From our attempt to place together as much as possible of Huxley's geological work in the last chapter, it followed that we anticipated much that falls properly within this chapter. The year 1859, the date of publication of _The Origin of Species_, is a momentous date in the history of this century, as it was the year in which there was given to the world a theory that not only revolutionised scientific opinion, but altered the trend of almost every branch of thought. To understand this great change, and the part played in it by Huxley, it is necessary to be quite clear as to what Darwin did. In the first place, he did not invent evolution. The idea that all the varied structures in the world, the divergent forms of rocks and minerals and crystals, the innumerable trees and herbs that cover the face of the earth like a mantle, and all the animal host of creatures great and small that dwell on the land or dart through the air or people the waters,--that all these had arisen by natural laws from a primitive unformed material was known to the Greeks, was developed by the Romans, and even received the approval of early Christian Fathers, who wrote long before the idea had been invented that the naive legends of the Old Testament were an authoritative and literal account of the origin of the world. After a long interval, in which scientific thought was stifled by theological dogmatism, the theory of evolution, particularly in its application to animals, began to reappear, long before Darwin published _The Origin of Species_. Buffon, the great French naturalist, and Erasmus Darwin, the grandfather of Charles, had expressed in the clearest way the possibility that species had not been created independently, but had arisen from other species. Lamarck had worked out a theory of descent in the fullest detail, and regarded it as the foundation of the whole science of biology. He taught that the beginning of life consisted only of the simplest and lowest plants and animals; that the more complex animals and plants arose from these, and that even man himself had come from ape-like mammals. He held that the course of development of the earth and of all the creatures upon it was a slow and continuous change, uninterrupted by violent revolutions. He summed up the causes of organic evolution in the following propositions[D]: "1. Life tends by its inherent forces to increase the volume of each living body and of all its parts up to a limit determined by its own needs. "2. New wants in animals give rise to new movements which produce organs. "3. The development of these organs is in proportion to their employment. "4. New developments are transmitted to offspring."