CHAPTER VI.
Characters as Hereditary and Acquired
(conclusion[84]).
In the foregoing chapters I have endeavoured to be, before all things, impartial; and if it seems that I have been arguing chiefly in favour of the Lamarckian principles, this has been because the only way of examining the question is to consider what has to be said on the affirmative side, and then to see what the negative side can say in reply. Before we are entitled to discard the Lamarckian factors in toto, we must be able to destroy all evidence of their action. This, indeed, is what the ultra-Darwinians profess to have done. But is not their profession premature? Is it not evident that they have not sufficiently considered certain general facts of nature, or certain particular results of experiment, which at all events appear inexplicable by the theory of natural selection alone? In any case the present discussion has been devoted mainly to indicating such general facts and particular results. If I have fallen into errors, either of statement or of reasoning, it is for the ultra-Darwinians to correct them; but it may be well to remark beforehand, that any criticism of a merely general kind touching the comparative paucity of the facts thus adduced in favour of Lamarckian doctrine, will not stand as a valid criticism. For, as we have seen in the opening part of the discussion, even if use-inheritance and direct action of the environment have been of high importance as factors of organic evolution, it must be in almost all cases impossible to dissociate their influence from that of natural selection—at any rate where plants and animals in a state of nature are concerned. On the other hand, experiments expressly devised to test the question have not hitherto been carried out. Besides, the facts and arguments here adduced are but comparatively few. For, unless it can be shown that what has been said of reflex action, instinct, so-called "self-adaptation" in plants, &c., is wrong in principle, the facts which tell in favour of Lamarckian theory are absolutely very numerous. Only when considered in relation to cases where we are unable to exclude the conceivable possibility of natural selection having been at work, can it be said that the facts in question are not numerous.
Comparatively few, then, though the facts may be of which I have given some examples, in my opinion they are amply sufficient for the purpose in hand. This purpose is to show that the question which we are now considering is very far from being a closed question; and, therefore, that the school of Weismann is much too precipitate in alleging that there is neither any necessity for, nor evidence of, the so-called Lamarckian factors[85]. And this opinion, whatever it may be worth, is at all events both deliberate and impartial. As one of the first to doubt the transmission of acquired characters, and as one who has spent many years in experimental inquiries upon the subject, any bias that I may have is assuredly against the Lamarckian principles—seeing that nearly all my experiments have yielded negative results. It was Darwin himself who checked this bias. But if the ultra-Darwinians of the last ten years had succeeded in showing that Darwin was mistaken, I should be extremely glad to fall into line with them. As already shown, however, they have in no way affected this question as it was left by Galton in 1875. And if it be supposed a matter of but little importance whether we agree with Galton in largely diminishing the comparative potency of the Lamarckian principles, or whether we agree with Weismann in abolishing them together, it cannot be too often repeated that such is an entirely erroneous view. No matter how faintly or how fitfully acquired characters may be transmitted, in so far as they are likewise adaptive characters, their transmission (and therefore their development) must be cumulative. Hence, the only effect of attenuating our estimate of their intensity, is that of increasing our estimate of their duration—i.e. of the time over which they have to operate in order to produce important results. And, even so, it is to be remembered that the importance of such results is not to be estimated by the magnitude of modification. Far more is it to be estimated by the character of modification as adaptive. For if functionally produced changes, and changes produced in adaptive response to the environment, are ever transmitted in a cumulative manner, a time must sooner or later arrive when they will reach a selective value in the struggle for existence—when, of course, they will be rapidly augmented by natural selection. Thus, if in any degree operative at all, the great function of these principles must be that of supplying to natural selection those incipient stages of adaptive modifications in all cases where, but for their agency, there would have been nothing of the kind to select. Themselves in no way dependent on adaptive modifications having already attained a selective value, these Lamarckian principles are (under the Darwinian theory) direct causes of determinate variation in adaptive lines; and variation in those lines being cumulative, the result is that natural selection is in large part presented with the raw material of its manufacture—special material of the particular kinds required, as distinguished from promiscuous material of all kinds. And the more complex the manufacture the more important will be the work of this subordinate factory. We can well imagine how the shell of a nut, for instance, or even the protective colouring of an insect, may have been gradually built up by natural selection alone. But just in proportion as structures or organs are not merely thus of passive use (where, of course, the Lamarckian principles cannot obtain), but require to be actively used, in that proportion does it become difficult to understand the incipient construction of them by natural selection alone. Therefore, in many such cases, if the incipient construction is not to be explained by the Lamarckian principles, it is difficult to see how it is to be explained at all.
Furthermore, since the question as to the transmission of acquired characters stands now exactly as it did after the publication of Mr. Galton's Theory of Heredity twenty years ago, it would seem that our judgement with regard to it should remain exactly what it was then. Although we must "out-Darwin Darwin" to the extent of holding that he assigned too large a measure of intensity to the Lamarckian factors, no sufficient reason has been shown for denying the existence of these factors in toto; while, on the other hand, there are certain general considerations, and certain particular facts, which appear to render it probable that they have played a highly important part in the process of organic evolution as a whole. At the same time, and in the present state of our information, this judgement must be deemed provisional, or liable eventually to be overturned by experimental proof of the non-inheritance of acquired characters. But, even if this should ever be finally accomplished, the question would still remain whether the principle of natural selection alone is capable of explaining all the facts of adaptation; and, for my own part, I should then be disposed to believe that there must be some other, though hitherto undiscovered, principle at work, which co-operates with natural selection, by playing the subordinate role which was assigned by Darwin to the principles of Lamarck.
Finally, let it be noted that no part of the foregoing argument is to be regarded as directed against the principle of what Professor Weismann calls "continuity." On the contrary, it appears to be self-evident that this principle must be accepted in some degree or another by every one, whether Darwinians, Neo-Darwinians, Lamarckians, Neo-Lamarckians, or even the advocates of special creation. Yet, to hear or to read some of the followers of Weismann, one can only conclude that, prior to his publications on the subject, they had never thought about it at all. These naturalists appear to suppose that until then the belief of Darwinians was, that there could be no hereditary "continuity" between any one organic type and another (such, for instance, as between Ape and Man), but that the whole structure of any given generation must be due to "gemmules" or "somato-plasm," derived exclusively from the preceding generation. Nothing can show more ignorance, or more thoughtlessness, with regard to the whole subject. The very basis of the general theory of evolution is that there must always have been a continuity in the material substance of heredity since the time when the process of evolution began; and it was not reserved for our generation, or even for our century, to perceive the special nature of this material substance in the case of sexual organisms. No, the real and the sole question, where Weismann's theory of heredity is concerned, is simply this—Are we to hold that this material substance has been absolutely continuous "since the first origin of sexual propagation," always occupying a separate "sphere" of its own, at all events to the extent of never having been modified by the body substance in which it resides (Lamarckian factors); or, are we to hold that this "germ-plasm," "stirp," or "formative-material," has been but relatively continuous, so as to admit of some amount of commerce with body-substance, and therefore to admit of acquired characters, when sufficiently long continued as such, eventually becoming congenital? If this question be answered in the latter sense, of course the further question arises as to the degree of such commerce, or the time during which acquired characters must continue to be acquired in successive generations before they can sufficiently impress themselves on the substance of heredity to become congenital. But this is a subordinate question, and one which, in the present state of our information, it seems to me almost useless to speculate upon. My own opinion has always been the same as that of Mr. Galton; and my belief is that eventually both Weismann and his followers will gravitate into it. It was in order to precipitate this result as far as possible that I wrote the Examination. If it ever should be accomplished, Professor Weismann's elaborate theory of evolution will have had its bases removed.