Heredity of Instincts. 1 7 



to all media, conform to all circumstances, or vary and modify its 

 actions in a thousand ways ; yet it is capable of modification within 

 certain limits, when subjected to strong and lasting influences. 



Two causes chiefly produce these variations : external conditions 

 and domestication. Climate, soil, food; the dangers which habitually 

 surround the animal, and the impressions it receives, modify its 

 organism and consequently its instincts. The action of man is still 

 more powerful on the animal than that of Nature : by training, man 

 fashions and bends it to his needs or his wishes. It is not for us to 

 inquire here how these acquired or modified instincts are produced. 

 We have only to ask whether they are hereditary. Experience 

 answers in the affirmative ; many facts show that acquired instincts, 

 as well as those which are natural, are transmitted by heredity. 

 Such are the following : 



G. Leroy observes that in districts where a sharp war is waged 

 against the fox, the cubs, on first coming out of their earths, and 

 before they can have acquired any experience, are more cautious, 

 crafty, and suspicious than are old foxes in places where no attempt 

 is made to trap them. This he explains by the hypothesis of a 

 language among animals. F. Cuvier has furnished the solution of 

 the enigma by referring the fact to the heredity of modifications 

 which are acquired by instinct. There is no doubt that the 

 instinct of fear is acquired in many wild animals, and transmitted 

 to their descendants. Knight, who for sixty years devoted 

 himself to systematic observation of this class of facts, says 

 that during that time the habits of the English woodcock under- 

 went great changes, and that its fear of man was considerably 

 increased by its transmission through several generations. The 

 same author discovered similar changes of habit, even in bees. 

 Darwin has established the fact that animals living in desert 

 islands gradually acquire a fear of man, in proportion as they 

 become acquainted with our methods of destroying them. He 

 says that in England large birds are much more shy than small 

 ones, and this, no doubt, because they are much more persecuted 

 by man. The proof that this is the reason of the difference is 

 found in the fact that in uninhabited islands large birds are not 

 any more timid than small ones. 1 



1 Origin of Species, p. 260. Fifth Edition, 1869. Lucas, ii. 482. 



