168 EVOLUTION 



There is another consideration which Darwin 

 had certainly in mind, and which, like that 

 just explained, has often been lost sight of 

 since. It is illustrated, for instance, by the 

 researches of Bumpus and of Crampton on 

 the survival of sparrows and pupae respectively. 

 The point was, that the survivors seemed to 

 survive, not because of 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 victorious 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 



