112 NATURAL SELECTION. Chap. IV. 



this head from our domestic productions. We shall here 

 find something analogous. A fancier is struck by a 

 pigeon having a slightly shorter beak ; another fancier 

 is struck by a pigeon having a rather longer beak ; and 

 on the acknowledged principle that " fanciers do not 

 and will not admire a medium standard, but like ex- 

 tremes," they both go on (as has actually occurred 

 with tumbler-pigeons) choosing and breeding from birds 

 with longer and longer beaks, or with shorter and 

 shorter beaks. Again, we may suppose that at an early 

 period one man preferred swifter horses ; another 

 stronger and more bulky horses. The early differences 

 would be very slight ; in the course of time, from the 

 continued selection of swifter horses by some breeders, 

 and of stronger ones by others, the differences would 

 become greater, and would be noted as forming two 

 sub-breeds ; finally, after the lapse of centuries, the sub- 

 breeds would become converted into two well-established 

 and distinct breeds. As the differences slowly become 

 greater, the inferior animals with intermediate cha- 

 racters, being neither very swift nor very strong, will 

 have been neglected, and will 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 in- 

 crease, 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, 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." 



