen at the social plane. But even if the dawn of similar variations in lower species did not raise a probability of the definite rather than fortuitous nature of such variations, the unity of all the four aspects of organic evolution is none the less given up.
The theory of natural selection is now, however, itself undergoing an evolution which promises fair for an escape from these difficulties, and this on all hands. In its classic form it assumed selection to operate upon an indefinite number of individual variations, which Darwin, at least in some moods, was quite ready to admit might be produced by environment, increased by function, and the like; but which, once selected, were preserved by heredity and frequently increased by new spontaneous variations in the same direction. Now, however (see HEREDITY), we have an ultra-Darwinian school founded by Weismann, and followed by Lankester and many others, which, denying the heredity of acquired characters, pushes back the origin of all variations of species-making importance into the protoplasm of the sex-elements, and so seems to leave natural selection as the only factor of evolution which we can really hope intelligently to grasp, variation seeming inscrutable. The neo-Lamarckian school, on the other hand, with which Spencer must also be reckoned, holds a very different doctrine, that of the importance of individual function and the transmission of its modifications; while the influence of environment is also coming to be studied with not only speculative acuteness but experimental detail. Variation is again being more and more frequently regarded as taking place on a few definite lines; and the origin of species is viewed as a literal development of internal conditions in the species as in the development of the individual, which environment can only bend and colour, and natural selection no more than prune. Such views (see VARIATION), too often formulated with excessive generality and indeed vagueness, yet on the whole with increasing concrete application to detail, are maintained by Nägeli, Cope, Eimer, and many others, including the present writer. It will at any rate be recognised that there is ample room for such inquiries, and that the importance claimed by natural selection cannot be safely established until they have been disposed of in favour of that hypothesis of indefinite variability upon which this importance essentially depends. It is becoming more and more apparent that it is the problem of variation which is fundamental to selection.
Amid so many various opinions Mr Wallace has come to stand almost alone as an avowed exponent of the theory of natural selection in its classic form; yet even he not only makes the reserve as to human descent above alluded to, but seeks to replace Mr Darwin's sexual selection (see SEX) by a new hypothesis, and so enlists the services of that heresy of definite variation which is so irreconcilable with Mr Darwin's general argument.
The general drift of the contemporary discussion is thus beginning to be apparent: all theories and criticisms have hitherto started with the individual as the unit, and the origin and differentiation of the self-maintaining structures and functions as the primary problem; after which the origin and differentiation of reproductive and species regarding processes have been left only a secondary and subsequent place. But we are beginning to discover that this method of approach, however natural to the individual thinker, is artificial as respects nature; we have above been noting how many different lines of research are turning from the self-maintaining to the species-maintaining process; and the centre of gravity of the science is in fact undergoing a revolutionary change. In thinking of a species we have been wont to call up and investigate the individual type, and to recognise the process of reproduction subsequently only as giving us a less or more varied repetition of this type; but this is a survival of the static and anatomical view. What the general physiologist is now coming to recognise in the species, and what accordingly the evolutionist a fortiori must keep in view, is primarily its living continuity, no longer the details of its separate links. From this most general point of view both are coming to see the most complex individual lives, in Foster's phrase, as but the 'by-play of ovum-bearing organisms.' The species is a continuous undying chain of unicellular reproductive units which indeed build out of and around themselves transient multicellular bodies; but the processes of nutritive differentiation and other individual development of these is the secondary, not the primary question.
Instead, therefore, of beginning with the origin and adaptation of the details of self-maintaining advantage, coming later to those of reproduction and sex, and only recognising the mysterious control of the principle of correlation of organs in the background of the whole process, as Darwin and other evolutionists have been wont to do, a fuller initial recognition of the reproductive process raises the question of correlation between the reproductive and individual functions at the outset. We see the sexual development of animal, and still more obviously of plant, everywhere becoming a most potent determinant of its adult character, and one of classificatory importance far deeper than the mere individual characteristics of the separate species. We see again how the nature and degree of relation to offspring gives a new key to the larger aspects of classification. Thus it is the central generalisation of botany that despite the individual differentiation of fern, selaginella, cycad, conifer, and flower, these turn out on deepest analysis to be but the surviving phases of a continuous and definite increase in the subordination of the sexual parents to their asexual offspring (see FLOWER). Or in the same way, while we define the orders and sub-orders, genera and species of the mammalia by help of the individual apparatus for maintenance or struggle, the larger question of the characteristics of the mammalia, and of their main subdivisions, does not depend upon any mere accumulation of these, as Darwin's very natural application of Lyell's well-known argument would require: for not only the mammal but its essential types, monotremes, marsupial and placental, and even again the subdivisions of the latter, express so many stages in the progress of maternal sacrifice for offspring. In the same way with the evolution of sociality which arises from reproductive aggregation in so many species, we see this subordinating struggle, greatly facilitating not only the increase in numbers of the species, but their higher specialisation as well. We escape from the conception that progress depends primarily upon internecine struggle for existence—i.e. the subordination of the species to the individual, instead of primarily upon that of the individual to the maintenance of the species in sex, offspring, and society. Thus our ethical difficulty at length disappears, since the greater steps of advance in the organic world compel us to interpret the general scheme of evolution as primarily a materialised ethical process underlying all appearance of 'a gladiator's show.'
The corresponding progress in the historic and individual world from sex and family up to tribe or city, nation and race, and ultimately to the conception of humanity itself, also becomes increasingly apparent. Competition and survival of the fittest are never wholly eliminated, but reappear on each new plane to work out the predominance of the higher, the more integrated and associated type; the phalaux being victorious till in turn it meets the legion. But this service no longer compels us to regard these agencies as the essential mechanism of progress, to the practical exclusion of the associative factor upon which the victory depends, as economist and biologist have too long misled each other into doing. For we see that it is possible to interpret the ideals of ethical progress—through love and sociality, co-operation and sacrifice, not as mere utopias contradicted by experience, but as the highest expressions of the central evolutionary process of the natural world. To continue the generalisation of the process of evolution, organic and super-organic, which Mr Spencer, himself repeating on a higher spiral the thought-cycle of many an earlier thinker, has so fully reopened, is to raise anew all the problems of philosophy, which are indeed in a state of evolutionary flux. The singers too of evolution are gathering fuller voice; we have not only indeed fully entered upon evolutionary reorganisation of thought but the corresponding leavening of all forms of art and even of practical life.
See books cited at DARWINIAN THEORY; articles on the subjects above mentioned, particularly CELL, EMBRYOLOGY, HEREDITY, MIMICRY, PROTOPLASM, and VARIATION; those on special authors, as LAMARCK, SPENCER, WALLACE (A. R.), WEISMANN, &c.; also Romanes, Darwin and after Darwin (1892-95); H. F. Osborne, From the Greeks to Darwin (1894). For Evolution in Arithmetic, see INVOLUTION.