no A Factor in Evolution 



the individual organism. The general fact is that the organ- 

 ism reacts by concentration upon the locality stimulated, 

 for the continuation of the conditions, movements, stimu- 

 lations, which are vitally beneficial, and for the cessation 

 of the conditions, movements, stimulations, which are 

 vitally depressing and harmful. In the case of bene- 

 ficial conditions we find a general increase of movement, 

 an excess discharge of tJie energies of movement in the 

 channels already open and habitual ; and with tliis, on 

 the psychological side, pleasurable consciousness and at- 

 tention. Attention to an organ is accompanied by in- 

 creased vaso-motor activity, with higher muscular power, 

 and a general dynamogenic heightening in that organ. 

 The thought of a movement tends to discharge motor 

 energy into the channels already established for the exe- 

 cution of that movement. By this organic concentration 

 and excess of movement many combinations and vari- 

 ations are brought out, from which the advantageous and 

 adaptive movements may be selected for their utility. 

 These then give renewed pleasure, excite pleasurable 

 associations, and again stimulate the attention, and by 

 these influences the adaptive movements thus struck are 

 selected and Jie Id as permanent acquisitions. This form of 

 concentration of energy upon stimulated localities, with the 

 resulting renewal through movement of conditions that are 

 pleasure-giving and beneficial, and the subsequent repeti- 

 tions of the movements, is called 'circular reaction.' 1 It 

 seems to be the physiological basis of the selective property 



1 With the opposite (withdrawing, depressive effects) in injurious and 

 painful conditions. This general type of reaction was described and illus- 

 trated, in a different connection, by Pfliiger in 1877 in Pfliiger's Archiv f. d. 

 ges. Physiologic, Bd. XV. (Note added 1902.) 



