14 EVOLUTION OF BIRD-SONG 



and glottis, excited in the above manner, may 

 have first given rise to the emission of vocal 

 sounds." 



The most violent contractions of the muscles of 

 the chest and glottis would certainly have occurred 

 during combat, and it is therefore fair to assume 

 that the voice was first produced during the fights 

 of animals, although possibly its earliest tones were 

 little more than coughs or grunts, or a hoarse 

 murmur due to panting. Darwin observed (tbid.\ 

 " The principle also of association, which is so 

 widely extended in its power, has likewise played 

 its part. Hence it follows that the voice, from 

 having been habitually employed as a serviceable 

 aid under certain conditions, inducing pleasure, pain, 

 rage, etc., has commonly been used whenever the 

 same sensations or emotions are excited under 

 quite different conditions or in a lesser degree." 



We may be certain that the perception of a 

 threatened attack is only a mental anticipation of 

 the combat which experience, or inherited instinct, 

 suggests as a probable consequence of the approach 

 of an enemy. It is easy to imagine that, among 

 animals which survived by the agency of their speed, 

 the excitement due to the approach of an enemy 

 would cause an involuntarily increased rapidity in 



