Chap. iv. Divergence of Character. Sy 



head from our domestic productions. We shall here find something 

 analogous. It will be admitted that the production of races so 

 different as short-horn and Hereford cattle, race and cart horses, 

 the several breeds of pigeons, &c, could never have been effected by 

 the mere chance accumulation of similar variations during many 

 successive generations. In practice, a fancier is, for instance, 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 extremes," they both go on (as has 

 actually occurred with the sub-breeds of the tumbler-pigeon) 

 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 of history, the men of one nation or district required 

 swifter horses, whilst 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 

 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-established 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 dis- 

 appear. 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 principle 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 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 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 

 act, it can succeed in increasing (the country not undergoing any 

 change in conditions) only by its varying descendants seizing on 

 places at present occupied by other animals : some of them, for 



