EFFECT OF ISOLATION 275 



ended, how can this be? An answer to the 

 question will be found in the fact that a bird 

 has an innate capacity to return to the neigh- 

 bourhood of its birthplace, or to the place 

 wherein it had previously reared offspring — 

 which means that the results of prior process 

 persist as the basis and starting - point of 

 subsequent process. 



Bearing then in mind that the seeming 

 peace in bird life around us in the spring is 

 but the expression of transitory adjustments in 

 the distribution of individuals and of species ; 

 bearing in mind how widespread is the search for 

 isolation each recurring season, how frequently 

 the search leads to competition and competition 

 to failure, and how failure implies a renewal of 

 the search ; bearing in mind that situations, 

 which appear to be eminently suitable for 

 breeding purposes, are passed by year after year 

 and remain unoccupied, just because, for reasons 

 which have yet to be ascertained, the environ- 

 ment fails to supply some condition which is 

 essential if the inherited nature of the bird is to 

 respond — can there be any doubt that the 

 general result of the functioning of the disposi- 

 tion will be expansion ; or, since no limit is 

 placed upon it from within but only from 

 without — that is, by unfavourable circumstances 

 in the external world, that the expansion will 

 not merely be in one direction but in every 

 direction ? 



If now, when reproduction is ended, all 

 the impulses relating to it die away, and the 



