160 THE ORIGIN OF SPECIES 



tory, the men of one nation or district required swifter 

 horses, while those of another required stronger and 

 bulkier horses. The early differences would be very 

 slight; but, in the course of time, from the continued 

 selection of swifter horses in the one case, and of 

 stronger ones in the other, the differences would be- 

 come greater, and would be noted as forming two sub- 

 breeds. Ultimately, after the lapse of centuries, these 

 sub-breeds would become converted into two well-estab- 

 lished and distinct breeds. As the differences became 

 greater, the inferior animals with intermediate characters, 

 being neither very swift nor very strong, would not have 

 been used for breeding, and will thus have tended to 

 disappear. Here, then, we see in man's productions the 

 action of what may be called the principle of divergence, 

 causing differences, at first barely appreciable, steadily 

 to increase, and the breeds to diverge in character, both 

 from each other and from their common parent. 



But how, it may be asked, can any analogous prin- 

 ciple apply in nature ? I believe it can and does apply 

 most efficiently (though it was a long time before I saw 

 how), from the simple circumstance that the more diver- 

 sified the descendants from any one species become in 

 structure, constitution, and habits, by so much will they 

 be better enabled to seize on many and widely diversified 

 places in the polity of nature, and so be enabled^_to 

 increase in numbers. 



We can clearly discern this in the case of animals 

 with simple habits. Take the case of a carnivorous 

 quadruped, of which the number that can be supported 

 in any country has long ago arrived at its full average. 

 If its natural power of increase be allowed to aet, it can 



