382 ELEMENTARY ZOOLOGY. 



380. Variability as an Evidence. The changeableness of 

 organisms is the fact that makes it impossible for the 

 biologist to deny evolution. Every day we see differences 

 in organisms of the same species, which differences have 

 been brought about by differences in the surroundings, 

 by the behavior of the organisms themselves, by cultiva- 

 tion by man, or by something inherited from their parents. 

 We know that man can take advantage of these differences 

 and can select certain types; can cultivate and select again 

 in such a way as to get, in a few generations of cultivation 

 and breeding, animals strikingly different from those 

 with w T hich he started. After a certain time these new 

 forms seem to breed reasonably true, and a new race is 

 said to be established. In this way the different breeds 

 or varieties of dogs, pigeons, chickens, and many other 

 domestic animals have apparently arisen. This is not 

 merely a proof of evolution; it is evolution. Any one 

 who believes in this is an evolutionist by just that much. 



There can be no reasonable doubt that just this kind 

 of thing is happening in nature, without the help of man. 

 It cannot take place, however, so rapidly as when man 

 deliberately aids the process, by artificial selecting and 

 breeding according to his preference, and then eliminates 

 those that he does not want. It often happens, both in 

 nature and in cultivation, that large variations (" sports" 

 or "mutations") appear suddenly, and breed true in 

 succeeding generations. These marked variations are not 

 so frequent as the slighter ones, but seem to be more per- 

 sistent when they once appear. 



381. Evidences from Geographical Distribution. In the 

 wild state, the changes in animals are too slow for us to 

 detect, within a human generation or so, that there has 



