THE KINSHIP OF LIFE. 



31 



plants can live has been thousands of times discovered, 

 its colonization a thousand times attempted. In these 

 efforts there is no co-operation. Every individual is for 

 himself, every struggle a struggle for life and death. 

 To each species each member of every other species is 

 an alien and a savage. 



The study of geographical distribution shows the re- 

 lations of creative processes to space. The forms in- 

 habiting one district are the children of 



. . the earlier inhabitants. The survival 



the existing. 



of these forms is due to that which I 

 have elsewhere called the " survival of the existing," for 

 it is certain that in any part of the world a totally dif- 

 ferent grouping of animals or plants would have been 

 equally fitted to the environment. The laws of geo- 

 graphical distribution may be summed up thus : The 

 reason why any given species of animal or plant is 

 not found in a given district is (a) because it could not 

 get there from its own habitat, or {l>), being there, it 

 could not maintain itself either in competition with 

 others or from the stress of environment, or else (r) it 

 has in maintaining itself become altered into a distinct 

 species. 



In like manner the facts of geological distribution 

 have a meaning when we view them in the light of the 



^ , . , ,. theory of descent. The birth, increase, 



Geological dis- ■, ,■ j /- , , 



tribution declme, and final change or disappear- 



ance of species or types in geological 

 history are necessary parts of the Darwinian theory. 

 They would be inexplicable on any other hypothesis. 

 These changes represent the survival of the fittest as 

 related to time. With the lapse of time come changes 

 m environment, and these changes produce correspond- 

 ing changes in animal or plant life. But these changes 

 on the earth and in its life are for the most part gradual 

 4 



