NATURAL SELECTION THE ORIGIN OF INSTINCT 75 



On the arrival of the expedition, the animals were perfectly- 

 tame and fearless ; but advantage was taken of this to hunt them 

 down and secure their flesh as meat for the European visitors, 

 and by the end of the winter the animals were already difficult 

 to approach. The following winter, when another exploring 

 party arrived in those parts, the walrus fled whenever it per- 

 ceived a human form in the distance ; it had grown to recognise 

 man as its enemy, and took refuge in instinctive flight. Here 

 is an example of an act of volition which, with the progress 

 of time, has become instinctive ; it is an instinct which is 

 dictated by the necessities of the life of the species, which con- 

 sequently owes its origin and development alike to natural 

 selection. 



The changes effected in the nervous centres of the insect, 

 which flies immediately upwards and in the contrary direction 

 when it perceives the quickly approaching shadow of an object 

 about to pounce upon it, are likewise due to natural selection. 

 Those insects whose nervous mechanism did not respond to the 

 movement of the approaching object must soon have been 

 extirpated, and natural selection is here again the originator of 

 the instinct of fhght. But the instinct of flight in the case of 

 an insect, unlike that in the case of the walrus, is not the result 

 of an intellectual or voUtional process. It cannot be, for the 

 simple reason that the insect does not know what death is, and 

 is consequently unable to take measures to escape it. If the 

 insect be caught by an approaching object, it is instantly killed, 

 and no opportunity is afforded it of learning by experience. 

 And, furthermore, the necessary intelligence for a reasoned 

 volitional process is lacking in the case of the fly or the butter- 

 fly. Flies and butterflies know nothing of death ; but a certain 

 external movement reacts mechanically on their nervous centres, 

 and causes them to fly away instantly and in an opposite direc- 

 tion. Obviously this instinct, essential to the very existence 

 of the species, is a fundamental characteristic of that species, 



