Produced by Bryan Ness, Keith Edkins, and the Online Distributed Proofreading Team at https://www.pgdp.net. Pages scanned by Bryan Ness. Transcriber's note: A few typographical errors have been corrected: they are listed at the end of the text. * * * * * Princeton University THE LOUIS CLARK VANUXEM FOUNDATION LECTURES FOR 1915-1916 * * * * * The Louis Clark Vanuxem Foundation of Princeton University was established in 1912 with a bequest of $25,000 under the will of Louis Clark Vanuxem, of the Class of 1879. By direction of the executors of Mr. Vanuxem's estate, the income of the foundation is to be used for a series of public lectures delivered in Princeton annually, at least one half of which shall be on subjects of current scientific interest. The lectures are to be published and distributed among schools and libraries generally. The following lectures have already been published or are in press: 1912-13 The Theory of Permutable Functions, by Vito Volterra 1913-14 Lectures delivered in connection with the dedication of the Graduate College of Princeton University by Emile Boutroux, Alois Riehl, A. D. Godley, and Arthur Shipley 1914-15 Romance, by Sir Walter Raleigh 1915-16 A Critique of the Theory of Evolution, by Thomas Hunt Morgan * * * * * LOUIS CLARK VANUXEM FOUNDATION A CRITIQUE OF THE THEORY OF EVOLUTION BY THOMAS HUNT MORGAN PROFESSOR OF EXPERIMENTAL ZOOLOGY IN COLUMBIA UNIVERSITY LECTURES DELIVERED AT PRINCETON UNIVERSITY FEBRUARY 24, MARCH 1, 8, 15, 1916 PRINCETON UNIVERSITY PRESS PRINCETON LONDON: HUMPHREY MILFORD OXFORD UNIVERSITY PRESS 1916 * * * * * Copyright, 1916, by PRINCETON UNIVERSITY PRESS Published October, 1916 [Illustration] * * * * * PREFACE Occasionally one hears today the statement that we have come to realize that we know nothing about evolution. This point of view is a healthy reaction to the over-confident belief that we knew everything about evolution. There are even those rash enough to think that in the last few years we have learned more about evolution than we might have hoped to know a few years ago. A _critique_ therefore not only becomes a criticism of the older evidence but an appreciation of the new evidence. In the first lecture an attempt is made to put a new valuation on the traditional evidence for evolution. In the second lecture the most recent work on heredity is dealt with, for only characters that are inherited can become a part of the evolutionary process. In the third lecture the physical basis of heredity and the composition of the germ plasm stream are examined in the light of new observations; while in the fourth lecture the thesis is developed that chance variation combined with a property of living things to manifold themselves is the key note of modern evolutionary thought.