An Examination of Weismannism

by George John Romanes

At first sight it may well appear that we have here a very formidable array of assumptions. But Darwin ably argues in favour of each of them by pointing to well-known analogies, drawn from the vital processes of living cells both in the protozoa and metazoa. For example, it is already a well-recognized doctrine of physiology that each cell of a metazoon, or multicellular organism, though to a large extent dependent on others, is likewise to a certain extent independent or autonomous, and has the power of multiplying by self-division. Therefore, as it is certain that the sexual elements (and also buds of all descriptions) include formative material of some kind, the first assumption—or that which supposes such formative matter to be participate—is certainly not a gratuitous assumption.

Again, the second assumption—viz., that this particulate and formative material is dispersed throughout all the tissues of the organism—is sustained by the fact that, both in certain plants and in certain invertebrated animals, a severed portion of the organism will develop into an entire organism similar to that from which it was derived, as, for example, is the case with a leaf of Begonia, and with portions cut from certain invertebrated animals, such as sea-anemones, jelly-fish, &c. This well-known fact in itself seems enough to prove that the formative material in question must certainly admit, at all events in many cases, of being distributed throughout all the tissues of living organisms.

The third assumption—or that which supposes the formative material to be especially aggregated in the sexual elements—is not so much an assumption as a statement of obvious fact; while the fourth, fifth, sixth, and seventh assumptions all follow deductively from their predecessors. In other words, if the first and second assumptions be granted, and if the theory is to comprise all the facts of heredity, then the remaining five assumptions are bound to follow.

To the probable objection that the supposed gemmules must be of a size impossibly minute—seeing that thousands of millions of them would have to be packed into a single ovum or spermatozoon—Darwin opposes a calculation that a cube of glass or water, having only one ten-thousandth of an inch to a side, contains somewhere between sixteen and a hundred and thirty-one billions of molecules. Again, as touching the supposed power of multiplication on the part of his gemmules, he alludes to the fact that infectious material of all kinds exhibits a ratio of increase quite as great as any that his theory requires to attribute to gemmules. Furthermore, with respect to the elective affinity of gemmules, he remarks that “in all ordinary cases of sexual reproduction, the male and female elements certainly have an elective affinity for each other”: of the ten thousand species of Compositae, for example, “there can be no doubt that if the pollen of all these species could be simultaneously placed on the stigma of any one species, this one would elect, with unerring certainty, its own pollen.”

Such, in brief outline, is Mr. Darwin’s theory of Pangenesis.

Professor Weismann’s theory of Germ-plasm is fundamentally based upon the great distinction, in respect of their transmissibility, between characters that are congenital and characters that are acquired. By a congenital character is meant any individual peculiarity, whether structural or mental, with which the individual is born. By an acquired character is meant any peculiarity which the individual may subsequently develop in consequence of its own individual experience. For example, a man may be born with some malformation of one of his fingers; or he may subsequently acquire such a malformation as the result of accident or disease. Now, in the former case—i.e., in that where the malformation is congenital—it is extremely probable that the peculiarity will be transmitted to his children; while in the latter case—i.e., where the malformation is subsequently acquired—it is virtually certain that it will not be transmitted to his children. And this great difference between the transmissibility of characters that are congenital and characters that are acquired extends universally as a general law throughout the vegetable as well as the animal kingdom, and in the province of mental as in that of bodily organization. Of course this general law has always been well known, and more or less fully recognized by all modern physiologists and medical men. But before the subject was taken up by Professor Weismann, it was generally supposed that the difference in question was one of degree, not one of kind. In other words, it was assumed that acquired characters, although not so fully—and therefore not so certainly—inherited as congenital characters, nevertheless were inherited in some lesser degree; so that if the same character continued to be developed successively in a number of sequent generations, what was at first only a slight tendency to be inherited would become by summation a more and more pronounced tendency, till eventually the acquired character might be as strongly inherited as any other character which was ab initio congenital. Now it is the validity of this assumption that is challenged by Professor Weismann. He says there is no evidence of any acquired characters being in any degree inherited; and, therefore, that in this important respect they may be held to differ from congenital characters in kind. On the supposition that they do thus differ in kind, he furnishes a very attractive theory of heredity, which serves at once to explain the difference, and to represent it as a matter of physiological impossibility that any acquired character can, under any circumstances whatsoever, be transmitted to progeny.

But, in order fully to comprehend this theory, it is desirable first of all to explain Professor Weismann’s views upon certain other topics which are intimately connected with—and, indeed, logically sequent upon—the use to which he puts the distinction just mentioned.

Starting from the fact that unicellular organisms multiply by fission and gemmation, he argues that, aboriginally and potentially, life is immortal. For when a protozoon divides itself into two more or less equal parts by fission, and each of the two halves thereupon grows into another protozoon, it does not appear that there has been any death on the part of the living material involved; and inasmuch as this process of fission goes on continuously from generation to generation, there is seemingly never any death on the part of such protoplasmic material, although there is a continuous addition to it as the numbers of individuals increase. Similarly, in the case of gemmation, when a protozoon parts with a small portion of its living material in the form of a bud, this portion does not die, but develops into a new individual; and, therefore, the process is exactly analogous to that of fission, save that a small instead of a large part of the parent substance is involved. Now, if life be thus immortal in the case of unicellular organisms, why should it have ceased to be so in the case of multicellular? Weismann’s answer is, that all the multicellular organisms propagate themselves, not exclusively by fission or gemmation, but by sexual fertilization, where the condition to a new organism arising is that minute and specialized portions of two parent organisms should fuse together. Now, it is evident that with this change in the method of propagation, serious disadvantage would accrue to any species if its sexual individuals were to continue to be immortal; for in that case every species which multiplies by sexual methods would in time become composed of individuals broken down and decrepit through the results of accident and disease—always operating and ever accumulating throughout the course of their immortal lives. Consequently, as soon as sexual methods of propagation superseded the more primitive a-sexual methods, it became desirable in the interests of the sexually-propagating species that their constituent individuals should cease to be immortal, so that the species should always be recuperated by fresh, young, and well-formed representatives. Consequently, also, natural selection would speedily see to it that all sexually-propagating species should become deprived of the aboriginal endowment of immortality, with the result that death is now universal among all the individuals of such species—that is to say, among all the metazoa and metaphyta. Nevertheless, it is to be remembered that this destiny extends only to the parts of the individual other than the contents of those specialized cells which constitute the reproductive elements. For although in each individual metazoon or metaphyton an innumerable number of these specialized cells are destined to perish during the life, or with the death, of the organism to which they belong, this is only due to the accident, so to speak, of their contents not having met with their complements in the opposite sex: it does not belong to their essential nature that they should perish, seeing that those which do happen to meet with their complements in the opposite sex help to form a new living individual, and so on through successive generations ad infinitum. Therefore the reproductive elements of the metazoa and metaphyta are in this respect precisely analogous to the protozoa: potentially, or in their own nature, they are immortal; and, like the protozoa, if they die, their death is an accident due to unfavourable circumstances. But the case is quite different with all the other parts of a multicellular organism. Here, no matter how favourable the circumstances may be, every cell contains within itself, or in its very nature, the eventual doom of death. Thus, of the metazoa and metaphyta it is the “germ-plasms” alone that retain their primitive endowment of everlasting life, passed on continuously through generation after generation of successively perishing organisms.

So far, it is contended, we are dealing with matters of fact. It must be taken as true that the protoplasm of the unicellular organisms, and the germ-plasm of the multicellular organisms, has been continuous through the time since life first appeared upon this earth; and although large quantities of each are perpetually dying through being exposed to conditions unfavourable to life, this, as Weismann presents the matter, is quite a different case from that of all the other constituent parts of multicellular organisms, which contain within themselves the doom of death. Furthermore, it appears extremely probable that this doom of death has been brought about by natural selection for the reasons assigned by Weismann—namely, because it is for the benefit of all species which perpetuate themselves by sexual methods, that their constituent individuals should not live longer than is necessary for the sake of originating the next generation, and fairly starting it in its own struggle for existence. For Weismann has shown, by a somewhat laborious though still largely imperfect research, that there is throughout all the metazoa a general correlation between the natural lifetime of individuals composing any given species and the age at which they reach maturity, or first become capable of procreation. This general correlation, however, is somewhat modified by the time during which progeny are dependent upon their parents for support and protection. Nevertheless, it is evident that this fact tends rather to confirm the view that expectation of life on the part of individuals has in all cases been determined with strict reference to the requirements of propagation, if under propagation we include the rearing as well as the production of offspring. I may observe in passing that I do not think this general law can be found to apply to plants in nearly so close a manner as Weismann has shown it to apply to animals; but, leaving this consideration aside, I think that Weismann has made out a good case in favour of such a general law with regard to animals[3].