THE SELECTING POWER OF ENEMIES 53 



going on. Then the common environment 

 will be a selecting agent and will select either 

 Sj or S 2 ; one or other must be selected, for 

 they cannot both be alike re the environment. 

 The selected one will then include the common 

 environment in its specific environment, as 

 in Fig. 7. If they are very similar, then 

 different parts of the environment having 

 slightly different selecting powers, because of 

 its diversity, will select, some S 1? some S 2 . 



FIG. 6. 



The common environment will become divided, 

 one part joining the specific environment of 

 S x ; the other part, the specific environment 

 of S 2 , as shown in Fig. 8. In neither 

 case will the species be in any way changed. 



This competition with the common environ- 

 ment cannot cause the origin of a new species, 

 but it may possibly lead to the extinction 

 of one. 



Attention must here be drawn to the dif- 

 ference between competition occurring within 



