166 RELATION OF SONG TO THE TERRITORY 



are degrees of suggestiveness, which well there 

 may be, some males will mate sooner than others 

 and some will remain mateless — this is the 

 theory of sexual selection. The question to be 

 decided here is whether the biological emphasis 

 is on loudness, or specific distinctness, or pitch, 

 or modulation, or the manner in which the 

 phrases are combined — that is, on some qualities 

 in preference to others — or whether the emphasis 

 is on the whole. We have already seen, and it 

 is well known, that there is much variation in 

 the voices of different individuals of the same 

 species, and thus the first condition of the theory 

 is fulfilled. Now the conditions which lead to 

 variation are threefold — immaturity, seasonal 

 sexual development, and isolation. Of the 

 three, the variation in the case of the immature 

 bird is the most instructive ; the tone is not so 

 pure, the .combination of phrases is incomplete, 

 and elaboration is imperfect, and yet, notwith- 

 standing all these imperfections, we can observe' 

 that the bird pairs as readily as does the adult. 

 But even if we lacked this demonstrative 

 evidence, we should still be justified in assuming 

 that such must be the case, for we know from 

 experience in the preservation of game, where 

 there is no surer way of reducing the stock than 

 by leaving too high a percentage of old cocks, 

 that for the young bird to be at «,ny disadvantage 

 in competition with the adult is detrimental, if 

 not disastrous, to the species. So that while 

 there is plenty of evidence of variation in those 

 particular qualities which appeal to our assthetic 



