I. This tolerant method of thought has gained greatly in popularity since Darwin proved its capacity to solve the problem of the origin of man. The possibility that all forms of life, even the highest, are results of a natural process of gradual development has often been suggested by poets and philosophers. The probability was much discussed by men of science early in the nineteenth century; but it was not until 1858 that sufficient evidence was presented to justify acceptance of evolution as anything better than merely a theory. Twenty-one years had then elapsed since Darwin began a long series of investigations. In the first place, he collected an irresistible number of cases of the influence of environment in causing variations in structure, and of the tendency of such variations to be inherited. Most men who accepted these propositions admitted their insufficiency to account for the multiplicity of species; but the explanation became complete when Darwin discovered that any plant or animal which is peculiarly fit for survival in the continual struggle for existence is likely to become largely represented in the next generation. A spontaneous variation which prolongs the life of its possessor may thus become not only more common but more firmly fixed in successive generations, until a new species is established. To this tendency Darwin gave the name "natural selection"; but this term literally implies a deliberate choice by some superhuman power. Herbert Spencer proposed the phrase, "survival of the fittest"; but it must be remembered that the fitness is not necessarily that of greater moral worth. There may be merely such a superiority in strength and cunning as enables savages to devour a missionary. Spencer says that "the expression, 'survival of the fittest,'" merely means "the leaving alive of those which are best able to utilise surrounding aids to life, and best able to combat or avoid surrounding dangers." Weeds are fitter than flowers for natural growth; and Joan of Arc proved unfit to survive in the contest against wicked men.