"3. The development of these organs is in proportion to their employment.
"4. New developments are transmitted to offspring."
He supported especially the last two propositions by a series of examples as to the effects of use and disuse; and the most famous of these, the theory that giraffes had produced their long necks by continually stretching up towards the trees on which they fed, is well known to everyone. However, the ingenious speculations of Lamarck were unsupported by a sufficient range of actual knowledge of anatomy, and lacked experimental proof. He entirely failed to convince his contemporaries; and Darwin himself, in a letter to Lyell, declared that he had gained nothing from two readings of Lamarck's book. There can be little doubt but that several Continental writers, in particular Haeckel, have exaggerated Lamarck's services to the development of the idea of evolution. On the other hand, Lyell, although he strongly opposed the ideas of Lamarck and some curious notions of progressional creation due to the great Agassiz, had prepared the way for Darwin by his advocacy of natural causes and slow changes in opposition to the catastrophic and miraculous views in vogue. Above all, Herbert Spencer had argued most strenuously in favour of evolution. Thus, in an important passage quoted by Mr. Clodd from the Leader of March 20, 1852, Spencer had written as follows:
"Those who cavalierly reject the theory of evolution, as not adequately supported by facts, seem quite to forget that their own theory is not supported by facts at all. Like the majority of men who are born to a given belief, they demand the most rigorous proof of any adverse belief, but assume that their own needs none. Here we find, scattered over the globe, vegetable and animal organisms numbering, of the one kind (according to Humboldt) some 320,000 species, and of the other, some 2,000,000 species (see Carpenter); and if to these we add the numbers of animal and vegetable species that have become extinct, we may safely estimate the number of species that have existed, and are existing, on the earth, at no less than ten millions. Well, which is the most rational theory about these ten millions of species? Is it most likely that there have been ten millions of special creations; or is it most likely that by continual modifications, due to change of circumstances, ten millions of varieties have been produced, as varieties are being produced still?... Even could the supporters of the development hypothesis merely shew that the origination of species by the process of modification is conceivable, they would be in a better position than their opponents. But they can do much more than this. They can shew that the process of modification has effected, and is effecting, decided changes in all organisms subject to modifying influences.... They can shew that in successive generations these changes continue, until ultimately the new conditions become the natural ones. They can shew that in cultivated plants, domesticated animals, and in the several races of men, such alterations have taken place. They can show that the degrees of difference so produced are often, as in dogs, greater than those on which distinctions of species have been founded. They can shew, too, that the changes daily taking place in ourselves—the facility that attends long practice, and the loss of aptitude that begins when practice ceases,—the strengthening of the passions habitually gratified, and the weakening of those habitually curbed,—the development of every faculty, bodily, moral, intellectual, according to the use made of it—are all explicable on this principle. And thus they can shew that throughout all organic nature there is at work a modifying influence of the kind they assign as the cause of these specific differences; an influence which, though slow in its action, does, in time, if the circumstances demand it, produce marked changes—an influence which, to all appearance, would produce in the millions of years, and under the great varieties of condition which geological records imply, any amount of change."
These and many other instances which might be brought together from the published writings of the half-century before the publication of the Origin, show conclusively that the idea of evolution was far from new, and that all through the first part of this century dissatisfaction with the doctrine of the fixity of species and of their miraculous creation was growing. The great contribution of Darwin was this: First, by his theory of natural selection, he brought together the known facts of variation, of struggle for existence, and of adaptation to varying conditions, in such a way that they provided men with a rational and known cause, a cause the operation of which could be seen, for the origin of species by means of preservation of favoured races. Next, as to the origin of species, he brought together not only proofs of the actual operation of natural selection, but a body of evidence in favour of the fact of evolution that was, beyond all comparison, more striking than had been adduced by any earlier philosophical or biological writer. He convinced naturalists that evolution was by far the most probable way in which the living world had come to be what it is, and he made them turn to examination of the animal and vegetable kingdoms with a lively hope that the past history of the living world was not an insoluble problem. Darwin's doctrine brought a new life into biological study, and the result of the incomparably greater bulk of investigation that followed the year 1859 was a continual increase of evidence in favour of the probability of evolution, until now the whole scientific world, and the majority of those who are unscientific, are content to accept evolution as the only reasonable explanation of the living world. It is well to remember that while Darwin, by bringing forward the theory of struggle for existence and resulting survival of the fittest, was the actual cause of the present assured position of evolution as a first principle of science, it by no means follows that the survival of the fittest has become similarly a first principle of science. At cross roads a traveller may choose the right path from a quite unsatisfactory reason. Darwin himself, in the act of bringing forward his own theory of natural selection, admitted the possibility of the co-operation of many other agencies in evolution, and at various times during the course of his life he was inclined to attach, now more now less, importance to these additional agencies. Huxley, as we shall soon come to see, never wavered in his adhesion to the facts of evolution after 1859; but, from first to last, regarded natural selection as only the most probable cause of the occurrence of evolution. Other naturalists, of whom the best-known are Weismann in Germany, Ray Lankester in England, and W.K. Brooks in America, have come to attach a continually increasing importance to the purely Darwinian factor of natural selection; while others again, such as Herbert Spencer in England, and the late Professor Cope and a large American school, have advocated more and more strongly the importance of what may be called the Lamarckian factors of evolution,—the inherited effects of increased or diminished use of organs, the direct influence of the environment, and so forth. From the fact that Darwin has persuaded the world of the truth of evolution, evolution is often called Darwinism; and in this historically just though scientifically inaccurate sense of the term, Huxley was a strict Darwinian, a Darwinian of the Darwinians. From the facts that, although natural selection had been formulated by several writers before Darwin, and had been simultaneously elaborated by Wallace and Darwin, the Origin of Species was the foundation of the modern acceptation of evolution, and natural selection was the key-note of the origin of species, natural selection may be called Darwinism with both historical and scientific accuracy; and in this sense of the term Huxley was a Darwinian; a convinced but free-thinking and broad-minded Darwinian, who was far from persuaded that his tenet had a monopoly of truth, and who delighted in shewing the distinctions between what seemed to him probable and what was proved, and in absorbing from other doctrines whatever he thought worthy to be absorbed. The present writer has thought it so important to distinguish between these two sides of the word Darwinism, that for the sake of clearness he has stated what he believes to be the truth of Huxley's relation to Darwin before beginning detailed exposition of it.
In consideration of Huxley's position before 1859, the most interesting feature of his zoölogical work is the gradual preparation that it was making in his mind for the doctrine of the Origin. He was like an engineer boring a tunnel through a mountain, but ignorant of how near he was to the pleasant valley on the other side; and, above all, ignorant how rapidly he was being met by a much more mighty excavation from the other side. To use what is perhaps a more exact simile: he was like a child with half the pieces of a puzzle-map, slowly linking them together as far as they would fit, and quite ignorant that presently the remaining half would suddenly be given him, and with almost no trouble would at once fit into the gaps he had necessarily left, and transform a meaningless pattern into a perfect and intelligible whole. Let us consider some of these map pieces. The ultimate picture was the conception of the whole world of life, past and present, as a single family tree growing up from the simplest possible roots, and gradually spreading out first into the two main branches of animals and plants, and then into the endless series of complicated ramifications that make up living and extinct animals and plants. Huxley was piecing together the scattered fragments, and gradually learning to see here and there whole branches, as yet separate at their lower ends, but in themselves shapely, and showing a general resemblance to one another in the gradual progression from simple to complex. The greatest of these branches that he had pieced together was the group of Medusæ and their allies, now known as Cœlenterates. He had formed similar branches for the Molluscs and minor branches for the Salps and Ascidians, and, in his general lectures on the whole animal kingdom, he had shadowed out the broad arrangement of the main divisions, or, as he called them, types. He had seen in each particular branch the clearest evidence of the laws of growth which had directed its development, and had realised that these laws of growth, consisting of gradual modifications of common typical structures, were identical in the different branches. He had taken clear hold of Von Baer's conception that the younger stages of different types were more alike than the adult stages, and here and there he had made comparisons between the younger stages or simplest forms of his different branches, and had shown that, without completely realising it, he was ready for the idea that just as the separate pieces could be arranged to form orderly branches, so the separate branches might come to be arranged as a single tree. And finally, in his lectures on "Protoplasm and Cells," and on the "Common Structure of the Animal and Plant Kingdoms," he had reached the conclusion that the two main divisions of the living world were formed of the same stuff, displayed in identical fashion the elementary functions of life, and were creatures of the same order. But, notwithstanding this close approach to modern conceptions, he was not an evolutionist. When, in public, he expressed deliberate convictions, these convictions were against the general idea of evolution, until very shortly before 1859. In this opposition he was supported partly by the critical scepticism of his mind, which in all things made him singularly unwilling to accept any theories of any kind, but chiefly from the fact that the books of the two chief supporters of evolutionary conceptions impressed him very unfavourably. Huxley writes:
"I had studied Lamarck attentively, and I had read the Vestiges with due care; but neither of them afforded me any good ground for changing my negative and critical attitude. As for the Vestiges, I confess that the book simply irritated me by the prodigious ignorance and thoroughly unscientific habit of mind manifested by the writer. If it had any influence on me at all, it set me against evolution; and the only review I ever have qualms of conscience about, on the ground of needless savagery is one I wrote on the Vestiges while under that influence. With respect to the Philosophie Zoologique, it is no reproach to Lamarck to say that the discussion of the species question in that work, whatever might be said for it in 1809, was miserably below the level of the knowledge of half a century later. In that interval of time, the elucidation of the structure of the lower animals and plants had given rise to wholly new conceptions of their relations; histology and embryology, in the modern sense, had been created; physiology had been reconstituted; the facts of distribution, geological and geographical, had been prodigiously multiplied and reduced to order. To any biologist whose studies had carried him beyond mere species-mongering, in 1850 one-half of Lamarck's arguments were obsolete, and the other half erroneous or defective, in virtue of omitting to deal with the various classes of evidence which had been brought to light since his time. Moreover his one suggestion as to the cause of the gradual modification of species—effort excited by change of conditions—was, on the face of it, inapplicable to the whole vegetable world. I do not think that any impartial judge who reads the Philosophie Zoologique now, and who afterwards takes up Lyell's trenchant and effective criticism (published as far back as 1830) will be disposed to allot to Lamarck a much higher place in the establishment of biological evolution than that which Bacon assigns to himself in relation to physical science generally—buccinator tantum".
On the other hand, Huxley's friendship with Darwin and with Lyell began to make him less certain about the fixity of species. He tells us that during his first interview with Darwin, which occurred soon after his return from the Rattlesnake, he
"expressed his belief in the sharpness of the lines of demarcation between natural groups and in the absence of transitional forms, with all the confidence of youth and imperfect knowledge. I was not aware at that time that he had been many years brooding over the species question; and the humorous smile which accompanied his gentle answer, that such was not altogether his view, long haunted and puzzled me."