What distinguishes Weismann, and makes him especially useful for our present purpose of coming to an understanding in regard to the theory of selection is, that his views are unified, definite and consistent. In his case we have not to clear up the ground and to follow things out to their conclusions, nor to purge his theories from irrelevant, vitalistic, or pantheistic accessory theories, as we have, for instance, in the case of Haeckel. His book, too, is kept strictly within its own limits, and does not attempt to formulate a theory of the universe in general, or even a new religion on the basis of biological theories. Let us therefore inquire what has to be said in regard to this clearest and best statement of the theory of selection when we consider it from the point of view of the religious conception of the world.
Whatever else may be said as to the all-sufficiency of natural selection there can be no doubt that it presupposes two absolute mysteries which defy naturalistic explanation and every other, and which are so important that in comparison with them the problem of the struggle for efficacy and its meaning fades into insignificance. These are the functions and capacities of living organisms in general, and in particular those of variation and inheritance, of development and self-differentiation. What is, and whence comes this mysterious power of the organism to build itself up from the smallest beginnings, from the germ? And the equally mysterious power of faithfully repeating the type of its ancestors? And, again, of varying and becoming different from its ancestors? Even the “mechanical” theory of selection is forced to presuppose the secret of life. Weismann indeed attempts to solve this riddle through his germ-plasm theory, the predisposition of the future organism in the “ids,” determinants, and biophors, and through the variation of the determinants in germinal selection, amphimixis and so on. But this is after all only shifting the problem to another place, and translating the mystery into algebraical terms, so to speak, into symbols with which one can calculate and work for a little, which formulate a definite series of observations, an orderly sequence of phenomena, which are, however, after all, “unknown quantities” that explain nothing.