EVOLUTION, the act of unrolling or unfolding. The word is used as a term in science and philosophy to indicate the development of an organism toward greater differentiation of organs and functions, and a more complex and high er state of being. Some regard HERBERT SPENCER (q. v) as the author of the Doctrine of Evolution, others CHARLES DARWIN (q. v.) In astronomy, the nebular hypothesis, which regards the planetary bodies as evolved from nebular or gaseous matter, is an example of evolution; in geology the old view, which considered the ani mal and vegetable life of each geological period as a new and separate organic creation, has given place to the evolu tionary theory of a process of develop ment from earlier types to those of the later periods. But the evolution of the more complex from the simple organisms probably never exhibits a linear series of advances. Evolution is a law, the operation of which is traceable through out every department of nature; it is equally well illustrated from the history of philosophy or the arts, or from the historical development of society. Evolu tion has been most discussed (in connec tion with the evolutionary theory of the Origin of Species), as it affirms that all forms of life in both the animal and vegetable kingdoms have been developed by modifications of parts from one low form of life consisting of a minute cell. The steps by which this process has been accomplished, and the causes that have been mainly at work in it, form a department of research to which many notable scientists—Lamarck, St. Hilaire, Goethe, Schelling, Haeckel, Spencer, Dar win, Wallace, and others have contrib uted. John Fiske, in his doctrine of evolution, brings out vividly before us the ever-present God, destroying the con ception of the world as a mere cosmic machine.
The origin of all mammals from one common parent form upward to man is an established fact. Man's evolution can be traced upward from a fish in 12 steps or stages. This fish ancestor of ours be longed to the order of the Selachii, the best existing species of which is the shark. In another direction this primitive fish gave rise to the higher forms of vertebrate amphibious animals leading up to man. The next higher class of
vertebrates, leading toward man, are the batrachians or amphibians. The axolotl of Mexico, a fish-like animal with a long tail, belongs to this class. It has both gills and lungs, and can either respire water through the gills or air through the lungs. Similar are the numerous kinds of salamanders. An experiment was made of keeping the axolotl perma nently out of the water. It lost its gills and became permanently mature and ac customed to its environment. Resembling these are the various kinds of toads and frogs, after which animals come the pro tamnians (lizard-like reptiles). These, losing their gills and breathing only through lungs, were a step farther re moved from fishes. In the formation of the group of Stegocephala, from which man descended, a distinct advance occurs. \. partition wall forms within the simple ventricle of the heart, dividing it into right and left ventricles. Progress is also noticed in the development of the brain, the skeleton, and the muscular system. The period at which the important ad vances occurred which laid the founda tions for the mammal class, to which man belongs, was probably the Triassic. Out of that epoch came the monotremate mammal, of which the modern duck-bill or Plaifypus of Australia is a remnant. The next step higher in development was that of the marsupials, or animals whose females carry their young in pouches. From a branch of such pouched animals, the parent form of the higher or Pla cental mammals, of which man is an extremely specialized type, afterward sprang. Hence we reckon a whole series of pouched animals among the ancestors of the human race. The Placental mam mals mark another distinct advance in evolution. To this group belong the carnivore, of which the lion, the tiger, the dog family and the bear family, are members. A special stage is that of the semi-apes, and probably our ancestor among the semi-apes resembled the exist ing lemurs, and like these, led a quiet life climbing trees. Immediately following are the true apes. Beyond a doubt, of all animals, the apes are the most nearly allied to man. A thousand million of years may have been consumed in this evolution of man.