It seems ill-mannered, if not ill-natured, that the year of the centenary of Charles Darwin’s birth should have been chosen by owners of anonymous pens in order to alarm the public mind with the preposterous statement that his celebrated and universally accepted theory of the origin of the species or kinds of plants and animals by natural selection, or “the survival of favoured races in the struggle for life,” is undermined and discredited. Such a statement once coolly made in the public Press is necessarily believed by a large number of uninformed readers, and, like all calumny, is none the less relished by the foolish, and, for the moment, none the less harmful, because it is baseless.

Those who seek to belittle Darwin’s theory show, whenever they venture to enter into particulars, that they do not know what Darwin’s theory is. They confuse it with other theories, and even imagine that some enthusiastic Darwinians who have tried to add a chapter here or there to Darwin’s doctrine, are opponents of the great theory. Let me briefly state what that theory is:

It rests on three groups of facts—matters of observation, which are not theory or guess work at all—but admitted by every one and demonstrated every day. These are—(1) Living things, each in its kind, produce a far larger number of young than can possibly grow up to maturity, since the kind of food and the situation necessary to each kind are limited and already occupied. Only one oyster embryo out of every five million produced (the reader may refer to p. 137 on this subject) grows up through all the successive stages of youth to the adult state. The total number of a species of animal or plant on the whole area where it is found does not increase. Even in those which produce a small number of young, there is great destruction, and taking all the individuals into consideration, only a single pair of young arrive at maturity to replace their parents. There is no exception to the rule that every organic being naturally multiplies at so high a rate that, if not destroyed, the progeny of a single pair would soon cover the earth. The elephant is reckoned the slowest breeder of known animals; it commences to breed at 30 years of age, dies at 100, and has six young in the interval. After 750 years, supposing all the offspring of a single pair fulfilled the rule and were not destroyed in an untimely way, there would be nearly nineteen million elephants alive descended from the first pair. There is then no doubt as to the enormous excess in the production of young living things, nor as to their necessary competition with one another of the most severe and inexorable kind; nor again as to the necessary death, in many species, of hundreds and thousands, for every one which survives to maturity and in its turn breeds.

(2) The second great fact is that among all the young born to a pair of parents, no two are exactly alike, nor are any exactly like their parents; nor are any two taken from all produced by all parents of that species exactly alike. They all resemble their parents at the corresponding age, in a general way and even very closely; but the resemblance is far from amounting to identity. This is called “variation.” It is familiar to us all in the case of the organism which we know best, and observe most closely, namely, man. It is also a matter of common observation in the case of dogs, cats, horses, and other domesticated animals. Many of these “variations” are exhibited in points of size, proportion, and colour, which are easily noted at once by the eye. But “variation” is really a deep-seated thing, and depends on causes which lie below the surface. We know that the offspring of men and of animals and of plants, give evidence of variations in what we call constitution, tendency, temperament, aptitude, strength, and that the colour, and even size of this or that part, are really only indications of a deep-seated difference in the living chemistry, the forces of nutrition and growth which reside in the living substance. The fact that many thousands of a species may be born and only a few survive, means therefore that many thousand varieties, often varieties not readily measured by the eye, are produced in each generation, from which a few individuals are in some way “selected” for survival.(3) The third great fact is that though there is variation, amongst all the offspring in each generation, there is also a continual and definite inheritance by offspring of the qualities and structure of their parents to a degree which altogether preponderates over the variations. To put it in another way, we all know that every parental organism transmits to its young not only the qualities and structure of the species, or of the race, or of the family, but also transmits its own peculiarities or variations in which it departed from its parents, and from its brothers and sisters. This is best illustrated by our daily experience of human families.

These facts being admitted, and abundantly illustrated and traced in detail by years of observation and experimental breeding in all kinds of living things by hundreds of careful observers who have published the records of their studies, we come to the step where Darwin makes use of supposition or hypothesis. The question is, “Does the one which, out of the thousands of slightly different varieties, survives—do so by haphazard? or is there a necessarily acting state of things which selects that one special variety for survival?” Gardeners and breeders of pigeons, dogs, and cattle deliberately select the variations which they desire, breed from them, and so carry on by inheritance the special variation—whilst they ruthlessly destroy or restrain from breeding the numerous other variations in their “stock” which they do not desire. “If,” said Darwin, “there is any necessarily selective mechanism in Nature which could act as the breeder does, new varieties might be ‘naturally’ selected, and changes of form and appearance naturally established, which in the course of long ages would amount to such marked differences as separate what we call one species from another.” He showed that there is a natural mechanism of the required kind. “Since,” he says, “the competition among the members of any one kind or species for a place in life is so very severe, and the hostile circumstances so varied, and since all the competing offspring differ by ‘variation’ ever so little from one another, those varieties which are better suited in even the smallest degree to hold their own not merely in fighting with the others, but in withstanding injurious influences, in escaping enemies, and in procuring food, will be the ones which will survive, when a large number of cases, many thousands, extending over a large area and many years, are considered. Those which are ‘best fitted’ to get through the exceedingly numerous dangers and difficulties of life will be the survivors.” Hence we get the survival of the fit—the fit variations—by natural selection in the struggle for life. This, it will be observed, is an inference, and not a direct observation.

So long as the conditions remain practically or effectively unchanged, the animal or plant already “fitted” to them will be succeeded by those of its offspring which most resemble it in the essential points of “fitness.” But we know that in the course of ages, more or less rapidly, climates change, land emerges from the sea, islands join continents, continents become scattered islands, animals and plants migrate into regions previously uninhabited by them. As such changes gradually come on, the natural selection of favoured varieties will necessarily lead to the survival of others than those previously favoured, other variations better suited to the new conditions will survive.

The natural selection of favoured variations would not amount to much, were the variations not perpetuated by transmission to the young which they produce. This, it is common knowledge [see (3)], does take place. It is known also that a variation so established is as a result of the regular process of variation presented in larger volume or emphasised in character in some individuals of subsequent generations, and by continued “natural selection” it may become more and more a prominent or dominant feature of the race.

So far, the only assumption made by Mr. Darwin is that any or some of the endless variations which occur in all the offspring of wild plants and animals, in various combinations and degree in each individual, can be sufficiently important to determine the survival or non-survival of the organisms possessing them. That is a matter which has been largely studied and discussed. The verdict of those who have studied on the spot (as Darwin himself did) the teeming life of the tropics, the insects, birds, and plants of those regions, is that we are justified in considering that small variations are sufficiently important to turn the scale in favour of survival or non-survival. It is not easy for a man who is not a determined naturalist, constantly observing the ways of wild living things, to appreciate the evidence as to the efficacy of small variations, even were I able here to submit it to him. It is to be found in the published works of an army of investigators. In any case it is granted that effective variations—whether small or great—occur in nature, and that natural selection favours and perpetuates the new and fitter variety to the exclusion of the less fit.

The real difficulty to most people comes in the supposition next made by Mr. Darwin—namely, that this slow process of change by natural selection of favoured variations and their transmission and perpetuation by inheritance is sufficient to effect by its continued operation through enormous ages of time the conversion of a race of ancestral three-toed zebras into the one-toed horse of to-day; before that, of five-toed beasts into three-toed; at an earlier stage of fishlike creatures into four-footed land animals, and so on. You have to picture the whole series of animals and of plants which are now or ever have been, as two gigantic family trees or pedigrees, meeting in common ancestors of the simplest grade of microscopic life. All the diverging branches and twigs of these great “family trees” have been determined by the adaptation of living form to the endlessly varied conditions of life on this planet, by the natural selection or survival of variations and the transmission and accumulation of those variations from parent to offspring. This is a tremendous demand on the imagination. It is, however, not a difficult one to concede, when one is acquainted with the facts and conclusions of geology. The history of the crust of the earth was explained twenty years before the date of Darwin’s theory by Charles Lyell as due to the continued action through immense periods of time of the same natural forces which are now at work. And, moreover, the examination of the successive stratified deposits of the earth’s crust has yielded the remains of whole series of animals and of plants (simpler in character the older and deeper the rock in which they occur), which can be satisfactorily explained and interpreted as the ancestral forms from which present organisms have been developed.

The theory of the natural selection of variations as the moving spring in the gradual development of living forms from simplest living matter is Darwin’s theory. It is not possible to find any naturalist of consideration who does not accept it. There are various views held and discussed as to the cause of variation, as to the importance of small and of big variations, as to the non-transmissibility of some kinds of variation, and as to various peculiarities in regard to inheritance. They do not for the most part touch the main features of Mr. Darwin’s theory. No doubt we are learning and shall learn more about the facts of variation and the details of the process of hereditary transmission, but such increase of knowledge has not tended to undermine Mr. Darwin’s theory, and does not seem at all likely to do so.

On the occasion of the celebration at Cambridge in 1909 of the centenary of Darwin’s birth, I was invited by the Vice-Chancellor, on behalf of the University, to deliver in the Senate-house an address, others being given by representatives of the United States (Prof. Osborne), of Germany (Prof. Hertwig), and of Russia (Prof. Metchnikoff). The following is the text of that address:—

“I feel it a great honour to be called upon to speak here to-day, and to stand, on behalf of the naturalists of the British Empire, by the side of the distinguished men whose orations you have just heard.

“I think that the one thing about Charles Darwin which the large majority of British naturalists would wish to be to-day proclaimed, in the first place—with no doubtful or qualifying phrase—is that, in their judgment, after these fifty years of examination and testing, his ‘theory of the origin of species by means of natural selection or the preservation of favoured races in the struggle for life’ remains whole and sound and convincing, in spite of every attempt to upset it.

“I am not stating more than the simple truth when I say that, in the judgment of those who are best acquainted with living things in their actual living surroundings, ‘natural selection’ retains the position which Mr. Darwin claimed for it of being the main means of the modification of organic forms.

“Our admiration for the vast series of beautiful observations and interesting inquiries carried out by Darwin during his long life must not lead us to forget that they were devised by him in order to test the truth of his theory and to meet objections to it, and that they were triumphantly successful. They, together with the work of Alfred Russel Wallace and many of their followers, have more and more firmly established Darwin’s theory. On the other hand, no attempt to amend that theory in any essential particular has been successful.

“The nature of organic variation and of the character of the variations upon which natural selection can and does act was not, as we are sometimes asked to believe, neglected or misapprehended by Darwin. The notion that these variations are large and sudden was considered by him, and for reasons set forth by him at considerable length rejected. That notion has in recent years been resuscitated, but its truth has not been rendered probable by evidence either of such an accurate character or of such pertinence as would justify the rejection of Darwin’s fundamental conception of the importance of minute and ubiquitous variations.

“Further, in regard to the important facts of heredity connected with the cross-breeding of cultivated varieties, especially in regard to the blending or non-blending of their characters in their offspring and as to prepotency, it seems to me important that we should now and here call to mind the full and careful consideration given to this subject by Darwin. We cannot doubt that he would have been deeply interested in the numerical and statistical results associated with the name of Mendel. Those results tend to throw light on the mechanisms concerned in hereditary transmission, but it cannot be shown that they are opposed in any way to the truth of Darwin’s great theoretical structure—his doctrine of the origin of species.

“It has often been urged against Darwin that he did not explain the origin of variation, and especially that he has not shown how variations of sufficient moment to be selected for preservation in the struggle for existence have in the first place originated. The brief reply to the first objection is that variation is a common attribute of many natural substances of which living matter is only one. In regard to the second point, I desire to remind this assembly that Darwin described with special emphasis instances of what he calls ‘correlated variability.’ In my opinion he has thus furnished the key to the explanation of what are called useless specific characters and of incipient organs. That key consists in the fact that a general physiological property or character of utility is often selected and perpetuated, which carries with it distinct, even remote, correlated growths and peculiarities obvious to our eyes, yet having no functional value. At a later stage in the history of such a form these correlated growths may acquire value and become the subject of selection.

“It is thus, as it seems to me, and as, I believe, to the great body of my brother naturalists, that Darwin’s theory stands after fifty years of trial and application.

“The greatness of Charles Darwin’s work is, and will be for ever, one of the glories of the University of Cambridge. It is fitting on the present occasion that one who speaks on behalf of English men of science should call to mind the nature of his connection with this great University and the peculiarly English features of his life-story and of that fine character which endears his memory to all of us as much as his genius excites our admiration and reverence. Darwin was not, like so many a distinguished son of Cambridge, a scholar or a fellow of his college, nor a professor of the University. His connection with the University and the influence which it had upon his life belong to a tradition and a system which have survived longer in our old English universities than in those of other lands. Darwin entered the University, not seeking a special course of study with the view of professional training, nor aiming at success in competitive examinations for honours and emolument. He came to Cambridge intending to become a clergyman, but blessed with sufficient means and leisure to enable him to pursue his own devices, to collect beetles, to explore the fen country, and to cultivate his love of nature. It was thus that he became acquainted with that rare spirit Henslow, the Cambridge professor of botany, and it is through Henslow and the influence of his splendid abilities and high personal character upon Darwin that Cambridge acquired the right to claim the author of the ‘Origin of Species’ as a product of her beneficence and activity as a seat of learning.

“As an Oxford man and a member of Exeter College, I may remind this assembly that in precisely the same way Darwin’s dearest friend and elder brother in science, Charles Lyell, had a few years earlier entered at Exeter College, and by happy chance fallen under the influence of the enthusiastic Buckland, the University reader in geology and a Canon of Christ Church. The wise freedom of study permitted and provided for in those long-passed days by Oxford and Cambridge is what has given the right to claim the discovery, if not the making, of Lyell to the one and of Darwin to the other.

“Darwin’s love of living nature and of the country life are especially English characteristics; so, too, I venture to think, are the unflinching determination and simple courage—I may even say the audacity—with which he acquired, after he had left the University, the wide range of detailed knowledge in various branches of science which he found necessary in order to deal with the problem of the origin of the species of plants and animals, the investigation of which became his passion.

“The unselfish generosity and delicacy of feeling which marked Darwin’s relations with a younger naturalist, Alfred Russel Wallace, are known to all. I cannot let this occasion pass without citing those words of his which tell us most clearly what manner of man he was and add to his splendid achievements as an intellectual force—a light and a beauty of which every Englishman must be proud. When in old age he surveyed his life’s work he wrote:—‘I believe that I have acted rightly in steadily following and devoting my life to science.’

“To have desired to act ‘rightly,’ and to be able to think of success in life as measured by the fulfilment of that desire, is the indication and warrant of true greatness of character. We Englishmen have ever loved to recognise this noble kind of devotion in our national heroes.”