Evolution / by Patrick Geddes and J. Arthur Thomson.

  • Patrick Geddes
Date:
[1911?]
Catalogue details

Licence: Public Domain Mark

Credit: Evolution / by Patrick Geddes and J. Arthur Thomson. Source: Wellcome Collection.

    131/264 (page 127)
    sudden though minute change. It is perhaps appropriate to compare such a change with a chemical substitution.” 44 The name I propose to give to this 4 species-forming5 variability is Mutability —a term in general use before Darwin’s time. The changes brought about by it, the Muta¬ tions, are phenomena as to the exact nature of which we understand very little so far. The best known examples of such mutations are the so-called spontaneous variations (the 4 single variations ’ of Darwin) by which new and distinct varieties arise. They are also termed, fitly enough, sports. In spite of the fact that they occur fairly often, they are usually not noticed until the new form has already appeared, when of course it is too late to study the phenomenon of its origin ex¬ perimentally. These new forms can be sought for in cultivated species, which are seldom of pure origin; as well as in Nature. But as yet we have no power of inducing them at will. It is my belief that all the simple characters of animals and plants arise in this way.” 44 Under the general term variation, then, are included two distinct phenomena : muta¬ bility, and fluctuation or ordinary variation.” 44 The methods of artificial selection cor¬ respond to these two types of variability.