Compelled by external forces, they changed the hue of their skin and the shade of their hair; they grew tall of stature or sunk to pygmies; their skulls altered in shape, and their long bones rounded, or else flattened like those of apes. Not less surprising were the alterations in their minds. Some felt no desire for fixed abodes, and ever wandered, while others sowed fields and built cities; some remained in small, ungoverned bands, while others founded great empires and enacted iron codes; some were satisfied to compel the Unknown by magical rites, while others sought the wisdom of God and the secrets of Nature. These variations, however, meant Progress; for repetition is not progress, and it is only by ceaseless change and endless experiment that one can find out the best. The separation of man into families and tribes and peoples was, in fact, a necessary condition to his improvement as a species. From the seeming chaos of changing forms the highest type emerged, as, in Greek myth, from the surging seas rose the perfect form of Aphrodite Anadyomene. The chaos is indeed but seeming. The differences among men are the results of physiological processes, proceeding in definite directions under fixed laws, and adjusted so that they bring about calculable results. Let us turn to the examination of these processes, in their universal expressions operative everywhere, as well in the psychical as the physical world. Psychical as well as physical; for the new conditions which transformed the bodies of the primitive horde left their impress also on the minds of its members, not erasing any trait which made them Man, but bringing them into closer likeness between themselves, and by that act into sharper contrast to their neighbours. The varied practical needs of life fostered their peculiarities, and created a similarity of feelings and purposes, and a community of knowledge in each band. This acted as a sort of intellectual mother-water in which each individual mind of the band crystallised into the same shape, readily accepted the beliefs, imbibed the same prejudices, looked at the world through the same spectacles. We may well believe that it was not long before contests arose between the primitive hordes. We are told, indeed, by a venerable authority that they began between the first two brothers. Then these diversities of body and mind decided the conflict. The stronger slew the weaker or drove them from the field; unless, indeed, by craft or superior skill the weaker foiled the stronger, as, so endowed, in the long run they surely would. Thus the great law of Natural Selection, of the destruction of the less fit, exercised its sway to preserve that horde which, on the whole, was better adapted for preservation and gave it power over the land.