But by far the most striking figure among the early Greek philosophers who gave their attention to natural history was Aristotle, (384-322). He lived more than three hundred years before the Christian era, and was a pupil of Plato and a teacher of Alexander the Great. He wrote upon a wide variety of subjects--politics, rhetoric, metaphysics, psychology, philosophy, and natural history--and published several hundred works, most of which have been lost. It is true that Aristotle’s books are full of errors, and if the philosopher were to be judged by the standards of twentieth century science he would not appear very important. But it must be remembered that he was a pioneer who, by the force of his own ability created the serious study of natural history. The workers who had preceded him had discovered relatively little; their works were mostly speculations and vague hypotheses. As Aristotle himself says, “I found no basis prepared; no models to copy.... Mine is the first step, and therefore a small one, though worked out with much thought and hard labor. It must be looked at as a first step and judged with indulgence. You, my readers, or hearers of my lectures, if you think I have done as much as can be fairly required for an initiatory start, as compared with more advanced departments of theory, will acknowledge what I have achieved and pardon what I have left for others to accomplish.” In his two books, “Physics” and “Natural History of Animals” are set forth Aristotle’s views on nature, and his remarkably accurate observations of both plants and animals. He distinguished about five hundred species of mammals, birds, and fishes, besides showing an extensive knowledge of corals and their allies, sponges, squids, and other marine animals. He understood the adaptation of animals and their parts to the needs placed upon them, and was familiar with the commoner principles of heredity. He considered life to be a function of the animal or plant exhibiting it, and not a separate entity, given out by some divine power, or mysterious force. Aristotle devised a hereditary chain, extending from the simplest animals of which he had knowledge to the highest, man. This chain was a very direct affair, not at all resembling the modern “evolutionary tree” in its various ramifications and irregularities. And yet, despite its deficiencies, this chain was the best conception of animal development and descent to be produced in more than twenty centuries.