Fetal hormones and the brain: Effect on sexual dimorphism of behavior-A review

Experimental animal studies of the influence of prenatally or neonatally administered sex hormones on subsequent manifestations of sexual behavior implicate an organizing action of sex hormones and related substances on the brain, probably in the region of the hypothalamus. The rule would appear to be that female-male bipotentiality applies initially, prior to the influence of any sex hormone in the course of brain development. Bipotentiality would appear to persist when the early hormonal environment is feminine, so that either the feminine or the masculine component of mating behavior can be elicited in adulthood, dependent, among other things, on whether the eliciting hormone is estrogen or androgen. Bipotentiality is resolved in favor of unipolar masculinity of mating behavior if the early hormonal influence at the critical differentiating period is androgenic. The feminine component is then inhibited. Once this is accomplished, the feminine component will, in many, though perhaps not all species, be elicited only under special conditions, for example, direct brain stimulation, or not at all. In the course of normal differentiation, the initial completeness of inhibition of feminine potential varies across species. Thus, it is more complete in the rat than the hamster. In man it is probably not very complete, and is perhaps individually variable, as well.