SOCIAL TRANSITIONS 25 1 



different functions within the colony. With many 

 social insects the division of labor has developed 

 to such an extent that the animals which do dif- 

 ferent work have bodies that are more or less struc- 

 turally appropriate to their principal tasks. The 

 reproductive female has a greatly enlarged ab- 

 domen; the soldier grows up to possess large jaws 

 and heavy armor or other protective and attacking 

 devices; a worker may be large or small or medium 

 in size, according as its size will best suit for some 

 of the varied tasks necessary for the life of the whole 

 colony. The situation is greatly different from that 

 among human social castes, where a member of the 

 aristocracy may be as husky of body and as empty 

 of mind as the most menial of the working caste. 



The only physically distinct castes to be found in 

 man and the higher vertebrates are those associated 

 with sex. In sexual forms there is always a division 

 of labor with regard to the primary sexual functions 

 except in those rare cases, usually low in the evo- 

 lutionary scale, which at one and the same time are 

 both male and female. With many, aside from pro- 

 ducing eggs rather than sperm, it is difficult to find 

 a division of labor or of appearance between the 

 sexes. With others, particularly among the more 

 specialized animals, there are differences in sexual 

 behavior and responsibilities which are associated 



