ZOOLOGY 



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 sometimes happens, both in nature and in cultivation, that 

 large variations (''sports" or "mutations") appear suddenly, 

 and breed true in succeeding generations. These marked varia- 

 tions are not so frequent as the slighter ones, but seem to be 

 more persistent when they once appear. 



482. Evidences from Geographical Distribution. In the 

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

 within a few human generations, that there has been any change 

 in a species; yet we do have some evidence on a broader scale 

 which is of a nature quite similar to that in the last section. 

 In the way in which animals occur on the face of the earth a 

 great many interesting factors enter, and it sometimes happens 

 that we get some good indication of the long-time effects of 

 variation. Sometimes we find two forms of plant or animal 

 flourishing in two regions that are separated from, each other 

 by some kind of a barrier which does not allow them to pass 

 back and forth and thus to mingle. These forms are in general 

 similar, and yet are constantly and recognizedly different. 

 Sometimes we can find that these two regions (b and c) have 

 been stocked from some third region (a), and that both varieties 

 are apparently descendents of the same ancestors. Indexed, we 

 may be able to find forms of all grades connecting "a" with "b" 

 on one side, and other intermediate types connecting "a" with 

 ' ' c " on the other side. In cases like this, which are by no means 

 infrequent, it is believed that "b" and "c" have migrated into 

 their respective regions and in becoming adapted to their new 

 condition of life have so evolved as to become different from their 

 parent stock and from each other. 



In a similar way, but on a much larger scale and in a form 

 too complex to discuss here, we find evidences of change and 



