2 QO NATURAL HISTORY. 



improvements of this kind in the domestic pig. He does 

 not, for example, wish to increase its muscular power 

 and consequent activity; because he wants it to fatten 

 readily, and vigorous exercise tends to keep an animal 

 lean. What is true of the pig is true of all our domestic 

 animals, though it is more evident in some than in others. 

 The variations, for instance, which separate the different 

 breeds of the dog from one another are exceedingly well 

 marked, and they are all variations which adapt particular 

 breeds for the special purposes for which man wants them. 

 On the other hand, the different breeds of the Goose differ 

 little from one another, or from their wild form (the Grey 

 Lag Goose), because man's demands from the goose are 

 few and simple, and are quite well answered by the 

 ordinary form of the species. 



The causes of the above-mentioned peculiarities of 

 domesticated animals, as compared with wild ones, have 

 been fully expounded by Mr Darwin, and are readily 

 intelligible. As regards the first of them namely, the 

 tendency to excessive variation shown by domestic animals 

 the cause is to be found in the varied character and 

 artificial nature of the conditions under which they live. 

 Wild animals are exposed, as regards each species, to an 

 approximately uniform and unvarying set of conditions, 

 and the conditions are alike for all the individuals of the 

 species. Variation does not become excessive, because 

 the tendency of natural selection is to destroy all variations 

 which are not good for the individual itself in its natural 

 condition. On the other hand, domestic animals are 

 kept by their masters under veiy different sets of condi- 

 tions, as regards different individuals of the species, and 



