But a persistently philosophical mind at once raises the question of the origin of this primeval nebula itself, with a definite organization and a vast potential energy that must, after all, be regarded as a part of nature rather than its source. Several courses are here open to naturalism. It may maintain that the question of ultimate origin is unanswerable; it may regard such a process of concentration as extending back through an infinitely long past;[243:12] or, and this is the favorite alternative for more constructive minds, the historical cosmical process may be included within a still higher type of periodic process, which is regarded as eternal. This last course has been followed in the well-known synthetic naturalism of Herbert Spencer. "Evolution," he says, "is the progressive integration of matter and dissipation of motion." But such a process eventually runs down, and may be conceived as giving place to a counter-process of devolution which scatters the parts of matter and gathers another store of potential motion. The two processes in alternation will then constitute a cosmical system without beginning or end. In such wise a sweeping survey of the physical universe may be thought in the terms of natural science. The uniformitarian method in geology, resolving the history of the crust of the earth into known processes, such as erosion and igneous fusion;[244:13] and spectral analysis, with its discoveries concerning the chemical constituents of distant bodies through the study of their light, have powerfully reënforced this effort of thought, and apparently completed an outline sketch of the universe in terms of infra-organic processes. [Sidenote: Life. Natural Selection.] § 112. But the cosmos must be made internally homogeneous in these same terms. There awaits solution, in the first place, the serious problem of the genesis and maintenance of life within a nature that is originally and ultimately inorganic. The assimilation of the field of biology and physiology to the mechanical cosmos had made little real progress prior to the nineteenth century. Mechanical theories had, indeed, been projected in the earliest age of philosophy, and proposed anew in the seventeenth century.[245:14] Nevertheless, the structural and functional teleology of the organism remained as apparently irrefutable testimony to the inworking of some principle other than that of mechanical necessity. Indeed, the only fruitful method applicable to organic phenomena was that which explained them in terms of purposive adaptation. And it was its provision for a mechanical interpretation of this very principle that gave to the Darwinian _law of natural selection_, promulgated in 1859 in the "Origin of Species," so profound a significance for naturalism. It threatened to reduce the last stronghold of teleology, and completely to dispense with the intelligent Author of nature.