The argument and method is therefore purely historical. Here and there we will try to find why and how things had to be so. But all such digressions are of small account compared with the fact that things were or are thus and so. And a mistaken explanation will not invalidate the facts of history. The subject of our history is the development, not of a single human race nor of the movements of a century, but the development of animal life through ages. And even if our attempts to decipher a few pages here and there in the volumes of this vast biological history are not as successful as we could hope, we must not allow ourselves to be discouraged from future efforts. Even if our translation is here and there at fault, we must never forget the existence of the history. Some of the worst errors of biologists are due to their having forgotten that in the lower stages the germs of the higher must be present, even though invisible to any microscope. Our study of the worm is inadequate and likely to mislead us, unless we remember that a worm was the ancestor of man. And a biologist who can tell us nothing about man is neglecting his fairest field. Conversely history and social science will rest on a firmer basis when their students recognize that many human laws and institutions are heirlooms, the attainments, or direct results of attainments, of animals far below man. We are just beginning to recognize that the study of zoölogy is an essential prerequisite to, and firm foundation for, that of history, social science, philosophy, and theology, just as really as for medicine. An adequate knowledge of any history demands more than the study of its last page. The zoölogist has been remiss in not claiming his birthright, and in this respect has sadly failed to follow the path pointed out by Mr. Darwin. For palæontology, zoölogy, history, social and political science, and philosophy are really only parts of one great science, of biology in the widest sense, in distinction from the narrower sense in which it is now used to include zoölogy and botany. They form an organic unity in which no one part can be adequately understood without reference to the others. You know nothing of even a constellation, if you have studied only one of its stars. Much less can the study of a single organ or function give an adequate idea of the human body. Only when we have attained a biological history can we have any satisfactory conception of environment. As we look about us in the world, environment often seems to us to be a chaos of forces aiding or destroying good and bad, fit and unfit, alike.