COURTSHIP AND SEX 191 



produce a sound when the out-breathed air passes rapidly 

 over them. Now there seems no doubt that the original 

 use of a voice was as a signal between would-be mates, for 

 that is its use to-day in the humblest vocal animals — the 

 frogs. 



But in the course of evolution the significance of the 

 voice broadened out. It became a parental call ; it became 

 an infant's cry. Thus the unhatched crocodile pipes from 

 within the egg which is buried in the ground, and the mother 

 hearing this cry unearths the eggs, and saves her offspring 

 from being buried alive at birth. 



Broadening still, the voice became a kin-signal, enabling 

 members of the same species to recognise one another in the 

 dark and in the intricacies of the forest. 



Ages passed, and the voice rose on another turn of the 

 evolutionary spiral, to be expressive of particular emotions 

 outwith the immediate circle of sex — emotions of joy and of 

 fear, of jealousy and of content. Later on, the animal began 

 to give utterance to particular " words," indicative not 

 merely of emotions, but of particular things with an emotional 

 halo, such as " food," " enemy," " home." There can be 

 no doubt that such birds as rooks have several words. 



To man belongs the prerogative of using words as counters 

 or symbols in his intellectual processes and of expressing 

 judgments in sentences. What began as a sex-call became 

 a medium of rational discourse. 



§ 7. The Variety of Bird Song 



Birds inherited their voice as part of their legacy from 

 reptilian ancestors, among which it had probably become a 

 kin-call, a means of telling certain pieces of news, and an 

 expression of emotion. Birds re-invested this legacy, as it 

 were, in their own avian constitution, and thence came song. 

 It would be plainly a misunderstanding to think of the song 

 of the mavis or the lark as having evolved directly from the 

 croaking of frogs. 



One does not forget that there are many birds that do 



