_Natura simplex est_, said Newton, _et sibi semper consonans_. (Nature is simple and always agrees with herself.) Bewilderingly multiple in her phenomena, she is superbly simple in her principles. By the operation of her one great Law of Gravitation, she sustains the mighty Solar systems--and brings the apple to the ground. By the extension, counterpoise and co-operation of one Primal Cosmic Energy--with its dual impulses, Centripetal and Centrifugal--she has generated all the diverse marvels of a Universe. And in view of her simplicity of Principle, it is conceivable that the Duality of Sex may be an extension into Life of that same principle of Duality which characterises the vaster Cosmic phenomena. If this be true, Man and Woman are the complex resultant of infinitely many and varied evolutionary differentiations and associations of the two modes of Primal Energy. If so, the principle of Sex must have existed before Matter; must have been inherent in Creation before Creation began to evolve. And if so, Evolution would seem to have had for its purpose the ever further and fuller manifestation of these dual and contrary inherences in terms of Life and Sex. While, to judge by effects, it has had for its means such ever more intimate and intricate co-operations of these as have resulted in the progressively diverse and complex developments found to-day in Human Life and Human Sex-Characteristics. CHAPTER III THE MYSTERY OF SEX AND SEX-TRANSMISSION "The idea that the female is naturally and really the superior sex seems incredible, and only the most liberal and emancipated minds, possessed of a large store of biological information, are capable of realising it."--_Professor Lester Ward._ I Those happy persons who do not perplex themselves concerning the intrinsic causes behind all physical phenomena see it as only "natural" that two parents of opposite sex should produce offspring of both sexes. And yet it is not only a great mystery, but, on the face of it, it is an anomaly that a child who may possess an admixture of all the physical and mental characteristics of its two parents, bears, nevertheless, the sex and the sex-characteristics of one only. Sex, male or female, breeds true in nearly every case; the rare exceptions merely emphasising the rule. The mystery deepens when we realise that every individual is a product of countless such admixtures of the qualities, throughout countless generations, of countless forefathers and foremothers. And although such a man or woman may hark back to any one, or more, of the traits of his or her innumerable forbears, he or she, nevertheless, "breeds true" in the factors of sex and sex-characteristics.