These matters may seem at first sight to be far removed from the territory of the naturalist as such, and quite exempt from the control of laws which determine the nature and history of the human individual in physical, mental, and social respects. Yet one reason alone would impel us onward: we cannot close the present examination into the basic facts of evolution and into the scope of the doctrine without asking to what extent a belief in its truth may affect our earlier formed conceptions of nature and supernature. Heretofore these possible effects upon what may be dearly cherished intellectual possessions have received no attention, so that we might learn how evolution works in the lower fields of organic life in general and human life in particular without being disturbed by them. No doubt, however, the conviction has grown with each step in our progress that the principles we have learned must cause us to readjust our views of the highest elements in human thought to a degree that must be inversely proportional to our previous acquaintance with the laws and processes of nature. But the seeker after truth is fearless of consequences. He knows that truth cannot contradict itself; and if those to whom he looks for authority give him conflicting accounts of nature's history, he knows that one of these must be less surely grounded than the other. The investigator soon learns to withhold final judgment, realizing that the primary conditions for intellectual development are the plasticity and openness of mind that dogmatism and finality destroy. He knows that while his researches may be, and indeed must be, iconoclastic, they provide him with better icons in place of the old.
Let us recall the steps in our progress through one and another field of knowledge, from which representative facts have been chosen for classification and summary. We began with the basic principles of organic structure and workings, and then we examined serially the larger categories of the evidences relating to evolution as a fact, and to the mode of its accomplishment by natural factors. Proceeding to the special case of our own species, we learned that human beings are inevitably a part of nature and not outside it; in structure, development, and palæontological history, mankind is subject to the control of the uniform laws which operate throughout the entire range of living things. Finally, the mental characters and the social relations of human organisms were derived from beginnings lower down in the scale, and were proved to be no more exceptional than the physical constitution of a single human being.
Are we to forget all of these things when we try to put in order our ideas belonging to the categories of higher thought? Can we hope to find the truth if we fail to employ the methods of scientific common-sense which only yield sure results? It is no more justifiable to discard our hard-earned knowledge than it would be for an advocate to undertake the conduct of a case in deliberate disregard of what he had learned of the law, or for a surgeon to leave his knowledge at the door when he entered the operating room.
Too often we are bidden to view the larger conceptions of nature and supernature as something outside the realm of ordered knowledge too frequently we are given statements upon authority that takes no account of reason, and we are asked to accept these views whether or not they accord with the demonstrated facts of common-sense. But those who have followed the present description of evolution can readily recognize their obligation to use for the further analysis of higher human life the means which have given in that doctrine the most reasonable explanation of the natural phenomena already investigated.
I need hardly say that we now enter upon the most difficult stage of our progress. The regions we have traversed were more readily explored because they were remote from the matters now before us; even in the case of man's mental and social evolution it was possible to take a partially impersonal view of certain of the essential elements in human life, which we cannot do now. For ethics and religion and philosophy are groups of ideas that are familiar to us as the property of mankind alone. Countless obstacles are in the way. Much mental inertia must be overcome, for it is far easier to accept the average and traditional judgments of other men--to let well enough alone--than it is to win our own way to the heights from which we may survey knowledge more fully.
Human prejudices confront us as a veritable jungle, hemming us in and obstructing our vision on all sides; and perhaps much underbrush must be cut away if we are to see widely and wisely. Nevertheless, to those imbued with a desire to learn truth, anything and everything gained must surely repay a thousand times all efforts to obtain clearness of vision and breadth of view. With our perspective thus rectified by our backward glance, we turn to the three divisions of human thought now to be examined. The conceptions of ethics come first for reasons that must be apparent from the classification of the facts of social evolution; just as mental attributes and communal organization are inseparable, so rules of conduct arise _pari passu_ with the origin of a biological association.
Religion and theology form the second division, which takes its origin in part from the first, for these two groups of ideas are largely concerned with the authority for right conduct and with human responsibility for taking the right attitude toward the entire visible and unseen universe. Finally, science and philosophy are briefly treated as evolved products which include within their scope all that there is in human knowledge; for this reason they take the highest place, instead of the position below religion usually assigned to them. At the last, having reached our final standing ground, we must look back in order that we may clearly define the lessons and ultimate values of the whole doctrine of evolution.