organic forms, we nowhere find a standing-still, a resting, or completion of action, but all rather fluctuates in constant movement." In an interesting passage in his autobiography, he tells us that he had come to the conclusion "that the various plant forms which surround us are not originally determined or fixed, but that there is lent to them, in spite of a persistent generic and specific stability, a happy mobility and pliantness, in order that they may be able to adapt themselves to the various conditions which act upon them all round the circuit of the world, forming and transforming themselves accordingly." Underlying all this variability, this action and reaction, we are, however, gradually forced to the conviction that there must exist a fundamental type or idea, the plan on which nature works. There is an internal formative tendency or "centripetal" force, which determines the building up of an organism, and the final relation of its perfected parts to one another. But over and against this tendency, another, or "centrifugal" force is at work, viz., that of metamorphosis or adaptation. While the organism remains ever true to its original type, it is subject to a constant necessity of adjustment to external circumstances. "Variations in the soil," for example, as Goethe says, "may come into consideration. Richly nourished in the damp valley, stunted by the drought of the mountains, protected from frost and heat in every degree, or unavoidably exposed to both, the genus resolves itself into species, the species into variety, and this again, under other conditions, into endless changes of form."

While Goethe thus attained a clear conception of the mutability of nature, he was a strict opponent of the doctrine of geological cataclysms, which, during his day, was accepted as a dogma of natural science, and did not receive its final blow till the appearance of Sir Charles Lyell's great work in 1830.* "The violent and revolutionary character of this theory of cataclysms," Goethe says, "is offensive to me because it is contrary to nature." In fact there could be nothing more alien to the genius of Goethe than any sympathy with a doctrine which implied repeated arbitrary interruptions of the great march of natural law. To one who was so convinced of the unity and uniformity of nature, no words were strong enough to express his reprehension of all such "lumber-room" conceptions of the universe, as he calls them.

Perhaps nothing is so remarkable about the speculations of Goethe as the uncompromising honesty with which he was prepared to carry them to their logical issue. As a result of his profound and varied investigations in every branch of natural science, we cannot therefore be surprised that he was led to the following very striking

* "Principles of Geology, being an enquiry how far the former changes of the earth's surface are referable to causes now in operation," 1830-1832,

generalisation, which may almost be considered as reaching the highwater mark of evolutionary speculation prior to the advent of Darwin. "Without hesitation," Goethe says in a memorable passage," we are now able to declare that all highly developed organic creatures, amongst which we recognise the fishes, amphibia, birds, and mammals, and at the summit of the last, man himself, are all formed upon one primary type, deviating, it is true, in its stationary elements, but forming and transforming itself by endless reproduction."

III.

In short, it is impossible to read through the scientific writings of Goethe without being struck with the remarkable way in which he seems to have grasped the fundamental conceptions of the doctrine of evolution. Haeckel, the chief exponent of the doctrine in Germany, places him along with Lamarck as the most distinguished of all the precursors of Darwin. It was a misfortune that Goethe himself was not acquainted with the writings of the great French naturalist whose name has just been mentioned, for had he been so he would have found much in them that was fully in line with his own speculative tendencies. Jean Lamarck published his celebrated "Philosophie Zoologique" in 1809, but for many years no one paid any attention to it. It was not, indeed, till fifty years later, when Darwin had enunciated his great theory, that it was seen how clearly Lamarck had realised the idea of the mutability of species at a time when men's minds were still bound in the trammels of medieval orthodoxy. His speculations showed a considerable advance in clearness and exactness on those of Goethe, and to Lamarck, therefore, will always belong the distinction of "having for the first time," as Haeckel says, "worked out the theory of descent as an independent concept of the first order, and as the philosophical basis of the whole science of biology." Lamarck reached the important conclusion that all animal and plant forms, which we distinguish as species, possess only a relative and temporary persistence, and that varieties are commencing species. The course of development of the earth and its organic inhabitants was continuous, not interrupted by violent revolutions. In the first beginnings the very simplest and lowest animals and plants came into existence; those of a more complex organisation only at a later period. The differences in the conditions of life on the one hand, and the use and disuse of organs on the other hand, have a constant transforming influence upon the organisms; these factors cause, by adaptation, a gradual change in form, the fundamental characters, however, being carried on from generation to generation by inheritance. The whole system of

animals and plants is therefore to be considered as a genealogical tree, "which unveils for us the circumstances of their bloodrelationship."

Present-day science stands very much in debt to these bold and farreaching conceptions of Lamarck. They constitute the true programme of evolution, which it has been the task of modern science to carry out into its details. I do not need to tell you that the theory of evolution is now accepted all along the line. It is true that we do not now think much of the services of Goethe and Lamarck as the founders of the doctrine. Their names have been overshadowed by the transcendent achievement of Charles Darwin, which has made evolution a household word in the domain of natural science. Yet we must remember that Darwinism is only a part of evolution. It was Darwin who gave the theory a thoroughly scientific groundwork, but he was by no means its originator. Indeed, his concern was almost solely with its biological aspects, and he did not trench much upon other fields. Evolutionism must be looked upon as a complicated intellectual movement. Its obscure beginnings date back many centuries, as we have seen; but in its latest developments it is peculiarly a product of the nineteenth century, and the joint conception of a number of scientific workers and theorists of different degrees of eminence. After all has been said, however, there is no doubt that Darwin's labours, as Grant Allen puts it, form "the central keystone of the complex and many-sided evolutionary system. For what others suspected, he was the first to prove; while others speculated, he was the first to observe, to experiment, to demonstrate, and to convince."

The leading doctrines of the Darwinian theory, as you are aware, are expressed in the now familiar phrases, "struggle for existence," and "natural selection" or the "survival of the fittest." Starting from the well-known phenomenon of the variability of offspring, Darwin shows that individual differences constantly arise amongst plants and animals, both in a state of nature and under domestication. The extraordinary diversity in domesticated animals has been due to the careful selection by man of useful or pleasing varieties, and the perpetuation and accentuation of their good qualities by interbreeding. In nature, however, there is no such artificial selection; the process is purely automatic. Every organism is so constituted that it possesses the power of almost unlimited reproduction, but the restrictions of space and of food render it impossible for more than a very minute fraction of all the eggs or seeds that are produced ever coming to maturity. A fierce struggle for existence takes place, and only the most vigorous embryos, or those possessing some advantage over their fellows in function or structure, are able to survive and perpetuate

the species. This is what is meant by natural, or "unconscious" selection, as it might be called.

It is to these two great factors that Darwin chiefly attributes the unfolding of the vast and varied panorama of organic nature as we see it to-day, and as we know it has existed during past geological ages. "Growth, with reproduction; inheritance, which is almost implied by reproduction; variability, from the indirect and direct action of the conditions of life, and from use and disuse; a ratio of increase so high as to lead to a struggle for life, and as a consequence to natural selection, entailing divergence of character and the extinction of the less improved forms." These, in his own words, are the causes which, "from the war of nature, from famine and death," have led to the production of the diversified organic life which peoples the globe.

IV.

I have thus, in a very imperfect and fragmentary manner, endeavoured to trace the "evolution of evolution," as one might say, from its earliest beginnings to its present-day maturity, dwelling more especially upon the part played by the great German poet and philosopher in its inception and fundamental embodiment. But our interest, as students of natural science, is rather with the immediate application of the theory to our own special department of work. I shall therefore hasten on to refer very briefly to some of the most recent developments of the doctrine of descent, and I shall, in so doing, endeavour to indicate to you the present-day trend of opinion regarding the whole subject.

The great advance which Darwin made over all previous evolutionists was, as we have seen, in the discovery of an adequate cause for the diversity of species. Lamarck's explanation was insufficient, and hence his speculations made little impression on his contemporaries. He laid too much stress upon the use and disuse of organs, and though he grasped the great fundamental principles of adaptation and inheritance, he failed to realise their true relation to each other. There was one question, however, of transcendent importance raised by Lamarck, which was not answered finally by Darwin, and which, at the present moment, is the subject of burning controversy. One of the essential conceptions of the Lamarckian doctrine was that new characters acquired by the parent, through use or disuse, or through habit or changed conditions, may be transmitted directly to the offspring. Darwin only goes the length of saying "that these factors of use and habit have, in some cases, played a considerable part in the modification of the constitution and structure; but that the effects have often been largely combined with,

D

and sometimes overmastered by, the natural selection of innate variations."

The camp of the new evolutionists is therefore at present divided into two great factions. On the one hand we have the school of the neo-Lamarckians, chiefly represented in America and France, whose contention is that variations in an individual organism may be directly caused by the force of external circumstances, such as climate, the conditions of nutrition, or the influence of disease, and that these acquired changes can be directly inherited. On the other hand we have a powerful movement, headed by the now famous name of August Weismann, whose celebrated doctrines of heredity and the continuity of the germ-plasm, involve a direct negative to the views of the neo-Lamarckians. As these doctrines of Weismann are of great importance, and have received very considerable support in this country, even more than in Germany, it will be necessary to consider them in a little detail.

V.

Starting from the familiar yet extraordinary circumstance “that, in the higher organisms, the smallest structural details, and the most minute peculiarities of bodily and mental disposition, are transmitted from one generation to another," and from the further consideration that this transference occurs through the medium of a single cell or ovum thrown off by the parent, and capable of gradual but, strictly speaking, independent growth into the new individual, Weismann states the great problem of heredity in the following sentence: "How is it that such a single cell can reproduce the tout ensemble of the parent with all the faithfulness of a portrait?" Darwin had already given a provisional answer to the question by supposing that gemmules are given off from the cells of the mature organism, which become congregated in the sexual cell, and thus determine its power of heredity. After showing that such and all other suggested theories are inconceivable, and do not explain the facts, Weismann proceeds to state his belief that the essential element of the germ cells is not derived at all from the body of the individual, but proceeds directly from, and is a continuation of, the parent germ cells. The germplasm he illustrates by the metaphor of a long creeping root-stalk, from which plants arise at intervals, these latter representing the individuals of successive generations. This is the fundamental conception upon which Weismann builds up a system of remarkable consistency, though in some of its details of great complexity. It would be impossible to go further into these at present. You will, however, at once see the trenchant nature of these speculations,