The two lines of approach have this important difference, that the nature with which man is born is looked on by the politician as fixed, while the environment into which man is born is rapidly and indefinitely changing. It is not to changes in our nature, but to changes in our environment only--using the word to include the traditions and expedients which we acquire after birth as well as our material surroundings--that all our political development from the tribal organisation of the Stone Ages to the modern nation has apparently been due. The biologist looks on human nature itself as changing, but to him the period of a few thousands or tens of thousands of years which constitute the past of politics is quite insignificant. Important changes in biological types may perhaps have occurred in the history of the world during comparatively short periods, but they must have resulted either from a sudden biological 'sport' or from a process of selection fiercer and more discriminating than we believe to have taken place in the immediate past of our own species. The present descendants of those races which are pictured in early Egyptian tombs show no perceptible change in their bodily appearance, and there is no reason to believe that the mental faculties and tendencies with which they are born have changed to any greater degree. The numerical proportions of different races in the world have, indeed, altered during that period, as one race proved weaker in war or less able to resist disease than another; and races have been mingled by marriage following upon conquest. But if a baby could now be exchanged at birth with one born of the same breeding-stock even a hundred thousand years ago, one may suppose that neither the ancient nor the modern mother would notice any startling difference. The child from the Stone Age would perhaps suffer more seriously than our children if he caught measles, or might show somewhat keener instincts in quarrelling and hunting, or as he grew up be rather more conscious than his fellows of the 'will to live' and 'the joy of life.' Conversely, a transplanted twentieth-century child would resist infectious disease better than the other children in the Stone Age, and might, as he grew up, be found to have a rather exceptionally colourless and adaptable character. But there apparently the difference would end. In essentials the type of each human stock may be supposed to have remained unchanged throughout the whole period. In the politics of the distant future that science of eugenics, which aims at rapidly improving our type by consciously directed selective breeding, may become a dominant factor, but it has had little influence on the politics of the present or the past. Those new facts in our environment which have produced the enormous political changes which separate us from our ancestors have been partly new habits of thought and feeling, and partly new entities about which we can think and feel.