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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    A.—Historical Part. HERBERT SPENCER was practically the first in the present generation to attempt a theoretical explanation of heredity when he propounded his theory of ' physiolo- gical units.' The regeneration of lost parts, e.g., of a leg or the tail of a salamander, led him to the conception of these units, ' in all of which there dwells the intrinsic aptitude to aggregate into the form of that species ; just as in the atoms of a salt there dwells the intrinsic aptitude to crystallise in a particular way.' He calls this aptitude the ' polarity of the organic units,' and defines the latter as being intermediate between the ' chemical units' or molecules and the ' morphological units or cells. They must be ' immensely more complex than the chemical units,' and must therefore correspond to groups of molecules. It is very interesting at the present day, now that we have advanced somewhat further towards a theory of heredity, to summarise the various aptitudes and forces which Herbert Spencer thought it necessary to ascribe to his ' physio- logical units,' in order to arrive at an explanation of the phenomena. Although the sections on Heredity and Regene- ration constitute only a small portion of his great work on the ' Principles of Biology,' and cannot therefore contain a detailed treatment of the phenomena of heredity, his opinions on this subject are evident. Spencer considers, on the one hand, that the whole organism is composed of these units, which are all alike in kind, and on the other, that the germ-cells also contain small groups of them. The former supposition makes regeneration possible to each sufficiently large portion of the body, while the latter gives the germ-cell the power of reproducing the whole : inasmuch as the A