The universal belief in the independent creation of living organisms was revised by Linnaeus and was put upon a new foundation. Before him the genera were supposed to be created, the species and minor forms having arisen from them through the agency of external conditions. In his first book Linnaeus adhered to this belief, but later changed his mind and maintained the principle of the separate creation of species. The weight of his authority soon brought this conception to universal acceptance, and up to the present time the prevailing conception of a species has been chiefly based on the definition given by Linnaeus. His species comprised subspecies and varieties, which were in their turn, supposed to have evolved from species by the common method. Darwin tried to show that the links which bind species to genera are of the same nature as those which determine the relationship of [3] subspecies and varieties. If an origin by natural laws is conceded for the latter, it must on this ground be granted for the first also. In this discussion he simply returned to the pre-Linnean attitude. But his material was such as to allow him to go one step further, and this step was an important and decisive one. He showed that the relation between the various genera of a family does not exhibit any features of a nature other than that between the species of a genus. What has been conceded for the one must needs be accepted for the other. The same holds good for the large groups. The conviction of the common origin of closely allied forms necessarily leads to the conception of a similar descent even in remote relationships. The origin of subspecies and varieties as found in nature was not proved, but only generally recognized as evident. A broader knowledge has brought about the same state of opinion for greater groups of relationships. Systematic affinities find their one possible explanation by the aid of this principle; without it, all similarity is only apparent and accidental. Geographic and paleontologic facts, brought together by Darwin and others on a previously unequalled scale, point clearly in the same direction. The vast amount of evidence of all [4] comparative sciences compels us to accept the idea. To deny it, is to give up all opportunity of conceiving Nature in her true form. The general features of the theory of descent are now accepted as the basis of all biological science. Half a century of discussion and investigation has cleared up the minor points and brought out an abundance of facts; but they have not changed the principle. Descent with modification is now universally accepted as the chief law of nature in the organic world. In honor of him, who with unsurpassed genius, and by unlimited labor has made it the basis of modern thought, this law is called the "Darwinian theory of descent."