Where did Life Begin ? 3 



out other occupants of the same territory, and 

 in turn will be undoubtedly, by similar changes 

 and means, crowded out themselves. All 

 kinds of plants and animals which have re- 

 mained in one locality until they have lost the 

 means of movement, which cannot or will not 

 travel, must sooner or later first degenerate 

 and then be exterminated. For instance, a 

 rain-belt or an area of dew-fall veers slowly 

 but permanently from the north to the south ; 

 an arid soil is made fertile, and a fertile soil 

 is left arid ; the grass and flowering plants in 

 endless variety move with the dew or the 

 rain-belt ; the deer follow the grass, and the 

 wolves follow the deer; a thousand varieties 

 of insects follow the flowering plants, and the 

 insectivorous birds and other animals, herbiv- 

 orous and carnivorous, bring up the rear, and 

 so on through all the interdependencies of 

 life, the change of a single essential condi- 

 tion, the movement of one variety, causes a 

 disturbance and movement of all in the neigh- 

 borhood. Thence comes all this ceaseless and 

 migratory activity among the flora and fauna 

 of the earth. 



