164 RELATION OF SONG TO THE TERRITORY 



to that which we have discussed, forms part of 

 the life behaviour of certain mammals, and of 

 its existence much lower in the scale of life 

 evidence is not wanting ; from which we can 

 infer that it is not of recent origin, but that 

 the conditions in the external environment 

 demanded such a system at a remote period of 

 avian development. Now even in its incipient 

 stages the system must have involved a separa- 

 tion of the sexes, and howsoever slight the 

 degree of separation may have been in com- 

 parison with that which can be observed to-day, 

 inasmuch as the power of locomotion was then 

 less highly developed, mating could only have 

 proceeded satisfactorily providing that males fit 

 to breed had some adequate means of disclosing 

 their positions. Thus there is reason to think 

 that from the very commencement of the 

 process variations of emotional disposition 

 expressed through the voice would have been of 

 survival value. 



But expressed in what direction, in loudness 

 and persistency of utterance, these are the 

 qualities which, I imagine, would have been 

 more likely to have facilitated the search of the 

 female ? Yet if she were uncertain as to the 

 owner of the voice, neither loudness nor per- 

 sistent repetition would avail much ; and as 

 species multiplied and the competition for the 

 means of living became increasingly severe, so 

 the necessity of a territory would have become 

 intensified, and so, too, with the extension of 

 range, would the separation of the sexes have 



