330 MAN --AN ADAPTIVE MECHANISM 



laugh less. Women laugh more than men. The 

 healthy happy young woman on the verge of maturity 

 laughs perhaps most of all, especially when slightly 

 embarrassed. 



What causes laughter? Good news, high spirits, 

 tickling, hearing and seeing others laugh ; droll stories ; 

 flashes of wit and passages of humor ; averted injury ; 

 threatened breaches of the conventions; and numer- 

 ous other causes. At first glance it would seem im- 

 probable that a single principle underlies all these 

 diverse causes. Let us examine them, however, in the 

 light of the fact that man is fundamentally a motor 

 being, and that, in common with other responses to 

 environmental stimulation, laughter is a muscular re- 

 action. 



We have postulated (Chapter III) that the laughter 

 excited by adequate stimulation of ticklish areas of 

 the body is a recapitulation of ancestral struggles 

 against the physical attack of biting and clawing foes 

 on these parts. In other words, the laughter excited 

 by tickling is a substitute for the motor act of defense 

 against injury, and is a reaction imposed by the need 

 for giving vent to the energy mobilized in the kinetic 

 organs at the command of the phylogenetic stimulus. 

 The resultartt action is purposeless, instead of purpose- 

 ful ; but the result in the expenditure of energy is the 

 same. If the laughter excited be sufficiently intense or 

 prolonged, the individual is as exhausted as if he had 

 actually struggled with an enemy. 



In like manner, the laughter excited by a psychic 

 image is accompanied by a psychic conception, either 

 clearly recognized or vaguely glimpsed, but none the 



