Evolution, the term now generally applied to the doctrine that the existing universe has been gradually unfolded by the action of natural causes in the immeasurable course of past time. The question how the present order of things originated seems natural to the human mind, and has been put by all the races of men. The answer given in their cosmogonies, that it was created as we now see it by supernatural power, has been generally accepted as a matter of religious faith. The early Greek philosophers first brought the question into the field of speculation, and taught that all natural things have sprung from certain primal elements, such as air, water, or fire. As regards the origin of life, Anaximander is said to have held that animals were begotten from earth by means of moisture and heat, and that man did not originate in a perfectly developed state, but was engendered from beings of a different form. Empedocles taught that the various parts of animals, arms, feet, eyes, etc, existed separately at first; that they combined gradually, and that these combinations, capable of subsisting, survived and propagated themselves. Anaxagoras believed that plants and animals owe their origin to the fecundation of the earth whence they sprung by germs contained in the air.
Aristotle, the father of natural history, entertained much more rational views upon the subject, and it is maintained that he held opinions as to the causes of diversity in living beings similar to those that are entertained by the latest zoologists. It has been asserted that some of the early theologians, including St. Augustine and St. Thomas Aquinas, announced doctrines that harmonize apparently with the modern views of evolution.We however find no development of the ideas thus shadowed forth. Linngaeus and Buf-fon seem to have been the first among modern naturalists who formed definite conceptions of a progressive organic development, but they did little to elucidate the idea. Immanuel Kant announced in 1755 his theory of the mechanical origin of the universe, and supposed that the different classes of organisms are related to each other through generation from a common original germ. Dr. Erasmus Darwin, grandfather of Charles Darwin, in his Zoono-mia (1794), maintained the natural genesis of organic beings. But the first to frame a distinct hypothesis of development was Lamarck, who published his Philosophie zoologique in 1809, and developed his views still further in 1815 in his Histoire naturale des animaux sans vertebres.
He held that all organic forms, from the lowest to the highest, have been developed progressively from living microscopic particles. Similar conclusions were arrived at by Goethe in Germany, and by Geoffroy Saint-Hilaire in France in his work Sur le principe de l'unite de composition organique, published in 1828. The views thus far were of a general and highly speculative nature, and without firm scientific ground-work. It was only when the question was narrowed down to that of the mutability or immutability of species, and to the causes and extent of variation as determined by observation and experiment, that the real difficulties of the case were grappled with, and the inquiry assumed a strictly scientific character. In 1813 Dr. W. C.Wells read a paper before the London royal society, in which he recognized distinctly the principle of natural selection as applied to certain races of mankind. In 1822 the Rev.William Herbert, afterward dean of Manchester, declared his conviction that botanical species are only a higher and more permanent class of varieties;" and he extended this opinion to animals.
Leopold von Buch, in his Physihalische Beschreibung der Canarischen Inseln (1825), expresses the opinion that varieties change gradually into permanent species, which are no longer capable of intercrossing. In 1826 Prof. Grant of Edinburgh published a paper on the spongilla in the "Philosophical Journal," in which he held that species are descended from other species, and that they become improved in the course of modification. Karl Ernst von Baer, in his Ueber Entwickelungsgeschichte der Thieve (1828), maintains similar views as to animals. Oken, in his Naturphilosophie (1843), published his belief in the development of species; and in 1846 J. d'Omalius d'Halloy of Brussels expressed his opinion that probability favors this theory rather than that of separate creations. Isidore Geoffroy Saint-Hilaire, in his lectures published in 1850, gives reasons for his belief in the modification of species by circumstances, and in the transmission of differences thus produced. In 1852 Herbert Spencer argued that species have undergone modification through change of circumstances.
M. Nau-din in the same year published a paper on the origin of species in the Revue horticole, in which he averred his belief that botanical species are formed in a manner analogous to varieties under cultivation; and Franz Unger, also in 1852, expressed similar opinions in his Versuch einer Geschichte der Pflanzenwelt. In 1863 Dr. Schaffhausen, in a paper published in the Verhandlungen des Naturhistorischen Vereins despreussischen Rheinlands, etc, maintained the doctrine of progressive development of organic forms. On July 1, 1858, two essays were read before the Linnaean society, one by Charles Robert Darwin, entitled "On the Tendency of Species to form Varieties, and on the Perpetuation of Species and Varieties by means of Natural Selection;" the other by Alfred Russell Wallace, entitled On the Tendency of Varieties to depart indefinitely from the Original Type." These papers showed that these two naturalists had arrived at almost exactly the same general conclusions; but the priority may safely be assigned to Darwin, who, although he had not previously made public his views, had submitted a sketch of them as early as 1844 to Sir Charles Lyell, Dr. Hooker, and others.
In 1859 he published the treatise entitled On the Origin of Species by means of Natural Selection," which was the means of diffusing so widely the theory, elaborated by him through years of patient and careful investigation, that it is commonly designated by his name. In this work he did not apply the doctrine of evolution to the human race, although he had long held the opinion that man must be included with other organic beings; and it was not until after Huxley, Spencer, Lyell, Lubbock, Gegenbaur, Vogt, Rolle, Haeckel, Canestrini, Francesco, and others, had accepted the extreme conclusion, that he published " The Descent of Man, and Selection in Relation to Sex (1871). In 1872 Haeckel, who previously had discussed the genealogy of man in Naturliche Schop-fungsgeschichte (1868), published his Monographic der Kalkschwamme, in which he claims to give an analytical demonstration of the problem of the development of species.-The theory as now generally held is thus stated by Prof. Huxley: Those who hold the theory of evolution (and I am one of them) conceive that there are grounds for believing that the world, with all that is in it, did not come into existence in the condition in which we now see it, nor in anything approaching that condition.