216 INSTINCT. Chap. VII. 



young pheasants, though reared under a hen. It is not 

 that chickens have lost all fear, but fear only of dogs 

 and cats, for if the hen gives the danger-chuckle, they 

 will run (more especially young turkeys) from under 

 her, and conceal themselves in the surrounding grass or 

 thickets ; and this is evidently done for the instinctive 

 purpose of allowing, as we see in wild ground-birds, their 

 mother to fly away. But this instinct retained by 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 domestic 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 actions, which at first appeared from what we must 

 in our ignorance call an accident. In some cases com- 

 pulsory habit alone has sufficed to produce such inhe- 

 rited mental changes ; in other cases compulsory habit 

 has done nothing, and all has been the result of selec- 

 tion, pursued both methodically and unconsciously ; but 

 in most cases, probably, habit and selection have acted 

 together. 



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, out of 

 the several which I shall have to discuss in my future 

 work, — namely, the instinct which leads the cuckoo to 

 lay her eggs in other birds' nests; the slave-making 

 instinct of certain ants ; and the comb-making power of 

 the hive-bee : these two latter instincts have generally, 

 and most justly, been ranked by naturalists as the most 

 wonderful of all known instincts. 



It is now commonly admitted that the more imme- 

 diate and final cause of the cuckoo's instinct is, that 



