" 1916 J Huxley, Bird-watching and Biological Science. 161 



Plover, for instance, {/Egialitis hiaticula) usually breeds on the 

 seashore, and there lays its eggs among the stones. A certain 

 number, however, breed on inland heaths, but even these pave 

 their nests with small stones (Newton, '93, p. 482). 



Such a discussion will make it easier to comprehend that it is 

 possible to answer in various ways that question "why does such- 

 and-such a species of bird perform such-and-such an action?" 

 "Why do the Grebes shake their heads at each other?" The 

 Evolutionist answers that the cause lies in Mutual Selection, which 

 has developed the action for the good of the race. The Physiolo- 

 gist sees the reason in the activity of the gonads; these exert by 

 chemical means a stimulus on the nervous system, which in its 

 turn is arranged in such a way as to cause the stimulus to run down 

 and set the appropriate muscles to working. The Psychologist 

 sees in it a self-exhausting psychological process accompanied by a 

 pleasurable expression of emotion — the bird does it because it 

 enjoys doing it. In reality, all are right — in their degree; and 

 it is from a failure to get a sufficiently broad point of view, a failure 

 to distinguish between ultimate cause, immediate cause, and mere 

 necessary machinery, that so much of the barren disputes of 

 biology are due. 



{To be concluded.) 



