We cannot run over all the peoples of the earth in this way, but will briefly glance at the lower races of the various continents. A branch of the second phase of developing humanity, the negroid stock, spread eastward over the Asiatic islands and Australia, and westward into Africa. The extreme wing of this army, the Australian blacks, too clearly illustrates the principle to need further reference. It has retained for ages the culture of the middle Palaeolithic. The negritos who penetrated to the Philippines are another extreme instance of isolation. The Melanesians of the islands of the Indian and Pacific Ocean are less low, because those islands have been slowly crossed by a much higher race, the Polynesians. The Maoris of New Zealand, the Tongans, Hawaians, etc., are people of our own (Caucasic) stock, probably diverging to the south-east while our branch of the stock pressed westward. This not only explains the higher condition of the Maoris, etc., but also shows why they have not advanced like their European cousins. Their environment is one of the finest in the world, but--it lies far away from the highways of culture. In much the same way can we interpret the swarming peoples of Africa. The more primitive peoples which arrived first, and were driven south or into the central forests by the later and better equipped invaders from the central zone, have remained the more primitive. The more northern peoples, on the fringe of, or liable to invasion from, the central zone, have made more advance, and have occasionally set up rudimentary civilisations. But the movements from the north to the south in early historical times are too obscure to enable us to trace the action of the principle more clearly. The peoples of the Mediterranean fringe of Africa, living in the central zone of stimulation, have proved very progressive. Under the Romans North Africa was at least as civilised as Britain, and an equally wise and humane European policy might lead to their revival to-day.