There is scarcely any subject to which this principle applies more completely than it does to Evolution; for what is called “the doctrine of Evolution” is only a theory. It is not a collection of facts, but a theory which some of its warmest advocates—as, _e.g._, Professor Drummond—declare to be “still unproved.” {3} While, therefore, we fully recognise that it would be the utmost folly “to debate a point of natural history with Darwin, or a question of comparative anatomy with Owen,” we may, by the aid of common-sense, form an opinion possibly as sound at theirs on the unproved theory which has been founded on the ascertained facts which those great investigators have placed within our reach. This is all that I would attempt to do in the present paper. I do not propose to call in question a single fact ascertained by men of science. All that I would venture to do is to exercise the ordinary powers of thought in considering one of the theories which some scientific men have suggested as an explanation of those facts. I say “some scientific men,” for there is a very great difference of opinion amongst scientific men, and no one can read the admirable papers produced by the Victoria Institute without perceiving now much accurate observation, how wide a scientific knowledge, and how great a force of Baconian philosophy is arrayed against the theory just now in the fashion. Let us begin, then, with a few facts respecting which we are all agreed, and which as they are sometimes called by the name of Evolution, are supposed to supply evidence of the correctness of the theory. (1) We all believe in _growth_. It is a matter of fact that the world is full of growth. And this growth is not limited to gradual, or continuous, enlargement or development; but consists sometimes in most remarkable sudden changes, as when the egg becomes a chicken, the caterpillar a chrysalis, and the chrysalis a butterfly. Every living creature, whether plant or animal, has its own mode of growth; and no living creature is born into the world in the fulness of its stature. The man was once in his cradle, the eagle in its egg, the oak in its acorn; and no one can point to any living thing, either in the animal or vegetable kingdom, that began life with the full development of all the powers or properties of its species. Whatever men may think of any theory, as a matter of fact there is invariably growth as the first, and most certain, accompaniment of life.