Nest-building, Incubation, and Migration. 243 



young cuckoo who did not eject his foster brothers would 

 run no little risk of elimination by starvation, especially 

 when the foster parents were small and unable to bring 

 supplies of food to satisfy his capacious appetite as well as 

 the needs of their own offspring — though here, indeed, it 

 might fairly be contended that his larger size and greedy 

 voracity would itself doom the others to starvation. The 

 eliminative steps in the establishment of the central habit 

 of depositing the eggs in an alien nest are not so easy to 

 explain even conjecturally. Darwin's account of the process 

 needs modification in any case. He suggested that the 

 habit began by the occasional laying of eggs in alien nests. 

 But it would seem that the cuckoo lays her egg on the 

 ground and then carries it to a nest in her bill. For such 

 a habit the occasional laying of an egg in an alien nest 

 would be no preparation. It would seem more probable 

 that it began by laying eggs on the ground when the hen 

 was forced to deposit them unprepared. And the habit of 

 polyandrous intercourse, correlated with the preponderant 

 number of males, may have been in some way associated 

 with the gradual loss of the instinct of nidification. Guess 

 as we may, however, it must be confessed that, if the 

 instinct be due to natural selection, little is known of the 

 stages of development. But, on the other hand, it is not 

 less difficult to see how the strange instinct of the cuckoo 

 could have arisen as the result of intelligently acquired 

 habit, in a bird of somewhat remarkably low intelligence. 

 The theory of individual acquisition, transmitted from 

 parent to offspring, even if unaccompanied by the bio- 

 logical difficulties involved in any form of such trans- 

 mission, seems to involve not merely the intelUgent 

 utihzation of the results of experience, but the exercise of 

 truly rational powers of what appears to us a peculiarly 

 depraved order. 



