Darwin, and After Darwin, Volume 2 of 3 / Post-Darwinian Questions: Heredity and Utility

by George John Romanes

Let us now proceed to the experimental evidence which has been adduced on the side of Weismannism.

Taking this evidence in order of date, we have first to mention that on which the school of Weismann has hitherto been satisfied almost exclusively to rely. This is the line of negative evidence, or the seeming absence of any experimental demonstration of the inheritance of acquired characters. This kind of evidence, however, presents much less cogency than is usually supposed. And it has been shown in the last chapter that the amount of experimental evidence in favour of the transmission of acquired characters is more considerable than the school of Weismann seems to be aware—especially in the vegetable kingdom. I do not think that this negative line of evidence presents much weight; and, to show that I am not biassed in forming this judgement, I may here state that few have more reason than myself for appreciating the weight of such evidence. For, as already stated, when first led to doubt the Lamarckian factors, now more than twenty years ago, I undertook a research upon the whole question—only a part of which was devoted to testing the particular case of Brown-Séquard's statements, with the result recorded in the preceding chapter. As this research yielded negative results in all its divisions—and, not only in the matter of Brown-Séquard's statements—I have not hitherto published a word upon the subject. But it now seems worth while to do so, and for the following reasons.

First, as just observed, a brief account of my old experiences in this field will serve to show what good reason I have for feeling the weight of such negative evidence in favour of Continuity as arises from failure to produce any good experimental evidence to the contrary. In the second place, now that the question has become one of world-wide interest, it would seem that even negative results deserve to be published for whatever they may be worth on the side of Neo-Darwinism. Lastly, in the third place, although the research yielded negative results in my hands, it is perhaps not undesirable to state the nature of it, if only to furnish suggestions to other physiologists, in whose hands the experiments—especially in these days of antiseptics—may lead to a different termination. Altogether I made thousands of experiments in graft-hydridization (comprising bines, bulbs of various kinds, buds, and tubers); but with uniformly negative results. With animals I tried a number of experiments in grafting characteristic congenital tissues from one variety on another—such as the combs of Spanish cocks upon the heads of Hamburgs; also, in mice and rats, the grafting together of different varieties; and, in rabbits and bitches, the transplantation of ovaries of newly-born individuals belonging to different well-marked breeds. This latter experiment seems to be one which, if successfully performed (so that the transplanted ovaries would form their attachment in a young bitch puppy and subsequently yield progeny to a dog of the same breed as herself) would furnish a crucial test as to the inheritance or non-inheritance of acquired characters. Therefore I devoted to it a large share of my attention, and tried the experiment in several different ways. But I was never able to get the foreign ovary—or even any portion thereof—to graft. Eventually the passing of the Vivisection Act caused me to abandon the whole research as far as animals were concerned—a research, indeed, of which I had become heartily tired, since in no one instance did I obtain any adhesion. During the last few years, however, I have returned to these experiments under a licence, and with antiseptic precautions, but with a similar want of success. Perhaps this prolonged and uniformly fruitless experience may now have the effect of saving the time of other physiologists, by warning them off the roads where there seems to be no thoroughfare. On the other hand, it may possibly lead some one else to try some variation in the method, or in the material, which has not occurred to me. In particular, I am not without hope that the transplantation of ovaries in very young animals may eventually prove to be physiologically possible; and, if so, that the whole issue as between the rival theories of heredity will be settled by the result of a single experiment. Possibly some of the invertebrata will be found to furnish the suitable material, although I have been unable to think of any of these which present sufficiently well-marked varieties for the purpose. But, pending the successful accomplishment of this particular experiment in the grafting of any animal tissue, I think it would be clearly unjustifiable to conclude against the Lamarckian factors on the ground of any other experiments yielding negative results in but one generation or even in a large number of sequent generations.

For instance, the latter consideration applies to the negative results of Mr. Francis Galton's celebrated Experiments in Pangenesis.[82]. These consisted in transfusing the blood of one variety of rabbit into the veins of both sexes of another, and then allowing the latter to breed together: in no case was there any appearance in the progeny of characters distinctive of the variety from which the transfused blood was derived. But, as Mr. Galton himself subsequently allowed, this negative result constitutes no disproof of pangenesis, seeing that only a portion of the parents' blood was replaced; that this portion, even if charged with "gemmules," would contain but a very small number of these hypothetical bodies, compared with those contained in all the tissues of the parents; and that even this small proportional number would presumably be soon overwhelmed by those contained in blood newly-made by the parents. Nevertheless the experiment was unquestionably worth trying, on the chance of its yielding a positive result; for, in this event, the question at issue would have been closed. Accordingly I repeated these experiments (with the kind help of Professor Schäfer), but with slight differences in the method, designed to give pangenesis a better chance, so to speak.

Thus I chose wild rabbits to supply the blood, and Himalayan to receive it—the former being the ancestral type (and therefore giving reversion an opportunity of coming into play), while the latter, although a product of domestication, is a remarkably constant variety, and one which differs very much in size and colour from the parent species. Again, instead of a single transfusion, there were several transfusions performed at different times. Moreover, we did not merely allow the blood of one rabbit to flow into the veins of the other (whereby little more than half the blood could be substituted); but sacrificed three wild rabbits for refilling the vascular system of each tame one on each occasion. Even as thus improved, however, the experiment yielded only negative results, which, therefore, we never published.

Subsequently I found that all this labour, both on Mr. Galton's part and our own, was simply thrown away—not because it yielded only negative results, but because it did not serve as a crucial experiment at all. The material chosen was unserviceable for the purpose, inasmuch as rabbits, even when crossed in the ordinary way, never throw intermediate characters. Needless to say, had I been aware of this fact before, I should never have repeated Mr. Galton's experiments—nor, indeed, would he have originally performed them had he been aware of it. So all this work goes for nothing. The research must begin all over again with some other animals, the varieties of which when crossed do throw intermediate characters.

Therefore I have this year made arrangements for again repeating the experiments in question—only, instead of rabbits, using well-marked varieties of dogs. A renewed attack of illness, however, has necessitated the surrender of this research to other hands, with a consequent delay in its commencement.

My ignorance of the unfortunate peculiarity displayed by rabbits in not throwing intermediate characters has led to a further waste of time in another line of experiment. On finding that mammalian ovaries did not admit of being grafted, it seemed to me that the next best thing to try would be the transplantation of fertilized ova from one variety to another, for the purpose of ascertaining whether, if a parturition should take place under such circumstances, gestation by the uterine mother would affect the characters of the ovum derived from the ovarian mother—she, of course, having been fertilized by a male of her own variety. Of course it was necessary that both the mothers should be in season at about the same time, and therefore I again chose rabbits, seeing that in the breeding season they are virtually in a chronic state of "heat." I selected Himalayans and Belgian hares, because they are well-marked varieties, breed true, and in respect of colour are very different from one another. It so happened that while I was at work upon this experiment, it was also being tried, unknown to me, by Messrs. Heape and Buckley who, curiously enough, employed exactly the same material. They were the first to obtain a successful result. Two fertilized ova of the Angora breed having been introduced into the fallopian tube of a Belgian hare, developed there in due course, and gave rise to two Angora rabbits in no way modified by their Belgian hare gestation[83].

But, interesting and suggestive as this experiment is in other connexions, it is clearly without significance in the present one, for the reason already stated. It will have to be tried on well-marked varieties of other species of animals, which are known to throw intermediate characters. Even, however, if it should then yield a similarly negative result, the fact would not tell against the inheritance of acquired characters; seeing that an ovum by the time it is ripe is a finished product, and therefore not to be expected, on any theory of heredity, to be influenced as to its hereditary potentialities by the mere process of gestation. On the other hand, if it should prove that it does admit of being thus affected, so that against all reasonable expectation the young animal presents any of the hereditary characters of its uterine mother, the fact would terminate the question of the transmission of acquired characters—and this quite as effectually as would a similarly positive result in the case of progeny from an ingrafted ovary of a different variety. In point of fact, the only difference between the two cases would be, that in the former it might prove possible to close the question on the side of Lamarckianism, in the latter it would certainly close the question, either on this side or on the opposite as the event would determine.

The only additional fact that has hitherto been published by the school of Weismann is the result of Weismann's own experiment in cutting off the tails of mice through successive generations. But this experiment does not bear upon any question that is in debate; for no one who is acquainted with the literature of the subject would have expected any positive result to follow from such a line of inquiry. As shown further back in the text, Darwin had carefully considered the case of mutilations, and explained that their non-transmissibility constitutes no valid objection to his theory of pangenesis. Furthermore, it may now be added, he expressly alluded in this connexion to the cutting off of tails, as practised by horse-breeders and dog-fanciers, "through a number of generations, without any inherited effect." He also alluded to the still better evidence which is furnished by the practice of circumcision. Therefore it is difficult to understand the object of Weismann's experiment. Yet, other than the result of this experiment, no new fact bearing on the question at issue has been even so much as alleged.