INTEGRATION OF AGGREGATIONS 87 



AGGREGATION INTEGRATION 



As has been said before, a decided advance toward social life is 

 made by the appearance of tolerance for other animals in a limited 

 space, where they have collected as a result of random movements or 

 of tropistic reactions to their environment. This may occur in con- 

 nection with some phase of breeding activity, but it may also be 

 exhibited without sexual significance. Some of the less complex of 

 these aggregations may exist because there is an absence of dis- 

 sociating factors among a group of animals that have been hatched 

 out in a restricted locality or that have been brought together by 

 any other process. Thus, some of the aggregations resulting from 

 tropistic responses may well owe whatever permanency they possess 

 to the absence of disruptive factors rather than to any inherent gre- 

 garious tendency or apparent advantage. 



Another advance in social life is made when these groupings con- 

 fer especial survival values upon at least some of the individuals 

 composing them. Such an advantage is illustrated by the slower 

 rate of moisture change in an aggregation of land isopods out of 

 water equilibrium with the surroundings. Under conditions of 

 drought this results in a definite prolongation of life for the members 

 of a group. Other examples will be discussed later. 



The land isopods and Ophioderma have gone little beyond such a 

 stage in their social development. There is some slight evidence of 

 mutual attraction, but the experiments to date do not indicate how 

 much of this would also be exhibited toward similar inanimate ob- 

 jects. There is also slight evidence of integrated group behavior, in 

 that the bunch shows occasional periods of activity apparently 

 originating in one individual and passed mechanically through the 

 group. Such activity may be the beginning of disintegration of the 

 group; but it frequently results in a closer aggregation, because the 

 animals may move closer together during their brief period of ac- 

 tivity. 



The state of development of integration by means of which the 

 group, once it appears, acts as a unit is a very important criterion of 

 the degree of social development it has attained. When there is no 



