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Updated: May 17, 2025
It is well known that, on the theory of the "continuity of the germ-plasm," maintained by Weismann, the sexual elements of the generating organism pass on their properties directly to the sexual elements of the organism engendered.
A logical result of the theory is the impossibility of the transmission of acquired characters, since the molecular structure of the germ-plasm is already determined within the embryo; and Weismann 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.
Edith remained in the hall, softly walking up and down, and sometimes pausing to listen. After a little, the door opened. It was only Solomon Weismann, who asked for warm water, lint, and a quantity of old linen.
According to Weismann, the individual parts and characteristics of the organism are represented in the germ-plasm, not in finished form, but as “determinants” in a definite system which is itself the directing principle in the building up of the bodily system, and with definite characteristics, which determine the peculiarities of the individual organs and parts, down to scales, hairs, skin-spots, and birth-marks.
I have nothing, however, to do with Mr. Darwin's theory of pangenesis beyond avoiding the pretence that I understand either the theory itself or what Professor Weismann says about it; all I am concerned with is Professor Weismann's admission, made immediately afterwards, that the somatic cells may, and perhaps sometimes do, impart characteristics to the germ-cells.
And yet Nägeli, and especially Weismann, have had so marked an influence on modern thought that we cannot afford to neglect their theories. We will briefly notice these in the closing chapter. The story of a human life can be told in very few words. A youth of golden dreams and visions; a few years of struggle or of neglected opportunities; then retrospect and the end.
Let us, then, first remind ourselves how the individual, whether male or female, is to be looked upon in the light of the work of Weismann in especial, and how this great truth, discovered by modern biology and especially by the students of heredity, affects our understanding of the difference between man and woman.
Weisbach, Dr., measurement of men of different races; on the greater variability of men than of women; on the relative proportions of the body in the sexes of different races of man. Weismann, Prof., colours of Lycaenae. Welcker, M., on brachycephaly and dolichocephaly; on sexual differences in the skull in man. Wells, Dr., on the immunity of coloured races from certain poisons.
Darwin's conclusion was that "the effects of injuries, especially when followed by disease, or perhaps exclusively when thus followed, are occasionally inherited." Let us now see what Professor Weismann has to say against this. He writes: "The only cases worthy of discussion are the well-known experiments upon guinea-pigs conducted by the French physiologist, Brown-Sequard.
But Professor Weismann does not like such cases, and admits that he cannot explain the facts in connection with the climatic varieties of certain butterflies, except "by supposing the passive acquisition of characters produced by the direct influence of climate." Nevertheless in his next paragraph but one he calls such cases "doubtful," and proposes that for the moment they should be left aside.
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