ORGAXIC EVOLUTION' — PHYSICAL 9 



useful, that those indi\'iduals 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 ofispring, 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 

 ofispring, whereas individuals that vary unfavourably 

 tend to be eliminated and have no offiipring, 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 col- 

 lectively furnish confirmation so absolute that, piTicti- 

 cally 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 



