III
Evolution of Species and evolution of the Individual occur on different planes
The Evolution of Species progresses in every generation by way of each Sex having derived from the other Sex a new and opposite potential to engender, in every alternate generation, the further evolution of its Sex-traits along its own (and contrary) lines.
It may be considered therefore that Type, or Species, evolves to higher inherences by way of progressive divergences of Sex-characteristics. While the Evolution of the individual progresses in every generation in proportion as parents of both sexes had mated, in the previous generation, with such members of the opposite sex as were best fitted to supply, in the gametes contributed to offspring, complements which, by union with their own, so matched and supplemented their own as to have quickened and energised the development of offspring to the fullest and the most efficient issues. In any line, however, a strain of greatness or of other inherence descends in alternating succession, now in the female, now in the male line; receding now into the potential, and then evolving in development. So that while the Individual normally evolves in every generation, the Type evolves only in alternate generations.
The evolution of Type, or Species, is the intrinsic function of the spontaneous Evolution of Life into two orders of Sex. It occurs on a wholly different plane from that of the evolution of the Individual. But by way of his, or her, complement to the biological constitution of offspring, members of both sexes contribute alike to the evolution of Species and to that of the Individual—according as such complement enhances the power of the traits of the opposite Sex to manifest, and further to evolve in offspring.
The intensification in the one sex of its own inherences stimulates a proportional intensification of the opposite inherences in the other Sex, both as regards the evolution of the Type and of the Individual. The phenomenon would seem to be akin to that increase of one electrical potential evoking a proportional increase of the other electrical potential, to complement it. When one sex fails to supply its due potential, or complement, to the other, the evolution both of Type and Individual receives a check.
And because the evolution of Type is achieved by the Germ-plasm derived from a parent of one sex obtaining new increment from being invested in the organisation of offspring of the opposite sex, it is not until the new Typal-inherence of this Germ-plasm is revivified again in the organisation of a member of the Sex from which the plasm was derived, that such new impulse manifests. Hence the phenomenon of characteristics being transmitted from parents to offspring of opposite sex. So that daughters of normal womanly organisation reproduce the Typal characteristics of their fathers' maternal line; while in sons of normal male organisation those of their mothers' paternal line emerge.
Hence too, the reversion of offspring of hybrid plants to the types,—pure Dominant and pure Recessive—of their grandparents.
IV
Progressive segregation of Male and Female traits in opposite sides of body ever further intensifies and differentiates their intrinsic qualities