104 Darwin- Wallace Celebration. 



in a state of nature, and from the undisputed fact that 

 varieties do frequently occur. It is not, however, contended 

 that this result would be invariable ; a change of physical 

 conditions in the district might at times materially modify it, 

 rendering the race which had been the most capable of sup- 

 porting existence under the former conditions now the least 

 so, and even causing the extinction of the newer and, for a 

 time, superior race, while the old or parent species and its 

 first inferior varieties continued to flourish. Variations in 

 unimportant parts might also occur, having no perceptible 

 effect on the life-preserving powers ; and the varieties so 

 furnished might run a course parallel with the parent species, 

 either giving rise to further variations or returning to the 

 former type. All we argue for is, that certain varieties have 

 a tendency to maintain their existence longer than the 

 original species, an,d this tendency must make itself felt ; for 

 though the doctrine of chances or averages can never be 

 trusted to on a limited scale, yet, if applied to high numbers, 

 the results come nearer to what theory demands, and, as we 

 approach to an infinity of examples, become strictly accurate. 

 Now the scale on which nature works is so vast the numbers 

 of individuals and periods of time with which she deals 

 approach so near to infinity, that any cause, however slight, 

 and however liable to be veiled and counteracted by 

 accidental circumstances, must in the end produce its full 

 legitimate results. 



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 

 inclemency of the seasons, and in providing for the sub- 

 sistence 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 con- 

 tinual 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 



