636 Reflexes, Instincts, and Intelligence 



"My investigations on the heliotropism of animals led me to analyze in 

 a few cases the conditions which determine the apparently accidental direc- 

 tion of animal movements which, according to traditional notions, are called 

 voluntary or instinctive. Wherever I have thus far investigated the cause 

 of such 'voluntary' or 'instinctive' movements in animals, I have without 

 exception discovered such circumstances at work as are known in inanimate 

 nature as determinate movements. By the help of these causes it is possi- 

 ble to control the 'voluntary' movements of a living animal just as securely 

 and unequivocally as the engineer has been able to control the movements 

 in inanimate nature. What has been taken for the effect of 'will' or 

 * instinct ' is in reality the effect of light, of gravity, of friction, of chemical 

 forces, etc." 



But Jennings, a very careful and tireless investigator of the behavior of 

 the protozoa, closes a fascinating volume on his work with the following 

 paragraph : 



" The present paper may be considered as the summing up of the general 

 results of several years' work by the author on the behavior of the lowest 

 organisms. This work has shown that in these creatures the behavior is 

 not as a rule on the tropism plan a set, forced method of reacting to each 

 particular agent but takes place in a much more flexible, less directly 

 machine-like way, by the method of trial and error. This method involves 

 many of the fundamental qualities which we find in the behavior of higher 

 animals, yet with the simplest possible basis in ways of action; a great por- 

 tion of the behavior consisting often of but one or two definite movements, 

 movements that are stereotyped in their relation to the environment. This 

 method leads upward, offering at every point opportunity for development, 

 and showing even in the unicellular organisms what must be considered the 

 beginnings of intelligence and of many other qualities found in higher animals. 

 Tropic action doubtless occurs, but the main basis of behavior is in these 

 organisms the method of trial and error." 



In a rough way the responses or reactions of animals to stimuli, their 

 behavior, in a word, are grouped into reflex behavior or reflexes, instinctive 

 behavior or instincts, and intelligent behavior or action from reason. To 

 distinguish sharply between reflexes and instincts on the one hand, and 

 instincts and reason on the other is impossible. Reflexes may be defined 

 to be local responses of congenital type (that is, not acquired by experience, 

 imitation, or teaching) which usually involve, in higher animals, only a par- 

 ticular organ or definite group of muscles, and which are initiated by more 

 or less specialized external stimuli. Instincts may be defined as complex 

 groups of coordinated acts which are, on their first occurrence, independent 

 of experience; which tend to the well-being and preservation of the race; 

 which are due to the cooperation of external and internal stimuli; which are 



