1506 THE STORY OF THE UNIVERSE 



with longer and longer beaks, or with shorter and 

 shorter beaks. Again, we may suppose that at an 

 early period of history, the men of one nation or 

 district required swifter horses, while those of an- 

 other 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 become 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-es- 

 tablished and distinct breeds. As the differences 

 became greater, the inferior animals with interme- 

 diate 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 differ- 

 ences, 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 be- 

 fore I saw how), from the simple circumstance that 

 the more diversified 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 



