48 FIFTY YEAKS OF DARWINISM 



EVOLUTION CONTINUOUS OR DISCONTINUOUS 



Darwin fully recognized the limits which may 

 be set to the results achieved by the artificial 

 selection in one direction of individual variations. 

 Thus he wrote, Aug. 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 certain 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 experience, that a little more improve- 

 ment could not be got in the course of a centuiy , and theoreti- 

 cally very improbable that after a few thousands [of years] 

 rest there would not be a start in the same line of variation.' l 



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 Morgan, 

 and Osborn to meet this very difficulty, as ex- 

 pressed in the following paragraph quoted from 

 the present writer's address to the American 

 Association for the Advancement of Science at 

 the Detroit meeting, Oct. 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 times in which the needed 

 inherent variations are not forthcoming.' 2 



1 More Letters, i. 314. 



2 Development and Evolution, J. M. Baldwin, New York (1902), 350. 



