George John Romanes

“ So that, on the whole, we may say that natural selection is ever waiting and watching for such combinations of germ-plasm as will give the resulting organisms the best possible chance in their struggle for existence; while, at the same time, it is remorselessly destroying all those combinations of germ-plasm which are handed over to the custody of organisms not so well fitted to their conditions of life. ”

“ There is nothing to show the necessary non-inheritance of acquired characters. The only evidence which one can recognize as good, is that which makes equally in favour of the theory of stirp—or rather, of the well-known fact that congenital characters are at any rate much more heritable than are acquired: which, it is needless to repeat, is a widely different thing from proving—or even rendering probable—the absolute restriction of germ-plasm to a separate “sphere” of its own “since the origin of life.” ”

“ The whole mechanism of heredity has been now planned out in such minuteness of detail and assurance of accuracy, that in reading the account one is reminded of that which is given by Dante of the topography of Inferno. For not only is the “sphere” of germ-plasm now composed of nine circles (molecules, biophores, determinants, ids, idants, idio-plasm, somatic-idioplasm, morpho-plasm, apical-plasm) , but in most of these regions our guide is able to show us such strange and interesting phenomena, that we return to the fields of science with a sense of having been indeed in some other world. ”

“ Although it is true that the unicellular organisms propagate by fission, and although we grant, for the sake of argument, that they never propagate by way of sexual unions—even so this can no longer be taken to argue that none of their innumerable species owe their origin to natural selection. And, although it is probably true that the sexual methods of propagation constitute one source of hereditary individual variation among the multicellular organisms, there is no vestige of any independent reason for supposing that this is the only source of such variation ”

“ For, at least, the germ-plasm derives its nourishment from the soma in which it resides; and who shall say that the process of mere imbibition is not amply sufficient to admit of the passage of “gemmules”? Call them what we choose, the “carriers of heredity” must be so unimaginably small, that in relation to histological cells they must be as gnats to camels. Yet we know that even camels in the form of “migrating cells” of various kinds are able to pass through living membranes; and we also know that the microbes of syphilis can penetrate both ova and spermatozoa. ”

“ Darwin’s theory of heredity is the theory of Pangenesis: it supposes that all parts of the organism generate anew in every individual the formative material which, when collected together in the germ-cells, constitutes the potentiality of a new organism; and that this new organism, when developed, resembles its parents simply because all the formative material in each of the parents has been thus generated by, and collected from, all parts of their respective bodies. ”

“ The whole organization of any multicellular organism is composed of two entirely different kinds of cells—namely, the germ-cells, or those which have to do with reproduction, and the somatic-cells, or those which go to constitute all the other parts of the organism. Now, the somatic-cells, in their aggregations as tissues and organs, may be modified in numberless ways by the direct action of the environment, as well as by special habits formed during the individual lifetime of the organism. ”

“ I contrasted the body (soma) with the germ-cells, and explained heredity by the hypothesis of a “Vererbungs-substanz” in the germ-cells (in fact the germ-plasma) , which is transmitted without breach of continuity from one generation to the next. I was not then aware that this lay only in the nucleus of the ovum, and could therefore contrast the entire substance of the ovum with the substance of the body-cells, and term the latter “somato-plasm.” ”

“ We now proceed to examine Weismann’s theory of germ-plasm, and as this in its various developments has now become a highly complex theory, we had best begin by marking out the lines on which the examination will be conducted.
As I have already pointed out, the Weismannian system is not concerned only with the physiology of reproduction: it is concerned also—and in an even larger measure—with the doctrine of descent. The theory of germ-plasm as a whole is very much more than a theory of heredity; it is a new theory of evolution. ”

“ For seeing that the rate of increase in most of the unicellular organisms is quite as high as—and in most cases very much higher than—the rate that obtains in any of the multicellular, it becomes on merely antecedent grounds incredible that the struggle for existence should here not lead to any survival of the fittest. When, for instance, we learn from Maupas that [102] a single Stylonichia is potentially capable of yielding a billion descendants within a week, we should need some extraordinarily good evidence to make us believe that as regards this organism natural selection is inoperative. ”

“ It cannot be seriously maintained that the whole body of the embryo is developed solely from the germ-plasm of the ovum. On the contrary, since the embryo is developed from the whole of the nucleus and more or less of the cytoplasm of the ovum, it must be admitted that the non-germ-plasm of the ovum provides a large part of the material in embryogeny. ”

“ Seeing that sexual propagation is so general as to be practically universal among multicellular organisms, it is obvious that in some way or another it must have had a most important part to play in the general scheme of organic evolution. What, then, is the part that it does play? What is its raison d’être? Briefly, according to Weismann, its function is that of furnishing congenital variations to the ever-watchful agency of natural selection, in order that natural selection may always preserve the most [12] favourable, and pass them on to the next generation by heredity. ”

“ For it is hardly conceivable that such a complex mass of germ-plasms as the nucleus of a fertilized ovum must be could ever present in any two eggs precisely the same proportional representation of the “carriers of heredity,” after one half of each set had been thus discharged from each egg. Therefore, if the second polar body removes from each egg one half of the ancestral germ-plasms, “every egg will contain a somewhat different combination of hereditary tendencies, and thus the offspring which arise from the different germ-cells of the same mother can never be identical [11] . ”

“ But this rejoinder is of cogency only if it be supposed that at each nuclear division of an immature ovum, “the ancestral idio-plasms” (germ-plasm) are incapable of the power of self-multiplication which soon afterwards becomes one of its most essential characters. Why, then, should we suppose this substance to be totally incapable of increase in the multiplying ova of ontogeny, when at the same time we are to suppose the same substance capable of any amount of increase in the multiplying ova of phylogeny? ”

“ If we suppose that the germinal substance of one organism may thus directly act upon the somatic tissues of another, and that changed conditions of life are able to [146] produce simultaneously an acquired character in the soma and a precisely identical character as congenital in the germ (pp. 129-30) , we are plainly inviting ourselves to abandon the complex explanation of living material in “two kinds,” where one is capable in all sorts of ways of communicating with the other, while the possibility of any reciprocal action is excluded. ”

“ Hence, the nuclear contents (nucleo-plasm) of every cell, whether germinal or somatic, present two substances, which we may, in the absence of any better terms supplied by Weismann himself, respectively designate “idio-plasm-A” and “idio-plasm-B.” Idio-plasm-A is the substance which has to do only with the formation and control of the individual cell in which it resides, like a mollusc in its shell. ”

“ Weismann’s theory on the other hand, while adopting the first assumption, rejects the second; and assumes in its stead that living material exists in “two kinds,” only one of which has been continuous, while the other is discontinuous—being, in fact, formed anew at each ontogeny. Therefore, to my mind, it seems more needful to argue the point wherein his theory differs from these other theories of heredity, than it is to argue the point wherein it agrees with them. We look to him for a proof of the discontinuity of somato-plasm much more than we do for a proof of the continuity of germ-plasm. ”

“ Thus we get proof that relatively pure constitutions predominate in progeny over much mixed constitutions. The reason is not difficult to see. Every organism tends to become adapted to its conditions of life; and all the structures of a species, accustomed through multitudinous generations to the climate, food, and various influences of its locality, are moulded into harmonious co-operation favourable to life in that locality: the result being that in the development of each young individual, the tendencies conspire to produce the fit organization. ”

“ For this most singular statement can only stand on a prior acceptance of Weismann’s own assumption, as to amphigony being the only possible cause of individual hereditary variation. Only if we have already, and with absolute certainty, embraced the whole Weismannian creed, could we consent to affirm that “natural selection is an impossibility in a species propagated by a-sexual reproduction.” ”

“ If, as we have seen, “formative material” and “germ-plasm” agree in being particulate; in constituting the material basis of heredity; in being mainly lodged in highly specialized, or germinal, cells; in being nevertheless also distributed throughout the general cellular tissues, where they are alike concerned in all processes of regeneration, repair, and a-sexual reproduction; in having an enormously complex structure, so that every constituent part of the future organism is already represented in them by corresponding particles ”

“ The truly scientific attitude of mind with regard to the problem of heredity is to say, as Galton says, “that we might almost reserve our belief that the structural [i.e., somatic] cells can react on the sexual elements at all, and we may be confident that at most they do so in a very faint degree; in other words, that acquired modifications are barely, if at all, inherited, in the correct sense of that word.” But for Weismann’s further theory of evolution, it is necessary to postulate the two additional doctrines in question ”

“ If in any progeny certain traits not belonging to the sire, but belonging to a sire of preceding progeny, are reproduced, how is it that such anomalously-inherited traits are not observed in domestic animals, and indeed in mankind? ”

“ Now, whether or not he is right as regards these latter points, I think there can be no question that sexual propagation is, at all events, one of the main causes of congenital variation; and seeing of what enormous importance congenital variation must always have been in supplying material for the operation of natural selection, we appear to have found a most satisfactory answer to our question,—Why has sexual propagation become so universal among all the higher plants and animals? ”

“ 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. ”

“ Now if this is shown to be the case with breeds the purest of which have been adapted to their habitats and modes of life during some few hundred years only, what shall we say when the question is of a breed which has had a constant mode of life in the same locality for ten thousand years or more, like the quagga? In this the stability of constitution must be such as no domestic animal can approach. ”

“ Now, in the great majority of organisms, there is an infinitely greater number of germ-cells (both male and female) than can possibly be required either for the purpose of getting rid of any excess of germ-plasms in the nucleus of each cell, or of preventing the germ-plasms of any one germ-cell precisely resembling those of any other. If every plant or animal produced only a single female-cell or a single male-cell, then indeed we might require from Professor Weismann a demonstration of some special mechanism to secure the expulsion of half its ancestral germ-plasms ”

“ It does not require to be proved that all variations produced by changed conditions of life are inherited. If only some—even though it be but an extremely small percentage—of such variations are proved to be inherited, the many millions of years that separate the germ-plasm of to-day from its supposed origin in the protozoa, must have furnished opportunities enough for the occurrence of such variations to have obliterated, and re-obliterated numberless times, any aboriginal differences in the germ-plasms of incipiently sexual organisms. ”