224 The Science of Life. 



minded marshalling of the "evidences " which sug- 

 gest the doctrine of descent he won the conviction of 

 _ . . the biological world. He made the old idea 



Darwinism. > * n i T * 1 



current intellectual com. In so doing he 

 was greatly aided by Spencer and Wallace, Haeckel 

 and Huxley, (b) He applied the conception to various 

 sets of facts, such as the expression of the emotions, 

 and the descent of man, and showed what a powerful 

 organon it was. Here again he was greatly aided by 

 his contemporaries, and Spencer's work in this direction 

 is even more important than Darwin's. (c) At the 

 same time as Alfred Russel Wallace he promulgated 

 the theory of natural selection a generalization second 

 in importance only to the general doctrine of evolution. 

 It may be briefly stated as follows : 



Offspring very frequently differ from their parents in 

 possessing some new feature or variation. In other 

 words, there is something novel in the expression of 

 the inheritance. The reasons for this are obscure, but 

 as to the fact of the frequent occurrence of variations 

 there is no doubt. 



In the course of nature there is a manifold struggle 

 for existence, due to a variety of causes, such as the 

 tendency of population to outrun the means of sub- 

 sistence, or the inconstancy of external conditions. 

 As the result of this struggle, only a small percentage 

 of the organisms born become adults or reproductive. 

 In this process of elimination there will tend to be a 

 weeding out of those with relatively less fit variations, 

 and a survival of those with relatively more fit variations. 



Moreover, the favourable congenital variation pos- 

 sessed by the survivors is handed on in inheritance to 

 their offspring, and tends to be intensified when the new 

 generation is bred from parents both possessing the 

 happily advantageous character. 



The natural elimination of the relatively less fit vari- 

 ants, or, what comes to the same thing, the natural 

 selection of the relatively more fit variants, explains 

 the transformation and adaptation of species, and the 

 general progress from simpler to higher forms of life. 



Darwin held that " natural selection has been the 



