168 EVOLUTION 



single peculiarities, but because of their 

 general stability and efficiency. As we have 

 already hinted, we must still admit what 

 Darwin admitted more than fifty years ago- 

 that it is extraordinarily difficult to say 

 precisely why one species has been victori- 

 ous over another in the great battle for life. 

 Part of the difficulty is to be found in the 

 fact that there is seldom a simple issue. 



As Russell puts it: 



"We should think of each creature as 

 being, as it were, the point of intersection of 

 a number of selection processes, of as many 

 processes as there are significant characters; 

 and since the significance of characters must 

 change with the development and growth of 

 the organism and with every alteration in 

 its environment, so the sum of selection 

 processes to which the organism is subjected 

 must be an ever-changing one." 



"The survival or non-survival of the 

 organism will be determined by the resultant 

 of all these selection processes, and though 

 the exact manner of it be extremely complex, 

 it will be the most generally efficient organ- 

 ism which will on the average survive. Its 

 characters will be such as have remained 

 'useful' throughout its life, such as have 

 adapted the organism to the generality of 

 life-conditions under which it has lived." 



