A YOUNG CUCKOO 69 



hand, it was improbable that variability in the egg 

 of the Cuckoo, whatever were the type of egg 

 originally laid by it, would be sufficient to meet the 

 needs of extreme cases in which the eggs of foster- 

 parents were of a markedly different type. Thus it 

 arises that agreement is more rarely found in such 

 cases. 



It is true that eggs, stated to be Cuckoos' eggs, are 

 reported to have been found resembling the more 

 pronounced types of eggs laid by some foster-parents, 

 but such cases are relatively very rare. Nevertheless, 

 being rare, and concerned with foster-parents laying 

 more pronounced and diverse types of eggs, they are 

 crucial. Even in such cases, Professor Newton tells 

 us : "The operation of this kind of Natural Selection 

 would be most needed in those cases where the 

 species are not easily duped, that is, in those cases 

 which occur the least frequently. Here it is we find 

 it, for observation shows that the eggs of the Cuckoo 

 deposited in nests of the Red-backed Shrike, of the 

 Bunting, of the Redstart, and of the I cterine Warbler, 

 approximate in their colouring to eggs of those 

 species species in whose nests the Cuckoo rarely 

 (in comparison with others) deposits eggs." 



It is therefore by a more rigorous application of 

 Natural Selection, that is, by refusing to hatch 

 any Cuckoo's egg that did not attain a marked 

 degree of resemblance to their own, that these four 

 species got rid of would-be patrons among the 

 Cuckoos save such as laid eggs so like their own 

 that they escaped detection, and were hatched, these 

 four fortunate strains of Cuckoos being thereby 

 preserved. 



