VI On the Songs of Birds 147 



abbreviated edition of the strain we know so well. 

 The object may have been to let his wife know that 

 he had done his duty and that it was her turn next, 

 or it naay have been merely his way of expressing 

 his own satisfaction with himself and his lot ; but it 

 had beyond doubt a meaning, and one in no way 

 connected with courtship. 



It is time I should sum up what I have been 

 saying about the nature and objects of songs. I am 

 inclined to think that in this particular instance 

 Darwin was not in possession of a sufficient amount 

 of evidence, and that his theory of sexual selection 

 cannot by itself account for all we know about the 

 singing of birds. Wallace, whose experience of 

 living animals was larger, and perhaps more truly 

 sympathetic, takes a different view.^ If I under- 

 stand him rightly, he thinks that song is really only 

 " an outlet for superabundant nervous energy," which 

 natural selection has intensified and differentiated as 

 being useful in many ways, among which we must 

 certainly reckon the courting of the females by the 

 males. Where vitality is not expended in producing 

 brilliant colour in one or both sexes, it has been 

 spent in producing brilliant song of a particular type 

 and tone. This theory seems to me to account for 

 the facts better than the other. It is in the main the 

 same conclusion at which Mr. Hudson arrived in the 

 ' A. E. Wallace, Darwinism, p. 284. 



