Evolution or development has been a prominent idea in the history of thought since the time of Aristotle, but descent is, so to speak, a modern upstart. According to long-established modes of thought, to _evolve_ means to pass from δυνάμει to ἰνεργεία εἴναι, from _potentia_ to _actus_, from the existence of the rudiment as in the seed to full realisation as in the tree. In the course of its development the organism passes through many successive phases, which are related to one another like steps, each rising directly from the one beneath, and preparing for the one above. Thus all nature, and especially the realm of life, implies a ladder of “evolution.” What is “potentially” inherent in the lowest form of life has in the highest, as in man, become actual or “realised” through a continuous sequence of phases, successively more and more evolved. This view in its earlier forms was very far from implying that each higher step was literally “descended” from the one below it, through the physical and mental transformation of some of its representatives. As the world, in Aristotle’s view for instance, had existed from all eternity, so also had the stages and forms of life, each giving rise again to its like. Indeed, the essential idea was that each higher step is simply a development, a fuller unfolding of the lower stage, and finally that man was the complete realisation of what was potentially inherent in the lowest of all. This doctrine of evolution was in modern times the fundamental idea of Leibnitz and Kant, of Goethe, Schelling and Hegel. It brought unity and connectedness into the system of nature, united everything by steps, denied the existence of gaping chasms, and proclaimed the solidarity of all the forms of life. But to all this the idea of actual descent was unnecessary. An actual material variation and transition from one stage to another seemed to it a wooden and gross expression of the evolution idea, an “all too childish and nebulous hypothesis” (Hegel).