88. Division of labor and basis of communal life.-We have learned in Chapters II and IV that the complexity of the bodies of the higher animals depends on a specialization or differentiation of parts, due to the assumption of different functions or duties by different parts of the body; that the degree of structural differentiation depends on the degree or extent of division of labor shown in the economy of the animal. It is obvious that the same principle of division of labor with accompanying modification of structure is the basis of colonial and communal life. It is simply a manifestation of the principle among individuals instead of among organs. The division of the necessary labors of life among the different zooids of the colonial jelly-fish is plainly the reason for the profound and striking, but always reasonable and explicable modifications of the typical polyp or medusa body, which is shown by the swimming zooids, the feeding zooids, the sense zooids, and the others of the colony. And similarly in the case of the termite community, the soldier individuals are different structurally from the worker individuals because of the different work they have to do. And the queen differs from all the others, because of the extraordinary prolificacy demanded of her to maintain the great community. 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 honey-bee individuals differ but little; indeed, 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 honey bee, is the presence of the worker individual, which differs from the usual individuals in but little more than the rudimentary condition of the reproductive glands. Finally, in the case of man, with whom the communal or social habit is so FIG. 102. Fur-seal rookeries or groups of homes at Zapalata on Medni, one of the Commander Islands, off Kamchatka. The seals are the small spots gathered in groups on the white beach at the foot of the cliffs. THOMPSON and A. MARRETT. The fur seals live gregariously. Photograph by D. W. 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 examples 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 honey-bee workers do different kinds of work: some gather food, some care for the young, and some make wax and build cells, but the individuals 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 reproduction. With the ants there is, in some cases, a considerable structural divergence among individuals, as in the genus Atta of South America with six kinds of individualsnamely, 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 can do but one kind of thing, which thing it must always do. The increase of inielligence, the development of the power of reasoning, is the most potent factor in the development of a highly specialized social life. Man is the example of the highest development of this sort in the animal kingdom, but the highest form of social development is not by any means the most perfectly communal. 89. Advantages of communal life. The advantages of communal or social life, of co-operation and mutual aid, are real. The animals that have adopted such a life are among the most successful of all animals in the struggle for exist ence. The termite individual is one of the most defenseless, and, for those animals that prey on insects, one of the most toothsome luxuries to be found in the insect world. But the termite is one of the most abundant and widespread and successfully living insect kinds in all the tropics. Where ants are not, few insects are. The honeybee is a popular type of a successful life. The artificial protection afforded the honey-bee by man may aid in its struggle for existence, but it gains this protection because of certain features of its communal life, and in Nature the honey-bee takes care of itself well. The Little Bee People of Kipling's Jungle Book, who live in great communities in the rocks of Indian hills, can put to rout the largest and fiercest of the jungle animals. Co-operation and mutual aid are among the most important factors which help in the struggle for existence. Its great advantages are, however, in some degree balanced by the fact that mutual help brings mutual dependence. The community or society can accomplish greater things than the solitary individuals, but co-operation limits freedom, and often sacrifices the individual to the whole. |