5 



WHAT ANIMALS HAVE ATTAINED ON LAND 



/^NLY one-fifth of the species of animals on the earth are aquatic 

 ^"^^ (Harms, 1929) . Though conditions of life on land are in 

 some respects severe, they appear to have been, and are today, favor- 

 able for the formation of new species. Animals which have strug- 

 gled up the long evolutionary trail from marine and fresh-water 

 habitats and stand today on dry land are the dominant ones of the 

 earth. They are the successful. What is success? Has the struggle 

 been justified? 



Success is continual improvement (Pearse, 1926a) . It is the re- 

 sult of competition for a place to live. There are of course various 

 degrees of success. The mere fact that an animal is alive is a 

 certification that it is to some degree successful. Among land ani- 

 mals, ants exceed all other types combined in individuals (Wheeler, 

 1910) . They are successful and dominant among those which have 

 attained land because they are progressive yet generalized. Ants 

 are active, keen of sense, modern, and so progressive that they have 

 built up a social organization that has long excited wonder and 

 admiration among successful, dominant, and social vertebrates. Yet 

 ants have not generally limited their food to one or two peculiar 

 substances as the honey bee has, and they have not lost the thermal 

 and aqueous stability that goes with close association with soil. A 

 successful animal is both plastic and progressive. It must always live 

 in the world as it is and to some extent do such living with greater 

 efficiency than its rivals. 



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