VIII. 



INDUCTION. 



A T 7HEN Darwin had once grasped the idea 

 * * of the descent of species, and natural 

 selection as the cause determining modifica- 

 tion, it was inevitable that he should look upon 

 all classes of biological facts as consequences 

 of these. Accordingly, nearly all the investi- 

 gations which he carried on were pursued as 

 deductions from his general principles. But 

 although the larger outlines and a large part 

 of the details of his work were deductive, he 

 was frequently obliged to pass by induction 

 from facts to the subordinate principles which 

 he established 



One of the earliest of the many instances in 

 which he felt compelled to re-interpret whole 

 groups of facts was that relating to human ex- 

 pression. When, in 1838, he read Sir Charles 

 Bell's great work on the "Anatomy of Expres- 

 sion," the view of the latter that man had been 

 created with certain muscles especially adapted 

 for the expression of his feelings struck him 



