[page] 64

DARWIN AND MODERN EVOLUTION.

Our list of honorary members suffers, as I had the sad duty of announcing at a former meeting, by the removal of the universally-revered name of Charles Darwin, who breathed his last on April 19th, 1882, at his residence, Down, Kent, in the seventy-fourth year of his age. Much has already been said and written about Mr. Darwin, and I cannot hope to give you on the present occasion anything beyond a general sketch of the enormous services rendered to every branch of natural science by this greatest of philosophic naturalists during a life of active work extending over more than half a century. Darwin was born at Shrewsbury in 1809, and on the side of both his parents came of celebrated lineage. He was grandson to Erasmus Darwin, the poet-naturalist, and

[page] 65

his mother was a daughter of Josiah Wedgwood, the renowned Etrurian potter. Darwin's scientific career may be considered to have commenced by his appointment as naturalist to H.M. Surveying Ship 'Beagle,' under Captain, afterwards Admiral, Fitzroy. The 'Beagle' left England in 1831, and was absent for nearly five years. Soon after his return Darwin settled at Down, and from that time his life— a most uneventful one from a biographical point of view— was mainly devoted to those researches -which have resulted in nothing less than a complete revolution in our conceptions of organic nature.

Such ample notices of Darwin's works appealed in the various newspapers at the time of his death that it is quite unnecessary for me to do more than to name them, pending the appearance of the complete biography which all are anxiously awaiting. Omitting the shorter papers contributed to the publications of the learned societies, the following is the list of works in the order of publication:—

1842. 'The Structure and Distribution of Coral Reefs.' 2nd ed., 1874.

1844. 'Geological Observations on the Volcanic Islands and Parts of South America visited during the Voyage of H.M.S. ''Beagle.''' 2nd ed., 1877.

1845. 'A Naturalists Voyage round the World.' New ed., 1860.

1851-1854: 'A Monograph of the Cirripedia.' 2 vols. (Ray Society).

1851. 'A Monograph of the Fossil Lepadidæ or Pedunculated Cirripeds of Great Britain.' (Palæontographical Society.)

1854. 'A Monograph of the Fossil Balanidæ and Verrucidæ of Great Britain.' (Palæontographical Society.)

1859. 'The Origin of Species by means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.' 6th ed., 1872.

1862. 'On the Various Contrivances by which British and Foreign Orchids are fertilised by Insects.' 2nd ed., 1877.

1868. 'The Variation of Animals and Plants under Domestication.' 2nd ed., 1876.

1871. 'The Descent of Nan, and Selection in Relation to Sex.' 2nd ed., 1874.

[page] 66

1872. 'The Expression of the Emotions in Man and Animals.'

1875. 'The Movements and Habits of Climbing Plants.' 2nd ed. (A re-publication, with additions, of a memoir published in the 'Journal of the Linnean Society' for 1865.)

1875. 'Insectivorous Plants.'

1876.'The Effects of Cross- and Self-Fertilisation in the Vegetable Kingdom.'

1877. 'The Different Forms of Flowers on Plants of the same Species.' (A reprint, with additions, of a series of papers published in the 'Journal of the Linnean Society' in the years 1862, 1863, 1864, and 1868.)

1880. 'The Power of Movement in Plants.' In conjunction with Francis Darwin.

1880. 'The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits.'

Such is the legacy bequeathed by Charles Darwin to the science of the nineteenth century! The mere list of works above catalogued gives no adequate idea to those unacquainted with their contents of the marvellous powers of observation, the fertility of resource, the great experimental skill, the inexhaustible patience over the minutest details, or the grand faculty of generalisation possessed by this master worker.

For years to come he has left materials for thought and work to the school of younger naturalists that has grown up under his inspiration.

Whilst bearing our humble share of the loss which the whole civilised world has sustained, we have the satisfaction of knowing that Darwin was personally interested in our success. It will be remembered that he was among the first to give us his support at the time of our inauguration, and on subsequent occasions he showed an active appreciation of our labours. The last expression of encouragement which I received from him was in a letter dated August 8th, 1881, wherein he wrote, "I am glad to see how extremely flourishing your Essex Club appears to be." We can with the greater reason lay claim to a direct sympathy in Darwin's work, for he was himself in the strictest sense a field-naturalist as

[page] 67

distinguished from a museum-naturalist. It was during the five years' cruise of the 'Beagle,' of which the personal narrative was given to the world in his celebrated 'Naturalist's Voyage,' that the future philosopher was first led to ponder over those phenomena of living nature with which he was brought into contact, and which, as he tells us in the 'Origin of Species,' induced him on his return to speculate on the great problem indicated in the title of that work. When in later life he continued his studies in this country, it was always living animals and plants that were appealed to when possible; his most important experiments and observations were made upon materials growing in his greenhouse or garden, or were collected from the surrounding country; and in his broader generalisations, which necessitated a wider survey of facts, he always made use of the observations of those to whom Nature had spoken face to face. Even when failing health compelled him to abandon the great literary undertakings which were promised to supplement the 'Origin of Species,' he delighted in minute observation as a recreation.1 To his friend and co-worker, Mr. A. R. Wallace, he once remarked:— ''When I am obliged to give up observation and experiment, I shall die." [A. R. Wallace. 1891. Natural selection and tropical nature; essays on descriptive and theoretical biology. London & New York: Macmillan & Co., p. 472.] Nature was to Darwin a living, organically-connected whole; with him science did not begin and end with the accumulation of series of dried and labelled specimens.

In spite of all that has been written for and against the Darwinian theory, it is surprising how much this doctrine is still misunderstood by the general public. Ask any non-scientific person what he imagines to be conveyed by the word ''Darwinism," and he will probably tell you that it is the theory that man is descended from a monkey, which is about as explicit as saying that the Newtonian theory of gravitation is something to do with an apple. Indeed I may

 

1 The difficulties besetting the experimental investigator are forcibly recalled to my mind by a remark once made to me by Mr. Darwin. Speaking on this subject I said that Nature, when thus questioned, often gives an evasive answer, to which he replied, ''She will tell you a direct lie if she can.''

[page] 68

venture to say that there are many extreme specialists, even within the pale of science, who have but a vague idea of the extremely important influence which this hypothesis has upon their studies. On such an occasion as the present, when, after recording our deep sense of gratitude to the man who so nobly dedicated his life to the advancement of knowledge, it becomes my duty to direct your attention to his works, I think that I cannot do better than occupy your time by recapitulating the main points in the theory of the origin of species.

Starting with the simple calculation showing the rate of increase of any species as deduced from the numbers of young produced at a birth, and comparing this with the actual number of individuals at present existing, we find that an immensely greater number of young must be produced than ever survive. Thus, in the case of the elephant, which ''is reckoned the slowest breeder of all known animals," it is seen that a single pair, supposing their offspring to survive and to breed at the rate of six during a lifetime of a century, would in the course of 740 to 750 years have given rise to nearly nineteen million elephants living at the end of that period.2 Similarly with birds, if we allow that one pair produce four young ones per annum and breed but four times during their life, in fifteen years this pair will have increased to more than two thousand millions.3 Some instructive data have been quite recently given by Mr. P. L. Simmonds4 with reference to the rabbit in Australia and New Zealand, where this animal has become a perfect pest within a period of twenty years since its first introduction. ''From New Zealand alone eight and a half millions of rabbit-skins were exported in 1880, but this does not probably represent one-tenth part of those actually destroyed. In that climate the rabbit breeds nearly every month in the year. But even supposing that a pair of rabbits do not breed

 

2 'Origin of Species,' 6th ed., p. 51.

3 A. R. Wallace's 'Contributions to the Theory of Natural Selection,' p. 29.

4 Journ. Soc. Arts, Dec. 22nd, 1882, p. 99

[page] 69

oftener than in England, which is seven times a year, and that they only bring forth eight young at a time, they would multiply in the course of four years to a million and a quarter."

Granting this fact, that all organisms tend to increase at a geometrical rate, it is clear that every species must have in itself the potentiality of unlimited extension, and must constantly be endeavouring to extend itself at the expense of others; every species must be waiting to fill any vacancy in the polity of Nature; there must be a perpetual competition going on—a continual ''struggle for existence'' which keeps in check the undue increase of any particular species. Thus the animals and plants of any region are in a state of nicely balanced equilibrium, the result of long ages of adjustment to then· surroundings both organic and inorganic. ''In looking at Nature, it is most necessary to keep the foregoing considerations always in mind—never to forget that every single organic being may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals. Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount."5

The science of Geology teaches us that the face of Nature is undergoing slow but constant change, so that the inorganic environment of species is by no means immutable; and since geological changes must entail rearrangement of life, the organic environment is similarly in a state of fluctuation. The equilibrium between a species and its environment is thus subject in the course of time to be disturbed; new conditions of life gradually come on, the region inhabited becomes more or less extended, climatic changes may supervene, the amount of atmospheric moisture and the annual rainfall may increase or diminish, the mean annual temperature may become higher or lower, new competing forms or other foes may extend their range into the area—in short,

 

5 'Origin of Species,' 6th ed. pp. 52-53.

[page] 70

the equilibrium between the species and its environment has to be readjusted or extinction would follow. Now Darwin has shown that there is no compromise in this readjustment between Nature and her children-her motto is, ''change or die.'' The adaptations of species to their life-conditions are only effected by a process of transformation, the raw material for such modification being furnished by the slight variability which is natural to every organism. All naturalists know what is meant by variability. The individuals of any species are not all absolutely alike as though cast in one mould, but present differences in all or in certain characters, the nature and amount of the difference depending upon the particular species; in some cases the aberration is great and conspicuous, but such ''sports'' are not considered by Darwin as having played any important part in the modification of specific forms. The offspring of any animal or plant thus differ more or less from their parents and from one another; the aphorism that ''like produces like'' is true only with a certain latitude, and those: fluctuations of form which interfered so seriously with the "plan of creation" of the older naturalists furnish the means by which living beings can become adapted to new conditions of existence.

A geometrical ratio of increase leading to a struggle for life, individual variability, and incessant change of external conditions being admitted facts, the next question is, how does the organism become adapted to changed conditions of life? –how is the equilibrium between a species and its environment maintained? In answer to this, Darwin appeals to domesticated animals and plants, and shows how races are modified by artificial selection, how by selective breeding the various animals and plants kept by man have been apparently moulded to man's use by the long-continued selection and accumulation of those slight variations which the breeder has learnt to distinguish. Substitute for the art of the breeder the struggle for life, and we have a motive power competent to restore the equilibrium between an organic form and a changed environment. Instead of artificial selection by man, we have a process of ''natural selection''; the

[page] 71

rigorous necessity of coping with new conditions is met by a call upon the variational resources of the species, those individuals which are best adapted to the new requirements surviving and leaving offspring which inherit the advantageous qualities, whilst the less favoured individuals succumb in the struggle. The process has been happily termed by Herbert Spencer, "the survival of the fittest.'' In this way a species becomes gradually transformed, or, when occupying an extended area, may give rise to two or more species; and since Nature's operations are seldom conducted by cataclysms, the changes in external conditions come on slowly, the adaptation being perfected from generation to generation by the continuous selection of the fittest—by the summing up of all the advantageous variations through inheritance. Making use of a mechanical simile, we may say that the individual constituents of the species move in the direction of least resistance towards the position of new equilibrium.

The struggle for life is necessarily the more severe the more nearly alike are the competing organisms, because the nearer the relationship between the latter the more closely do they agree in their requirements—the greater is the similarity in their structure, habits, and constitution. ''We may assume that the modified descendants of any one species will succeed so much the better as they become more diversified in structure, and are thus enabled to encroach on places occupied by other beings.''6 Now survival of the fittest involves the extinction of the unfitted, and as diversity gives the greater chance of success to the larger number of organisms, there is a tendency for variational extremes to survive at the expense of the less divergent varieties—a tendency for species to break up into heterogeneous forms through ''divergence of character."

Such in broad outline is the theory of Natural Selection advanced by Darwin to account for the origin of species, and it has now become a part of the scientific history of our time that very similar, if not identical, views were put forward by

 

6 'Origin of Species,' 6th ed., p. 90.

[page] 72

Mr. A. R. Wallace—whose name, I am happy to see, still graces our list of Honorary Members—in the year 1858. Having had the privilege of personal acquaintance with the late Mr. Darwin, and still enjoying the friendship of Mr. Wallace, I cannot resist the pleasure of once more detailing the history of the birth of this theory, since this history conveys a lesson in scientific etiquette well worthy of those from whom the doctrine emanated. Having been struck during the voyage of the 'Beagle' by many facts in the distribution of animals and plants which seemed to throw light on the origin of species, on his return to this country Darwin in 1837 began to collect materials, and for five years went on ''accumulating and reflecting on all sorts of facts'' that appeared to have any bearing on the problem. After this period, as he tells us, he allowed himself to speculate, and had formulated his conclusions in 1844, but not with a view to immediate publication. In 1858, twenty-one years after he had first taken the question seriously in hand, he had nearly completed his task, although he then foresaw that many more years' work would be necessary in order to fully elaborate his views. It is to the fortunate circumstance that Mr. Wallace had independently arrived at similar conclusions that we are indebted for the accelerated publication of the 'Origin of Species' in 1859. Mr. Wallace, who, after spending some years in Tropical America with Mr. Bates, had gone to the Malay Archipelago to study nature in the Old World tropics, sent from Sarawak in 1855 his first contribution to the theory of descent. In this paper, which appeared in the 'Annals and Magazine of Natural History' for September, 1855, under the title of ''The Law which has regulated the Introduction of new Species," Mr. Wallace shows by various lines of argument that ''every species has come into existence coincident both in time and space with a pre-existing closely allied species." In 1858 Mr. Wallace sent from Ternate another paper, ''On the tendency of Varieties to depart indefinitely from the Original Type,'' which embodied the theory of Natural Selection. This paper was sent to Mr. Darwin, who showed it to his friends, Dr.

[page] 73

Hooker and Sir Charles Lyell, by the latter of whom it was communicated to the Linnean Society, and was published in the 'Proceedings' for August, 1858.7 At the same meeting of the Society Mr. Darwin gave an outline of his theory, and his paper appeared at the same time as Wallace's. The slight sketch published by Darwin in 1858 was elaborated the following year into his epoch-making work on the 'Origin of Species,' the first edition of which was published on November 24th, 1859. On learning that Darwin had for more than twenty year's been accumulating facts which had led him to the same conclusions, Wallace with the greatest generosity relinquished his claim in favour of his great compeer.8 In these days, when we hear of petty squabbles about the "priority'' of claim for having attached a label to some new insect, the following· remarks from the Preface to Wallace's 'Contributions to the Theory of Natural Selection' (1870) read with refreshing magnanimity:-''The present work will, I venture to think, prove that I both saw at the time the value and scope of the law which I had discovered, and have since been able to apply it to some purpose in a few original lines of investigation. But here my claims cease. I have felt all my life, and I still feel, the most sincere satisfaction that Mr. Darwin had been at work long before me, and that it was not left for me to attempt to write the 'Origin of Species.' I have long since measured my own strength, and know well that it would be quite unequal to that task. Far abler men than myself may confess that they have not that untiring patience in accumulating, and that wonderful skill in using large masses of facts of the most varied kind,—that wide and accurate physiological knowledge,—that acuteness in devising and skill in carrying out experiments,—and that admirable style of composition, at once clear, persuasive, and judicial,—

 

7 Mr. Wallace has narrated to me that one of his correspondents, a well known entomologist, wrote to say that it was a general remark in natural history circles, with respect to this paper, that it was much to be regretted that the author had not more confined himself to statements of fact!

8 Lyell states that Darwin was also "willing to waive his claim to priority.'' 'Principles of Geology,' 12th ed., vol. ii., p. 278.

[page] 74

qualities which in their harmonious combination mark out Mr. Darwin as the man, perhaps of all men now living, best fitted for the great work he has undertaken and accomplished.''

I have thus far dealt only with the 'Origin· of Species' because, of Darwin's literary productions, this is doubtless the one which has had the greatest influence upon contemporary thought. It must be remembered that this work was considered by its author to be a mere abstract of the vast body of evidence and the enormous array of facts which he had collected, and he promised to expand the various chapters into future volumes. The 'Variation of Animals and Plants under Domestication' was the fulfilment of this promise with respect to the first chapter of the 'origin.' The storm raised by the publication of the latter book, both within and without the ranks of science, will be long remembered by those who were contemporaneous with this first truly scientific attack upon the older doctrine of the special creation of species by miraculous agency. It is somewhat difficult for those who, like ourselves, have, so to speak, been brought up in the school of evolution to realise the state of mind of pre-Darwinian naturalists with respect to this question of species. The supposed authority of ancient tradition had, without doubt, stultified all enquiry in this direction, and workers intent only upon recording and describing had fallen into a state of intellectual torpor as regards that philosophical stimulus so vital to progress in all departments of natural knowledge. Occasional attempts had certainly been made to overthrow the current belief in the immutability of species, but these had not produced any permanent effect. It was Darwin's 'Origin of Species' that first caused a rattling among the dry bones of the venerable dogmas that had so long· usurped the place of scientific thought; with the appearance of this work superstition was driven from its last stronghold in the realm of natural science.

If, as some writers assert, virulence of attack is a criterion of the truth of a new doctrine, the 'Origin of Species' certainly came into the world under very favourable auspices.

[page] 75

It would indeed be a most interesting study in psychological evolution to compare some of the earliest with some of the later opinions on the Darwinian theory. This is a task which I commend to those who have time an opportunity for collecting materials for such a comparison. Now, in the peace following the strife, it seems perhaps a reversion to ancestral savagery to execute a war-dance over the prostrate bodies of the slain; but, for my own part, acknowledging that as a youth, I fell into the ranks of Darwinism, I cannot but own that a recent perusal of some of these early attacks has afforded me considerable satisfaction. Looked at in the present state of knowledge it is seen that many of these criticisms were prompted by nothing else than the animus of bigotry, or were the ignorant vituperation of extreme specialism; nor is it perhaps, necessary to say that some of the loudest clamour was raised by those having· no shadow of a claim of any kind to make themselves heard. Of these multifarious expressions of opinion the majority were, it is needless to state, devoid of value, and in many cases the critics, perhaps from an incapacity for handling the true weapons of scientific discussion, descended to personal aspersions upon Mr. Darwin's character. But, on the other hand, the views advanced were more ably handled by the larger-minded and more competent thinkers in the world of science. From these appeared some criticisms of real importance, which led Darwin, with that splendid candour which was part of his nature, to modify certain details of his theory in the later editions of the 'Origin.'

In the meantime, in the quiet seclusion of his Kentish home, Darwin pursued his labours with ''philosophic calm,'' answering his critics with gentleness, and turning a deaf ear to personalities, knowing that he had a great truth to proclaim to the world, and upheld by the knowledge that the leaders of biological science had become his disciples. In this country Sir Charles Lyell, the illustrious founder of Uniformitarian Geology, Dr. Hooker, Herbert Spencer, Prof. Huxley, and Sir John Lubbock, were among the first to give the weight of their support to the Darwinian hypothesis;

[page] 76

Prof. Huxley, indeed, became so zealous a champion that he diverted on to his own head some of the vials of wrath that had been prepared for Mr. Darwin, and by his able exposition of the doctrine of development contributed to no small extent in securing its firm establishment in our country.9 But while the battle for truth was going on here, on the Continent, and more especially in Germany, the new doctrines were received and discussed with even greater warmth and enthusiasm. A school of the most able naturalists rallied round the Darwinian standard, their zeal often carrying them beyond the bounds of that prudence and caution displayed by their leader. More than once, as Darwin told me on one occasion, has he had to privately chide his too zealous adherents. Foremost amongst those who have taken the greatest part in promulgating and contributing to Darwinism in Germany stands the name of Prof. Ernst Haeckel, of Jena; and work of the highest order of importance has been contributed also by Prof. Carl Vogt, Moritz Wagner, Prof. August Weismann, G. Th Fechner, the brothers Fritz and Hermann Müller, Prof. Oscar Schmidt, and others; whilst from the philosophical side the theory has been most ably expounded by Frederick Albert Lange.10

The rapid spread of the Darwinian theory among those most competent to form a true estimate of its value soon made itself felt in the field of biological literature, and many works of lasting importance to scientific knowledge appeared as living witnesses to the vitality of the doctrine. Specialists in every department of biology contributed materials, and indeed many workers on the Continent became specialists with the express object of testing the vitality of the views advanced in the 'Origin of Species.' ''From the hour of its

 

9 The advocacy of those who—like Prof. Tyndall, W. (now Sir William) R. Grove, and the late talented Prof. W. K. Clifford—spoke from the ranks of physical rather than of natural science, did great service in promoting the cause of evolution among the wider circles of the general public.

10 'Geschichte des Materialismus,' 3rd ed., 1877, vol. ii. Eng. Translation by E. Chester Thomas, vol. iii., 1881, chap. iv.

[page] 77

appearance,'' says Lyell,11 ''it gave, as Professor Huxley truly said, 'a new direction to biological speculation,' for even where it failed to make proselytes, it gave a shock to old and time-honoured opinions, from which they have never since recovered. It effected this not merely by the manner in which it explained how new races and species might be formed by Natural Selection, but also by showing that, if we assume the principle, much light is thrown on many very distinct and otherwise unconnected classes of phenomena, both in the present condition and past history of the organic world." In the year 1869, at a meeting of the German ''Naturforscher Versammlung,'' a society analogous to our British Association, Prof. Helmholtz—of world-wide fame as mathematician, physicist, chemist, and physiologist—in his opening address at Innsbruck, in reviewing the doctrine of Natural Selection, said, ''Darwin's theory contains an essentially new creative thought,''12 a dictum which is all the more weighty as coming from one who has himself obtained such a many-sided and profound insight into Nature's laws.

But tempting as is this theme, time compels me to refrain from any further reference to contemporary scientific opinions on the Darwinian theory. It will suffice to say, in the words of its illustrious author—''Now things are wholly changed, and almost every naturalist admits the great principle of evolution.''13 On the very last occasion that I had the pleasure of an interview with Mr. Darwin, he said that he looked upon the 'Origin' as a book of the past; it had done its work, and might now be shelved. But here, as in many other cases, his inborn modesty led him to undervalue his own work, and I feel confident that I express the views of every worker in biology when I say that for many years hence the 'Origin of Species 'will be at hand as a repository of carefully digested facts, and a storehouse of suggestions for future work.

Now the theory of species established by Darwin is

 

11 'Principles of Geology,' 12th ed., vol. ii., pp. 281, 282.

12 'Popular Scientific Lectures,' 1873, p. 385.

13 'Origin,' 4th ed., p. 424,

[page] 78

based, as previously stated, upon certain indisputable facts, viz., the high rate of multiplication of living beings, the struggle for existence, change of environment, and the principle of heredity. Every species is, on this view, genetically descended from some previously existing species; and since the changes of external conditions take place on the whole with extreme slowness, the process of modification must have proceeded with corresponding slowness. It is of the utmost importance to bear in mind that, in admitting the Darwinian theory, we forever exclude the possibility of any '' innate tendency'' to change in species; the modification of living forms is mainly brought about by external factors, and we cannot regard a species as a production endowed with a predisposition to grow into some other form by virtue of an internal law of growth making itself manifest only with the lapse of time. As long as the external conditions remain unchanged the species remains fixed. Paraphrasing Newton's first law of motion, we might say that a species perseveres in its existing state unless acted upon by external forces. Whether the modification of species has always proceeded at the same rate is perhaps an open question, but considering the vicissitudes both astronomical and geological through which over earth has passed, and supposing that life appeared as soon as permitted by the temperature of the globe cooling down from a molten condition, it seems to me that change, both geological and organic, may have taken place at a greater. rate in past ages than at the present time, in which case the slow present rate of transformation may be no absolute measure of the past rate of modification, and the large demands upon time made by many supporters of the descent theory may permit of being more or less curtailed.

The classification of animals and plants into species, genera, orders, classes, &c., according to their "affinities," now, as in pre-Darwinian times, continues to occupy the attention of large numbers of our working naturalists, but in the light of the theory of descent it is seen that this arrangement into groups within groups is no less than an attempt to

[page] 79

reconstruct genealogies from the surviving remnants of past faunas and floras. For the term ''affinity'' we may now substitute the expression, blood-relationship. Thus, taking any group of allied forms, such as the species of a genus, we say that these have descended from a common ancestral form now extinct. The wider the group which we are considering the further back in time should we have to go to arrive at the point from which the various forms composing the group diverged; in other words, the degree of difference between species is a measure of the amount of their divergence from a common parent. The science of Palæontology, which deals with the life of the past as preserved to us in fossil remains, becomes linked by inseparable bonds to Taxonomy. It is to the geological record that we have to appeal to fill up those links which are necessary for the completion of our pedigrees.

How vastly increased in importance becomes the determination of true morphological affinity—with what surpassing interest does Homology become endowed—when we know that the structural resemblance of two animals, however externally disguised, is due to community of descent from an ancestor that lived in the remote ages of geological antiquity.

Until the publication of the 'Origin of Species' geologists had never fully realised the fact that their fossil collections represented but an infinitesimal fraction of the whole number of animals and plants that had peopled the earth from the earliest times. Darwin says on this point:—''I look at the geological record as a history of the world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.''14 ''The crust of the earth, with its imbedded remains, must not be looked at as a well-filled museum, but as a poor collection made at hazard and at rare intervals."15

When, from the standpoint of modern Geology, we consider how small is the chance of the preservation of an animal or plant in the state favourable for fossilization and when we

 

14 'Origin,' 6th ed., p. 289. 15 Ibid., p. 427.

[page] 80

further reflect upon the vicissitudes to which fossiliferous strata are and have been at all times exposed by denudation, erosion, and metamorphism, it appears to me that there is not much matter for marvel in this poverty of the geological record, but rather that we should wonder at its comparative richness. In fact the geological record, however imperfect it may be, has furnished the very strongest evidence in favour of the Darwinian theory, and since the year 1859 the progress of Palæontology has enabled many gaps between the most diverse groups of animals to be filled up. What more distinct in external form and mode of life than birds and reptiles? These two classes had, however, long been known to anatomists to be structurally related, and on the principle of evolution the existence of intermediate forms might have been anticipated. In 1862, after Darwin had predicted the existence of such connecting links,16 there was found in the Solenhofen limestone of the Upper Jurassic series, in Bavaria, the now well-known Archæopteryx, an animal uniting the characters both of birds and reptiles. Professor Huxley subsequently pointed out that a family of extinct gigantic reptiles, the Dinosauria of the Oolite and or Cretaceous formations, presented certain distinctly avian characters. These discoveries culminated, in 1875, in Professor Marsh's great find of toothed birds, the Odontornithes of the Cretaceous beds of Kansas,17 a discovery which, as Professor Huxley says, ''removed Mr. Darwin's proposition that 'many animal forms of life have been utterly lost, through which the early progenitors of birds were formerly connected with the early progenitors of the other vertebrate classes,' from the region of hypothesis to that of demonstrable fact.''18 In a similar manner the pedigree of the horse has been traced back by Professor Marsh to the Eocene species of Eohippus,19 an animal about the size of a fox; and the pedigrees of the

 

16 'Origin,' 1st ed., p. 431.

17 Vol. i., 'Memoirs of Peabody Museum of Yale College'" vol. vii., ''Geological Exploration of the 40th Parallel."

18 ''The Coming of Age of the 'Origin of Species,'" 'Nature,' May 6th, 1880, p. 3.

19 Amer. Jour. Sci., 1879.

[page] 81

Camels and Hyænas have been worked out by Professor Cope20 and M. Gaudry21 respectively. In Palæontology, as in every other branch of Biology, the Darwinian theory has in fact become incorporated as a part of common knowledge; witness the following extracts from the latest text-book of Geology published in this country:—''It must be conceded that on the whole the testimony of the rocks is in favour of the doctrine of evolution."22 ''But to the palæontologist it is a matter of the utmost importance to feel assured that, though he may never be able to trace the missing links in the chain of being, the chain has been unbroken and persistent from the beginning· of geological time."23 ''From this point of view the investigations of Palæontological Geology are invested with the profoundest interest, for they bring before us the history of that living creation of which we form a part.''24

Returning once again to the principles of the selection theory, we see that every modification of an organism implies the addition to, or the modification of, some structure or function already possessed. It is most essential to bear in mind that Darwin's prime mover, natural selection, acts not only upon external characters, but likewise upon internal organisation; minute constitutional or physiological deviations at present utterly beyond the ken of science, can be seized upon and perpetuated by this agency when of any advantage to the possessor. The survival of the fittest is utilitarianism in excelsis. From the dawn of life upon this earth there must thus have been on the whole a tendency for living beings to increase in complexity of structure and function,—a tendency to a more complete biological division of labour both in individuals and in races,— a tendency to become more and more specialised, or , as it is said, to ''advance in organisation.'' It is almost needless for me to pause here in order to point

 

20 Amer. Nat., 1880.

21 'Les enchainements du Monde Animal.'

22 Geikie, p. 624.

23 Ibid., p. 626.

24 Ibid., p. 627.

[page] 82

out how completely the facts of Palæontology accord with this view. But although it is thus permissible to speak of the Darwinian theory as a theory of evolution, it must not be forgotten that evolution is not necessarily Darwinism. It is the more necessary to remember this in order to fully realise the vast change in thought wrought by Darwin. Long before the appearance of the 'Origin of Species' there had been evolutionists. In 1809 Jean Lamarck published his 'Philosophie Zoologique'; in 1828 Geoffroy St. Hilare [sic] declared his belief in evolution; the author of the 'Vestiges of Creation' (1844) was an evolutionist; many others, and among them Göethe, the Shakespeare of German literature, had expressed—the doctrine of evolution before Darwin; but it was our own great countryman who convinced the world of its truth. The bare facts of morphology, of classification, and of geological succession, are suggestive of evolution, but it required a Darwin to point out how evolution had taken place in organic nature.

The causes of transmutation of species assigned by the older evolutionists were in fact inadequate. For Lamarck these causes were mainly habit and the direct action of external conditions; the author of the 'Vestiges' found the causes of evolution in ''impulses' 'implanted in living beings, tending to adapt them to their surroundings, and causing them to rise in the scale of organisation. It was reserved for Darwin to clothe the skeleton hypothesis of evolution with the flesh and blood that converted it into a living theory.

To my mind, no more convincing proof of the force of Darwin's reasoning is to be found than in the conversion of Sir Charles Lyell, for the whole spirit of this great geologist's teaching was in every essential evolutionary; and yet he had rejected the Lamarckian hypothesis in the early editions of his 'Principles,' wherein he had advanced long and elaborate arguments showing the insufficiency of the French naturalist's theory. But in the thirteen years' interval that elapsed between the publication of the ninth and tenth editions of the 'Principles of Geology,' the author's opinions on this question had undergone a change; and in the latter

[page] 83

edition, as also in his 'Antiquity of Man,' he not only gave a masterly exposition of the Darwinian theory, but added considerably to its weight, and enforced its acceptance by several new and striking lines of argument.

It would lead me too far astray on this occasion were I to attempt to go in any detail over the various lines of evidence converging upon the central idea of evolution. It suffices to say that many large groups of biological facts that had before appeared isolated and inexplicable were not only in the strictest scientific sense explained, but ' as by the stroke of the enchanter's wand'' the various great subdivisions of Biology fell into, and became part of, Darwin's scheme of Nature. ''Every ray is gathered into one focus, and the rich development of theory guides the apparently most remote phenomena of organic life into the stream of proof.''25 Let us consider, for instance, the generalised facts of Embryology. The development of an organism from the first germ to the mature state is essentially a process of evolution. The researches of embryologists, beginning with the illustrious Karl Ernst von Baer, and ending alas! in recent times with the lamented Francis Maitland Balfour, have shown that in the course of its individual development an animal passes through stages which approximate it at first to the lowest types, and then in succession to types of increasing specialisation.

The individual in fact ''rises in organisation'' in the same sense as does the species. Specialisation increases with development, till finally the adult animal acquires all the characters of the species to which it belongs. How are such facts intelligible if we reject the theory of descent?

The researches of Darwin upon the laws of inheritance have shown that all characters tend to be transmitted by parents to their offspring at the same age or a little earlier than they appear in the parents. This is Haeckel's law of ''homochronic heredity.'' The embryonic phases of an organism are thus reminiscences of its past development—recapitulations of the stages through which its ancestors passed in the course of their evolution. The individual development or

 

25 Lange, l. c., vol. iii., p. 31.

[page] 84

ontogeny, as Haeckel expresses it, is the racial development or phylogeny in nuce. At a certain stage of its development the human embryo, for example, has gill-slits and branching arteries as in fishes, and at later stages it is tailed and hairy.

What do such facts mean, if they are not revelations that man's ancestors have passed through an aquatic stage, and later through that of a tailed hairy mammal? From the Darwinian standpoint the parallelism between embryos and fossil remains, so recently pointed out by Professor Agassiz, is not a mystery, but a necessity; and the science of Embryology becomes linked on the one hand to Taxonomy and on the other to Palæontology.

In a similar manner the geographical distribution of animals and plants, the relations of the faunas and floras of islands to those of the mainland, and the relation of existing to extinct faunas and floras of the same area, all become explicable by the aid of the descent theory, and are meaningless on any other hypothesis. But time presses, and I will only pause here to point out the somewhat interesting circumstance that the facts of this nature, which first led Darwin to speculate on the origin of species, have been left for their complete coordination and generalisation to the contemporary founder of modern evolution , Mr. A. R. Wallace, whose works on the 'Geographical Distribution of Animals' and 'Island Life 'may be regarded as the completion of the twelfth and thirteenth chapters of the 'Origin of Species.'.

Of other classes of facts explained by the principle of evolution I need only mention the existence of rudimentary organs, which are, on this view, the surviving remnants of structures that were useful to the organism at some former period of its existence. The next classes of cases to which I will allude are those of ' persistent types," and of retrograde development or ''degeneration.'' It must be remembered that Darwin's theory does not postulate, as is so frequently assu1ned, the continual advancement of every living creature.

Transformation only takes place when stimulated by the action of the environment. Under certain conditions, where by isolation or by constancy in the external conditions of life

[page] 85

the species is protected from Nature's strife., it may persist unaltered or with only slight modification throughout whole geological periods, as we see in the numerous slow forms of aquatic life, and higher in the scale in such types as Lepidosiren and Ornithorhynchus which Darwin speaks of as ''living fossils."26 Or again, through parasitism or other causes, a species may be driven to a mode of life in which high organisation is not only useless, but may be actually detrimental to its possessor. In such cases natural selection, having only the good of the species in view, would bring about a more lowly-organised condition in the adult animal, while the younger stages, by the law of homochronic heredity, would retain the higher structure of the ancestral form. This principle of ''degeneration'' is seen in such groups as the Ascidians, the parent-stock of all the vertebrate animals; in the barnacles, which are degenerate Crustacea; and in the Mexican Axolotl. The development of Darwinism in this direction will be found in works by Anton Dohrn27 and Prof. E. Ray Lankester.28

Before concluding this necessarily imperfect sketch of Darwin's chief work, there remain a few considerations to which I should like to direct attention. I may remind you, with reference to the various objections that have from time to time been urged against the theory of selection, that there has not been a more candid critic of this theory than Mr. Darwin himself, and in point of fact it is not going too far to say that hardly any difficulty of importance has been raised which was not suggested in the 'Origin of Species.' I will, with your permission, dwell briefly upon one or two objections which are still occasionally to be heard.

Variability, the basic factor of species-transformation, is

 

26 Just as this Address was completed there appeared in 'Nature' an interesting article by Prof. Hubrecht, in which the subject of persistent forms of life is treated in a somewhat novel way, under the title of ''The Hypothesis of. Accelerated Development by Primogeniture, and its place in the Theory of Evolution." Vol. xxvii., p. 279 and 301.

27 'Der Ursprung der Wirbelthiere und das Princip des Functionswechsels,' Leipzig, 1875.

28 Degeneration, a Chapter in Darwinism,' Macmillan, 1880.

[page] 86

sometimes spoken of as taking place in every direction; that is to say, it is supposed that every species presents an infinite number of variations for natural selection to act upon. Thus it may be fairly asked, why under these circumstances extinction should ever take place? If variability is infinite, why should there not be a capability on the part of any species to meet any contingency- to become modified in any direction? In reply to this question, it may be stated that the range of variability required by Darwin's theory, although wide, is not and cannot be unlimited. There are restraining forces within the organism. The force of heredity, by which the latter tends to retain not only the characters of its immediate parents, but likewise those of more remote ancestors, determines the physical constitution of the organism, and checks unlimited variability. The delicate balance of internal forces constituting the physiological equilibrium of the organism cannot admit of being displaced in every conceivable direction—there can be only a certain range of variability possible to each species. An organism may be compared to a bell, which, although capable of vibrating in a very great number· of ways and of giving out a great number of notes according to the way in which it is struck, nevertheless cannot be made to give out an infinite number of notes, because its molecules are constrained to vibrate in certain definite ways only by virtue of its physical construction. In every case of species-transformation there are thus involved two factors, ''the nature of the organism, and the nature of the conditions."29 It is to Professor Weismann that we owe the first full recognition of the important part played by the organism itself in the process of evolution, but it must be borne in mind that the part thus played is quoad modification, a purely passive one.

In connection with the foregoing considerations, there arise the questions of the causes of variability and the extent to which the latter takes place in particular species. It is very much to be regretted that Darwin was compelled by failing health to abandon his intention of discussing the subject of

 

29 'Origin,' 6th ed., p. 6.

[page] 87

'Variation under Nature,' in a work which was promised to follow his 'Variation of Animals and Plants under Domestication'; but it is well known that his system never completely rallied from the effects of the voyage of the 'Beagle,' and his work, herculean though it may be in the eyes of his contemporaries, becomes greatly enhanced in wonder when we consider that for years he laboured bravely under the most distressing physical disadvantages. But although the great task remains uncompleted in its details, much light was thrown upon this important subject by Darwin in his other works, and it has since been discussed in many able treatises emanating from the German school of Darwinians. With respect to the extent and origin of variability, I cannot do better than refer you to a very valuable paper by Mr. A. R. Wallace, in the 'Nineteenth Century' for January, 1880. This question of the origin of variability, however important on other grounds is in fact of secondary consideration as far as concerns the Darwinian theory proper. Ten years ago 30 I cited a certain class of cases in illustration of the fact that natural selection acts upon such variations as arise, with entire disregard to the causes of these variations. When, indeed, we look upon an individual organism, as we now must, as a being in which is epitomised the hereditary tendencies of a long chain of ancestors which have at various periods been exposed to the most diverse conditions, I cannot but agree with those who maintain that the problem should be inverted, and that it is not variability but constancy which demands an explanation. ''Does any one ask for a reason why no two gravel-stones or beach-pebbles, or even grains of sand, are absolutely identical in size, shape, surface, colour, and composition? When we trace back the complete series of causes and forces that have led to the production of these objects, do we not see that their absolute identity would be more remarkable than their diversity? So, when we consider how infinitely more complex have been the forces that have produced each individual animal or plant, and when we know that no two animals can possibly have

 

30 Proc. Zool. Soc., 1873, Pl), 153-162.

[page] 88

been subject to identical conditions throughout the entire course of their development, we see that perfect identity in the result would be opposed to everything we know of natural agencies. But variation is merely the absence of identity, and therefore requires no further explanation; neither do the diverse amounts of variation, for they correspond to the countless diversities of conditions to which animals have been exposed, either during their own development or that of their ancestors.''31

It would be doing an injustice to the memory of Charles Darwin were I to leave upon your minds the impression that he regarded natural selection as the sole cause of species transformation. In the 'origin' certain other important factors, such as the direct action of external conditions, use and disuse, compensation and economy of growth, correlated variability, &c., are discussed at some length. The principle of sexual selection—by which the difference in colour, ornamentation, weapons, &c., of such frequent occurrence between the sexes throughout the animal kingdom, is explained on the view that either the male or female in each species has throughout a long series of generations selected variations having these characteristics - was also laid down in the 'Origin,' and afterwards elaborated in great detail in the 'Descent of Man,' the main portion of this work being devoted to the establishing of this principle. But after giving due weight to these auxiliary factors the chief share in the work of modification is still assigned to natural selection, although the candid avowal is made that there may be other unknown processes in operation. The truly philosophical side of Darwin's character is perhaps nowhere better shown than in the admission that he had not explained everything—that his system was not to be taken as final. He has not given us a complete theory of things in the sense of ancient scholasticism, which for the bread of knowledge substituted a stone that stood as a stumbling-block in the way of further advancement. Darwin has demonstrated a vera causa, of organic evolution, but he has done even more

 

31 A. R. Wallace, 'Nineteenth Century,' Jan., 1880, p. 105.

[page] 89

in bequeathing to us the true spirit of inquiry into Nature's laws by legitimate method. The lustre shed by our Honorary Member upon the present age will not wax and wane with the fluctuations of opinion as to the efficiency of the "survival of the fittest,'' but his influence will be felt throughout generations of posterity by virtue of that plasticity of mind which he conferred upon his contemporaries, compelling them to reconsider old doctrines, and ultimately effecting a complete revulsion in thought. In a Society such as this, comprising as it does many young and aspiring naturalists, it is perhaps the more necessary to insist upon this moral conveyed by Darwin's teachings. It is true that there are some eminent men of science who, although evolutionists, do not admit the sufficiency of the Darwinian factors; but at the same time they could not deny that their acceptance of evolution in any form is entirely the result of Darwin's influence. The discovery of the theory of selection was a very great contribution to science, but the establishment of the principle of evolution was a still greater contribution to philosophy.

The question as to how far evolution can be legitimately admitted to have taken place in the organic world is by some considered to be open to discussion. It cannot be denied that the proof that natural selection is competent to modify species does not necessarily carry with it the proof that groups of great dissimilarity, such, for example, as the vertebrates and the molluscs, have sprung from a common stock. But those who admit evolution in principle need feel no distrust on this head, even if Palæontology has not as yet supplied the transitional links. In cases of this kind, however, arguments of another order come in, and homology, embryology, &c., may be appealed to for completing the evidence that is wanting to bridge over the gaps in the chain of being.

On this point Darwin is very explicit:-''Throughout whole classes various structures are formed on the same pattern, and at a very early age the embryos closely resemble each other therefore I cannot doubt that the theory of descent with modification embraces all the members of the same

[page] 90

great class or kingdom. I believe that animals are descended from at most only four or five progenitors, and plants from an equal or lesser number.''32 Carrying on the argument by analogy, which, as he cautions us, ''maybe a deceitful guide,'' he then shows that there is no well-defined distinction between the lowest animals and the lowest plants.'' Therefore, on the principle of natural selection with divergence of character, it does not seem incredible that, from such low and intermediate forms, both animals and plants may have been developed; and, if we admit this, we must likewise admit that all the organic beings which have ever lived on this earth may be descended from some one primordial form. But this inference is chiefly grounded on analogy, and it is immaterial whether or not it be accepted.''33

If I may venture to push Darwin's analogy still further, it appears to my mind that we can hardly stop even at the "primordial form." If continuity is a great law of Nature we cannot logically admit of any break between the organic and the inorganic worlds, and although, as I wish most strongly to emphasise, there is no necessary connection between Darwin's teachings and a belief in so-called ''spontaneous generation," it seems to me that if we accept evolution in its broadest meaning we are compelled to admit, with Lamarck and Haeckel, that at former periods, or possibly even at the present time, the very lowest beginnings of life have been or are being evolved by the operation of natural causes. For fear of misrepresentation let me here add that there is at present not a vestige of scientific proof countenancing such a belief. The reasoning of the consistent evolutionist in this matter is of precisely the same kind, only different in degree, as that which he employs when stating his belief that the gap between two widely divergent animals or plants, which at present appear isolated and distinct, is simply caused by the present imperfect state of palæontological or embryological knowledge concerning them.

Much as I could have wished to have given you some idea

 

32 'Origin,' 6th ed., p. 424. 33 Ibid., p. 425.

[page] 91

of the scope of Darwin's other works, this is quite beyond the bounds of possibility on the present occasion.34 The 'Variation of Animals and Plants under Domestication,' the 'Descent of Man,' and the 'Expression of the Emotions,' contain the direct applications of the theory of descent to particular groups of phenomena, and the conclusions arrived at in some of his other books have a certain bearing on this doctrine. The magnitude of his labours can be best estimated by striking out from the list which I have given all those works which are directly related to the 'Origin of Species,' and there will even then remain a body of researches which by themselves would be sufficient to have established for Darwin the reputation of being the most active and able observer of our time.

Of the personal character of Darwin, everything that can be said by those who knew him has already been expressed, and it is impossible to add anything to the weight of their testimony. By his intimate acquaintances he was venerated, by friend and foe he was alike respected. In conversation, which in later life his health prohibited him from maintaining for any length of time, his manner was vivacious and often humorous, his features lighting up with expression and shedding a genial warmth upon his listeners. When speaking on subjects that lay beyond the sphere of his own studies he would ask for and receive information with the most profound attention, although endeavoring to find some bond of connection between facts that were new to him and the already vast store of knowledge upon which he was always able to draw in illustration of his own remarks. He was simplicity personified, and the pretentiousness of professorial dignity was quite foreign to his disposition. He liked to be received in the character of the country squire rather than as the author of the 'Origin of Species.' I remember how

 

34 An excellent account of Darwin's scientific work appears in the current (January) number of the 'Century,' from the pen of Mr. Wallace. Those who wish to acquire a concise and sound idea of the doctrine of evolution cannot do better than consult Mr. Romanes' little work in 'Nature' Series, Macmillan & Co., 1882.

[page] 92.

with keen enjoyment he once related to me some of his early experiences among the pigeon- fanciers, into which select circle he desired to gain admission when studying· the variation of our domesticated productions. The motion having been put to the meeting and carried, ''Squire Darwin" was elected, but could not be admitted before payment of the subscription. The money was handed in, and the chairman of the club, even then apparently doubtful of the trustworthiness of the candidate, proceeded to test the coin by the usual methods before formally announcing his election.

Among the many noble qualities which endeared Darwin to his friends was his ever ready sympathy for the younger men that looked up to him as their master. There are many at the present time rising· into prominence who will carry with them to the grave the memory of the impetus given to their career by the kindly encouragement, the assistance and advice, so freely given by Darwin. How many will echo the sentiment expressed by an eminent German naturalist who, writing to me soon after Darwin's death, said:-''The loss of Darwin is certainly for nobody more irreparable than for me, for I have lived so completely isolated, and for long years have been accustomed to communicate to him all my little scientific results, always certain of his full participation and sympathy.''

Such was the life which, terminating last April, has left a void in the ranks of science that we can never hope to see filled up. The great doctrine of evolution founded by Darwin in our time has not only remodelled the science of Biology, but its influence extends through every department of human knowledge. The spirit of Darwinism pervades and animates the whole of modern science. Wherever Nature presents gradation, we now suspect deviation.

Branches and sub-branches of science, which, like Psychology, Anthropology, and Sociology, were formerly ill-defined and vague in scope, under the ruling idea of evolution have now acquired defined forms based on secure foundations. On the burning question of the assumed or actual theological bearing

[page] 93

of the theory of evolution it does not enter into my province to speak this evening. To my mind Darwin has exalted our conception of Nature beyond the theologies. He has taught us that there is no intermediate and direct interference with the course of natural law—he has enforced the lesson that in studying natural science we are concerned only with secondary causes. I cannot do better than conclude in the words of Bacon:—

''For certain it is that God worketh nothing in Nature but by second causes; and if they would have it otherwise believed, it is mere imposture, as it were in favour towards God; and all nothing else but to offer to the Author of Truth the unclean sacrifice of a lie"35

 

'35 'Advancement of Learning,' Book I.