48 FIFTY YEARS OF DARWINISM 



EVOLUTION CONTINUOUS OR DISCONTINUOUS 



Darwin fully recognized the limit to the results 

 which can be achieved by the artificial selection 

 in one direction of individual variations. Thus 

 he wrote/ August 7, 1869, to Sir Joseph 

 Hooker: — 



" I am not at all surprised that Hallett has found 

 some varieties of wheat could not be improved in cer- 

 tain desirable qualities as quickly as at first. All 

 experience shows this with animals; but it would, I 

 think, be rash to assume, judging from actual experi- 

 ence, that a little more improvement could not be got 

 in the course of a century, and theoretically very 

 improbable that after a few thousands [of years'] rest 

 there would not be a start in the same line of variation." 



The conception of evolution hindered or for a 

 time arrested for want of the appropriate varia- 

 tions is far from new. The hypothesis of organic 

 selection was framed by Baldwin, Lloyd Mor- 

 gan, and Osborn to meet this very difficulty, as 

 expressed in the following paragraph quoted 

 from the present writer's address to the Amer- 

 ican Association for the Advancement of Science 

 at the Detroit meeting, October 15, 1897 : — 



" The contention here urged is that natural selection 

 works upon the highest organisms in such a way that 

 they have become modifiable, and that this power of 

 purely individual adaptability in fact acts as the nurse 

 by whose help the species . . . can live through 



■ More Letters, I, p. 314. 



