118 A PHILOSOPHER WITH NATURE 



now have inevitably been with those birds which 

 from generation to generation obtained the most 

 food in the struggle which ever went on in the nest. 

 This is where, in all probabihty, we must look for 

 the origin in the young cuckoo of the habit of ejecting 

 its fellows from the nest, and the development in 

 the surviving birds, through the operation of natural 

 selection, of the pecuhar temperament which accom- 

 panies it. 



If we are right so far, it is probable that we are 

 now also in view of the explanation of the pheno- 

 menon of the great preponderance of males. It is 

 a weU-known fact that amongst most birds the 

 males are always the stronger and more active in the 

 nest. The advantage in such a struggle must always 

 have been with the males, and the broods of which 

 the greatest number survived were those of birds 

 which produced the largest proportion of males. 

 This selection may have continued after the cuckoo 

 had acquired its parasitic habits. It would operate, 

 it must be noticed, not simply by weeding out the 

 females, but by selecting for survival the descend- 

 ants of those cuckoos which produced a preponder- 

 ance of males, and which would consequently transmit 

 a similar tendency to their offspring. This tendency 

 thus developed through an immense number of 

 generations would inevitably become in course of 

 time what we find it to be at the present day, the 

 normal habit of the bird. 



The origin of the parasitic habit of the cuckoo 

 is now less difficult to account for. We have here, 

 in fact, only to follow in the main the explanation 

 already suggested by Darwin, always remembering, 

 however, that this habit is probably itself but an 



