Instinct and its Lessons 115 



admitted, that the more immediate and final 1 cause of 

 the Cuckoo's instinct, is that she lays her eggs, not 

 daily, but at intervals of two or three days, so that if 

 she were to make her own nest, and sit upon her own 

 eggs, those first laid would have to be left for some time 

 unincubated, or there would be eggs and young birds of 

 different ages in the same nest. If this were the case, 

 the process of laying and hatching might be incon- 

 veniently long, more especially as she has to migrate at 

 a very early period ; and the first hatched young would 

 probably have to be fed by the male alone." 



It is hard to see how this reasoning should on its own 

 merits gain common acceptance. Other birds, Owls 

 for instance, lay their eggs at intervals, as long, or longer, 

 and the owlets first hatched help to hatch the other 

 eggs ; so that we find in an Owl's nest " eggs and young 

 birds of very different ages." Again, the Cuckoo's stay 

 with us is not very much briefer than that of the 

 Swallow, which yet contrives to rear two broods or 

 perhaps more. That the Cuckoo could easily acquire 

 the habit of staying a little longer is evidenced by the fact 

 that young birds linger not uncommonly till September. 



But supposing that all the circumstances enumerated 

 rendered it hard for the Cuckoo to make its family 

 arrangements : what then ? The natural consequence 

 should be that the Cuckoo race would perish, too 

 heavily handicapped to struggle for survival. How 

 could its weaknesses in this regard have suggested their 

 own remedy ? 2 Here there is no question of a series 

 of acts graduated towards the completed habit. Either 

 an egg was laid inside another nest or outside. No egg 

 laid outside would benefit the bird at all. An egg laid 

 inside requires the instinct which it is supposed to 

 originate. 



1 The term final cause is, of course, not used here in its phil- 

 osophical sense. 



- It might, moreover, be suggested that cuckoos should have 

 learnt to lay their eggs at shorter intervals, those which did so 

 obtaining a marked advantage over the others. 



