Abstract
1. Female animals exposed to stimulation by testosterone in utero or very soon after birth may exhibit changes in adult mating behavior which are indicative of two independent types of modification. One is defeminization, and another quite different one is masculinization. The behavioral modifications are believed to represent changes in separate neural mechanisms, either of which can be altered without changing the other. The implication is, of course, that the CNS is originally bisexual with respect to its behavioral potential. 2. Independent changes which can be produced in males by eliminating the effects of endogenous testosterone during early development are demasculinization and/or defeminization. Here again, separate neural mechanisms are postulated. 3. In rodents and carnivores there are at least two types of behavior which are normally dimorphic in adulthood and are subject to modification by manipulation of androgenic stimulation during very early development. One type, represented by mating behavior, depends heavily upon concurrent hormonal stimulation in adulthood during the time it is being manifested. The other, represented by urination behavior in female dogs, is hormonally modifiable in utero but independent of gonadal hormones in adulthood. Female dogs genitally masculinized by testosterone pre- and neonatally exhibit male mounting responses as adults but only if they are injected with testosterone propionate before and during the time of testing. The same females display the male urination pattern as adults, but this behavior occurs without any concurrent androgenic stimulation and is in fact unaffected by testosterone injections. It would appear that certain sex differences in behavior which normally appear at the time of puberty are dependent upon both prenatal and pubertal hormonal action, whereas other differences may depend only upon hormonal action during development and emerge at the normal age of puberty without any additional endocrine facilitation.
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