SELECTION 167 



be detrimental to them and impede their move- 

 ments. Here again we see that natural selection is 

 not all-powerful. The song of birds, apart from 

 their calls, is also due to the love of pleasure. 

 Several of the forest birds of New Zealand sing 

 softly to themselves, and it is necessary to be very 

 near to hear them. This is, probably, the primitive 

 style of bird melody, and the loud-throated thrush 

 and sky-lark came later. All these songs are the 

 result of pure enjoyment ; there is. nothing useful in 

 them, so that they cannot be due to natural 

 selection. 



Preferential selection is entirely a mental action, 

 and has been the cause of much modification. It 

 may be that the absence of this motive in the vege- 

 table kingdom is the reason why its genealogical 

 tree is so much more simple than that of the animal 

 kingdom. 



