The Mystery of Sex, or Sex Polarity

...distinct sexes has been derived from it." Single-sex original: "unisexual" differentiation—occurring through the reduction of one type of reproductive system—takes place at very different stages in an organism's development. This often happens even after the sexual organs have reached a very advanced state of development. The first physical step in this separation would likely be the limiting of specific areas where both types of reproductive cells were still produced at different times within the same organism. In various individuals, the opposing tendencies we mentioned earlier became more dominant until single-sex organisms evolved from hermaphroditism the condition of having both male and female reproductive organs. Many experiments suggest that environmental conditions are effective in changing an organism from a hermaphroditic to a single-sex state. For example, it has been shown in certain flowering plants, such as the butcher's broom (Ruscus aculeatus), that the monoecious having male and female flowers on the same plant or dioecious having male and female flowers on separate plants condition can be triggered by changing the plant's nutrition.

A very different view considers hermaphroditism to be a secondary condition that evolved from an original single-sex state. Thus, Pelseneer Paul Pelseneer (1863–1945), a Belgian biologist famous for his study of mollusks argues that the "study of Mollusks, Myzostomids a group of small parasitic worms, Crustaceans, and Fish original Latin: "Mollusca, Myzostomidae, Crustacea, and Pisces" shows that in these groups, the separation of the sexes existed before hermaphroditism. Various cases in other groups suggest this is true everywhere, and the same conclusion applies to plants. In mollusks, crustaceans, and fish, at least, hermaphroditism is added onto the female sex."

As an example of the results of perfect and normal hermaphroditism in lower life forms, we can look at the method of fecundation fertilization among snails. We must remember that the snail possesses both male and female sexual organs, both of which are fully developed and active during reproduction. The process is described by Professor T. R. Jones Thomas Rymer Jones (1810–1880), a British zoologist, who says: "The way snails mate is quite strange. Their union is preceded by extraordinary 'flirting' original: "preparatory blandishments" that, to a bystander, might look more like a fight between deadly enemies than the tender advances of two lovers. After various caresses between the two, during which they show an...