INTRODUCTION 5 



rather larger than the other. In such case the smaller 

 is regarded as male, the larger as female. Here we have 

 the first sign of " sexual differentiation " or the evolution 

 of " male " and " female " individuals. 



Some such union, some such process of " rejuvenation " 

 by the importation of ** fresh blood " seems to be im- 

 perative for the continuance of existence throughout the 

 whole animal world, even though it may take place at 

 rare intervals of time. Why should this be ? Is this 

 strange meeting and commingling a matter of chance, or 

 is the one seeking the other possessed by a ravenous 

 mate-hunger ? 



As we ascend higher in the scale it becomes apparent 

 that Hfe has gathered force. That primitive speck of 

 jelly, the Amoeba, with which we started, gave but two 

 signs of animation — the power of movement, and hunger. 

 Whether these responses to internal stimuli can be called 

 instinctive is open to argument. But there can be no 

 question about the instinctive nature of the behaviour of 

 these higher animals. After the instinct to feed the 

 two most powerful are the desire for self-preservation — 

 the avoidance of danger — and the desire to mate. These 

 two are the dominating instincts throughout the rest of 

 the animal world, not even excepting man himself. ^• 



The tremendous power of " mate-hunger " has been 

 overlooked by a strange confusion between cause and 

 effect. Almost universally its sequel, the production of 

 offspring, has been regarded as the dominant instinct in the 

 higher animals. This view has no foundation in fact. 

 " Desire " for the sake of the pleasure it affords, and not 

 its consequences, is the only hold on life which any race 

 possesses. And this is true both in the case of man 

 himself and of the beasts that perish. Wherever this 



