162 EVOLUTION 



observed fact that most living creatures die 

 young it seems to most naturalists to follow 

 that natural selection is indeed a vera causa 

 and the survival of the fittest a reality. 



DIRECT EVIDENCE FOR NATURAL SELEC- 

 TION. One of the interesting steps of progress 

 since Darwin's day has been the attempt to 

 secure definite evidence of the operation of 

 natural selection. The theory works well as 

 an interpretation, but what we need is actual 

 proof of discriminate selection, actual evidence 

 that survivors do survive in virtue of par- 

 ticular qualities. A few examples of this in 

 present-day experience will give strength to 

 the belief that similar processes occurred, as 

 Darwin suggested, throughout the past. 



It is interesting to note that so strong 

 a selectionist as Weismann considers that 

 natural selection can be proved only indirectly. 

 He says : " A direct estimation of the relative 

 protective value of the two colours [of a 

 Sphingid caterpillar] is altogether out of the 

 question. The survival of the fittest cannot 

 be proved in nature, simply because we are 

 not in a position to decide a priori what the 

 fittest is." As Mr. E. S. Russell remarks: 

 " This is a significant admission from the pro- 

 tagonist of pure Darwinism, but he admits too 

 much. It is true we cannot decide a priori 



