THE SELECTING POWER OF ENEMIES 53 
going on. Then the common environment 
will be a selecting agent and will select either 
S, or S,; 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,, some §,. 
TO ea A 
IIE es TT aes 
iE 
The common environment will become divided, 
one part joining the specific environment of 
S,; the other part, the specific environment 
of S, 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 
=e 
Fie. 6. 
