194 ON THE ORIGIN OF SPECIES 



do make an attack, and are then beaten ; and if not 

 cured, they are destroyed ; so that habit, with soma 

 degree of selection, has probably concurred in civilising 

 by inheritance our dogs. On the other hand, young 

 chickens have lost, wholly by habit, that fear of the dog 

 and cat which no doubt was originally instinctive in 

 them, in the same way as it is so plainly instinctive in 

 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 compulsory habit alone has sufficed to 

 produce such 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, 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 im- 



