NATURAL SELECTION 405 



There is, however, much indirect evidence, which we will now 

 consider. 



820. Animals and Plants Under Domestication.— AH our 

 domestic animals and plants were originally wild species. They 

 have become so changed under domestication that most of them 

 bear little resemblance to their prototypes. The various 

 types of fancy pigeons, the carriers, fantail, tumbler, pouter, 

 etc., have probably all been produced by selective breeding 

 from the wild rock pigeon. The differences in structure of these 

 fancy pigeons is much more than enough to give them specific 

 standing. Such differences found in wild species would be 

 regarded as of generic value. How did they come about? 

 Simply by selection. The breeder selects those which conform 

 to a certain type and thus produces a ''breed." 



821. Our dogs may be descended from two or three wild dogs 

 or wolves, but the original type has little in common with the 

 hundreds of breeds of dogs, ranging from mastiff to greyhound 

 and from poodle to St. Bernard. In our horses and cattle, cats, 

 poultry, garden vegetables and cereals similar remarkable 

 effects have been produced. In some of these domestic breeds 

 selection has been at work for a long period, but often marked 

 results have been brought about in a short time. 



822. The conclusion which we may draw from the facts of 

 varieties under domestication is that species are not immutable, 

 and if man by selection can produce such results it is reasonable 

 to believe that nature by some process may bring about similar 

 results. The natural process is certainly slower, but the time 

 during which it has been at work is vastly longer. 



823. Geographical Distribution.— If such species had an 

 independent origin (not by descent) then there is no reason 

 why two similar species should be related geographically. 

 They may as well occupy islands on the opposite sides of the 

 globe, provided food, climate, etc., are the same, as live in adja- 

 cent countries. If, however, two species had a common origin 



