The Origin of Species 347 



factors may be shown to cause the appearance of 

 new forms, or incipient species, the survival of these 

 must depend upon natural selection. 



In the history of both the vegetable and animal 

 kingdoms, the most important event was the desert- 

 ing of the primitive aquatic environment for life 

 in the air. Fungi, Ferns, and Seed-plants on the 

 one hand ; Insects, Birds, and Mammals on the other, 

 prove the superiority of the land over the sea, as 

 a field for the work of evolution. 



