He rolled off geology. Cuvier’s theory of catastrophes, Linné’s belief in the immutability of species—all a purely theological cosmogony. The “philosophical theory of evolution” rises behind it like a Mene Tekel Pharshim. All living things, including those of past geological epochs, form one great _genealogical tree_. The word, the new leading word for zoology and botany, comes out with a flash. What is the system that has been awaited so long? It is the genealogical tree of life on our planet. Its roots lie deep in the remote past. “The thousands of green leaves on the tree that clothe the younger and fresher twigs, and differ in their height and breadth from the trunk, correspond to the living species of animals and plants; these are the more advanced, the further they are removed from the primeval stem. The withered and faded leaves, that we see on the older and dead twigs, represent the many extinct species that dwelt on the earth in earlier geological ages, and come closer to the primeval simple stem-form, the more remote they are from us.” This was the great new idea for science to work upon. Paleontology, the science of past life, found at last a common task with botany and zoology. Haeckel’s own programme for decades was unfolded. This phrase, too, was a birth-hour. In all the struggle that has followed as to the “how” of evolution this figure of the tree with the verdant branches as the new field of zoological and botanical work, and the withered branches for the paleontologist, has never been abandoned. A symbol from the living world itself, the branching tree, had at last taken a decisive place in the science and the classification of living things. With splendid clearness the speech then enumerates the Darwinian principles: variation, heredity, the struggle for life, selection, and adaptation. A vast duration is claimed for the geological epochs in the sense of Lyell; and it is pointed out that there is a progressive advance of forms throughout these periods. Special stress is laid on the ever-advancing, ever-uplifting element in evolution. Man is again introduced into the subject. He has “evolved” from the brutality of the animal. Language itself has been naturally “developed.” (What a shrewd perspective in such a brief phrase! How the philologists would stare!) So the “law of advance” traverses the whole field of culture. A fiery passage follows: “Reaction in political, social, moral, and scientific life, such as the selfish efforts of priests and despots have brought about at every period of history,” cannot permanently hinder this advance. The “advance” is “a law of nature,” and “neither the weapons of the tyrant nor the anathemas of the priest can ever suppress it.” We hear again the older Sethe thundering his intrepid reply: “You will have to shoot the law first.”