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Updated: May 22, 2025
Weismann says that the body of the parent is but the case containing the germ-plasm, so that all modifications of the living parent body perish with it, and do not affect the germ, which builds the next generation.
He now accepts the view that external influences may act upon the germ-plasm not only in protozoa but also in all higher animals. Variation is thus due to the action or stimulus of external influences, supplemented by sexual reproduction.
The general doctrine of a stable, "race-type" female and a highly variable male has been widely circulated. In tracing it back through voluminous literature, it appears to have been founded on an article published by W.I. Brooks in the Popular Science Monthly for June, 1879, fourteen years before Weissmann's enunciation of the theory of continuity of the germ-plasm.
If this modification does not involve the production of substances capable of changing the germ-plasm, or does not so affect nutrition as to deprive the germ-plasm of certain of its elements, it will have no effect on the offspring of the individual. This is probably the case as a rule.
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.
Is not the most natural hypothesis to suppose that things happen in this second case as in the first, and that the direct effect of the influence of the soma is a general alteration of the germ-plasm? If this is the case, it is by exception, and in some sort by accident, that the modification of the descendant is the same as that of the parent.
But if, perchance, experiment should show that acquired characters are transmissible, it would prove thereby that the germ-plasm is not so independent of the somatic envelope as has been contended, and the transmissibility of acquired characters would become ipso facto conceivable; which amounts to saying that conceivability and inconceivability have nothing to do with the case, and that experience alone must settle the matter.
After all, that does not mean that individuals exist and are worth Nature's while merely in order to see the germ-plasm on its way. To say that the individual exists for the race is to say that he, and, as we shall see, pre-eminently she, exist for future individuals; and that is not a destiny to be despised of any.
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.
In such case, there is inheritance of a defect, and the result is as if the soma of the parent had acted on the germ-plasm, although in reality soma and plasma have simply both suffered the action of the same cause. Now, suppose that the soma can influence the germ-plasm, as those believe who hold that acquired characters are transmissible.
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