Genetic principles in medicine and social science / by Lancelot Hogben.

  • Hogben, Lancelot Thomas, 1895-1975.
Date:
1931
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Genetic principles in medicine and social science / by Lancelot Hogben. Source: Wellcome Collection.

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    CHAPTER II SINGLE GENE SUBSTITUTIONS IN HUMAN PATHOLOGY § 1 The discovery of the phenomena of fertilisation, following the rise of the Cell Doctrine during the first half of the nineteenth century, necessitated a profound change in the attitude of biologists to the phenomena of hereditary transmission. The demonstration that a single sperm penetrates the egg in the act of fertilisation was given by Fol in 1879, twenty years after the publication of the first edition of The Origin of Species. In the ensuing decade the nuclear phenomena of fertilisation were successfully elucidated by Van Beneden, Boveri, and others. Henceforth hereditary resem blance was seen to have its basis in the material structure of the sperm and of the egg. Since then genetic differences have come to be regarded as those which are referable to structural differences in the sperm and the egg alone. This interpretation of hereditary resemblance implied a complete reorientation of biological concepts, leading, in the first place, to Weismann 's theory of the germ plasm. So long as there existed no clearly defined recognition of the physical nature of the link between two successive generations it had seemed natural to assume that modifications occurring during the lifetime of the parent could influence the course of development in the offspring. The pendulum then swung in the opposite direction. From a complete misunderstanding of the rôle of environment in the process of inheritance, biologists were now tempted to neglect the rôle of environment in the process of development. The neglect of the rôle of environment in the course of develop ment bore fruit in a tendency to interpret all differences between parents and offspring as genetic differences. This view is explicitly stated by Weismann in the following passage, which occurs in The Germ Plasm (p. 410) : We have seen that this transmission affects the whole organism and extends to the most trifling details, and we also know that it is never complete, and that the offspring and parent are never identical, but that the former