174 THE SOCIAL LIFE OF ANIMALS 



fishes, birds and rats shows evidence of distinct modi- 

 fication as a result of more than one being present, 

 we have another suggestion that there exists a 

 broad substratum of partially social behavior. There 

 are many indications that this extends through the 

 whole animal kingdom. From such a substratum, 

 given suitable conditions, societies emerge now and 

 again as they have among ants and men. At these 

 higher social levels, as is to be expected, the type 

 of behavior shown under many conditions is related 

 even more closely to the number of animals present 

 than with less social cockroaches and fish. 



