VII " THE ORIGIN OF SPECIES " 229 



champions of its leading doctrines, or at any rate 

 abstain from opposing them ; a host of young and 

 ardent investigators seek for and find inspiration 

 and guidance in Mr. Darwin's great work ; and the 

 general doctrine of evolution, to one side of which 

 it gives expression, obtains, in the phenomena of 

 biology, a firm base of operations whence it may 

 conduct its conquest of the whole realm of Nature. 



History warns us, however, that it is the cus- 

 tomary fate of new truths to begin as heresies and 

 to end as superstitions ; and, as matters now stand, 

 it is hardly rash to anticipate that, in another 

 twenty years, the new generation, educated under 

 the influences of the present day, will be in danger 

 of accepting the main doctrines of the " Origin of 

 Species," with as little reflection, and it may be 

 with as little justification, as so many of our con- 

 temporaries, twenty years ago, rejected them. 



Against any such a consummation let us all 

 devoutly pray ; for the scientific spirit is of more 

 value than its products, and irrationally held 

 truths may be more harmful than reasoned errors. 

 Now the essence of the scientific spirit is criticism. 

 It tells us that whenever a doctrine claims our 

 assent we should reply, Take it if you can compel 

 it. The struggle for existence holds as much in 

 the intellectual as in the physical world. A theory 

 is a species of thinking, and its right to exist is 

 coextensive with its power of resisting extinction 

 by its rivals. 



