36o ANIMAL AGGREGATIONS 



abundant in nature, as well as being widely distributed. It is upon 

 such evidence that we may conclude that the mutual interdepend- 

 ence, or automatic co-operation, of which we are speaking is a funda- 

 mental and important principle in biology. 



There is nothing in this recent work which displaces the earlier 

 conclusion that overcrowding is harmful; but this newer evidence 

 which we have been interested in presenting does show that under 

 proper conditions, and entirely apart from breeding or hibernation, 

 beneficial results may follow aggregations, in many organisms of the 

 same or of different species, within a limited space. This means 

 that in groupings caused by the tropistic reactions of individuals to 

 environmental factors there may be a natural co-operation effective 

 long before the physiological organization of the group has reached 

 the level of development which occurs in the groupings usually des- 

 ignated as being truly social. 



Symbiosis, commensalism, and intra-organismal relations aside, 

 such unconscious co-operation was unknown to Espinas or to 

 Kropotkin, who were much impressed by the evidences of mutual 

 aid among insects and the larger animals. It was unknown to Wheel- 

 er when he wrote the 1923 conclusion quoted above, to which he was 

 led by the studies of the ecologists and by his own knowledge of the 

 behavior of ants and other social insects. The knowledge which we 

 have summarized, showing that such general co-operation exists 

 among loosely organized, or among apparently unorganized, groups 

 of animals living even temporarily in the same region, gives us much 

 clearer evidence than has been available to these students of social 

 life, that their conclusion that co-operation is one of the major 

 biological principles is correct, and that its roots extend far below 

 the level of well integrated social activity. 



From this point of view the first step toward the development of 

 societies had probably already been taken when life came into 

 existence on this planet. These first living particles were probably 

 dependent on each other for the final adaptation of their physical 

 environment so that they could continue to live. In the course of 

 evolution they became more independent of close proximity to each 

 other. A further advance was made when such more or less solitary 



