This book, a first attempt to survey and define the whole field of eugenics, appears in the year which finds us celebrating the centenary of the birth of Charles Darwin and the jubilee of the publication of The Origin of Species. It is a humble tribute to that immortal name, for it is based upon the idea of selection for parenthood as determining the nature, fate and worth of living races, which is Darwin's chief contribution to thought, and which finds in eugenics its supreme application. The book is also a tribute to the august pioneer who initiated the modern study of eugenics in the light of his cousin's principle. A few years ago I all but persuaded Mr. Galton himself to write a general introduction to eugenics, but he felt bound to withdraw from that undertaking, and has given us instead his Memories, which we could ill have spared. The present volume seeks to supply what is undoubtedly a real need at the present day-a general introduction to eugenics which is at least considered and responsible. I am indebted to more than one pair of searching and illustrious eyes, which I may not name, for reading the proofs of this volume. My best hopes for its utility are based upon this fact. If there be any other reason for hope it is that during the last six years I have not only written incessantly on eugenics, but have spoken upon various aspects of it some hundreds of times to audiences as various as one can well imagine-a mainly clerical assembly at Lambeth Palace with the Primate in the[viii] Chair, drawing-rooms of title, working-class audiences from the Clyde to the Thames. It has been my rule to invite questions whenever it was possible. Such a discipline is invaluable. It gives new ideas and points of view, discovers the existing forms of prejudice, sharply corrects the tendency to partial statement. It is my hope that these many hours of cross-examination will be profitable to the present reader.