The above doctrines when enunciated by theologians need cause little surprise, but with the dawn of a scientific age it might have been expected that the prejudices resulting from those doctrines might disappear. When, however, we turn to the most advanced scientific writings of the present century, we find that the prejudices which throughout thousands of years have been gathering strength are by no means eradicated, and any discussion of the sex question is still rare in which the effects of these prejudices may not be traced. Even Mr. Darwin, notwithstanding his great breadth of mental vision and the important work which he accomplished in the direction of original inquiry, whenever he had occasion to touch on the mental capacities of women, or more particularly on the relative capacities of the sexes, manifested the same spirit which characterizes the efforts of an earlier age; and throughout his entire investigation of the human species, his ability to ignore certain facts which he himself adduced, and which all along the line of development tend to prove the superiority of the female, is truly remarkable. We usually judge of a man’s fitness to assume the rôle of an original investigator in any branch of human knowledge, by noting his powers of observation and generalization, and by observing his capacity to perceive connections between closely related facts; also, by tracing the various processes by which he arrives at his conclusions. The ability, however, to collect facts, and the power to generalize and draw conclusions from them, avail little, when brought into direct opposition to deeply rooted prejudices. The indications are strong that the time has at length arrived when the current opinions concerning sex capacity and endowment demand a revision, and when nothing short of scientific deductions, untainted by the prejudices and dogmatic assumptions of the past, will be accepted. As has been stated, the object of this volume is to set forth the principal data brought forward by naturalists bearing on the subject of the origin and development of the two lines of sexual demarcation, and by means of the facts observed by explorers among peoples in the various stages of development, to trace, so far as possible, the effect of such differentiation upon the individual, and upon the subsequent growth of human society. E. B. G. CONTENTS PAGE PREFACE TO SECOND EDITION iii PREFACE TO FIRST EDITION v PART I _THE THEORY OF EVOLUTION_ CHAPTER I.—DEVELOPMENT OF THE ORGANISM 3 II.—THE ORIGIN OF SEX DIFFERENCES 14 III.—MALE ORGANIC DEFECTS 35