The proposition which I have to defend is one which no one till recently would have questioned, and even now, those who look most askance at it do not venture to dispute it unreservedly; they every now and then admit it as conceivable, and even in some cases probable; nevertheless they seek to minimise it, and to make out that there is little or no connection between the great mass of the cells of which the body is composed, and those cells that are alone capable of reproducing the entire organism. The tendency is to assign to these last a life of their own, apart from, and unconnected with that of the other cells of the body, and to cheapen all evidence that tends to prove any response on their part to the past history of the individual, and hence ultimately of the race.
Professor Weismann is the foremost exponent of those who take this line. He has naturally been welcomed by English Charles-Darwinians; for if his view can be sustained, then it can be contended that use and disuse produce no transmissible effect, and the ground is cut from under Lamarck’s feet; if, on the other hand, his view is unfounded, the Lamarckian reaction, already strong, will gain still further strength. The issue, therefore, is important, and is being fiercely contested by those who have invested their all of reputation for discernment in Charles-Darwinian securities.
Professor Weismann’s theory is, that at every new birth a part of the substance which proceeds from parents and which goes to form the new embryo is not used up in forming the new animal, but remains apart to generate the germ-cells—or perhaps I should say “germ-plasm”—which the new animal itself will in due course issue.
Contrasting the generally received view with his own, Professor Weismann says that according to the first of these “the organism produces germ-cells afresh again and again, and that it produces them entirely from its own substance.” While by the second “the germ-cells are no longer looked upon as the product of the parent’s body, at least as far as their essential part—the specific germ-plasm—is concerned; they are rather considered as something which is to be placed in contrast with the tout ensemble of the cells which make up the parent’s body, and the germ-cells of succeeding generations stand in a similar relation to one another as a series of generations of unicellular organisms arising by a continued process of cell-division.” [30]
On another page he writes:—
“I believe that heredity depends upon the fact that a small portion of the effective substance of the germ, the germ-plasm, remains unchanged during the development of the ovum into an organism, and that this part of the germ-plasm serves as a foundation from which the germ-cells of the new organism are produced. There is, therefore, continuity of the germ-plasm from one generation to another. One might represent the germ-plasm by the metaphor of a long creeping root-stock from which plants arise at intervals, these latter representing the individuals of successive generations.” [31]
Mr. Wallace, who does not appear to have read Professor Weismann’s essays themselves, but whose remarks are, no doubt, ultimately derived from the sequel to the passage just quoted from page 266 of Professor Weismann’s book, contends that the impossibility of the transmission of acquired characters follows as a logical result from Professor Weismann’s theory, inasmuch as the molecular structure of the germ-plasm that will go to form any succeeding generation is already predetermined within the still unformed embryo of its predecessor; “and Weismann,” continues Mr. Wallace, “holds that there are no facts which really prove that acquired characters can be inherited, although their inheritance has, by most writers, been considered so probable as hardly to stand in need of direct proof.” [32]
Professor Weismann, in passages too numerous to quote, shows that he recognises this necessity, and acknowledges that the non-transmission of acquired characters “forms the foundation of the views” set forth in his book, p. 291.
Professor Ray Lankester does not commit himself absolutely to this view, but lends it support by saying (Nature, December 12, 1889): “It is hardly necessary to say that it has never yet been shown experimentally that anything acquired by one generation is transmitted to the next (putting aside diseases).”
Mr. Romanes, writing in Nature, March 18, 1890, and opposing certain details of Professor Weismann’s theory, so far supports it as to say that “there is the gravest possible doubt lying against the supposition that any really inherited decrease is due to the inherited effects of disuse.” The “gravest possible doubt” should mean that Mr. Romanes regards it as a moral certainty that disuse has no transmitted effect in reducing an organ, and it should follow that he holds use to have no transmitted effect in its development. The sequel, however, makes me uncertain how far Mr. Romanes intends this, and I would refer the reader to the article which Mr. Romanes has just published on Weismann in the Contemporary Review for this current month.