This grim conception of an internecine conflict, inevitable and unending, in which all races must play their part, hung for a generation after 1859 over the study of world-politics as the fear of a cooling sun hung over physics, and the fear of a population to be checked only by famine and war hung over the first century of political economy. Before Darwin wrote, it had been possible for philanthropists to think of the non-white races as 'men and brothers' who, after a short process of education, would become in all respects except colour identical with themselves. Darwin made it clear that the difficulty could not be so glossed over. Racial variations were shown to be unaffected by education, to have existed for millions of years, and to be tending perhaps towards divergence rather than assimilation. The practical problem also of race relationship has by a coincidence presented itself since Darwin wrote in a sterner form. During the first half of the nineteenth century the European colonists who were in daily contact with non-European races, although their impulses and their knowledge alike revolted from the optimistic ethnology of Exeter Hall, yet could escape all thought about their own position by assuming that the problem would settle itself. To the natives of Australia or Canada or the Hottentots of South Africa trade automatically brought disease, and disease cleared the land for a stronger population. But the weakest races and individuals have now died out, the surviving population are showing unexpected powers of resisting the white man's epidemics, and we are adding every year to our knowledge of, and therefore our responsibility for, the causation of infection. We are nearing the time when the extermination of races, if it is done at all, must be done deliberately. But if the extermination is to be both inevitable and deliberate how can there exist a community either of affection or purpose between the killers and the killed? No one at this moment professes, as far as I know, to have an easy and perfect answer to this question. The point of ethics lies within the region claimed by religion. But Christianity, which at present is the religion chiefly concerned, has conspicuously failed even to produce a tolerable working compromise. The official Christian theory is, apparently, that all human souls are of equal value, and that it ought to be a matter of indifference to us whether a given territory is inhabited a thousand years hence by a million converted Central African pigmies or a million equally converted Europeans or Hindus. On the practical point, however, whether the stronger race should base its plans of extension on the extermination of the weaker race, or on an attempt, within the limits of racial possibility, to improve it, Christians have, during the nineteenth century, been infinitely more ruthless than Mohammedans, though their ruthlessness has often been disguised by more or less conscious hypocrisy.