PDF - Wallace Online

30 NATURAL SELECTIONThe Partial Reversion of Domesticated Varieties explainedLet us now turn to domesticated animals, and inquire howvarieties produced among them are affected by the principleshere enunciated. The essential difference in the condition ofwild and domestic animals is this, that among the former,their well - being and very existence depend upon the fullexercise and healthy condition of all their senses and physicalpowers, whereas, among the latter, these are only partiallyexercised, and in some cases are absolutely unused. A wildanimal has to search, and often to labour, for every mouthfulof food to exercise sight, hearing, and smell in seeking it,and in avoiding dangers, in procuring shelter from the inclemencyof the seasons, and in providing for the subsistenceand safety of its offspring. There is no muscle of itsbodythat is not called into daily and hourly activity ;there is nosense or faculty that is not strengthened by continual exercise.The domestic animal, on the other hand, has food providedfor is it, sheltered, and often confined, to guard it againstthe vicissitudes of the seasons, is carefully secured from theattacks of its natural enemies, and seldom even rears itsyoungwithout human assistance. Half of its senses and facultiesbecome quite useless, and the other half are but occasionallycalled into feeble exercise, while even its muscular system isonly irregularly brought into action.Now when a variety of such an animal occurs havingincreased power or capacity in any organ or sense, suchincrease is totally useless, is never called into action, and mayeven exist without the animal ever becoming aware of it. Inthe wild animal, on the contrary, all its faculties and powersbeing brought into full action for the necessities of existence,any increase becomes immediately available, is strengthenedby exercise, and must even slightly modify the food, the habits,and the whole economy of the race. It creates as it were anew animal, one of superior powers, and which will necessarilyincrease in numbers and outlive those which are inferior to it.Again, in the domesticated animal all variations have anequal chance of continuance and those which would decidedlyrender a wild animal unable to compete with its;fellows and continue its existence are no disadvantage what-