The Germ-plasm : a theory of heredity / by August Weismann ; translated by W. Newton Parker and Harriet Ronnfeldt.

  • Weismann, August, 1834-1914.
Date:
1893
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Licence: Public Domain Mark

Credit: The Germ-plasm : a theory of heredity / by August Weismann ; translated by W. Newton Parker and Harriet Ronnfeldt. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    the consequences of his ' gemmule'-hypothesis when seeking for a purely formal explanation, than he would have been had he tried to adapt his hypothesis to the facts. The hypothesis, as stated by him, could not be regarded as a real solution of the problem of heredity, if only because it leaves unexplained the giving off of the gemmules into the blood, their circulation through the body, and inti'usion into the germ- and other cells. All these are assumptions without a basis in fact. This is evidently the reason why modifications of the theory of pangenesis were repeatedly made very soon afterwards. Before considering these modifications, I should like once more to state clearly the relation of Spencer's ' physiological units' to Darwin's 'gemmules.' Darwin himself considered the former to be closely related to his gemmules ; and, in fact, he would have regarded Spencer's ideas as essentially coinciding with his own, had he not noticed certain passages in Spencer's book which seemed to point to something quite different.* It will be apparent, I think, from what has already been said, that these two views are entirely different. What is common to both is that they assume the existence of minute living units, multiplying by fission : but the part taken by them in the con- stitution of the body is quite differently conceived. Spencer's units are the elements which exclusively compose the living body; while Darwin's gemmules only give rise to cells, i.e., they are elements which are present for the special purpose of bringing about heredity, without anything being specified as to their share in the composition of the living body. As will be shown more clearly later on, Spencer's hypothesis is superior in this respect to Darwin's. On the other hand, Spencer's simi- lar units are the bearers of all the characters of the species, owing to their complex molecular structure ; while the Dar- winian gemmules are primary constituents of individual cells, which are to be considered as differing in a manner correspond- ing to the difference of the individual cells. Spencei-'s theory is epigenetic, Darwin's evolutionaiy ; in this respect the latter is, in my opinion, superior to the former. Galton t was the first to make an attempt to improve on the ♦Charles Darwin, 'The Variation of Animals and Plants under Domes- tication,' 2nd ed., vol. ii., London, 1888; note on p. 371. t Francis Galton, ' A Theory of Heredity,' .Tour7ial of the Anthropologi- cal Institute, 1875.