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 and his reply will be definite, and uniformly the same: what he says, all chemists will repeat. Not so the zoologist. Sometimes he will class two animals as of different species, when they only differ in colour, in size, or in the numbers of tentacles, &c.; at other times he will class animals as belonging to the same species, although they differ in size, colour, shape, instincts, habits, &c. The dog, for example, is said to be one species with many varieties, or races. But contrast the pug-dog with the greyhound, the spaniel with the mastiff, the bulldog with the Newfoundland, the setter with the terrier, the sheepdog with the pointer: note the striking differences in their structure and their instincts: and you will find that they differ as widely as some genera, and as most species. If these varieties inhabited different countries—if the pug were peculiar to Australia, and the mastiff to Spain—there is not a naturalist but would class them as of different species. The same remark applies to pigeons and ducks, oxen and sheep.

The reason of this uncertainty is that the thing Species does not exist: the term expresses an abstraction, like Virtue, or Whiteness; not a definite concrete reality, which can be separated from other things, and always be found the same. Nature produces individuals; these individuals resemble each other in varying degrees; according to their resemblances we group them together as classes, orders, genera, and species; but these terms only express the relations of resemblance, they do not indicate the existence of such things as classes, orders, genera, or species.[*] There is a reality indicated by each term—that is to say, a real relation; but there is no objective existence of which we could say, This is variable, This is immutable. Precisely as there is a real relation indicated by the term Goodness, but there is no Goodness apart from the virtuous actions and feelings which we group together under this term. It is true that metaphysicians in past ages angrily debated respecting the Immutability of Virtue, and had no more suspicion of their absurdity, than moderns have who debate respecting the Fixity of Species. Yet no sooner do we understand that Species means a relation of resemblance between animals, than the question of the Fixity, or Variability, of Species resolves itself into this: Can there be any variation in the resemblances of closely allied animals? A question which would never be asked.

No one has thought of raising the question of the fixity of varieties, yet it is as legitimate as that of the fixity of species; and we might also argue for the fixity of genera, orders, classes; the fixity of all these being implied in the very terms; since no sooner does any departure from the type present itself, than by that it is excluded from the category; no sooner does a white object become gray, or yellow, than it is excluded from the class of white objects. Here, therefore, is a sense in which the phrase "fixity of species" is indisputable; but in this sense the phrase has never been disputed. When zoologists have maintained that species

et rien de pareil n'existe dans la nature; but species is not an abstraction!—See Lettres à Pfaff, p. 179.
 * CUVIER says, in so many words, that classes, orders, and genera, are abstractions,