The variety of species now current developed out of simpler forms of animal life, from which they are lineally descended. Their present forms and structures are modifications from the common forms possessed by their remote ancestors. These modifications are, in the stricter forms of Darwinian evolution, explained in mechanical terms by the theory of the "survival of the fittest." That is, those animals with variations adapted to their environment survive; those without, perish. In consequence when any individual in a species happens to be born with a variation specially adapted to its environment, in the sharp "struggle for existence" that characterizes animal life in a state of nature, it alone will be able to survive and reproduce its kind. All the variations of species current are, therefore, examples of this continuous process of descent with adaptive modifications. The origin of the human species came about through just such a variation or mutation from one of the higher mammals (we have reason to believe, a species similar to that of the anthrapoid ape). Man's ancestry, it seems, from the scientific evidence which has been marshaled, may be traced back biologically, in an almost unbroken chain to unicellular animals.[1] [Footnote 1: For detailed discussion see Scott: _Theory of Evolution_.] This theory profoundly affected theological thinking. In the first place, the evolutionary account not only of the origin of man, but of the origin of all species, as a descent with modification from simpler-animal forms, conflicts with the account of special creation, certainly in the literal form of the Biblical story. Secondly, the arguments from design which had been drawn from the adaptation of organic life to environment were, if not disproved, at least rendered dubious. Although evolution did not account for the first appearance of life on earth, it did account for the processes of adaptation, and without invoking design or purpose. The eye, for example, as explained by the theory of evolution, came to its present perfection through a series of fortunate and cumulative variations through successive generations. Even in its imperfect form, it was a variation with high "survival value." Even when it was no more than a pigmented spot peculiarly sensitive to light, so the theory holds, it was a variation that enabled a species to survive and perpetuate its kind. Those not possessing these fortunate variations were wiped out. The process of Nature, certainly, in the development of biological life thus appears to be no economical convergence of means upon an end. Nature has been recklessly prodigal. Millions more seeds of life are produced than ever come to fruition. And only animals perfectly adapted to their environment survive, while an incomparably greater number perish.