Volume 2

Darwin, and after Darwin : an exposition of the Darwinian theory and a discussion of post-Darwinian questions / by George John Romanes.

  • Romanes George John, 1848-1894.
Date:
1892-1897
Catalogue details

Licence: Public Domain Mark

Credit: Darwin, and after Darwin : an exposition of the Darwinian theory and a discussion of post-Darwinian questions / by George John Romanes. Source: Wellcome Collection.

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

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    the same variety are exposed during several generations to any change in their physical conditions of life, all, or nearly all, the individuals are modified in the same manner. A new sub-variety would thus be produced without the aid of selec- tion V As an example of the special instances that he gives, I may quote the following from the same work:— Each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the same cause were to act uniformly during a* long series of generations on many individuals, all probably would be modi- fied in the same manner. And, as instances of his more general statements in Chapter XXIII, these may suffice :— The direct action of the conditions of life, whether leading to definite or indefinite results, is a totally distinct consider- ation from the effects of natural selection The direct and definite action of changed conditions, in contra- distinction to the accumulation of indefinite variations, seems to me so important that I will give a large additional body of miscellaneous facts2. Then, after giving these facts, and showing how in the case of species in a state of nature it is often impossible to decide how much we are to attribute to natural selection and how much to the definite action of changed conditions, he begins his general summary of the chapter thus: — There can be no doubt, from the facts given in the early part of this chapter, that extremely slight changes in the conditions of life sometimes act in a definite manner on our already variable domesticated productions [productions, there- fore with regard to which uniformity and stability of modification are least likely to arise]; and, as the action of changed conditions in causing general or indefinite vari- i Variation, &c, vol. ii. p. 260. 2 Ibid. vol. ii. p. 261.