The doctrine of evolution is also called the theory of development--it must not, however, be confused with Darwinism--for they are not exactly synonymous. Darwinism is an attempt to explain the laws or manner of evolution. Strictly speaking, only the theory of selection should be called Darwinism, which was established in 1859. The theory of descent, or transmutation theory, or doctrine of filiation, should properly be called Lamarckism, who for the first time worked out the theory of descent as an independent scientific theory of the first order, and as the philosophical foundation of the whole science of biology. "According to the theory of development (evolution) in its simplest form," says Henry Hartshorne,[18] "the universe as it now exists is a result of 'an immense series of changes,' related to and dependent upon each other as successive steps, or rather growths, constituting a progress; analogous to the unfolding or evolving of the parts of a growing organism." Herbert Spencer defined evolution as consisting in a progress from the homogeneous to the heterogeneous, from general to special, from the simple to the complex; and this process is considered to be traceable in the formation of worlds in space, in the multiplication of the types and species of plants and animals on the globe, in the origination and diversity of languages, literature, arts and sciences, and in all changes of human institutions and society. [Illustration: FIG. I.--Skeleton of Platypus.--_Haeckel._] [Illustration: FIG. I.--Represents Pouched Animals (Marsupialia). Kangaroo. (Popular Science Monthly, Feb., 1876.)] Let us now apply this theory of evolution to the physical world. No determined opposition by the mass of people is likely to be manifested to the doctrine of evolution as applied to the physical world, or even to the vegetable or animal world up to man; but the minute man is included--then is a voice raised up against it, and it was for this reason that Darwin in his first work on the "Theory of Descent" did not mention man as being included in the evolutionary series. He knew too well the foolish human weakness that existed. In a recent work by Prof. Challes, he states that he regards the material universe as "a vast and wonderful mechanism of which the least wonderful thing is its being so constructed that we can understand it." The following is a brief description of the various theories of the world's formation: