The biological constitution of humans and of the other higher organisms differentiating them into two opposite symmetrical sides, in which, as development rises higher in the scale, the Dominance, or Maleness, in them is ever further and more perfectly segregated from the Recessiveness, or Femaleness, in them, secures the progressive intensification, respectively, of Maleness or of Femaleness in them, by ever further ranging the factors, or traits, of these on opposite sides of the biological equation; and by thus more effectively centralising the powers, according to sex, in one or the other side thereof. Mendel's peas, not thus differentiated into two sides, are bi-sexual and self-fertilising. Of the original stock, that order in which Dominant traits are prepotent is differentiating toward a male _genus_, however. While the Recessives are differentiating toward a female _genus_. Although regarded as "pure" Dominants and "pure" Recessives, they are nevertheless hybrids in respect of Sex. Being self-fertilising, both Dominants and Recessives are of low power, alike for reproduction and development. Because the Dominance, or Male developmental power, of the Recessives being inhibited by the Recessiveness, or Femaleness, in them, is of low Vigour. While the Recessiveness, or Female vital power in the Dominants being unduly expended by the Dominance, or Maleness, in them, is of low Vitality. The male sex-cells of the self-fertilising Dominants thus fertilise female sex-cells of low vitality. While the female sex-cells of the self-fertilising Recessives are fertilised by male sex-cells of low vigour.