ASPECTS OF KINETIC EVOLUTION 243 



merely gregarious condition in which the individuals are still 

 equal and alike, to those in which the diversity inside the same 

 species may be greater than that of genera and families in other 

 groups. In man himself social organization has scarcely gone 

 farther than the gregarious state, though some races of man- 

 kind have more pronounced social instincts than others, and 

 such instincts have undoubtedly been important factors in their 

 progress or backwardness in civilization. In some countries 

 distinct castes exist, but these are racial or historical in origin and 

 scarcely amount to the attainment of intraspecific diversification. 



By far the most compact and highly specialized forms of 

 social organization are to be found among the insects. Re- 

 markably similar conditions have been attained independently 

 in several different families belonging to two very different 

 orders, the termites and the hymenoptera. In these highly 

 specialized insects the individuals of a species are no longer 

 capable of independent existence, but, like the cells of the 

 higher plants and animals, have no meaning except as parts of 

 a collective, super-individual organism. The nest or colony 

 has become the true unit of the species, and its members are 

 differentiated into numerous castes adapted to particular func- 

 tions by pronounced differences of size and structure. Among 

 the hymenoptera only the females have social instincts and take 

 part in the labors of the nest or the hive, but among the termite 

 both sexes are equally involved. Reproduction is restricted to 

 a single royal pair, who do no work beyond burrowing in the 

 ground after their first and only flight. The king and queen 

 and their numerous progeny are fed and cared for, and the 

 architectural and agricultural labors of the state are performed 

 by hosts of sterile dwarfs, of which in some species there are as 

 many as four different castes — soldiers, foremen, workers and 

 nurses, each distinct in form and highly specialized in instincts 

 for its particular part in the labors of the city. 



The body of the termite queen may be hundreds of times the 

 size of that of a worker, and the head and mandibles of a soldier 

 twenty times as large as those of a nurse. Termite communities 

 often contain millions of inhabitants. They build structures far 

 exceeding, proportionally, anything attempted by man, and 



