Then he quotes with approval the following opinion:—

And, after displaying the proof rendered by Lyell of uniformitarianism in geology, and cordially subscribing thereto, Whewell adds:—

So much, then, for the state of the most enlightened and representative opinions on the question of evolution before the publication of Darwin’s work; and so much, likewise, for the only reasonable suggestions as to the causes of evolution which up to that time had been put forward, even by those few individuals who entertained any belief in evolution as a fact. It was the theory of natural selection that changed all this, and created a revolution in the thought of our time, the magnitude of which in many of its far-reaching consequences we are not even yet in a position to appreciate; but the action of which has already wrought a transformation in general philosophy, as well as in the more special science of biology, that is without a parallel in the history of mankind.

Although every one is now more or less well acquainted with the theory of natural selection, it is necessary, for the sake of completeness, that I should state the theory; and I will do so in full detail.

It is a matter of observable fact that all plants and animals are perpetually engaged in what Darwin calls a “struggle for existence.” That is to say, in every generation of every species a great many more individuals are born than can possibly survive; so that there is in consequence a perpetual battle for life going on among all the constituent individuals of any given generation. Now, in this struggle for existence, which individuals will be victorious and live? Assuredly those which are best fitted to live, in whatever respect, or respects, their superiority of fitness may consist. Hence it follows that Nature, so to speak, selects the best individuals out of each generation to live. And not only so; but as these favoured individuals transmit their favourable qualities to their offspring, according to the fixed laws of heredity, it further follows that the individuals composing each successive generation have a general tendency to be better suited to their surroundings than were their forefathers. And this follows, not merely because in every generation it is only the “flower of the flock” that is allowed to breed, but also because, if in any generation some new and beneficial qualities happen to arise as slight variations from the ancestral type, they will (other things permitting) be seized upon by natural selection, and, being transmitted by heredity to subsequent generations, will be added to the previously existing type. Thus the best idea of the whole process will be gained by comparing it with the closely analogous process whereby gardeners, fanciers, and cattle-breeders create their wonderful productions; for just as these men, by always “selecting” their best individuals to breed from, slowly but continuously improve their stock, so Nature, by a similar process of “selection” slowly but continuously makes the various species of plants and animals better and better suited to the conditions of their life.

Now, if this process of continuously adapting organisms to their environment takes place in nature at all, there is no reason why we should set any limits on the extent to which it is able to go, up to the point at which a complete and perfect adaptation is achieved. Therefore we might suppose that all species would eventually reach this condition of perfect harmony with their environment, and then remain fixed. And so, according to the theory, they would, if the environment were itself unchanging. But forasmuch as the environment (i. e. the sum total of the external conditions of life) of almost every organic type alters more or less from century to century—whether from astronomical, geological, and geographical changes, or from the immigrations and emigrations of other species living on contiguous areas, and so on—it follows that the process of natural selection need never reach a terminal phase. And forasmuch as natural selection may thus continue, ad infinitum, slowly to alter a specific type in adaptation to a gradually changing environment, if in any case the alteration thus effected is sufficient in amount to lead naturalists to name the result as a distinct species, it follows that natural selection has transmuted one specific type into another. Similarly, by a continuation of the process, specific types would become transmuted into generic, generic into family types, and so on. Thus the process is supposed to go on throughout all the countless forms of life continuously and simultaneously—the world of organic types being thus regarded as in a state of perpetual, though gradual, flux.

Now, the first thing we have to notice about this theory is, that in all its main elements it is merely a statement of observable facts. It is an observable fact that in all species of plants and animals a very much larger number of individuals are born than can possibly survive. Thus, for example, it has been calculated that if the progeny of a single pair of elephants—which are the slowest breeding of animals—were all allowed to reach maturity and propagate, in 750 years there would be living 19,000,000 descendants. Again, in the case of vegetables, if a species of annual plant produces only two seeds a year, if these in successive years were all allowed to reproduce their kind, in twenty years there would be 11,000,000 plants from a single ancestor. Yet we know that nearly all animals and plants produce many more young at a time than in either of these two supposed cases. Indeed, as individuals of many kinds of plants, and not a few kinds of animals, produce every year several thousand young, we may make a rough estimate and say, that over organic nature as a whole probably not one in a thousand young are allowed to survive to the age of reproduction. How tremendous, therefore, must be the struggle for existence! It is thought a terrible thing in battle when one half the whole number of combatants perish. But what are we to think of a battle for life where only one in a thousand survives?

This, then, is the first fact. The second is the fact so long ago recognised, that the battle is to the strong, the race to the swift. The thousandth individual which does survive in the battle for existence—which does win the race for life—is, without question, one of the individuals best fitted to do so; that is to say, best fitted to the conditions of its existence considered as a whole. Nature is, therefore, always picking out, or selecting, such individuals to live and to breed.

The third fact is, that the individuals so selected transmit their favourable qualities to their offspring by heredity. There is no doubt about this fact, so far as we are concerned with it. For although, as I have already hinted, considerable doubt has of late years been cast upon Lamarck’s doctrine of the hereditary transmission of acquired characters, it remains as impossible as ever it was to question the hereditary transmission of what are called congenital characters. And this is all that Darwin’s theory necessarily requires.

The fourth fact is, that although heredity as a whole produces a wonderfully exact copy of the parent in the child, there is never a precise reduplication. Of all the millions of human beings upon the face of the earth, no one is so like another that we cannot see some difference; the resemblance is everywhere specific, nowhere individual. Now this same remark applies to all specific types. The only reason why we notice individual differences in the case of the human type more than we do in the case of any other types, is because our attention is here more incessantly focussed upon these differences. We are compelled to notice them in the case of our own species, however small they may appear to a naturalist, because, unless we do so, we should not recognise the members of our own family, or be able to distinguish between a man whom we know is ready to do us an important service, and another man whom we know is ready to cut our throats. But our common mother Nature is able thus to distinguish between all her children. Her eyes are much more ready to detect small individual peculiarities than are the eyes of any naturalist. No slight variations in the cast of feature or disposition of parts, no minute difference in the arrangement of microscopical cells, can escape her ever vigilant attention. And, consequently, when among all the innumerable multitudes of individual variations any one arises which—no matter in how slight a degree—gives to that individual a better chance of success in the struggle for life, Nature chooses that individual to survive, and so to perpetuate the improvement in his or her progeny.

Now I say that all these several component parts of Darwinian doctrine are not matters of theory, but matters of fact. The only element of theory in his doctrine of evolution by natural selection has reference to the degree in which these observable facts, when thus brought together, are adequate to account for the process of evolution.

So much, then, as a statement of the theory of natural selection. But from this statement—i. e. from the theory of natural selection itself—there follow certain matters of general principle which it is important to bear in mind. These, therefore, I shall here proceed to mention.

First of all, it is evident that the theory is applicable as an explanation of organic changes in specific types only in so far as these changes are of use, or so far as such changes endow the species with better chances of success in the general struggle for existence. This is the only sense in which I shall always employ the terms use, utility, service, benefit, and so forth—that is to say, in the sense of life-preserving.

Next, it must be clearly understood that the life which it is the object, so to speak, of natural selection to preserve, is primarily the life of the species; not that of the individual. Natural selection preserves the life of the individual only in so far as this is conducive to that of the species. Wherever the life-interests of the individual clash with those of the species, that individual is sacrificed in favour of others who happen better to subserve the interests of the species. For example, in all organisms a greater or less amount of vigour is wasted, so far as individual interests are concerned, in the formation and the nourishment of progeny. In the great majority of plants and animals an enormous amount of physiological energy is thus expended. Look at the roe or the milt of a herring, for instance, and see what a huge drain has been made upon the individual for the sake of its species. Again, all unselfish instincts have been developed for the sake of the species, and usually against the interests of the individual. An ant which will allow her head to be slowly drawn from her body rather than relinquish her hold upon a pupa, is clearly acting in response to an instinct which has been developed for the benefit of the hive, though fatal to the individual. And, in a lesser degree, the parental instincts, wherever they occur, are more or less detrimental to the interests of the individual, though correspondingly essential to those of the race.

These illustrations will serve to show that natural selection always works primarily for the life-interests of the species—and, indeed, only works for those of the individual at all in so far as the latter happen to coincide with the former. Or, otherwise stated, the object of natural selection is always that of producing and maintaining specific types in the highest degree of efficiency, no matter what may become of the constituent individuals. Which is a striking republication by Science of a general truth previously stated by Poetry:—

Tennyson thus noted the fact, and a few years later Darwin supplied the explanation.

But of course in many, if not in the majority of cases, anything that adds to the life-sustaining power of the single life thereby ministers also to the life-sustaining power of the type; and thus we can understand why all mechanisms and instincts which minister to the single life have been developed—namely, because the life of the species is made up of the lives of all its constituent individuals. It is only where the interests of the one clash with those of the other that natural selection works against the individual. So long as the interests are coincident, it works in favour of both.

Natural selection, then, is a theory which seeks to explain by natural causes the occurrence of every kind of adaptation which is to be met with in organic nature, on the assumption that adaptations of every kind have primary reference to the preservation of species, and therefore also, as a general rule, to the preservation of their constituent individuals. And from this it follows that where it is for the benefit of a species to change its type, natural selection will effect that change, thus leading to a specific transmutation, or the evolution of a new species. In such cases the old species may or may not become extinct. If the transmutation affects the species as a whole, or throughout its entire range, of course that particular type becomes extinct, although it does so by becoming changed into a still more suitable type in the course of successive generations. If, on the other hand, the transmutation affects only a part of the original species, or not throughout its entire range, then the other parts of that species may survive for any number of ages as they originally were. In the one case there is a ladder-like transmutation of species in time; in the other case a possibly tree-like multiplication of species in space. But whether the evolution of species be thus serial in time or divergent in space, the object of natural selection, so to speak, is in either case the same—namely, that of preserving all types which prove best suited to the conditions of their existence.

Once more, the term “struggle for existence” must be understood to comprehend, not only a competition for life among contemporary individuals of the same species, but likewise a struggle by all such individuals taken collectively for the continuance of their own specific type. Thus, on the one hand, while there is a perpetual civil war being waged between members of the same species, on the other hand there is a foreign war being waged by the species as a whole against its world as a whole. Hence it follows that natural selection does not secure survival of the fittest as regards individuals only, but also survival of the fittest as regards types. This is a most important point to remember, because, as a general rule, these two different causes produce exactly opposite effects. Success in the civil war, where each is fighting against all, is determined by individual fitness and self-reliance. But success in the foreign war is determined by what may be termed tribal fitness and mutual dependence. For example, among social insects the struggle for existence is quite as great between different tribes or communities, as it is between different individuals of the same community; and thus we can understand the extraordinary degree in which not only co-operative instincts, but also largely intelligent social habits, have here been developed[30]. Similarly, in the case of mankind, we can understand the still more extraordinary development of these things—culminating in the moral sense. I have heard a sermon, preached at one of the meetings of the British Association, entirely devoted to arguing that the moral sense could not have been evolved by natural selection, seeing that the altruism which this sense involves is the very opposite of selfishness, which alone ought to have been the product of survival of the fittest in a struggle for life. And, of course, this argument would have been perfectly sound had Darwin limited the struggle for existence to individuals, without extending it to communities. But if the preacher had ever read Darwin’s works he would have found that, when thus extended, the principle of natural selection is bound to work in favour of the co-operative instincts in the case of so highly social an animal as man; and that of these instincts conscience is the highest imaginable exhibition.

What I have called tribal fitness—in contradistinction to individual fitness—begins with the family, developes in the community (herd, hive, clan, &c.), and usually ends with the limits of the species. On the one hand, however, it is but seldom that it extends so far as to embrace the entire species; while, on the other hand, it may in some cases, and as it were sporadically, extend beyond the species. In these latter cases members of different species mutually assist one another, whether in the way of what is called symbiosis, or in a variety of other ways which I need not wait to mention. For the only point which I now desire to make clear is, that all cases of mutual aid or co-operation, whether within or beyond the limits of species, are cases which fall under the explanatory sweep of the Darwinian theory[31].

Another important point to notice is, that it constitutes no part of the theory of natural selection to suppose that survival of the fittest must invariably lead to improvement of type, in the sense of superior organization. On the contrary, if from change of habits or conditions of life an organic type ceases to have any use for previously useful organs, natural selection will not only allow these organs in successive generations to deteriorate—by no longer placing any selective premium upon their maintenance—but may even proceed to assist the agencies engaged in their destruction. For, being now useless, they may become even deleterious, by absorbing nutriment, causing weight, occupying space, &c., without conferring any compensating benefit. Thus we can understand why it is that parasites, for example, present the phenomena of what is called degeneration, i. e. showing by their whole structure that they have descended from a possibly very much higher type of organization than that which they now exhibit. Having for innumerable generations ceased to require their legs, their eyes, and so forth, all such organs of high elaboration have either disappeared or become vestigial, leaving the parasite as a more or less effete representative of its ancestry.

These facts of degeneration, as we have previously seen, are of very general occurrence, and it is evident that their importance in the field of organic evolution as a whole has been very great. Moreover, it ought to be particularly observed that, as just indicated, the facts may be due either to a passive cessation of selection, or to an active reversal of it. Or, more correctly, these facts are probably always due to the cessation of selection, although in most cases where species in a state of nature are concerned, the process of degeneration has been both hastened and intensified by the super-added influence of the reversal of selection. In the next volume I shall have occasion to recur to this distinction, when it will be seen that it is one of no small importance to the general theory of descent.

We may now proceed to consider certain misconceptions of the Darwinian theory which are largely, not to say generally, prevalent among supporters of the theory. These misconceptions, therefore, differ from those which fall to be considered in the next chapter, i. e. misconceptions which constitute grounds of objection to the theory.

Of all the errors connected with the theory of natural selection, perhaps the one most frequently met with—especially among supporters of the theory—is that of employing the theory to explain all cases of Phyletic modification (or inherited change of type) indiscriminately, without waiting to consider whether in particular cases its application is so much as logically possible. The term “natural selection” thus becomes a magic word, or sesame, at the utterance of which every closed door is supposed to be immediately opened. Be it observed, I am not here alluding to that merely blind faith in natural selection, which of late years has begun dogmatically to force this principle as the sole cause of organic evolution in every case where it is logically possible that the principle can have come into play. Such a blind faith, indeed, I hold to be highly inimical, not only to the progress of biological science, but even to the true interests of the natural selection theory itself. As to this I shall have a good deal to say in the next volume. Here, however, the point is, that the theory in question is often invoked in cases where it is not even logically possible that it can apply, and therefore in cases where its application betokens, not merely an error of judgment or extravagance of dogmatism, but a fallacy of reasoning in the nature of a logical contradiction. almost any number of examples might be given; but one will suffice to illustrate what is meant. And I choose it from the writings of one of the authors of the selection theory itself, in order to show how easy it is to be cheated by this mere juggling with a phrase—for of course I do not doubt that a moment’s thought would have shown the writer the untenability of his statement.

In his most recent work Mr. Wallace advances an interesting hypothesis to the effect that differences of colour between allied species, which are apparently too slight to serve any other purpose, may act as “recognition marks,” whereby the opposite sexes are enabled at once to distinguish between members of their own and of closely resembling species. Of course this hypothesis can only apply to the higher animals; but the point here is that, supposing it to hold for them, Mr. Wallace proceeds to argue thus:—Recognition marks “have in all probability been acquired in the process of differentiation for the purpose of checking the intercrossing of allied forms,” because “one of the first needs of a new species would be to keep separate from its nearest allies, and this could be more readily done by some easily seen external mark[32].” Now, it is clearly not so much as logically possible that these recognition-marks (supposing them to be such) can have been acquired by natural selection, “for the purpose of checking intercrossing of allied forms.” For the theory of natural selection, from its own essential nature as a theory, is logically exclusive of the supposition that survival of the fittest ever provides changes in anticipation of future uses. Or, otherwise stated, it involves a contradiction of the theory itself to say that the colour-changes in question were originated by natural selection, in order to meet “one of the first needs of a new species,” or for the purpose of subsequently preventing intercrossing with allied forms. If it had been said that these colour-differentiations were originated by some cause other than natural selection (or, if by natural selection, still with regard to some previous, instead of prophetic, “purpose"), and, when so “acquired,” then began to serve the “purpose” assigned, the argument would not have involved the fallacy which we are now considering. But, as it stands, the argument reverts to the teleology of pre-Darwinian days—or the hypothesis of a “purpose” in the literal sense which sees the end from the beginning, instead of a “purpose” in the metaphorical sense of an adaptation that is evolved by the very modifications which subserve it[33].

Another very prevalent, and more deliberate, fallacy connected with the theory of natural selection is, that it follows deductively from the theory itself that the principle of natural selection must be the sole means of modification in all cases where modification is of an adaptive kind,—with the consequence that no other principle can ever have been concerned in the production of structures or instincts which are of any use to their possessors. Whether or not natural selection actually has been the sole means of adaptive modification in the race, as distinguished from the individual, is a question of biological fact[34]; but it involves a grave error of reasoning to suppose that this question can be answered deductively from the theory of natural selection itself, as I shall show at some length in the next volume.

A still more extravagant, and a still more unaccountable fallacy is the one which represents it as following deductively from the theory of natural selection itself, that all hereditary characters are “necessarily” due to natural selection. In other words, not only all adaptive, but likewise all non-adaptive hereditary characters, it is said, must be due to natural selection. For non-adaptive characters are taken to be due to “correlation of growth,” in connexion with some of the adaptive ones—natural selection being thus the indirect means of producing the former wherever they may occur, on account of its being the direct and the only means of producing the latter. Thus it is deduced from the theory of natural selection itself,—1st, that the principle of natural selection is the only possible cause of adaptive modification: 2nd, that non-adaptive modifications can only occur in the race as correlated appendages to the adaptive: 3rd, that, consequently, natural selection is the only possible cause of modification, whether adaptive or non-adaptive. Here again, therefore, we must observe that none of these sweeping generalizations can possibly be justified by deductive reasoning from the theory of natural selection itself. Any attempt at such deductive reasoning must necessarily end in circular reasoning, as I shall likewise show in the Second volume, where this whole “question of utility” will be thoroughly dealt with.

Once more, there is an important oversight very generally committed by the followers of Darwin. For even those who avoid the fallacies above mentioned often fail to perceive, that natural selection can only begin to operate if the degree of adaptation is already given as sufficiently high to count for something in the struggle for existence. Any adaptations which fall below this level of importance cannot possibly have been produced by survival of the fittest. Yet the followers of Darwin habitually speak of adaptative characters, which in their own opinion are subservient merely to comfort or convenience, as having been produced by such means. Clearly this is illogical; for it belongs to the essence of Darwin’s theory to suppose, that natural selection can have no jurisdiction beyond the line where structures or instincts already present a sufficient degree of adaptational value to increase, in some measure, the expectation of life on the part of their possessors. We cannot speak of adaptations as due to natural selection, without thereby affirming that they present what I have elsewhere termed a “selection value.”

Lastly, as a mere matter of logical definition, it is well-nigh self-evident that the theory of natural selection is a theory of the origin, and cumulative development, of adaptations, whether these be distinctive of species, or of genera, orders, families, classes, and sub-kingdoms. It is only when the adaptations happen to be distinctive of the first (or lowest) of these taxonomic divisions, that the theory which accounts for these adaptations accounts also for the forms which present them,—i. e. becomes also a theory of the origin of species. This, however, is clearly but an accident of particular cases; and, therefore, even in them the theory is primarily a theory of adaptations, while it is but secondarily a theory of the species which present them. Or, otherwise stated, the theory is no more a theory of the origin of species than it is of the origin of genera, families, and the rest; while, on the other hand, it is everywhere a theory of the adaptive modifications whereby each of these taxonomic divisions has been differentiated as such. Yet, sufficiently obvious as the accuracy of this definition must appear to any one who dispassionately considers it, several naturalists of high standing have denounced it in violent terms. I shall therefore have to recur to the subject at somewhat greater length hereafter. At present it is enough merely to mention the matter, as furnishing another and a curious illustration of the not infrequent weakness of logical perception on the part of minds well gifted with the faculty of observation. It may be added, however, that the definition in question is in no way hostile to the one which is virtually given by Darwin in the title of his great work. The Origin of Species by means of Natural Selection is beyond doubt the best title that could have been given, because at the time when the work was published the fact, no less than the method, of organic evolution had to be established; and hence the most important thing to be done at that time was to prove the transmutation of species. But now that this has been done to the satisfaction of naturalists in general, it is as I have said, curious to find some of them denouncing a wider definition of the principle of natural selection, merely because the narrower (or included) definition is invested with the charm of verbal associations[35].

So much for fallacies and misconceptions touching Darwin’s theory, which are but too frequently met with in the writings of its supporters. We must now pass on to mention some of the still greater fallacies and misconceptions which are prevalent in the writings of its opponents. And, in order to do this thoroughly, I shall begin by devoting the remainder of the present chapter to a consideration of the antecedent standing of the two theories of natural selection and supernatural design. This having been done, in the succeeding chapters I shall deal with the evidences for, and the objections against, the former theory.

Beginning, then, with the antecedent standing of these alternative theories, the first thing to be noticed is, that they are both concerned with the same subject-matter, which it is their common object to explain. Moreover, this subject-matter is clearly and sharply divisible into two great classes of facts in organic nature—namely, those of Adaptation and those of Beauty. Darwin’s theory of descent explains the former by his doctrine of natural selection, and the latter by his doctrine of sexual selection. In the first instance, therefore, I shall have to deal only with the facts of adaptation, leaving for subsequent consideration the facts of beauty.

Innumerable cases of the adaptation of organisms to their surroundings being the facts which now stand before us to be explained either by natural selection or by supernatural intention, we may first consider a statement which is frequently met with—namely, that even if all such cases of adaptation were proved to be fully explicable by the theory of descent, this would constitute no disproof of the theory of design: all the cases of adaptation, it is argued, might still be due to design, even though they admit of being hypothetically accounted for by the theory of descent. I have heard an eminent Professor tell his class that the many instances of mechanical adaptation discovered and described by Darwin as occurring in orchids, seemed to him to furnish better proof of supernatural contrivance than of natural causes; and another eminent Professor has informed me that, although he had read the Origin of Species with care, he could see in it no evidence of natural selection which might not equally well have been adduced in favour of intelligent design. But here we meet with a radical misconception of the whole logical attitude of science. For, be it observed, this exception in limine to the evidence which we are about to consider does not question that natural selection may be able to do all that Darwin ascribes to it. The objection is urged against his interpretation of the facts merely on the ground that these facts might equally well be ascribed to intelligent design. And so undoubtedly they might, if we were all simple enough to adopt a supernatural explanation whenever a natural one is found sufficient to account for the facts. Once admit the irrational principle that we may assume the operation of higher causes where the operation of lower ones is sufficient to explain the observed phenomena, and all our science and all our philosophy are scattered to the winds. For the law of logic which Sir William Hamilton called the law of parsimony—or the law which forbids us to assume the operation of higher causes when lower ones are found sufficient to explain the observed effects—this law constitutes the only barrier between science and superstition. It is always possible to give a hypothetical explanation of any phenomenon whatsoever, by referring it immediately to the intelligence of some supernatural agent; so that the only difference between the logic of science and the logic of superstition consists in science recognising a validity in the law of parsimony which superstition disregards. Therefore one can have no hesitation in saying that this way of looking at the evidence in favour of natural selection is not a scientific or a reasonable way of looking at it, but a purely superstitious way. Let us take, as an illustration, a perfectly parallel case. When Kepler was unable to explain by any known causes the paths described by the planets, he resorted to a supernatural explanation, and supposed that every planet was guided in its movements by some presiding angel. But when Newton supplied a beautifully simple physical explanation, all persons with a scientific habit of mind at once abandoned the metaphysical one. Now, to be consistent, the above-mentioned Professors, and all who think with them, ought still to adhere to Kepler’s hypothesis in preference to Newton’s explanation; for, excepting the law of parsimony, there is certainly no other logical objection to the statement, that the movements of the planets afford as good evidence of the influence of guiding angels as they do of the influence of gravitation.

So much, then, for the illogical position that, granting the evidence in favour of natural descent and supernatural design to be equal and parallel, we should hesitate in our choice between the two theories. But, of course, if the evidence is supposed not to be equal and parallel—i. e. if it is supposed that the theory of natural selection is not so good a theory whereby to explain the facts of adaptation as is that of supernatural design,—then the objection is no longer the one which we are considering. It is quite another objection, and one which is not prima facie absurd. Therefore let us state clearly the distinct question which thus arises.

Innumerable cases of adaptation of organisms to their environments are the observed facts for which an explanation is required. To supply this explanation, two, and only two, hypotheses are in the field. Of these two hypotheses one is intelligent design manifested directly in special creation; the other is natural causation operating through countless ages of the past. Now, the adaptations in question involve an innumerable multitude of special mechanisms, in most cases even within the limits of any one given species; but when we consider the sum of all these mechanisms presented by organic nature as a whole, the mind must indeed be dull which does not feel astounded. For, be it further observed, these mechanical contrivances[36] are, for the most part, no merely simple arrangements, which might reasonably be supposed due, like the phenomena of crystallization, to comparatively simple physical causes. On the contrary, they everywhere and habitually exhibit so deep-laid, so intricate, and often so remote an adaptation of means to ends, that no machinery of human contrivance can properly be said to equal their perfection from a mechanical point of view. Therefore, without question, the hypothesis which first of all they suggest—or suggest most readily—is the hypothesis of design. And this hypothesis becomes virtually the only hypothesis possible, if it be assumed—as it generally was assumed by natural theologians of the past,—that all species of plants and animals were introduced into the world suddenly. For it is quite inconceivable that any known cause, other than intelligent design, could be competent to turn out instantaneously any one of these intricate pieces of machinery, already adapted to the performance of its special function. But, on the other hand, if there is any evidence to show that one species becomes slowly transformed into another—or that one set of adaptations becomes slowly changed into another set as changing circumstances require,—then it becomes quite possible to imagine that a strictly natural causation may have had something to do with the matter. And this suggestion becomes greatly more probable when we discover, from geological evidence and embryological research, that in the history both of races and of individuals the various mechanisms in question have themselves had a history—beginning in the forms of most uniformity and simplicity, gradually advancing to forms more varied and complex, nowhere exhibiting any interruptions in their upward progress, until the world of organic machinery as we now have it is seen to have been but the last phase of a long and gradual growth, the ultimate roots of which are to be found in the soil of undifferentiated protoplasm.

Lastly, when there is supplied to us the suggestion of natural selection as a cause presumably adequate to account for this continuous growth in the number, the intricacy, and the perfection of such mechanisms, it is only the most unphilosophical mind that can refuse to pause as between the older hypothesis of design and the newer hypothesis of descent.

Thus it is clear that the a priori standing of the rival hypotheses of naturalism and supernaturalism in the case of all these pieces of organic machinery, is profoundly affected by the question whether they came into existence suddenly, or whether they did so gradually. For, if they all came into existence suddenly, the fact would constitute well-nigh positive proof in favour of supernaturalism, or creation by design; whereas, if they all came into existence gradually, this fact would in itself constitute presumptive evidence in favour of naturalism, or of development by natural causes. And, as shown in the previous chapters, the proof that all species of plants and animals came into existence gradually—or the proof of evolution as a fact—is simply overwhelming.

From a still more general point of view I may state the case in another way, by borrowing and somewhat expanding an illustration which, I believe, was first used by Professor Huxley. If, when the tide is out, we see lying upon the shore a long line of detached sea-weed, marking the level which is reached by full tide, we should be free to conclude that the separation of the sea-weed from the sand and the stones was due to the intelligent work of some one who intended to collect the sea-weed for manure, or for any other purpose. But, on the other hand, we might explain the fact by a purely physical cause—namely, the separation by the sea-waves of the sea-weed from the sand and stones, in virtue of its lower specific gravity. Now, thus far the fact would be explained equally well by either hypothesis; and this fact would be the fact of selection. But whether we yielded our assent to the one explanation or to the other would depend upon a due consideration of all collateral circumstances. The sea-weed might not be of a kind that is of any use to man; there might be too great a quantity of it to admit of our supposing that it had been collected by man; the fact that it was all deposited on the high-water-mark would in itself be highly suggestive of the agency of the sea; and so forth. Thus, in such a case any reasonable observer would decide in favour of the physical explanation, or against the teleological one.

Now the question whether organic evolution has been caused by physical agencies or by intelligent design is in precisely the same predicament. There can be no logical doubt that, theoretically at all events, the physical agencies which the present chapter is concerned with, and which are conveniently summed up in the term natural selection, are as competent to produce these so-called mechanical contrivances, and the other cases of adaptation which are to be met with in organic nature, as intelligent design could be. Hence, our choice as between these two hypotheses must be governed by a study of all collateral circumstances; that is to say, by a study of the evidences in favour of the physical explanation. To this study, therefore, we shall now address ourselves, in the course of the following chapters.

CHAPTER VIII.

Evidences of the Theory of Natural Selection.

First, it is a matter of observation that the struggle for existence in nature does lead to the extermination of forms less fitted for the struggle, and thus makes room for forms more fitted. This general fact may be best observed in cases where an exotic species proves itself better fitted to inhabit a new country than is some endemic species which it exterminates. In Great Britain, for example, the so-called common rat is a comparatively recent importation from Norway, and it has so completely supplanted the original British rat, that it is now extremely difficult to procure a single specimen of the latter: the native black rat has been all but exterminated by the foreign brown rat. The same thing is constantly found in the case of imported species of plants. I have seen the river at Cambridge so choked with the inordinate propagation of a species Of water-weed which had been introduced from america, that considerable expense had to be incurred in order to clear the river for traffic. In new zealand the same thing has happened with the european water-cress, and in australia with the common rabbit. So it is doubtless true, as one of the natives is said to have philosophically remarked, “the white man’s rat has driven away our rat, the european fly drives away our fly, his clover kills our grass, and so will the maoris disappear before the white man himself.” innumerable other cases to the same effect might be quoted; and they all go to establish the fact that forms less fitted to survive succumb in their competition with forms better fitted.

Secondly, there is a general consideration of the largest possible significance in the present connexion—namely, that among all the millions of structures and instincts which are so invariably, and for the most part so wonderfully, adapted to the needs of the species presenting them, we cannot find a single instance, either in the vegetable or animal kingdom, of a structure or an instinct which is developed for the exclusive benefit of another species. Now this great and general fact is to my mind a fact of the most enormous, not to say overwhelming, significance. The theory of natural selection has now been before the world for more than thirty years, and during that time it had stood a fire of criticism such as was never encountered by any scientific theory before. From the first Darwin invited this criticism to adduce any single instance, either in the vegetable or animal kingdom, of a structure or an instinct which should unquestionably be proved to be of exclusive use to any species other than the one presenting it. He even went so far as to say that if any one such instance could be shown he would surrender his whole theory on the strength of it—so assured had he become, by his own prolonged researches, that natural selection was the true agent in the production of adaptive structures, and, as such, could never have permitted such a structure to occur in one species for the benefit of another. Now, as this invitation has been before the world for so many years, and has not yet been answered by any naturalist, we may by this time be pretty confident that it never will be answered. How tremendous, then, is the significance of this fact in its testimony to Darwin’s theory! The number of animal and vegetable species, both living and extinct, is to be reckoned by millions, and every one of these species presents on an average hundreds of adaptive structures,—at least one of which in many, possibly in most, if not actually in all cases, is peculiar to the species that presents it. In other words, there are millions of adaptive structures (not to speak of instincts) which are peculiar to the species presenting them, and also many more which are the common property of allied species: yet, notwithstanding this inconceivable profusion of adaptive structures in organic nature, there is no single instance that has been pointed out of the occurrence of such a structure save for the benefit of the species that presents it. Therefore, I say that this immensely large and general fact speaks with literally immeasurable force in favour of natural selection, as at all events one of the main causes of organic evolution. For the fact is precisely what we should expect if this theory is true, while upon no other theory can its universality and invariability be rendered intelligible. On the beneficent design theory, for instance, it is inexplicable that no species should ever be found to present a structure or an instinct having primary reference to the welfare of another species, when, ex hypothesi, such an endless amount of thought has been displayed in the creation of structures and instincts having primary reference to the species which present them. For how magnificent a display of divine beneficence would organic nature have afforded, if all—or even some—species had been so inter-related as to have ministered to each others wants. Organic species might then have been likened to a countless multitude of voices, all singing in one great harmonious psalm. But, as it is, we see absolutely no vestige of such co-ordination: every species is for itself, and for itself alone—an outcome of the always and everywhere fiercely raging struggle for life.

In order that the force of this argument may not be misapprehended, it is necessary to bear in mind that it is in no way affected by cases where a structure or an instinct is of primary benefit to its possessor, and then becomes of secondary benefit to some other species on account of the latter being able in some way or another to utilise its action. Of course organic nature is full of cases of this kind; but they only go to show the readiness which all species display to utilise for themselves everything that can be turned to good account in their own environments, and so, among other things, the structures and instincts of other animals. For instance, it would be no answer to Darwin’s challenge if any one were to point to a hermit-crab inhabiting the cast-off shell of a mollusk; because the shell was primarily of use to the mollusk itself, and, so far as the mollusk is concerned, the fact of its shell being afterwards of a secondary use to the crab is quite immaterial. What Darwin’s challenge requires is, that some structure or instinct should be shown which is not merely of such secondary or accidental benefit to another species, but clearly adapted to the needs of that other species in the first instance—such, for example, as would be the case if the tail of a rattle-snake were of no use to its possessor, while serving to warn other animals of the proximity of a dangerous creature; or, in the case of instincts, if it were true that a pilot-fish accompanies a shark for the purpose of helping the shark to discover food. Both these instances have been alleged; but both have been shown untenable. And so it has proved of all the other cases which thus far have been put forward.

Perhaps the most remarkable of all the allegations which ever have been put forward in this connexion are those that were current with regard to instincts before the publication of Darwin’s work. These allegations are the most remarkable, because they serve to show, in a degree which I do not believe could be shown anywhere else, the warping power of preconceived ideas. A short time ago I happened to come across the 8th edition of the Encyclopædia Britannica, and turned up the article on “Instinct” there, in order to see what amount of change had been wrought with regard to our views on this subject by the work of Darwin—the 8th edition of the Encyclopædia Britannica having been published shortly before The Origin of Species by means of Natural Selection. I cannot wait to give any lengthy quotations from this representative exponent of scientific opinion upon the subject at that time; but its general drift may be appreciated if I transcribe merely the short concluding paragraph, wherein he sums up his general results. Here he says:—