ANIMAL AGGREGATIONS AND SOCIAL LIFE 351 



planes of social development continue to show the group attributes 

 characteristic of the lower levels. Survival values have been demon- 

 strated throughout this whole series and extend well below the 

 toleration social level to the threshold of primitive life. 



The first indication of structurally modified castes is to be found 

 in the dimorphism accompanying sex, and the division of labor 

 associated with sex runs not only through all the distinctly social 

 levels but also through the majority of all types of animals as well. 

 As we have suggested, sex itself, and therefore the divisions of labor 

 associated with it, may have arisen as an outgrowth of certain bene- 

 fits associated with primitive asexual aggregations. Sex phenomena 

 aside, we have just seen that the different types of social organiza- 

 tion, including even the physiological division of labor type, may 

 have developed from aggregations formed by the coming-together 

 of indi\dduals without direct sexual causation as well as from those 

 collections which have resulted from sexual appetite or from repro- 

 ductive activities. The most permanent societies appear to have 

 arisen when sexual and parental integration have operated in addi- 

 tion to the more elemental aggregation tendencies. 



