DARWIN'S THEORY 57 



declined to acknowledge any evidence of design in na- 

 ture's working, so that his use of the word was in this 

 respect metaphorical. The principle by which natural 

 selection is guided is indeed adaptation to environment, 

 and the utihty of variations in what has been termed 

 "struggle for existence." This adaptation, however, 

 is not due in Darwin's opinion to design, but to the 

 fact that among the multitude of variations which con- 

 stantly occur none, from the nature of things, can 

 hold their own which are not in harmony with environ- 

 ment and useful, whether directly or indirectly, for 

 the preservation of existence. Natural selection means 

 that Dame Nature destroys whatever is incapable of 

 adjusting itself to the requirements of existence; and 

 the prevalence of adaptation in nature is due, accord- 

 ing to Darwin, to this elimination of the unfit, or, to 

 use Herbert Spencer's phrase, to an inevitable and 

 exclusive "survival of the fittest." ^ 



Darwin's theory is based upon the facts of varia- 

 tion, heredity, and excessive multiplication of organ- 

 isms. The fact of variation is a matter of common 

 observation. No two organisms are alike in all par- 

 ticulars, and this variation appears between parents 

 and offspring, and between the offspring of the same 

 parents. Among these variations there occasionally 

 appear large and abnormal mutations or sports, and 

 such changes, by reason of their exceptional occur- 

 rence, are called "discontinuous" variations. But 



1 Origin of Species, chh. iii, iv. On the effect of Darwin's theory 

 on the argument for design, see pp. 112-116, below. 



