226 THE BREEDING OF ANIMALS 



to 10 ; so that the annual rate of increase can hardly be 

 more than one in six. Now in South America, where 

 the herds are half-wild, and therefore offer a nearly fair 

 standard of comparison, according to Azara the natural 

 increase of cattle on an estancia is from one-third to one- 

 fourth of the total number, or one in between three and 

 four, and this no doubt applies exclusively to adult ani- 

 mals fit for consumption. Hence the half-wild British 

 cattle which have long been inter-bred within the limits 

 of the same herd are relatively far less fertile. Although 

 in an unenclosed country like Paraguay there must be 

 some crossing between the different herds, yet even there 

 the inhabitants believe that the occasional introduction 

 of animals from distant localities is necessary to prevent 

 ' degeneration in size and diminution in fertility/ The 

 decrease in size from ancient times in the Chillingham 

 and Hamilton cattle must have been prodigious, for 

 Professor Rutimeyer has shown that they are almost 

 certainly descended from the gigantic bos primigenius. 

 No doubt this decrease in size may be largely attributed 

 to less favorable conditions of life ; yet animals roaming 

 over large parks, and fed during severe winters, can hardly 

 be considered as placed under very unfavorable condi- 

 tions." 



210. Deer in parks. In many English parks fallow 

 deer have been kept for many decades, and in-breeding 

 must often result. An investigation by Darwin dis- 

 closed the fact that the managers of such parks found it 

 necessary to introduce new blood to improve the size, 

 constitution, vigor and prevent the taint of " rick back," 

 which follows too close breeding. 



211. In-breeding among pigs. The evil results from 

 in-breeding are naturally more quickly apparent among 



