Theories of Evolution 3 



subspecies and varieties. If an origin by nat- 

 ural laws is conceded for the latter, it must, on 

 this ground be granted for the first also. In 

 this discussion he simply returned to the pre- 

 Linnean attitude. But his material was such 

 as to allow him to go one step further, and this 

 step was an important and decisive one. He 

 showed that the relation between the various 

 genera of a family does not exhibit any fea- 

 tures of a nature other than that between the 

 species of a genus. What has been conceded 

 for the one must needs be accepted for the 

 other. The same holds good for the large 

 groups. The conviction of the common origin 

 of closely allied forms necessarily leads to the 

 conception of a similar descent even in remote 

 relationships. 



The origin of subspecies and varieties as 

 found in nature was not proved, but only gen- 

 erally recognized as evident. A broader 

 knowledge has brought about the same state of 

 opinion for greater groups of relationships. 

 Systematic affinities find their one possible ex- 

 planation by the aid of this principle; without 

 it, all similarity is only apparent and accidental. 

 Geographic and paleontologic facts, brought to- 

 gether by Darwin and others on a previously 

 unequalled scale, point clearly in the same di- 

 rection. The vast amount of evidence of all 



