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and their proper place in the scheme of nature, the light that was shed by the new theory upon the subsidiary departments of embryology, palæontology, and distribution, the stimulus that was given to every branch of biological inquiry, all contributed to make the epoch a memorable one in the history of science, and to raise the conception of organic evolution to a position infinitely more important in the realm of thought than it had ever occupied before. The doctrine had never been left quite without a witness, but its supporters had for long become a mere remnant. Lamarck had failed to influence his contemporaries; Buffon could not even convince himself. But with the appearance of the Origin of Species the scene was changed. Huxley, Hooker, and Asa Gray, soon followed by Lyell, boldly ranged themselves on the side of Darwin, and the vox clamantis in deserto was speedily taken up by the combined shout of a great army.
At this point it is important to note that, undeniable as was the effect of Darwin's work in procuring acceptance for the theory of evolution, first among men of science, and then among the cultivated public at large, the converts that it made did not always adopt the actual Darwinian standpoint, Huxley, for example, though welcoming the suggestion of natural selection with the characteristic remark, "How extremely stupid not to have thought of that!" and though constantly keeping it in view as the best if not the only working hypothesis available, yet preserved to the end a certain scepticism as to its adequacy to perform the results claimed on its behalf. He was rather converted by than to natural selection, and the same was no doubt true of many others. Herbert Spencer, though already a supporter of evolution before the appearance of the Origin, has al'ways been inclined to limit the action
of natural selection within somewhat narrow boundaries. With Wallace, on the other hand, natural selection has been from the first the all-important factor.
The position of Darwin himself requires to be examined with some care. This is a subject on which misapprehension and misstatement are rife. It is perfectly justifiable to distinguish, as Huxley did, between the central theory of evolution and the particular views as to its methods and causes which were adopted by Darwin. Moreover it is most certainly the case that the really essential part of Darwin's presentment of the theory of evolution was the use that he made of the principle of natural selection. This is rightly fixed upon as the distinctive feature of his teaching. But it is not true to say, on the one hand, that the only factor in evolution admitted by Darwin was natural selection, nor, on the other hand, is it allowable to claim Darwin as a kind of disciple of Lamarck. Darwin's attitude towards the various factors suggested by Lamarck and Buffon, and his final estimate of their importance in relation to natural selection, have been so clearly stated by himself that it is surprising that any doubt on the matter should ever have arisen. As, however, his views on these points are still often misstated by speakers and writers whose words command respect, it may not be out of place once more to print his own emphatic declaration as given in the sixth edition of the Origin.
in relation to adaptive structures, whether past or present, by the direct action of external conditions, and by variations which seem to us in our ignorance to arise spontaneously. It appears that I formerly underrated the frequency and value of these latter forms of variation, as leading to permanent modifications of structure independently of natural selection. But as my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position-namely, at the close of the Introduction-the following words: 'I am convinced that natural selection has been the main ' but not the exclusive means of modification.''
From this and other passages it is abundantly clear that in Darwin there met two distinct lines of evolutionary theory. The words just quoted.contain an explicit recognition of Lamarck's and of Buffon's factors as auxiliaries to Darwin's own factor of natural selection. The first (the inherited effects of use and disuse) is spoken of as important, the second (the direct action of external conditions) as unimportant, but each is admitted as a vera causa. So far as Darwin was concerned, his own great illuminating principle of natural selection supplied what was wanting in the Lamarckian system, but did not entirely supersede it. There was room for Buffon's "direct action of the environment," and for Lamarck's "use and disuse of parts," by the side of Darwin's "natural selection."
So matters rested for a time, and as most believers in evolution, whether they were inclined to estimate natural selection at a high or at a low rate, found at least some part of Darwin's
In the sixth edition the words of the Introduction are, "the most important, but not the exclusive means of modification."
teaching agreeable to their views, there was little or no disposition to dispute his claim to the first place among exponents of the doctrine of development. But during the last twenty years the case has altered. The apple of discord has been thrown into the midst of the evolutionists' array, with the result of causing them to draw apart into two hostile camps, between which at present there seems small prospect of a reconciliation. The first name to be generally associated with the new evolutionary movement was that of Professor Weismann, to whose share in the controversy we now propose to devote some attention.
It will be evident to anyone who has appreciated the nature of the "Lamarckian factors" that they necessarily include the hereditary transmission of characters acquired by the individual. If the effects of use and disuse are confined to a single generation, it is plain that they cannot be invoked as the agents of progressive modification. It is only if the whole or at least a part of what has thus been gained by the individual is handed on to the offspring that the changes produced in that individual will take any share in the development of the race. That this self-evident truth was never looked upon as an objection to the views of Buffon and Lamarck was due to the remarkable fact that scarcely anyone had thought of questioning the power of heredity to transmit in a greater or less degree the characters that are known as "somatogentic," or, as Lloyd Morgan expresses it, "modifications due to individual plasticity." When, therefore, Weismann put forward his theory of the "continuity of the germ-plasm," which involved a denial of the hereditary transmission of somatogenetic characters, it had the effect of a bolt from the blue. It is true that similar views had been advanced nearly sixty years earlier by the great pioneer of
anthropology James Cowles Prichard, and also by Francis Galton in 1872, but it was reserved for Weismann to compel universal interest in the question, and to bring home to the defenders of the validity of the Lamarckian factors the necessity of proving their fundamental tenet of the transmission of acquired as distinct from congenital (or Inborn) characters. So much had this power of transmission been taken for granted, that it was difficult at first to convince many of its upholders that there was anything to argue about. In time, however, the wide difference with respect to heredity between "somatogenetic" and "blastogenetic" characters, i.e. between those imprinted on the body and those which take their origin from the germ, began to be generally recognized; and it was seen that the inheritance of the former in any degree, whether great or small, could not be regarded as an axiom. The burden of proof, therefore, was naturally considered to devolve upon those evolutionists who, like Herbert Spencer in this country and many others both in Europe and America, still maintained the species-forming capability of the Lamarckian factors to the partial, if not complete, exclusion of natural selection. The challenge has been taken up with vigor, and many attempts at the required proof have been made; but it cannot with truth be alleged that the Lamarckian view of the hereditary transmission of acquired characters rests as yet on a firm basis of either observation or experiment. All the facts hitherto brought forward in its support have proved capable of explanation on other lines; while the a priori difficulties in its way are, on physiological grounds, very great. There is, of course, no warrant for absolutely denying the possibility of such a phenomenon, but that little or nothing has yet been done to establish it as a fact is the opinion of many lead
ing evolutionists, among whom it may be sufficient to specify Professors Poulton, Lloyd Morgan, Karl Pearson, Meldola, Spengel, and Cossar Ewart, together with thoughtful writers like Mr. Headley (the author of Problems of Evolution) and the veteran Alfred Russel Wallace.
The validity of natural selection stands, of course, entirely outside the present controversy, for the existence of the individual variations which form the material for the selective process is an absolutely indisputable fact. Whether the diverse characters shown by these variations are "congenital," "centrifugal," "blastogenetic" on the one hand, or "acquired," "centripetal," "somatogenetic" on the other, makes no difference to the selective process, which, if it acts at all, must act indifferently on all the material presented to it, however that material may have originated. What is really at stake, therefore, in the issue between the supporters and the impugners of the "transmission of acquired characters" the claim to consideration of the factors alleged by Lamarck and Buffon; not the Darwinian principle of natural selection, which in the logical sense is entirely compatible with either view. Darwin himself, as we have seen, accepted Lamarckism as an auxiliary; the position of Romanes was not greatly dissimilar; and at the present day Plate in Germany argues stoutly in favor both of the potency of natural selection and of the transmission of characters individually acquired. Nevertheless there can be no doubt that, in spite of the efforts of "reconcilers" like Plate, there is now becoming visible a wellmarked cleavage in the ranks of evolutionists. The challenge thrown down by Weismann has had the effect of making the adherents of the Darwinian principle of natural selection reconsider their position with regard to the La
marckian factors. To many, if not to most of them, it has seemed that as natural selection is under no logical necessity for calling those factors to its aid, and as an indispensable link in the chain of evidence in their favor is still wanting, it is best to ignore them altogether, and to explain the course of organic evolution entirely on the basis of natural selection. To evolutionists of this school the name "Neo-Darwinian" is commonly applied-not without protest from their opponents, who point with justice to the fact that Darwin never denied the efficiency of the Lamarckian factors, and finally came to regard them with greater favor than at first. Still, inasmuch as the whole of Darwin's work was done under the inspiration of the principle of natural selection, as witness the full title of the Origin, and inasmuch as it is the adoption of this principle that constitutes the distinctive feature of his contribution to evolutionary theory, the immense importance and far-reaching influence of which contribution none will dispute, we think the school we have mentioned quite justified in continuing to rank themselves under the name of the great English evolutionist. The disposition to reject the Darwinian compromise is also seen in the formation of the hostile party of "NeoLamarckians," who, undeterred by the serious flaw in their case which has been already pointed out, are becoming more and more inclined to rely upon supposed "laws of growth," "orthogenesis," use-inheritance, and the transmission of the direct effects of the environment; to the minimizing or even the complete exclusion of natural selection. It is, of course, impossible to say what line Darwin would himself have taken in view of the present aspect of the controversy. We may, how ever, fairly regard it as inconceivable, or at least in the highest degree improbable, that he would ever have giv
en up natural selection. On the other hand Romanes assures us from private knowledge that the question of the transmissibility of acquired characters was constantly before Darwin's mind during the last few years of his life, and that he deliberately refused to renounce his belief in it. Nevertheless, when we consider the position now occupied by those biologists who have always been most in sympathy with Darwin's own views and methods, there seems to be fair ground for the conjecture that Darwin himself would eventually have been affected by the same scepticism with regard to the fundamental Lamarckian tenet. That he would have maintained the exact position indicated by the last edition of the Origin of Species is hard to believe.
The foregoing will have made clear what is meant by those who affirm that "Weismann is more Darwinian than Darwin himself." Weismann follows Darwin in adopting the principle of natural selection; he out-Darwins Darwin in sweeping all relics of Lamarckism out of his system, and in carrying the doctrine of selection into regions which Darwin left unexplored. But although from this point of view Weismann may be fairly described as an extreme Darwinian, there is another aspect of the matter in which, paradoxical as it may seem, he and Darwin are at opposite poles. To this we shall be brought by returning for a moment to Weismann's famous theory of heredity, which may be summed up in brief as the "continuity of the germ-plasm."
It is important that a clear distinction should be drawn between this latter question and that of the alleged transmission of acquired characters. The continuity of the germ-plasm, or reproductive material, from generation to generation, the bodies of successive individuals being regarded merely as buds from a perennial
stock, is a theory devised to account for the observed facts of inheritance, and with our present means of research is hardly capable of direct verification. The onus probandi of such a theory undoubtedly rests with its propounder. The transmission of acquired characters, on the other hand, is not so much a theory as a simple question of fact. Does it happen or does it not? Here it would seem that those who affirm that it does happen are bound to show when it occurs and where. Those who deny it, like Weismann, are simply appealing to the universal experience of mankind. The Chinese infant at birth has well-formed feet; nor is a young fox-terrier born with its ears and tail ready cropped. But instead of producing their evidence, the Neo-Lamarckians now seem inclined to rely on the often-repeated assertion that "Weismann has not proved his point." It may be perfectly true that he has not proved his theory of the germ-plasm, the verification of which in any case must needs be a most difficult undertaking; but these critics are apt to forget that the transmission of acquired characters, though it would fall of itself if Weismann could prove not only the continuity but also the stability of the germ-plasm, is not established by his failure to do so. The transmission doctrine must either be proved by its supporters or must be allowed to go by default. The universal negative of Weismann could be met by a particular affirmative. Why is the latter not forthcoming? The scientific world still waits for a single unequivocal instance of a character acquired by an organism in virtue of its individual plasticity, and passed on by inheritance to a succeeding generation.
We see, then, that Weismann's denial of the inheritance of acquired characters, though connected with his
theory of the continuity of the germplasm, does not necessarily stand or fall with that theory. The common failure to distinguish between the two positions is answerable for a great deal of misunderstanding which might easily have been avoided. It may be suspected that another source of misapprehension is to be found in Darwin's use of the term "pangenesis." To many people who get their ideas on these subjects at secondhand, the expression "theory of pangenesis" simply conveys the notion of a belief in the descent of all forms of life from a common stock. When, therefore, they hear it stated that the ultra-Darwinian Weismann's view of descent is diametrically opposed to Darwin's theory of pangenesis, they are nat urally puzzled. The fact is that "pangenesis" has nothing to do with the action of natural selection. The term is merely used by Darwin to express his conception of the relation of the reproductive material to the parent organism. According to Weismann, individuals are not manufacturers but only nourishers and carriers of the germ-plasm. This germplasm they have received from their ancestors; in due time they produce descendants,
Et quasi cursores vitai lampada tradunt.
In Darwin's view of the process of heredity the germ-plasm of the individual is not derived directly as such from the germ-plasm of the parent, but is constituted and reinforced by contributions from every part of the body of the individual itself: whence the term pangenesis. According to Weismann the germ makes the body; according to Darwin the body makes the germ. The opposition between these two views, which are sometimes spoken of respectively as "centrifugal" and "centripetal," is obvious, as