GROUP BEHAVIOR 173 



ence of additional numbers by no means always re- 

 tards, and is frequently stimulating. As before with 

 regard to other processes, we find that in certain 

 cases there are ill effects of undercrowding as well 

 as ill effects of overcrowding. Without careful ex- 

 perimental exploration, we cannot predict which 

 effect will emerge from a given situation. 



One other result comes from these studies which 

 will help us to clarify evidence still to be presented, 

 as well as to review that already given. We have 

 come upon another measure of the existence of so- 

 cial behavior. Reactions may be regarded as social 

 in nature to the extent that they differ from those 

 that would be given if the animals w^ere alone. Such 

 differences are frequently quantitative, as they have 

 been in the cases we have discussed, although quali- 

 tative differences occur as a result of a change in 

 the numbers present. 



From this point of view social behavior may have 

 or may lack positive survival value. All that is nec- 

 essary is that the behavior be different from that 

 which would be given if the animal were solitary. 

 In this sense all the animals whose behavior we have 

 been discussing are social to a considerable degree; 

 the more so, the greater the difference between their 

 behavior when grouped and when isolated. 



When the behavior of such animals as cockroaches, 



