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

  • August Weismann
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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    to arrive at a satisfactoiy epigenetic theory * which, starting from a germ-substance of comparatively simple structure, should exhibit the various differentiations of the organism as due to regular changes brought about by the division of this primary structure. But the more I considered the problem as time went on, the more I was convinced that such a solution was impossible. And in this book I trust that I shall be able to give a satisfactory proof that only one theory of evolution in Darwin's sense, i.e., the assumption of minute primary constitu- ents in the germ,is in accordance with the facts ; and the objection which for a long time prevented me from accepting this very simple assumption, disappears with the discovery that what is apparently impossible does really occur. 1 certainly consider even now that Darwin's theory must be looked upon, and that he probably considered it, rather as an inquiry into the problem of heredity than as a solution of the problem. His assumptions do not, properly speaking, explain the phenomena. They are to a certain extent a mere para- phrase of the facts, an explanation of a purely formal nature, based on speculative assumptions, which were made not because they seemed possible, or even likely, but because they provided a formal explanation of all the phenomena on one principle. If we suppose that each cell arises from a special gemmule, and that these gemmules are present wherever they are wanted, it is easy to see how that structure, the origin of which we wish to explain, may appear in any given position. Further, when a large number of cells is to arise in regular succession from one egg-cell, the desired sequence of cells must of course result if we assume that the gemmules present become active in the required order. But this supposition does not really explain the phenomena. Even at the present day our explanations are imperfect enough, and are far from going to the bottom of the matter, but they differ from Darwin's provisional hypothesis in that they attempt to find out the actual facts concerned in the processes, and to arrive at a real, and not merely a formal, solu- tion of the problem. The great naturalist's merit in having at once found the right foundation on which to base a real solution is not diminished by the fact of his having been less startled by * The indication of such a theory is given, e.g., in the essay entitled 'Die Continuitiit des Keimplasma's,' Jena, 1885, p. 386^ seq, (pp. 207 seq. of the English translation.)
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