An Examination of Weismannism

by George John Romanes

How can such a process [i.e. the passage of gemmules into growing germ-cells] be conceivable, when the colony becomes more complex, when the number of somatic cells becomes so large that they surround the reproductive cells with many layers, and when at the same time, by an increasing division of labour, a great number of different tissues and cells are produced, all of which must originate de novo from a single reproductive cell?

Here, again, the obvious answer is, that no one has ever propounded such a statement. Far from supposing that “all the different cells and tissues of a complex organism must originate de novo from a single reproductive cell,” the theory of pangenesis supposes the very contrary—viz., that somatic changes in the past history of the phyla have not thus originated in any reproductive cell. The idea of somatic changes originating in reproductive cells belongs to the theory of germ-plasm; but even this theory does not suppose all the great number of different cells and tissues which compose a complex organism to have ever originated de novo from a single reproductive cell.

The difficulty touching germ-cells becoming isolated, or buried, by the phylogenetic increase of somatic cells, is enforced in the immediately succeeding sentences, thus:—

Each of these various elements [somatic cells] must, ex hypothesi, give up certain molecules to the reproductive cells; hence those which are in immediate contact with the latter would obviously possess an advantage over those which are more remote. If, then, any somatic cell must send the same number of molecules to each reproductive cell[70], we are compelled to suspend all known physical and physiological conceptions, and must make the entirely gratuitous assumption of an affinity on the part of the molecules for the reproductive cells. Even if we admit the existence of this affinity, its origin and means of control remain perfectly unintelligible if we suppose that it has arisen from differentiation of the complete colony. An unknown controlling force must be added to this mysterious arrangement, in order to marshal the molecules which enter the reproductive cell in such a manner that their arrangement corresponds with the order in which they must emerge as cells at a later period.

Now I do not see much force in the suggestion that those somatic cells which happen to be in immediate contact with germ-cells, “must obviously possess an advantage over those which are more remote.” On the contrary, I do not see that mere proximity of one species of cell to another species within the same organism need have anything to do with the matter—still less that “we must suspend all physical and physiological conceptions,” if we demur to the statement that it “obviously must.” As for “physical conceptions,” how many thousands of cases might not be pointed to among chemical and mechanical processes where contact or proximity are conditions of comparatively little importance? And as for “physiological conceptions,” do we find that any part of the organism is affected by its distance, say, from the liver and kidneys, for getting rid of its effete products? Is it not rather the case that every gland in the body is wholly unaffected by its distance from any part of the body, in regard to its function of draining off the particular substances with which it is concerned? Why then should the reproductive gland constitute a conspicuous exception? Or how do we suspend all physiological conceptions, if we suppose that this gland resembles every other gland in being specialized to secrete a particular kind of “molecule,” which, because thus specially selected, may be said to have for that gland a special “affinity”? If there are such things as gemmules, I do not see any violation of physiological analogies—still less an “entirely gratuitous assumption”—in supposing that they can be filtered out from all parts of the body by the sexual glands, and there aggregated as a special product to be discharged in the form of sexual elements[71].

But, it is further represented, “even if we admit the existence of this affinity, an unknown controlling force must be added to this mysterious arrangement, in order to marshal the molecules which enter the [growing] reproductive cell in such a manner that their arrangement corresponds with the order in which they emerge as cells at a later period.” Surely, however, for Weismann of all naturalists it ought not to be difficult to find this “unknown controlling force.” For of all naturalists he is perhaps the most ready to invoke the agency of natural selection as sufficient to explain every case—actual or imaginable—of adaptation. Now, here is a case where natural selection, one would think, is positively bound to act—supposing that there be such things as gemmules. For, if “the carriers of heredity” are gemmules, it is evident that their mutual “affinities” must be adaptively “marshalled” at each step of phylogenetic evolution, before any further advance of such evolution can be possible. And I do not see anything more “inconceivable” in supposing the establishment of such mutual affinities step by step through natural selection, than in supposing any other course of adaptive development by similar means. For, as Darwin has well shown, while anticipating this particular objection to his theory,—“The assumed elective affinity of each gemmule for that particular cell which precedes it in due order of development is supported by many analogies.” The analogies which he then gives are so numerous that I must here refer to his own discussion of the subject[72]—a discussion which is entirely ignored by Weismann.

Lastly, the principal ground, as far as I can see, which Weismann has for regarding Darwin’s theory in any shape “inconceivable,” is his own supposition that there is as complete an anatomical separation between the soma and its germ-cells as there is, for example, between the mammalian soma and these same cells when afterwards detached from the ovary and developing as foetuses in utero. In other words, the only connexion is supposed to be that of deriving nourishment by way of imbibition. But, as regards the germ-cell while still forming in the ovary or testicle, there is for this supposition no basis in fact. There is nothing in the histology of spermatogenesis that lends countenance to the supposition, while in the case of the ovum such histological evidence as we possess makes altogether against it. As Professor Vines has remarked:—

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. It is an obvious inference that, under these circumstances, hereditary characters may be transmitted from the parent to the offspring, not only by the germ-plasm, but also by the somato-plasm, of the ovum[73].

Again, and apart from this consideration, it is now known that a very intimate network of protoplasmic fibres connects the cell-contents of cellular tissues, both in plants and animals. So that here we have another very possible means of communication between the germ-cells and the somatic-cells which together constitute a multicellular organism.