Essays on Life, Art and Science Part 9

"'1st. Appearance of epilepsy in animals born of parents having been rendered epileptic by an injury to the spinal cord.

"'2nd. Appearance of epilepsy also in animals born of parents having been rendered epileptic by the section of the sciatic nerve.

"'3rd. A change in the shape of the ear in animals born of parents in which such a change was the effect of a division of the cervical sympathetic nerve.

"'4th. Partial closure of the eyelids in animals born of parents in which that state of the eyelids had been caused either by the section of the cervical sympathetic nerve or the removal of the superior cervical ganglion.

"'5th. Exophthalmia in animals born of parents in which an injury to the restiform body had produced that protrusion of the eyeball. This interesting fact I have witnessed a good many times, and I have seen the transmission of the morbid state of the eye continue through four generations. In these animals modified by heredity, the two eyes generally protruded, although in the parents usually only one showed exophthalmia, the lesion having been made in most cases only on one of the corpora restiformia.

"'6th. Haematoma and dry gangrene of the ears in animals born of parents in which these ear-alterations had been caused by an injury to the restiform body near the nib of the calamus.

"'7th. Absence of two toes out of the three of the hind leg, and sometimes of the three, in animals whose parents had eaten up their hind- leg toes which had become anaesthetic from a section of the sciatic nerve alone, or of that nerve and also of the crural. Sometimes, instead of complete absence of the toes, only a part of one or two or three was missing in the young, although in the parent not only the toes but the whole foot was absent (partly eaten off, partly destroyed by inflammation, ulceration, or gangrene).

"'8th. Appearance of various morbid states of the skin and hair of the neck and face in animals born of parents having had similar alterations in the same parts, as effects of an injury to the sciatic nerve.'

"It should be especially observed that Brown-Sequard has bred during thirty years many thousand guinea-pigs from animals which had not been operated upon, and not one of these manifested the epileptic tendency.

Nor has he ever seen a guinea-pig born without toes, which was not the offspring of parents which had gnawed off their own toes owing to the sciatic nerve having been divided. Of this latter fact thirteen instances were carefully recorded, and a greater number were seen; yet Brown-Sequard speaks of such cases as one of the rarer forms of inheritance. It is a still more interesting fact, 'that the sciatic nerve in the congenitally toeless animal has inherited the power of pa.s.sing through all the different morbid states which have occurred in one of its parents from the time of the division till after its reunion with the peripheric end. It is not, therefore, simply the power of performing an action which is inherited, but the power of performing a whole series of actions, in a certain order.'

"In most of the cases of inheritance recorded by Brown-Sequard only one of the two parents had been operated upon and was affected. He concludes by expressing his belief that 'what is transmitted is the morbid state of the nervous system,' due to the operation performed on the parents."

Mr. Darwin proceeds to give other instances of inherited effects of mutilations:--

"With the horse there seems hardly a doubt that exostoses on the legs, caused by too much travelling on hard roads, are inherited. Blumenbach records the case of a man who had his little finger on the right hand almost cut off, and which in consequence grew crooked, and his sons had the same finger on the same hand similarly crooked. A soldier, fifteen years before his marriage, lost his left eye from purulent ophthalmia, and his two sons were microphthalmic on the same side."

The late Professor Rolleston, whose competence as an observer no one is likely to dispute, gave Mr. Darwin two cases as having fallen under his own notice, one of a man whose knee had been severely wounded, and whose child was born with the same spot marked or scarred, and the other of one who was severely cut upon the cheek, and whose child was born scarred in the same place. Mr. Darwin's conclusion was that "the effects of injuries, especially when followed by disease, or perhaps exclusively when thus followed, are occasionally inherited."

Let us now see what Professor Weismann has to say against this. He writes:--

"The only cases worthy of discussion are the well-known experiments upon guinea-pigs conducted by the French physiologist, Brown-Sequard. But the explanation of his results is, in my opinion, open to discussion. In these cases we have to do with the apparent transmission of artificially produced malformations . . . All these effects were said to be transmitted to descendants as far as the fifth or sixth generation.

"But we must inquire whether these cases are really due to heredity, and not to simple infection. In the case of epilepsy, at any rate, it is easy to imagine that the pa.s.sage of some specific organism through the reproductive cells may take place, as in the case of syphilis. We are, however, entirely ignorant of the nature of the former disease. This suggested explanation may not perhaps apply to the other cases; but we must remember that animals which have been subjected to such severe operations upon the nervous system have sustained a great shock, and if they are capable of breeding, it is only probable that they will produce weak descendants, and such as are easily affected by disease. Such a result does not, however, explain why the offspring should suffer from the same disease as that which was artificially induced in the parents.

But this does not appear to have been by any means invariably the case.

Brown-Sequard himself says: 'The changes in the eye of the offspring were of a very variable nature, and were only occasionally exactly similar to those observed in the parents.'

"There is no doubt, however, that these experiments demand careful consideration, but before they can claim scientific recognition, they must be subjected to rigid criticism as to the precautions taken, the nature and number of the control experiments, &c.

"Up to the present time such necessary conditions have not been sufficiently observed. The recent experiments themselves are only described in short preliminary notices, which, as regards their accuracy, the possibility of mistake, the precautions taken, and the exact succession of individuals affected, afford no data on which a scientific opinion can be founded" (pp. 81, 82).

The line Professor Weismann takes, therefore, is to discredit the facts; yet on a later page we find that the experiments have since been repeated by Obersteiner, "who has described them in a very exact and unprejudiced manner," and that "the fact"--(I imagine that Professor Weismann intends "the facts")--"cannot be doubted."

On a still later page, however, we read:--

"If, for instance, it could be shown that artificial mutilation spontaneously reappears in the offspring with sufficient frequency to exclude all possibilities of chance, then such proof [_i.e._, that acquired characters can be transmitted] would be forthcoming. The transmission of mutilations has been frequently a.s.serted, and has been even recently again brought forward, but all the supposed instances have broken down when carefully examined" (p. 390).

Here, then, we are told that proof of the occasional transmission of mutilations would be sufficient to establish the fact, but on p. 267 we find that no single fact is known which really proves that acquired characters can be transmitted, "_for the ascertained facts which seem to point to the transmission of artificially produced diseases cannot be considered as proof_" [Italics mine.] Perhaps; but it was mutilation in many cases that Professor Weismann practically admitted to have been transmitted when he declared that Obersteiner had verified Brown-Sequard's experiments.

That Professor Weismann recognises the vital importance to his own theory of the question whether or no mutilations can be transmitted under any circ.u.mstances, is evident from a pa.s.sage on p. 425 of his work, on which he says: "It can hardly be doubted that mutilations are acquired characters; they do not arise from any tendency contained in the germ, but are merely the reaction of the body under certain external influences. They are, as I have recently expressed it, purely somatogenic characters--viz., characters which emanate from the body (_soma_) only, as opposed to the germ-cells; they are, therefore, characters that do not arise from the germ itself.

"If mutilations must necessarily be transmitted" [which no one that I know of has maintained], "or even if they might occasionally be transmitted" [which cannot, I imagine, be reasonably questioned], "a powerful support would be given to the Lamarckian principle, and the transmission of functional hypertrophy or atrophy would thus become highly probable."

I have not found any further attempt in Professor Weismann's book to deal with the evidence adduced by Mr. Darwin to show that mutilations, if followed by diseases, are sometimes inherited; and I must leave it to the reader to determine how far Professor Weismann has shown reason for rejecting Mr. Darwin's conclusion. I do not, however, dwell upon these facts now as evidence of a transmitted change of bodily form, or of instinct due to use and disuse or habit; what they prove is that the germ- cells within the parent's body do not stand apart from the other cells of the body so completely as Professor Weismann would have us believe, but that, as Professor Hering, of Prague, has aptly said, they echo with more or less frequency and force to the profounder impressions made upon other cells.

I may say that Professor Weismann does not more cavalierly wave aside the ma.s.s of evidence collected by Mr. Darwin and a host of other writers, to the effect that mutilations are sometimes inherited, than does Mr.

Wallace, who says that, "as regards mutilations, it is generally admitted that they are not inherited, and there is ample evidence on this point."

It is indeed generally admitted that mutilations, when not followed by disease, are very rarely, if ever, inherited; and Mr. Wallace's appeal to the "ample evidence" which he alleges to exist on this head, is much as though he should say that there is ample evidence to show that the days are longer in summer than in winter. "Nevertheless," he continues, "a few cases of apparent inheritance of mutilations have been recorded, and these, if trustworthy, are difficulties in the way of the theory." . . .

"The often-quoted case of a disease induced by mutilation being inherited (Brown-Sequard's epileptic guinea-pigs) has been discussed by Professor Weismann and shown to be not conclusive. The mutilation itself--a section of certain nerves--was never inherited, but the resulting epilepsy, or a general state of weakness, deformity, or sores, was sometimes inherited. It is, however, possible that the mere injury introduced and encouraged the growth of certain microbes, which, spreading through the organism, sometimes reached the germ-cells, and thus transmitted a diseased condition to the offspring." {35}

I suppose a microbe which made guinea-pigs eat their toes off was communicated to the germ-cells of an unfortunate guinea-pig which had been already microbed by it, and made the offspring bite its toes off too. The microbe has a good deal to answer for.

On the case of the deterioration of horses in the Falkland Islands after a few generations, Professor Weismann says:--

"In such a case we have only to a.s.sume that the climate which is unfavourable, and the nutriment which is insufficient for horses, affect not only the animal as a whole but also its germ-cells. This would result in the diminution in size of the germ-cells, the effects upon the offspring being still further intensified by the insufficient nourishment supplied during growth. But such results would not depend upon the transmission by the germ-cells of certain peculiarities due to the unfavourable climate, which only appear in the full-grown horse."

But Professor Weismann does not like such cases, and admits that he cannot explain the facts in connection with the climatic varieties of certain b.u.t.terflies, except "by supposing the pa.s.sive acquisition of characters produced by the direct influence of climate."

Nevertheless in his next paragraph but one he calls such cases "doubtful," and proposes that for the moment they should be left aside.

He accordingly leaves them, but I have not yet found what other moment he considered auspicious for returning to them. He tells us that "new experiments will be necessary, and that he has himself already begun to undertake them." Perhaps he will give us the results of these experiments in some future book--for that they will prove satisfactory to him can hardly, I think, be doubted. He writes:--

"Leaving on one side, for the moment, these doubtful and insufficiently investigated cases, we may still maintain that the a.s.sumption that changes induced by external conditions in the organism as a whole are communicated to the germ-cells after the manner indicated in Darwin's hypothesis of pangenesis, is wholly unnecessary for the explanation of these phenomena. Still we cannot exclude the possibility of such a transmission occasionally occurring, for even if the greater part of the effects must be attributable to natural selection, there might be a smaller part in certain cases which depends on this exceptional factor."

I repeatedly tried to understand Mr. Darwin's theory of pangenesis, and so often failed that I long since gave the matter up in despair. I did so with the less unwillingness because I saw that no one else appeared to understand the theory, and that even Mr. Darwin's warmest adherents regarded it with disfavour. If Mr. Darwin means that every cell of the body throws off minute particles that find their way to the germ-cells, and hence into the new embryo, this is indeed difficult of comprehension and belief. If he means that the rhythms or vibrations that go on ceaselessly in every cell of the body communicate themselves with greater or less accuracy or perturbation, as the case may be, to the cells that go to form offspring, and that since the characteristics of matter are determined by vibrations, in communicating vibrations they in effect communicate matter, according to the view put forward in the last chapter of my book "Luck or Cunning," {36} then we can better understand it. I have nothing, however, to do with Mr. Darwin's theory of pangenesis beyond avoiding the pretence that I understand either the theory itself or what Professor Weismann says about it; all I am concerned with is Professor Weismann's admission, made immediately afterwards, that the somatic cells may, and perhaps sometimes do, impart characteristics to the germ-cells.

"A complete and satisfactory refutation of such an opinion," he continues, "cannot be brought forward at present"; so I suppose we must wait a little longer, but in the meantime we may again remark that, if we admit even occasional communication of changes in the somatic cells to the germ-cells, we have let in the thin end of the wedge, as Mr. Darwin did when he said that use and disuse did a good deal towards modification. Buffon, in his first volume on the lower animals, {37} dwells on the impossibility of stopping the breach once made by admission of variation at all. "If the point," he writes, "were once gained, that among animals and vegetables there had been, I do not say several species, but even a single one, which had been produced in the course of direct descent from another species; if, for example, it could be once shown that the a.s.s was but a degeneration from the horse--then there is no farther limit to be set to the power of Nature, and we should not be wrong in supposing that with sufficient time she could have evolved all other organised forms from one primordial type." So with use and disuse and transmission of acquired characteristics generally--once show that a single structure or instinct is due to habit in preceding generations, and we can impose no limit on the results achievable by acc.u.mulation in this respect, nor shall we be wrong in conceiving it as possible that all specialisation, whether of structure or instinct, may be due ultimately to habit.

How far this can be shown to be probable is, of course, another matter, but I am not immediately concerned with this; all I am concerned with now is to show that the germ-cells not unfrequently become permanently affected by events that have made a profound impression upon the somatic cells, in so far that they transmit an obvious reminiscence of the impression to the embryos which they go subsequently towards forming.

This is all that is necessary for my case, and I do not find that Professor Weismann, after all, disputes it.

But here, again, comes the difficulty of saying what Professor Weismann does, and what he does not, dispute. One moment he gives all that is wanted for the Lamarckian contention, the next he denies common-sense the bare necessaries of life. For a more exhaustive and detailed criticism of Professor Weismann's position, I would refer the reader to an admirably clear article by Mr. Sidney H. Vines, which appeared in _Nature_, October 24, 1889. I can only say that while reading Professor Weismann's book, I feel as I do when I read those of Mr. Darwin, and of a good many other writers on biology whom I need not name. I become like a fly in a window-pane. I see the sunshine and freedom beyond, and buzz up and down their pages, ever hopeful to get through them to the fresh air without, but ever kept back by a mysterious something, which I feel but cannot either grasp or see. It was not thus when I read Buffon, Erasmus Darwin, and Lamarck; it is not thus when I read such articles as Mr.

Vines's just referred to. Love of self-display, and the want of singleness of mind that it inevitably engenders--these, I suppose, are the sins that glaze the cas.e.m.e.nts of most men's minds; and from these, no matter how hard he tries to free himself, nor how much he despises them, who is altogether exempt?

Finally, then, when we consider the immense ma.s.s of evidence referred to briefly, but sufficiently, by Mr. Charles Darwin, and referred to without other, for the most part, than off-hand dismissal by Professor Weismann in the last of the essays that have been recently translated, I do not see how any one who brings an unbiased mind to the question can hesitate as to the side on which the weight of testimony inclines. Professor Weismann declares that "the transmission of mutilations may be dismissed into the domain of fable." {38} If so, then, whom can we trust? What is the use of science at all if the conclusions of a man as competent as I readily admit Mr. Darwin to have been, on the evidence laid before him from countless sources, is to be set aside lightly and without giving the clearest and most cogent explanation of the why and wherefore? When we see a person "ostrichising" the evidence which he has to meet, as clearly as I believe Professor Weismann to be doing, we shall in nine cases out of ten be right in supposing that he knows the evidence to be too strong for him.

THE DEADLOCK IN DARWINISM--PART III

Now let me return to the recent division of biological opinion into two main streams--Lamarckism and Weismannism Both Lamarckians and Weismannists, not to mention mankind in general, admit that the better adapted to its surroundings a living form may be, the more likely it is to outbreed its compeers. The world at large, again, needs not to be told that the normal course is not unfrequently deflected through the fortunes of war; nevertheless, according to Lamarckians and Erasmus-Darwinians, habitual effort, guided by ever-growing intelligence--that is to say, by continued increase of power in the matter of knowing our likes and dislikes--has been so much the main factor throughout the course of organic development, that the rest, though not lost sight of, may be allowed to go without saying. According, on the other hand, to extreme Charles-Darwinians and Weismannists, habit, effort and intelligence acquired during the experience of any one life goes for nothing. Not even a little fraction of it endures to the benefit of offspring. It dies with him in whom it is acquired, and the heirs of a man's body take no interest therein. To state this doctrine is to arouse instinctive loathing; it is my fortunate task to maintain that such a nightmare of waste and death is as baseless as it is repulsive.

The split in biological opinion occasioned by the deadlock to which Charles-Darwinism has been reduced, though comparatively recent, widens rapidly. Ten years ago Lamarck's name was mentioned only as a byword for extravagance; now, we cannot take up a number of _Nature_ without seeing how hot the contention is between his followers and those of Weismann.

This must be referred, as I implied earlier, to growing perception that Mr. Darwin should either have gone farther towards Lamarckism or not so far. In admitting use and disuse as freely as he did, he gave Lamarckians leverage for the overthrow of a system based ostensibly on the acc.u.mulation of fortunate accidents. In a.s.signing the lion's share of development to the acc.u.mulation of fortunate accidents, he tempted fortuitists to try to cut the ground from under Lamarck's feet by denying that the effects of use and disuse can be inherited at all. When the public had once got to understand what Lamarck had intended, and wherein Mr. Charles Darwin had differed from him, it became impossible for Charles-Darwinians to remain where they were, nor is it easy to see what course was open to them except to cast about for a theory by which they could get rid of use and disuse altogether. Weismannism, therefore, is the inevitable outcome of the straits to which Charles-Darwinians were reduced through the way in which their leader had halted between two opinions.

This is why Charles-Darwinians, from Professor Huxley downwards, have kept the difference between Lamarck's opinions and those of Mr. Darwin so much in the background. Unwillingness to make this understood is nowhere manifested more clearly than in Dr. Francis Darwin's life of his father.

In this work Lamarck is sneered at once or twice, and told to go away, but there is no attempt to state the two cases side by side; from which, as from not a little else, I conclude that Dr. Francis Darwin has descended from his father with singularly little modification.

Proceeding to the evidence for the transmissions of acquired habits, I will quote two recently adduced examples from among the many that have been credibly attested. The first was contributed to _Nature_ (March 14, 1889) by Professor Marcus M. Hartog, who wrote:--

"A. B. is moderately myopic and very astigmatic in the left eye; extremely myopic in the right. As the left eye gave such bad images for near objects, he was compelled in childhood to mask it, and acquired the habit of leaning his head on his left arm for writing, so as to blind that eye, or of resting the left temple and eye on the hand, with the elbow on the table. At the age of fifteen the eyes were equalised by the use of suitable spectacles, and he soon lost the habit completely and permanently. He is now the father of two children, a boy and a girl, whose vision (tested repeatedly and fully) is emmetropic in both eyes, so that they have not inherited the congenital optical defect of their father. All the same, they have both of them inherited his early acquired habit, and need constant watchfulness to prevent their hiding the left eye when writing, by resting the head on the left forearm or hand. Imitation is here quite out of the question.