theough cumulatiye segeegatiok. 221 



Competitive Diseuption. 



Before entering upon the discussion of the direct causes of 

 Cumulative Segregation, let us briefly consider a law resulting 

 from the competition of kindred with each other, which brings to 

 light the fact that such competition is one of the most important 

 factors in preparing the way for, and in giving intensity to, the 

 activities that lead to Segregation and divergent evolution. It 

 is manifest that competition for identical resources and Greogra- 

 phical Segregation are conditions which cannot exist at the same 

 time between the same members of any species; but it is also 

 manifest that, when there are no natural barriers separating the 

 different districts of an area part of which is occupied by a 

 species, pressure for food through a great increase in the popu- 

 lation will tend to distribute the species over the whole area ; 

 and, if the available resources in the different districts are consi- 

 derably diverse, the overflow of population from the crowded 

 district will be subjected to a necessary change of habits ; and 

 thus, through competition, there will be the disruption of old 

 relations to the environment, and the bringing in of conditions 

 that give the highest efficiency and the fullest opportunity to all 

 the activities that produce Segregation. In the case of animals, 

 no condition can tend more strongly to produce migration than 

 scarcity of food in the old habitat ; and in the case of both plants 

 and animals, a great increase in the numbers that are exposed to 

 the winds, currents, and other transporting influences of the 

 environment increases the probability that individuals will be 

 carried to new districts where circumstances will allow of their 

 multiplying, and where they will, at the same time, be prevented 

 from crossing with the original stock. In many cases the segre- 

 gation thus brought about will be in districts where the environ- 

 ment is the same, and in other cases the pressure for food or 

 other resources will lead portions of the species to take up new 

 habits in the effort to appropriate resources not previously used ; 

 and through these new habits they will often be segregated from 

 those maintaining the original habits. I shall hereafter show 

 that in both these cases there is a tendency to divergent 

 evolution. 



I at one time thought of describiug this principle as a form 

 of Segregation, calling it dominational segregation ; but fuller 

 reflection convinces me that the domination of the strong over 



LINN. JOUEN. — ZOOLOGY, VOL. XX. 18 



