BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 623 



greater in birds than in fishes, although the principal reaction types are the 

 same in both these classes, and may be recognized even in mammals. Thus 

 certain birds which were hatched or were reared by foster mothers belonging 

 to a different species, may flock with the strange species; they may even 

 mate with members of the latter provided the association has occurred at a 

 sufficiently early period of life. In this case, as in the induction of mutations, 

 definite sensitive periods do exist in developing organisms, which greatly 

 antedate the time when the reaction takes place. In this way, through learning, 

 even the species instinct may to some extent be overcome. 



A further indication of the complexity of behavior in certain birds comes 

 out also in reactions which lead to the hiding of food particles. In one species 

 these reactions may take place quite openly, in the presence of other birds, 

 and may thus be ineffective, while in another species they take place when 

 other birds are absent, and thus will be effective. Birds, through experience, 

 may learn to recognize dangerous instruments, such as guns during the 

 shooting season; individuals of the same species may behave differently in 

 city parks, where their experience has shown that they are safe, and in 

 other zones where they are exposed to attack. It appears, then, that modi- 

 fiability and individualization in behavior, in general, are greater in birds 

 than in fishes, greater in mammals than in birds, and greater among the 

 higher than among the more primitive mammals ; in animals, it reaches its 

 highest development in the anthropoid apes, which are, however, still much 

 inferior to man. Thus evolution of individuality signifies an increasing variety 

 and variability in individual reactions, a greater adaptabilty to and a greater 

 significance of the environment ; not only do the possible reactions of the 

 individual become more numerous, but also space and time become more 

 differentiated and they assume greater meaning in connection with the 

 reactions of the animal ; space and time become subdivided to a greater 

 extent; they also become more individualized. 



But, increasing complexity of behavior does not mean the actual loss of 

 instincts. Essentially the same instincts are present throughout the whole 

 vertebrate series ; they are, however, associated with and, in the highest 

 organisms, covered up by reactions in which the behavior is modified first 

 by memories of sense impressions and by the action of suggestions ; still 

 later, by thoughts and memories of thoughts, and by the increasing sig- 

 nificance of abstractions and new syntheses. Concomitantly, there is a de- 

 crease in the predictability of actions and attitudes of individuals. In order 

 to make predictions it becomes necessary not only to know and to analyze 

 the stimuli which act on or in an individual at a given moment, but also to know 

 his past history, the stimuli which have acted in previous times and the situations 

 which he has experienced. With the growing importance of thoughts and of 

 the manipulation of thoughts, with the greater power to make abstractions, 

 and syntheses, and the increasing significance of the imaginative, creative 

 mind, the predictability diminishes, not only in regard to the actions of others, 

 but also to the actions of ourselves. However, there is reason for assuming 

 that not only actions appear unpredictable, but also the formation of thoughts, 



