While this book is in no sense a work of “popular science,” I have sought to broaden its scope and interest by combining the scientific with the philosophic viewpoint. Certain portions of the text are unavoidably technical, but there is much, besides, that the general reader will be able to follow without difficulty. Students, especially of biology, geology, and experimental psychology, may use it to advantage as supplementary reading in connection with their textbooks. I wish to acknowledge herewith my indebtedness to the Editor of the _Catholic Educational Review_, Rev. George Johnson, Ph. D., to whose suggestion and encouragement the inception of this work was largely due. I desire also to express my sincere appreciation of the services rendered in the revision of the manuscript by the Rev. Edward Wenstrup, O.S.B., Professor of Zoölogy, St. Vincent College, Pennsylvania. BARRY O’TOOLE. ST. VINCENT ARCHABBEY, January 30, 1925. PART I EVOLUTION IN GENERAL CHAPTER I THE PRESENT CRISIS IN EVOLUTIONARY THOUGHT Three prominent men, a scientist, a publicist, and an orator, have recently made pronouncements on the theory of Evolution. The trio, of course, to whom allusion is made, are Bateson, Wells, and Bryan. As a result of their utterances, there has been a general reawakening of interest in the problem to which they drew attention. Again and again, in popular as well as scientific publications, men are raising and answering the question: “Is Darwinism dead?” Manifold and various are the answers given, but none of them appears to take the form of an unqualified affirmation or negation. Some reply by drawing a distinction between Darwinism, as a synonym for the theory of evolution in general, and Darwinism, in the sense of the particular form of that theory which had Darwin for its author. Modern research, they assure us, has not affected the former, but has necessitated a revision of ideas with respect to the latter. There are other forms of evolution besides Darwinism, and, as a matter of fact, not Darwin, but Lamarck was the originator of the scientific theory of evolution. Others, though imitating the prudence of the first group in their avoidance of a categorical answer, prefer to reply by means of a distinction based upon their interpretation of the realities of the problem rather than upon any mere terminological consideration.