BASIS OF PSYCHICAL-SOCIAL INDIVIDUALITY 617 



the female before copulation can take place. Here, the parents peck only the 

 foreign young, while they recognize and respond to the calls of their own ; 

 but in certain other species parents may take care of strange young as well as 

 of their own. The aggressiveness differs greatly among different species of 

 birds and the aggressive behavior may be a complex called forth by definite 

 stimuli. Thus the aggressive behavior of the falcon is not due to a general 

 tendency to attack other birds; but these reactions take place only when a 

 specific stimulus acts on a falcon and releases a chain of reflexes. Perhaps 

 the movement of another bird sets in motion this mechanism, which seems to 

 represent an inherited, fixed character. 



There is among birds individual recognition in the same sense as among 

 fishes ; yet, in both it is restricted in significance. Individuals are recognized 

 as mates, as inferiors or superiors in the order of dominance, as parent or 

 young, as members of a flock, but not as individuals in the strict sense of the 

 term. Again, it is a single and relatively simple character, such as color, design 

 of certain feathers, or sounds, or perhaps combinations of a few of such 

 signs, which determines recognition. The two partners composing a pair of 

 immature herons may recognize each other after a separation lasting as long 

 as twenty days ; voice and feathering serve as signs in this process. Artificial 

 feathering of the head interferes with recognition. Refeathering the head and 

 neck of both members of a pair of young herons does not prevent the recogni- 

 tion of a partner after the lapse of a few hours ; if, hower, the refeathered 

 birds have been separated for six or more days, they no longer recognize their 

 partners (Noble, Warm, and Schmitt). Recognition of individuals, as well as 

 of members of the same group and species, depends therefore in birds, as in 

 fishes, on mosaic characteristics, and the processes involved, as such, are 

 fixed by inheritance, as is also the range in which they are modifiable by 

 experience. 



In mammals essentially the same reflex systems and instincts are active, 

 which determine the behavior in fishes and birds ; these make possible the 

 distinction between their own and strange species, groups and individuals ; 

 they play a role in the intake of food, in the sexual life, in the relations 

 between parents and offspring, in the superiority-inferiority relations within 

 groups, and in the fight and flight reactions. The additions to the behavior 

 reactions of fishes and birds which are noted in mammals consist in a greater 

 modifiability of such reactions. Furthermore, the range of sense organs, 

 through which the environment acts, is enlarged; by way of olfactory, visual 

 and auditory stimuli the changes which affect mammals become, on the 

 whole, more varied and often much more delicate than those perceived by the 

 more primitive invertebrates. Memories of things and events help to influence 

 the behavior of mammals, especially of those belonging to the more differ- 

 entiated species, to a much higher degree than is observed in lower classes 

 of animals and the actions of mammals. may be purposeful, in the sense that 

 situations are sought which experience has shown to promise satisfaction of 

 certain instinctive needs. Among these desired activities is the act of playing, 

 a modified reproduction of instinctive activities ; but playing is indulged in 



