Experimental Pedigree-Cultures 571 



tempt to surmount it. Darwin tried to re- 

 place the unknown cause by natural agencies, 

 which lie under our immediate observation. 

 On this point Darwin was superior to his 

 antagonists, and it is chiefly due to the clear 

 conception of this point that his theory has 

 gained its deserved general acceptance. Accord- 

 ing to Darwin, changes occur in all directions, 

 quite independently of the prevailing circum- ' 

 stances. Some may be favorable, others detri- 

 mental, many of them without significance, 

 neither useful nor injurious. Some of them 

 will sooner or later be destroyed, while others 

 will survive, and which of them will survive, 

 is obviously incumbent on the question, 

 whether their particular changes agree with 

 the existing conditions or not. This is what 

 Darwin has called the struggle for life. 

 It is a large sieve, and it only acts as 

 such. Some fall through and are annihilated, 

 others remain above and are selected, as the 

 phrase goes. Many are selected, but more are 

 destroyed ; daily observation does not leave any 

 doubt upon this point. 

 ' How the differences originate is quite another 

 question. It has nothing to do with the theory 

 of natural selection nor with the struggle for 

 life. They have an active part only in the ac- 

 cumulation of useful qualities, and only in so 



