A YOUNG CUCKOO 67 



sufficiently similar to those of the species of bird 

 into whose nest they had been introduced, they are 

 assumed to have been hatched without suspicion, 

 the strain of Cuckoos laying that similar kind 

 of egg being thereby and to that extent " naturally 

 selected" by the agency of that foster-species. 

 On the other hand, the foster-species is assumed 

 to have refused to hatch Cuckoos' eggs not 

 sufficiently similar to its own, and the strain of 

 Cuckoos laying that dissimilar type of egg was, qua 

 that foster-species, eliminated. By elimination of 

 Cuckoos laying eggs different from those of the 

 foster-parent, only those Cuckoos whose eggs 

 corresponded more nearly with its own, survived to 

 continue to place their eggs in its nest. Such eggs 

 are said to have been assimilated by a process of 

 Natural Selection. In this process the discriminating 

 foster-species have been the " natural selectors," 

 and the degree of assimilation will depend upon the 

 extent to which discrimination has been exercised 

 by them. 



It will thus be seen that assimilation has no 

 object, and can have none, least of all "to render the 

 Cuckoo's egg 'less easily recognised by the foster- 

 parents as a substituted one.' ' For assimilation, by 

 the theory, is a by-product of the discrimination 

 exercised by foster-species against eggs unlike their 

 own, and to assign to it such an object is to ascribe 

 to foster-parents as the determining agents in the 

 process of assimilation, the object of selecting a type 

 of Cuckoo's egg most nearly resembling their own, 

 in order the more readily to deceive themselves ; 

 which is untenable. 



