It will be seen from all this that in questions relating to the evolution of Man, Herodotus exhibits--and shares with the whole thought of his time--precisely the opposite weakness to that of the pioneers of modern anthropology. His mistakes arise, not because he is unable to allow time enough for evolutionary changes, but because he tries to crowd too great an amplitude of change into the liberal allowance of time which he is prepared to grant. Ten thousand years, or even twenty thousand, would be a short allowance, in modern geology, for even so active a river as the Nile to fill up the whole Red Sea; but it is more than double the whole length allotted to ‘geological time’ within the memory of men still living. It will also be clear how deep was the impression created on the Greek mind by the minor changes of the seasons and of history. The formula of Heracleitus, πάντα ῥεῖ καὶ οὐδὲν μένει, had indeed its application to metaphysic; but its origin was in physical science, as a generalization from experience. It had its negative interest as an implement of sceptical destruction. But it had also a high positive value, for it formulated the present as transitional from the past to the future; it emphasized the kinetic and physiological aspect of nature and of science, which has ever been of so far higher value, in research, as in life, than the static and morphological; it substituted an analysis of processes for classification of the qualities of things. Now it is to this phase of scientific theory that we must assign the first intrusion into scientific terminology of the twin words φύσις and νόμος; in their primitive sense they denote nothing else than precisely such natural processes in themselves, on the one hand, and man’s formulation of such processes, on the other.