SOCIAL DIFFERENTIATION AND INTEGRATION 743
little more than the transplanting of civilization. It is social reproduction, and the universal condition to reproduction is decay. Social evolution is in this respect identical with organic evolution. The great types of animals and plants, as shown by their geological history, have similarly had their rise, culmina- tion, and decline. But out of them have arisen new and more vigorous types that have successively carried forward the work of structural development until the present floras and faunas of the globe are far higher than those of any past epoch. Pteri- dophytes succeeded thallophytes, spermatophytes succeeded lepidophytes, angiosperms succeeded gymnosperms, and dicoty- ledons at last crowned the series of vegetal dynasties. Vertebrates succeeded trilobites and molluscs, amphibians succeeded fishes, reptiles succeeded batrachians, birds and mammals succeeded reptiles. Finally the higher mammals succeeded the lower, and man came last to crown the animal series. It is true that the lower types did not become extinct, but in almost every case, both in the vegetable and in the animal kingdom, the leading form of each type perished, and only the less specialized forms have come down to us. Witness among plants, the Lepidodendron, Sigillaria, and Calamites of the Carboniferous, the Bennettitean cycads of the Mesozoic ; and among animals, the trilobites, the ganoid fishes, the dinosaurs, and the mammoth.
To maintain that because human races decline and degener- ate the human species must also do so, is the same as to maintain that because many types of vegetation and of animal life have become extinct all plants and all animals must ultimately do so. The logic is unsound, and there is nothing to prove that not only life but also man may not continue indefinitely.
From any such standpoint as that from which we are now viewing the races of men the world appears to be in an infantile state. Europe and North America, where the highest civiliza- tion is found, form much less than half the globe, and the population of those areas is proportionally still less. By far the greater part of the earth has scarcely been touched with the spirit of science. That this influence is destined to spread over the whole earth is scarcely open to doubt. But the scientific
