useful, that those individuals who possess the increase are no longer at such an advantage in the struggle for existence as to survive to an appreciable extent beyond those who have it not. Therefore since individuals vary each one from all others, since the offspring, while varying somewhat from their parents, tend to transmit the peculiarities of their parents, and since individuals that vary favourably tend of course to survive and have offspring, whereas individuals that vary unfavourably tend to be eliminated and have no offspring, it is deductively so certain that whenever there is a struggle for existence,—and throughout nature there is always such a struggle,—the survival of the fittest must lead to evolution, that it is scarcely necessary to appeal to facts for inductive confirmation. If, however, we do seek such confirmation, we find it in three great bodies of facts collected mainly in different fields of research, each of which is separately decisive, and which collectively furnish confirmation so absolute that, practically speaking, no student of biological science now believes otherwise than that the whole organic world arose by a process of evolution.
The first great mass of evidence is furnished by the science of Comparative Anatomy, especially by that branch of it which deals with Comparative Embryology. In the interests of the general reader, we may with advantage defer the consideration of it.
The second great mass of evidence is furnished by the science of Paleontology, which teaches, on the evidence of fossil remains, that the earth has not always been inhabited by the same forms of life, but that during the whole vast period which intervened between the deposit of the earliest fossiliferous rocks and the present age, there occurred a constant but gradual change of form, as a result of which type shaded into type, generally in an upward direction, and which can
