2 Darwin, and after Darwin. 



Must we regard survival of the fittest as the one 

 and only principle which has been concerned in the 

 progressive modification of living forms, or are we to 

 suppose that this great and leading principle has been 

 assisted by other and subordinate principles, without 

 the co-operation of which the results, as presented in 

 the animal and vegetable kingdoms, could not have 

 been effected ? Now Darwin's answer to this question 

 was distinct and unequivocal. He stoutly resisted 

 the doctrine that natural selection was to be regarded 

 as the only cause of organic evolution. On the other 

 hand, this opinion was and still continues to be 

 persistently maintained by Mr. Wallace ; and it con- 

 stitutes the source of all the differences between his 

 views and those of Darwin. Moreover, up to the time 

 of Darwin's death, Mr. Wallace was absolutely alone 

 in maintaining this opinion : the whole body of 

 scientific thought throughout the world being against 

 him ; for it was deemed improbable that, in the 

 enormously complex and endlessly varied processes 

 of organic evolution, only a single principle should be 

 everywhere and exclusively concerned 1 . But since 

 Darwin's death there has been a great revolution of 

 biological thought in favour of Mr. Wallace's opinion. 

 And the reason for this revolution has been, that 

 his doctrine of natural selection as the sole cause 

 of organic evolution has received the corroborative 

 support of Professor Weismann's theory of heredity . 

 which has been more or less cordially embraced by 

 a certain section of evolutionists, and which appears to 

 carry the doctrine in question as a logical corollary, so 

 far, at all events, as adaptive structures are concerned. 

 ' Contributions to the TTuory of Natural Selection, p. 47. 



