BIOLOGICAL VALUE OF THE WARFARE 251 



there were no control over the range of the 

 intolerance, the smaller bird would have no 

 chance in competition with the larger, and it 

 is doubtful whether the larger would gain an 

 advantage commensurate with the energy it 

 would expend in ridding its area of the smaller. 

 I have described battles in which the opponents 

 were only distantly related ; for instance, the 

 Moor- Hen will attack almost any bird — Part- 

 ridge, Lapwing, or Starling — that approaches its 

 territory even temporarily. Nevertheless the 

 antagonism between kindred forms is more 

 prevalent, and, as a rule, characterised by more 

 persistent effort ; and thus it seems as if the 

 susceptibility of the fighting instinct has its 

 limitations, the degree of the responsiveness 

 being dependent upon the affinity of the 

 opponents. 



Suppose now that we take an area inhabited 

 by a number of different species requiring like 

 conditions of existence, divide it into three 

 sections, and imagine that in one they were all 

 sociable, that in another they were all hostile, 

 and that in a third those which were closely 

 related were intolerant of one another. Let us 

 suppose further that each one of them was 

 represented by the full number of individuals 

 that the law of territory would allow. In 

 the first section an individual would establish 

 itself, and, becoming intolerant of its own 

 kind, would exercise dominion over an area 

 roughly sufficient, providing conditions were 

 normal, to insure an adequate supply of food for 



