Darwinians of the stamp of Mr. Thiselton Dyer, Professor Ray Lankester, or Mr. Romanes, insist on their pound of flesh in the matter of irrefragable demonstration. They complain of us for not bringing forward some one who has been able to detect the movement of the hour-hand of a watch during a second of time, and when we fail to do so, declare triumphantly that we have no evidence that there is any connection between the beating of a second and the movement of the hour-hand. When we say that rain comes from the condensation of moisture in the atmosphere, they demand of us a rain-drop from moisture not yet condensed. If they stickle for proof and cavil on the ninth part of a hair, as they do when we bring forward what we deem excellent instances of the transmission of an acquired characteristic, why may not we, too, demand at any rate some evidence that the unmodified beetles actually did always, or nearly always, get blown out to sea, during the reduction above referred to, and that it is to this fact, and not to the masterly inactivity of their fathers and mothers, that the Madeira beetles owe their winglessness? If we began stickling for proof in this way, our opponents would not be long in letting us know that absolute proof is unattainable on any subject, that reasonable presumption is our highest certainty, and that crying out for too much evidence is as bad as accepting too little. Truth is like a photographic sensitised plate, which is equally ruined by over and by under exposure, and the just exposure for which can never be absolutely determined.
Surely if disuse can be credited with the vast powers involved in Mr. Darwin’s statement that it has probably “been the main agent in rendering organs rudimentary,” no limits are assignable to the accumulated effects of habit, provided the effects of habit, or use and disuse, are supposed, as Mr. Darwin supposed them, to be inheritable at all. Darwinians have at length woke up to the dilemma in which they are placed by the manner in which Mr. Darwin tried to sit on the two stools of use and disuse, and natural selection of accidental variations, at the same time. The knell of Charles-Darwinism is rung in Mr. Wallace’s present book, and in the general perception on the part of biologists that we must either assign to use and disuse such a predominant share in modification as to make it the feature most proper to be insisted on, or deny that the modifications, whether of mind or body, acquired during a single lifetime, are ever transmitted at all. If they can be inherited at all, they can be accumulated. If they can be accumulated at all, they can be so, for anything that appears to the contrary, to the extent of the specific and generic differences with which we are surrounded. The only thing to do is to pluck them out root and branch: they are as a cancer which, if the smallest fibre be left unexcised, will grow again, and kill any system on to which it is allowed to fasten. Mr. Wallace, therefore, may well be excused if he casts longing eyes towards Weismannism.
And what was Mr. Darwin’s system? Who can make head or tail of the inextricable muddle in which he left it? The “Origin of Species” in its latest shape is the reduction of hedging to an absurdity. How did Mr. Darwin himself leave it in the last chapter of the last edition of the “Origin of Species”? He wrote:—
“I have now recapitulated the facts and considerations which have thoroughly convinced me that species have been modified during a long course of descent. This has been effected chiefly through the natural selection of numerous, successive, slight, favourable variations; aided in an important manner by the inherited effects of the use and disuse of parts, and in an unimportant manner—that is, 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.”
The “numerous, successive, slight, favourable variations” above referred to are intended to be fortuitous, accidental, spontaneous. It is the essence of Mr. Darwin’s theory that this should be so. Mr. Darwin’s solemn statement, therefore, of his theory, after he had done his best or his worst with it, is, when stripped of surplusage, as follows:—
“The modification of species has been mainly effected by accumulation of spontaneous variations; it has been aided in an important manner by accumulation of variations due to use and disuse, and in an unimportant manner by spontaneous variations; I do not even now think that spontaneous variations have been very important, but I used once to think them less important than I do now.”
It is a discouraging symptom of the age that such a system should have been so long belauded, and it is a sign of returning intelligence that even he who has been more especially the alter ego of Mr. Darwin should have felt constrained to close the chapter of Charles-Darwinism as a living theory, and relegate it to the important but not very creditable place in history which it must henceforth occupy. It is astonishing, however, that Mr. Wallace should have quoted the extract from the “Origin of Species” just given, as he has done on p. 412 of his “Darwinism,” without betraying any sign that he has caught its driftlessness—for drift, other than a desire to hedge, it assuredly has not got. The battle now turns on the question whether modifications of either structure or instinct due to use or disuse are ever inherited, or whether they are not. Can the effects of habit be transmitted to progeny at all? We know that more usually they are not transmitted to any perceptible extent, but we believe also that occasionally, and indeed not infrequently, they are inherited and even intensified. What are our grounds for this opinion? It will be my object to put these forward in the following number of the Universal Review.
THE DEADLOCK IN DARWINISM—PART II [29]
At the close of my article in last month’s number of the Universal Review, I said I would in this month’s issue show why the opponents of Charles-Darwinism believe the effects of habits acquired during the lifetime of a parent to produce an effect on their subsequent offspring, in spite of the fact that we can rarely find the effect in any one generation, or even in several, sufficiently marked to arrest our attention.
I will now show that offspring can be, and not very infrequently is, affected by occurrences that have produced a deep impression on the parent organism—the effect produced on the offspring being such as leaves no doubt that it is to be connected with the impression produced on the parent. Having thus established the general proposition, I will proceed to the more particular one—that habits, involving use and disuse of special organs, with the modifications of structure thereby engendered, produce also an effect upon offspring, which, though seldom perceptible as regards structure in a single, or even in several generations, is nevertheless capable of being accumulated in successive generations till it amounts to specific and generic difference. I have found the first point as much as I can treat within the limits of this present article, and will avail myself of the hospitality of the Universal Review next month to deal with the second.