478 



SCIENCE 



[N. S. Vol. XXXIII. No. J 



at a similar caterpillar more readily on a 

 second occasion. Something has appar- 

 ently reinforced the connection between 

 the visual impression produced by the 

 caterpillar and the pecking impulse. If, 

 on the other hand, the chick pecks at a 

 caterpillar having a nasty taste it is apt to 

 avoid pecking at it a second time. Some- 

 thing has happened to inhibit the response 

 that would otherwise occur. We com- 

 monly explain such behavior by ascribing 

 to the creature feelings of pleasure and 

 pain. We say that the chick pecks at one 

 kind of a caterpillar because of the pleas- 

 ant taste it derives, and avoids another 

 variety because its taste is bad. Pleasure 

 and pain apparently function as agents for 

 the reinforcement of certain reactions and 

 the stamping out of others. It is a general 

 rule, though not without certain excep- 

 tions, that what affords pleasure is con- 

 ducive to organic welfare, while that which 

 is productive of pain is injurious. The 

 upshot is that the associations that are the 

 outcome of the pleasure-pain response are 

 of just the kind that minister to the ani- 

 mals' needs. Beneficent arrangement! 

 Apparently we have to do with a selective 

 agency which preserves and intensifies cer- 

 tain kinds of behavior and rejects others 

 on the basis of their results — a kind of 

 "sorting demon" in the realm of behavior. 

 What could be more teleological ! 



The fact that what is pleasant is usually 

 beneficial and what is painful is usually 

 injurious may be explained with some 

 plausibility as the result of natural selec- 

 tion, as was first contended by Herbert 

 Spencer. Animals which took pleasure in 

 doing things which were bad for them and 

 which experienced pain in doing things 

 which were good for them would be very 

 apt to fare ill in the struggle for existence. 

 Natural selection would ever tend to bring 

 about a condition in which the pleasant 



means the organically good and the painful 

 means the reverse. We should not expect 

 the correspondence, if brought about in 

 this way, to be complete, and it is rather in 

 favor of the theory that we do not find it so. 



But granting this contention of Spencer, 

 there is the important question still left 

 unanswered, namely. Why do animals fol- 

 low what is pleasant and avoid what is 

 painful! In other words, why does pleas- 

 ure reinforce and why does pain inhibit? 

 Here is another fundamental problem and 

 we find that Spencer with his usual appre- 

 ciation of fundamental problems was on 

 the ground early with a theory. Pleasure, 

 according to Spencer, is the concomitant of 

 a heightened nervous discharge; pain the 

 concomitant of a lessened nervous dis- 

 charge. An act which brings pleasure 

 causes an influx of nervous energy to the 

 centers concerned in the movement; the 

 lines of discharge become "more per- 

 meable, ' ' and upon a repetition of the con- 

 ditions the same act follows with greater 

 readiness than before. If the act is fol- 

 lowed by pain with its concomitant of les- 

 sened nervous discharge, the diminution of 

 nervous energy serves to prevent the per- 

 formance of the act in response to the same 

 conditions. Closely similar explanations 

 of the physiology of the pleasure-pain re- 

 sponse have been given by Bain and by 

 Baldwin, the latter declaring that "pleas- 

 ure and pain can be agents of accommoda- 

 tion and development only if the one, 

 pleasure, carry with it the phenomenon of 

 motor excess — and the other, pain, the re- 

 verse — probably some form of inhibition or 

 of antagonistic contraction." 



The physiological concomitants of pleas- 

 ure and pain have afforded a subject for 

 numerous laboratory studies and almost no 

 end of theories. It has been impossible 

 thus far to discover that either of these 

 states is invariably accompanied by any 



