NATURAL SELECTION. 



139 



to observe the reversion of the modern sheep to its 

 aboriginal form is utterly impossible. That the horse 

 is derived from a striped aboriginal species is probable; 

 ' but notwithstanding the many generations during which 

 the great herds of feral horses in South America have 

 propagated themselves undisturbed, no such species has 

 been produced. Riitimeyer's minute researches on do- 

 mestic cattle have shown that, in Europe at least, three 

 well-defined species of the Diluvial period have contrib- 

 uted to their formation. Bos primigenius, longifrons, and 

 frontosus. These species once lived geographically 

 separate, but contemporaneously; and they and their 

 specific peculiarities have perished, to rise again in our 

 domestic races. These races breed together with un- 

 qualified fertility; in the form of skull and horns 

 they recall one or other of the extinct species; but 

 collectively they constitute a new main species. That 

 from their various breeds, the three or any one of 

 the aboriginal species would ever emerge in a state 

 of pristine purity, would be an utterly ludicrous as- 

 sertion. 



In all these domestic animals — dog, sheep, goat, horse, 

 and cattle — the transformation was initiated in an era of 

 civilization in which there was no idea of artificial breed- 

 ing in the modern sense, and in which the main factor of 

 transformation, independently of involuntary and uncon- 

 scious selection, consisted simply in the altered mode 

 of life. This introduces us to variations in a state of 

 nature, and to Natural Selection. Natural as well as 

 artificial selection both rest on the undisputed fact of the 

 idiosyncrasies of the most closely allied vegetal and ani- 

 mal individuals; and it has already become manifest 



