DEVELOPMENT OF BIOLOGY 



475 



mutability of species ; and by the theory of natural selection on the 

 basis of slight adaptive variations resulting in the survival of the 

 fittest in the struggle for existence — which, strange to say, Darwin 

 and Wallace (1822-1913) reached simultaneously and independ- 

 ently — Darwin "made the old idea current intellectual coin." 

 (Figs. 236, 239, 311, 312.) 



To-day, as we know, no representative biologist questions the 

 fact of evolution — "evolution knows only one heresy, the denial 



Fig. 311. —Alfred Russel Wallace. 



of continuity" — though in regard to the factors involved, there is 

 much difference of opinion. It is possible that we shall have reason 

 to depart widely from Darwin's interpretation of the effective prin- 

 ciples at work in the origin of species, but withal this will have 

 little influence on his position in the history of biology. The great 

 value which he placed upon facts was exceeded only by his demon- 

 stration that this "value is due to their power of guiding the mind 

 to a further discovery of principles." The Origin of Species brought 

 biology into line with the other inductive sciences, recast prac- 

 tically all of its problems, and instituted new ones. Darwin beauti- 

 fully and conservatively expressed this new outlook on nature in 

 the historically important concluding paragraph of his epoch- 

 making work : 



