52 AN INTRODUCTION' TO ZOOLOGY. 



and the huge St. Bei-narcl, brave and fearless of cold, 

 and weighing, like the prize dog " Plialimmon," a 

 couple of hundred pounds, are the opposite results of 

 artificial selection — results so opposite that we might 

 assign them, not merely to distinct species, but to dis- 

 tinct genera, if we did not know how such varieties 

 can be produced by artificial selection. Similarly, 

 in the region of vegetable life, we find that from such 

 wilding stocks as the crab and the sloe have been 

 produced by artificial selection the many varieties of 

 the apple and the plum. 



In some cases, such as that of the pigeon and the 

 fowl, it is easy to compare the variant race with the 

 original stock ; in other cases, the variation produced 

 has been so great that we are left in doubt as to the 

 original form. It would perhaps be taking an optimist 

 view of the chai-acter of either the wolf or the jackal, 

 if we allowed either of them to claim precedence over 

 the other as ancestor of the dog ; and there are other 

 cases regarding the origin of which we must similarly 

 remain at present in a state of uncertainty. One 

 explanation of the very wide variation produced by 

 selection lies in the following facts. One definite 

 characteristic, by a mysterious sympathy, or " correla- 

 tion of parts," often involves the existence of another; 

 thus, for instance, animals that are deficient in hair 

 are apt also to be deficient in teeth. Hence the in- 

 tentional selection of one character may result in the 

 unintentional selection of others ; and thus, in conse- 

 quence of this correlation of parts, the new race pro- 



