Compare the condition of a variable form like the male Ruff (or in a less degree the Red Grouse in both its sexes) with that of the common Pheasant which is comparatively constant. In the Pheasant no doubt variations do occur as in other wild birds, but apart from the effects of mongrelisation the species is unquestionably uniform. Could it seriously be proposed that we should regard the constancy of the pheasant's plumage in this country as depending on the special fitness of that type of colouration? Even if the pheasant be not an alien in Western Europe, it has certainly been protected for centuries, and for a considerable period has existed in a state of semi-domestication. Such conditions should give good opportunity for polymorphism to be produced. In some coverts various aberrations do of course occur and persist, yet there is nothing indicative of a general relaxation of the fixity of the specific type, and the pheasant remains substantially a fixed species.[17] The common pheasant (_Phasianus colchicus_) even shows little of that disposition to form local races which appears in the species of Further India. Are we not then on safer ground in regarding the fixity of our species as a property inherent in its own nature and constitution? Just as in ages of domestication no rose has ever given off a blue variety so has the pheasant never broken out into the polymorphism of the Ruff.
As soon as it is realised how largely the phenomena of variation and stability must be an index of the internal constitution of organisms, and not mere consequences of their relations to the outer world, such phenomena acquire a new and more profound significance.
[1] In _Mendel's Principles of Heredity_ (Cambridge University Press, 1909) I have dealt with this subject, giving an account of the principal facts discovered up to the beginning of 1909.
[2] Matthioli Opera, Ed. 1598, p. 8, originally published 1565.
[3] Ray's instances relate to Kales, and in most of these examples we can see that there was no question of mutation or transmutation at all, but that the occurrence was due either to mistake or to cross-fertilisation. Sharrock, to whom Ray refers, was inclined to discredit stories of transmutation, but he has also this passage (_History of the Propagation and Improvement of Vegetables by the Concurrence of Art and Nature_, Oxford, 1660, p. 29):