84 HEREDITY AND SELECTION IN SOCIOLOGY 



which was doubtless inherent in the ancestors of the domesticated hound, 

 as it is inherent in allied species of the canine genus ; and which is inherent 

 because it is indispensable to the existence of the species. And just as 

 the original hunting instinct is the result of natural selection, because 

 it is an indispensable adaptation to given conditions of life, so the develop- 

 ment of that instinct under domestication is the result of artificial selec- 

 tion, because the breeder treats it as an indispensable quality. The 

 same holds true of the instinct of fidehty in the watch-dog, of docihty 

 in the elephant under domestication, etc. These instuicts are not entirely 

 novel acquisitions, but are modifications of instincts which were, in their 

 fundamental form, characteristics of the species in question. The im- 

 proved expression is the necessary outcome of readaptation to changed 

 conditions. 



A curious instance of the inefficiency of the Lamarckian theory of 

 use and disuse as primordial factors in evolution is afforded by some 

 poisonous or unpalatable species of butterflies which are invariably 

 slow in their flying movements. We may exclude habit as a cause of this 

 modification of movement, as there is no reason to be found in the external 

 conditions which could have caused these butterflies to fly less quickly 

 than their ancestors. Even if we suppose a few varieties to have been 

 produced whose movements were slow, there is no Lamarckian reason why 

 these varieties alone should have survived ; and still less why the move- 

 ments should become ever slower in the course of succeeding generations. 

 Only when we apply the interpretation afforded by natural selection do 

 we get an explanation of this phenomenon. The varieties which arose 

 with slower movement were more easily recognised by hostile birds than 

 the quickly flying varieties, and were consequently more generally avoided 

 on account of their unpalatable or poisonous qualities. Consequently, 

 these slow-fljdng varieties survived in greater numbers, multiphed at the 

 expense of their competitors, and bequeathed their instinct for slow 

 movement to their progeny. The slowness of the movement will increase 

 in the course of generations, as long as an increase is advantageous. Once 

 the advantage of a greater sluggishness ceases, variation in that direction 

 ceases also, and the species is adapted to its environment. 



