74 HEREDITY AND SELECTION IN SOCIOLOGY 



fidelity in the house-dog, the instinct for hunting possessed by 

 the hound, and so on. 



^ Nevertheless, the explanation of the origin of instinct through 

 natural selection is not only sufficient, but also by far the most 

 rational explanation. Instincts depend upon a particular 

 mechanism of the brain, which is as variable as the other parts 

 of the organism ; they are, further, necessary in the majority of 

 cases for the survival of the species, and are consequently fully 

 and precisely adapted to the vital conditions of the species. 

 It is, therefore, only rational to attribute their origin and sub- 

 sequent evolution to natural selection. 



There is no great difference between instinctive and reflex 

 phenomena ; and reflex phenomena, established by habit, often 

 present the appearance of being instinctive. The act of winding 

 up our watch when undressing becomes so mechanical that we 

 perform it even when we change our clothes in the daytime ; and 

 all the complicated phenomena of walking, reading, speaking, 

 playing the piano, become eventually the purest reflex actions. 

 Yet reflex mechanism, so greatly strengthened by constant use 

 during the individual life, is not transmitted. This fact, com- 

 bined with that of the hereditability of those instincts which 

 manifest themselves but once in the individual life, shows that 

 the factor of use or disuse is an entirely negligible one in the 

 evolution and inheritance of instincts. 



The case of the fly or the butterfly, which takes rapidly to 

 flight on the approach of some enemy, is more rationally ex- 

 plained by natural selection than by the theory of use and disuse. 

 And selection is certainly the origin of that instinctive fear of 

 man shown by certain species — a fear which has its origin in an 

 act of volition, which becomes instinctive under the influence of 

 circumstances. The case of the walrus in the waters of the South 

 Sea Islands, visited by German explorers in 1799, is an instruc- 

 tive example of the volitional origin of this instinctive fear.^ 

 ^ Weismann, Vortrcige iiber Deszendenztheorie, ii. 63. 



