396 EVOLUTION AND ANIMAL LIFE 



dividuals because of the different work they have to do. And 

 the queen differs from all the others, because of the extraor- 

 dinary prolificacy demanded of her to maintain the great com- 

 munity. 



It is important to note, however, that among those animals 

 that show the most highly organized or specialized communal 

 or social life, the structural differences among the individuals 

 are the least marked, or at least are not the most profound. 

 The three kinds of honeybee individuals differ but little; in- 

 deed, as two of the kinds, male and female, are to be found in 

 the case of almost all kinds of animals, whether communal 

 in habit or not, the only unusual structural specialization in 

 the case of the honeybee, is the presence of the worker indi- 

 vidual, which differs from the other individuals primarily in 

 the rudimentary condition of the reproductive glands. Finally, 

 in the case of man, with whom the communal or social habit 

 is so all-important as to gain for him the name of "the social 

 animal," there is no differentiation of individuals adapted 

 only for certain kinds of work. Among these highest ex- 

 amples of social animals, the presence of an advanced mental 

 endowment, the specialization of the mental power, the power 

 of reason, have taken the place of and made unnecessary the 

 structural differentiation of individuals. The honeybee work- 

 ers do different kinds of work: some gather food, some care for 

 the young, and some make wax and build cells, but the in- 

 dividuals are interchangeable; each one knows enough to do 

 these various things. There is a structural differentiation in 

 the matter of only one special work or function, that of re- 

 production. 



With the ants there is, in some cases, a considerable struc- 

 tural divergence among individuals, as in the genus Atta of 

 South America with six kinds of individuals namely, winged 

 males, winged females, wingless soldiers, and wingless workers 

 of three distinct sizes. In the case of other kinds with quite 

 as highly organized a communal life, there are but three kinds 

 of individuals; the winged males and females and the wingless 

 workers. The workers gather food, build the nest, guard the 

 "cattle" (aphids), make war, and care for the young. Each 

 one knows enough to do all these various distinct things. Its 

 body is not so modified that it is limited to doing but one 

 kind of thing. 



