Crude speculations regarding the derivation of living forms are very ancient, and we may say that the doctrine of organic evolution was foreshadowed in Greek thought. The serious discussion of the question, however, was reserved for the nineteenth century. The earlier naturalists accepted animated nature as they found it, and for a long time were engaged in becoming acquainted merely, with the different kinds of animals and plants, in working out their anatomy and development; but after some progress had been made in this direction there came swinging into their horizon deeper questions, such as that of the derivation of living forms. The idea that the higher forms of life are derived from simpler ones by a process of gradual evolution received general acceptance, as we have said before, only in the last part of the nineteenth century, after the work of Charles Darwin; but we shall presently see how the theory of organic development was thought out in completeness by Lamarck in the last years of the eighteenth century, and was further molded by others before Darwin touched it. Vagueness Regarding Evolution.--Although "evolution" is to-day a word in constant use, there is still great vagueness in the minds of most people as to what it stands for; and, what is more, there is very little general information disseminated regarding the evidence by which it is supported, and regarding the present status of the doctrine in the scientific world. In its broad sense, evolution has come to mean the development of all nature from the past. We may, if we wish, think of the long train of events in the formation of the world, and in supplying it with life as a story inscribed upon a scroll that is being gradually unrolled. Everything which has come to pass is on that part so far exposed, and everything in the future is still covered, but will appear in due course of time; thus the designation of evolution as "the unrolling of the scroll of the universe" becomes picturesquely suggestive. In its wide meaning, it includes the formation of the stars, solar systems, the elements of the inorganic world, as well as all living nature--this is general evolution; but the word as commonly employed is limited to organic evolution, or the formation of life upon our planet. It will be used hereafter in this restricted sense.