Editorial. 137 



brings about those changes which determine the course of the 

 development of activity in the race, changes in the scope of reac- 

 tion. The trial and error series may be longer in the offspring 

 than in the parent; if so we speak of the animals greater scope of 

 reaction and of its greater originality or initiative. The connect- 

 ing link between ontogenetic and phylogenetic development has 

 to be sought in the value of habits to the race. If the results of 

 individual experience are transmitted, it is clear that a species may 

 gain a larger fund of instincts while at the same time becoming 

 capable of a wider range of reactions. Variations form the ba- 

 sis of changes in the scope of reaction; the inheritance of acquir- 

 ed tendencies to action accounts for changes in instinctive ac- 

 tion. Each new generation may possess new instinctive acts, 

 in addition to new possibilities of voluntary action. 



But the animal kingdom presents, instead of uniform in- 

 crease of plasticity and fixity (scope of reaction and mechaniza- 

 tion) with increase in complexity of structure, divergent lines of 

 development. Certain animals are markedly plastic or volun- 

 tary in their behavior, others are as markedly fixed or instinct- 

 ive. In the primates plasticity has reached its highest known 

 stage of development ; in the insects fixity has triumphed, in- 

 stinctive action is predominant. The ant has apparently sacri- 

 ficed adaptability to the development of ability to react quickly, 

 accurately and uniformly in a certain way. Roughly, animals 

 might be separated into two classes : those which are in high 

 degree capable of immediate adaptation to their conditions, and 

 those which are apparently automatic since they depend upon 

 instinctive tendencies to action instead of upon rapid adaptation. 



Attention to these and other striking differences in behav- 

 ior should enable us to make a valuable classificatian of animals 

 on the basis of activity. Certainly it is apparent, and it can 

 not be better exhibited than by reference to such facts as those 

 under consideration, that there has been no one direct course 

 of development in animal behavior ; rather, there seem to be 

 several directions of development, of which the present highest 

 stage of one is marked by the insecta, that of another by the 

 primates. Robert m. yerkes. 



