88 HEREDITY AND SELECTION IN SOCIOLOGY 



The difficulty is avoided if we seek tlie origin of animal instinct 

 in natural selection, and if we are content to see in instinct a 

 case of adaptation — not of conscious, but of unconscious adapta- 

 tion — called forth by the elementary necessities of life itself. 

 Reflex action is admitted by all to be unconscious. The closing 

 of the eyelids when the retina is suddenly struck by a vivid 

 flash of light, or stimulated by the movement of a rapidly ap- 

 proaching object, is purely reflex and automatic. The light 

 which strikes the retina stimulates the sensory nerves at the 

 periphery, and this stimulus is communicated by the nervous 

 channels to certain cerebral centres, from which it is recom- 

 municated to the periphery, where it manifests itself in an act 

 which is nothing but the reaction of the organism to the original 

 external stimulus. The life of the individual, whether organic 

 or psychical, is but a sum of reactions to the stimuli of the en- 

 vironment. According to Spencer, it consists in a correspon- 

 dence of the individual with the environment ; and this sum of 

 actions and reactions which make up life constitutes a continual 

 adjustment of internal to external conditions. 



When we gain some insight into the mechanism of nervous 

 reaction, we are in a better position to understand the nature of 

 instinct. The same material basis — that is to say, the nervous 

 system — serves as a condition of both reflex and instinctive 

 actions. The wasp which is instinctively aware of its victim— 

 a grasshopper or a certain caterpillar — which attacks it, paralyses 

 it with a sting, drags it into its retreat, places it in one of the 

 cells which it has already constructed for the future progeny, 

 lays an egg on top of the insect, and closes the cell — this wasp, 

 which exhibits so wonderful a succession of acts all tending to 

 the same end — the providing of food for its progeny — is merely 

 obeying the dictates of its nervous system. For instinct is but 

 a succession of reflex combinations, the first act determining 

 the second, the second determining the third, and so forth. 

 'Every instinct has its origin in an external stimulus acting on 



