The universe, of which he knows so little, is but in a slight degree a mystery. Wonder—the first sense of philosophy, as it has been so aptly termed by Aristotle—exists in his mind only as superstition. We are too apt to think that primitive or savage man must be appalled by the presence of nature, forgetting that his universe is limited to his own unaided senses. We forget that, in our own life, philosophic problems present themselves only as we approach maturity, and, generally, then only if our studies have led us in their direction. To see how little the "natural man" comprehends these problems, observe the answers he gives to those questions in which it is customary to assume that the wayfaring man, though a fool, does not err.
Man is naturally a "realist." Things are to him what they seem. Mind is his sole measure of nature. He looks nowhere else for an interpreter, and knows no other source of knowledge. He interprets natural phenomena by mental qualities, and this prepossession colors all his theories. The history of science is the history of the gradual demolition of this tendency. The mental distance from a savage that personifies the tree, the forest, and the stream, to a Kepler that conceives it necessary to place a guiding spirit in the planets to keep them in their courses, is, of course, immense, and each is indicative of the thought of his time; but we now know that each was in error in positing some utterly unknowable substance to explain the unknown elements.
The person who to-day expects to make the phenomena of life more clear by attributing them to the effects of "vitality" is making a dangerous mental concept do duty in place of exact knowledge, however limited. The frequency with which this attempt occurs, even among men eminent in science, shows that continued protests are needed. However little real knowledge we may possess upon a given subject, our only way to get more is to approach it humbly and laboriously as a question that can be solved only by constant reference to the facts that appertain to it. All experience teaches that an analysis of mental notions has never yet yielded a particle of natural knowledge, but, on the contrary, has often proved a barrier to the acceptance of true theories. We can not expect to be more fortunate ourselves. The principal objection to the development theory has been on the ground of its opposition to preconceived notions as to the reality of the mental conception "species," and to certain beliefs in vogue concerning the genesis of man, rather than to its assumed opposition to the facts of nature. Every theory has to run the gantlet of this extra-scientific criticism, and only when it is shown to have no possible bearing upon preconceived notions is it allowed to be settled simply upon its merits and by scientific methods.
Instead of reverting to the experience of our ancestors and showing the futility of all previous attempts to extract light from mental sunbeams, we might have deduced the same conclusion from the known