VOLUNTARY ACTION 225 



Every man enjoys rest when wearied. On every one comes 

 the periodic craving for sleep. Examining our own minds 

 we see that an instinct is an emotion, a desire, an impulse 

 to action, aroused in us by a given stimulus and prompting 

 us to definite acts the instinctive acts by which the desire 

 is gratified. Since we have inherited our instincts from pre- 

 human ancestors, we shall not be very wrong if we suppose 

 that the instincts of lower animals are of much the same 

 nature as our own that they are emotions and desires, 

 having their springs in present or prospective pleasures and 

 pains. In all probability, therefore, the feelings of sexual 

 and parental love, for example, do not differ altogether in 

 the human being, the tiger, and the spider. 



382. Clearly it is the presence of this prompting emotion, 

 this desire to achieve pleasure or avoid pain, that dis- 

 tinguishes an instinctive act from a mere reflex. Very low 

 animals may possess reflexes ; but the existence of the 

 emotion marks an advanced stage in evolution. Before it 

 can be felt and gratified the animal must have a compara- 

 tively highly-developed nervous system, connected with 

 organs of sense and movement. Instinctive actions, besides, 

 are usually very much more complex than reflex actions. 

 They are directed to ends that are often immensely more 

 distant. Compare, for instance, any of the reflexes in the 

 body of the spider or the dragon-fly with the long series of 

 instinctive movements which the one makes in spinning a 

 web and the other in seeking his prey. A reflex may be, 

 and often is, quite unaccompanied by any manifestation of 

 mind. But mind, often highly developed, must be present 

 during every performance of an instinctive act. Imagine, for 

 instance, a dragon-fly darting hither and thither in a wood, 

 keenly observant of obstacles, of enemies, of possible food, 

 and possible mates. A flood of sense-impressions must pour 

 on his mind, and awaken a constantly changing stream of 

 emotions. Imagine a spider approaching a huge wasp en- 

 tangled in his web, or his equally formidable mate. As 

 desire and fear, hope and apprehension, chase each other 

 through his mind and contend for mastery he hesitates, 

 advances, and retreats. Amid the conflict of emotions some- 

 thing very like what we term intelligence is born. He 

 chooses his line of action in a sense as real as a man would 

 do under similar circumstances. 



383. It is impossible of course to indicate the precise 

 stage of evolution the particular kind of animals in which 

 instinct first arose. We can only say that it must have 



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