30 NATURAL SELECTION 



The Partial Reversion of Domesticated Varieties explained 



Let us now turn to domesticated animals, and inquire how 

 varieties produced among them are affected by the principles 

 here enunciated. The essential difference in the condition of 

 wild and domestic animals is this, that among the former, 

 their well - being and very existence depend upon the full 

 exercise and healthy condition of all their senses and physical 

 powers, whereas, among the latter, these are only partially 

 exercised, and in some cases are absolutely unused. A wild 

 animal has to search, and often to labour, for every mouthful 

 of food to exercise sight, hearing, and smell in seeking it, 

 and in avoiding dangers, in procuring shelter from the inclem- 

 ency of the seasons, and in providing for the subsistence 

 and safety of its offspring. There is no muscle of its body 

 that is not called into daily and hourly activity ; there is no 

 sense or faculty that is not strengthened by continual exercise. 

 The domestic animal, on the other hand, has food provided 

 for it, is sheltered, and often confined, to guard it against 

 the vicissitudes of the seasons, is carefully secured from the 

 attacks of its natural enemies, and seldom even rears its young 

 without human assistance. Half of its senses and faculties 

 become quite useless, and the other half are but occasionally 

 called into feeble exercise, while even its muscular system is 

 only irregularly brought into action. 



Now when a variety of such an animal occurs having 

 increased power or capacity in any organ or sense, such 

 increase is totally useless, is never called into action, and may 

 even exist without the animal ever becoming aware of it. In 

 the wild animal, on the contrary, all its faculties and powers 

 being brought into full action for the necessities of existence, 

 any increase becomes immediately available, is strengthened 

 by exercise, and must even slightly modify the food, the habits, 

 and the whole economy of the race. It creates as it were a 

 new animal, one of superior powers, and which will necessarily 

 increase in numbers and outlive those which are inferior to it. 



Again, in the domesticated animal all variations have an 

 equal chance of continuance ; and those which would de- 

 cidedly render a wild animal unable to compete with its 

 fellows and continue its existence are no disadvantage what- 



