54 CONTROLLED NATURAL SELECTION 



a species, and competition between two or 

 more species ; to the difference between intra- 

 and inter-specific struggles. 



In intra-specific struggles, because the indi- 

 viduals are very similar, the struggle will be 

 prolonged : very small differences will decide 



FIG. 7. 



FIG. 8. 



life and death. Under these conditions evolu- 

 tion will proceed. 



In inter-specific struggles, which take place 

 within common environments (when they be- 

 come overcrowded) because the individuals 

 are not similar in structure, the struggle will 

 be soon over. One species is bound to be 

 vastly more fit than the other, and will there- 

 fore quickly displace it. Can a struggle be 



