270 ORIGIN OF SPECIES 



our chickens has become useless under domestication, for the 

 mother-hen has almost lost by disuse the power of flight. 



Hence, we may conclude, that under domestication instincts 

 have been acquired, and natural instincts have been lost, 

 partly by habit, and partly by man selecting and accumulating, 

 during successive generations, peculiar mental habits and ac- 

 tions, which at first appeared from what we must in our 

 ignorance call an accident. In some cases compulsory habit 

 alone has sufficed to produce inherited mental changes; in 

 other cases, compulsory habit has done nothing, and all has 

 been the result of selection, pursued both methodically and 

 unconsciously: but in most cases habit and selection have 

 probably concurred. 



SPECIAL INSTINCTS 



We shall, perhaps, best understand how instincts in a state 

 of nature have become modified by selection, by considering 

 a few cases. I will select only three, — namely, the instinct 

 which leads the cuckoo to lay her eggs in other birds' nests; 

 the slave-making instinct of certain ants ; and the cell-making 

 power of the hive-bee. These two latter instincts have gener- 

 ally and justly been ranked by naturalists as the most won- 

 derful of all known instincts. 



Instincts of the Cuckoo. — It is supposed by some naturalists 

 that the more immediate cause of the instinct of the cuckoo 

 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 on 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 inconveni- 

 ently long, more especially as she migrates at a very early 

 period; and the first hatched young would probably have to 

 be fed by the male alone. But the American cuckoo is in this 

 predicament; for she makes her own nest, and has eggs and 

 young successively hatched, all at the same time. 'It has been 

 both asserted and denied that the American cuckoo occasion- 

 ally lays her eggs in other birds' nests ; but I have lately heard 

 from Dr. Merrell, of Iowa, that he once found in Illinois a 

 young cuckoo together with a young jay in the nest of a Blue 



