TENDENCY OE SPECIES TO FORM VAEIETIES. 59 



But this new, improved, and populous race might itself, in course 

 of time, give rise to new varieties, exhibiting several diverging 

 modifications of form, any of which, tending to increase the facili- 

 ties for preserving existence, must, by the same general law, in their 

 turn become predominant. Here, then, we have progression mid 

 coiUinued divergence deduced from the general laws which regulate 

 the existence of animals in a state of nature, and from the undis- 

 puted fact that varieties do frequently occur. It is not, however, 

 contended that this result would be invariable ; a change of phy- 

 sical conditions in the district might at times materially modify it, 

 rendering the race which had been the most capable of supporting 

 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 con- 

 tinued to flourish. Variations in unimportant parts might also 

 occur, having no perceptible eflfect on the life-preserving powers j 

 and the varieties so furnished might run a course parallel with 

 the parent species, either giving rise to further variations or re- 

 turning to the former type. All we argue for is, that certain 

 varieties have a tendency to maintain their existence longer than 

 the original species, and 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 va- 

 rieties 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 subsistence and safety of its offspring. There is no muscle of 



