PubMed1990
Plato conceptualized primordial humans as androgynes, the children of the moon. The primordial hermaphroditism of the mammalian embryo became known 2 1/2 millennia later in the mid-19th century. By 1864 Ulrichs had transposed the new knowledge from embryology to sexology to explain those to whom he gave the name Urnings (after Uranus who gave womanless birth to Venus from sea spume) as having "a woman's mind trapped in a man's body" (anima muliebris corpore virili inclusa). Urning became displaced by sexual inversion, and eventually by homosexual, a term coined together with heterosexual by Kertbeny as recently as 1869. The embryological principle of primordial hermaphroditism became linked to evolutionary Darwinism by way of Haeckel's principle of recapitulation, epitomized as "ontogeny recapitulates phylogeny." The recapitulation principle became linked, in turn, to the principle of intrapsychic primordial bisexuality, which became a cornerstone of Freud's psychoanalytic theory. Genetics influences the outcome of bipotentiality not directly but by way of hormonal programming of the brain, prenatally or neonatally, rather than pubertally and in maturity. Bipotentiality within the brain has been investigated chiefly in the hypothalamus where male/female dimorphism has been recognized, but its determinants and stages of differentiation, both prenatal and postnatal, remain to be fully ascertained. Neuroanatomical research on the outcome of male/female bipotentiality as gay, straight, or in between is politically and morally opposed by those who postulate a bipotential preference or voluntary choice. In stimulus-response associationism, to which behavior-modification theory belongs, bisexuality is equipotential, and either alternative may be evoked, ostensibly, dependent on the stimulus situation. In ethological theory, the effectiveness of stimulus-response bonding is confined chronologically to a critical period of development and is restricted phylogenetically by an innate recognition mechanism and an innate releasing mechanism. These limits are compatible, however, with some degree of both individual and ethnic variation.