i8 POPULAR SCIENCE MONTHLY. 



The variety would now have replaced the species, of which it would 

 be a more perfectly developed and more highly organized form. It 

 would be in all respects better adapted to secure its safety, and to pro- 

 long its individual existence and that of the race. Such a variety 

 could not return to the original form; for that form is an inferior 

 one, and could never compete with it for existence. Granted, there- 

 fore, a 'tendency' to reproduce the original type of the species, still the 

 variety must ever remain preponderant in numbers, and under adverse 

 physical conditions again alone survive. 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, tend- 

 ing to increase the facilities for preserving existence, must, by the same 

 general law, in their turn l)ecome predominant. Here, then, we have 

 progression and continued divergence deduced from the general laws 

 which regulate the existence of animals in a state of nature, and from 

 the undisputed fact that varieties do frequently occur. It is not, how- 

 ever, contended that this result would be invariable ; a change of phys- 

 ical conditions in the district might at times materially modify it, ren- 

 dering the race which had been the most capable of supporting existence 

 under the former conditions now the least so, and even causing the ex- 

 tinction 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 per- 

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

 nished 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, 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 in- 

 finity 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, how- 

 ever slight, and however liable to be veiled and counteracted by acci- 

 dental 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 

 depends 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 ex- 



