THE ORIGIN AND DEVELOPMENT OF ORGANISMS 339 



thus been produced artificially, are greater than differences 

 found among many of the wild birds that are regarded as 

 belonging to distinct species. In the case of the pigeons, it is 

 known from historical evidence that these different strains have 

 all come from a common type by methods of breeding. 



The dogs. Another example, perhaps even better known, is 

 that of the breeds of dogs. Dogs have been domesticated for 

 a period almost as long as man has been civilized. At the 

 present time the variety of dogs is very great, ranging in size 

 from the great Newfoundland to the tiny poodle, and varying 

 in color, type of hair, disposition, and almost every other 

 respect. We can hardly conceive of two animals being much 

 more unlike than the tiny lap-dog and the massive bloodhound 

 or mastiff, and it is hardly possible to believe that these ani- 

 mals have all come from the same type. But the most careful 

 study of the characters and history of the breeds of dogs has 

 led to the unquestioned conclusion that all forms of domes- 

 tic dogs with which we are familiar belong to one species of 

 animal, and all came from the same type far back in history. 

 Some varieties of dogs, like the dingo of Australia, belong possi- 

 bly to a different species; but all of our common forms belong to 

 one species and have been derived from the same fundamental 

 stock. Here, as in the case of pigeons, the breeds have been the 

 result of a long series of unconscious breeding experiments. 

 Different families of human beings have had a liking for certain 

 types of dogs and have kept by them such individuals as pleased 

 their fancy. These have been bred together and their masters 

 have selected from the pups those which most pleased them. 

 This process has gone on, similar individuals being bred with 

 each other over and over again, until the whole race has become 

 slowly changed. Different types of dogs were selected for differ- 

 ent purposes. The shepherd took a fancy to a different type of 

 animal from that which was most desirable as a house dog. By 

 selecting the dogs who could drive sheep, or the big dogs, or the 

 fierce dogs, or the little dogs, etc., and breeding together those 



