Preoccupation with sexual dimorphism is as old as mankind itself, but in the last few decades there has been a flood of new information concerning both the initial genetic process of sex determination and the endocrine mechanisms which subsequently direct sexual differentiation. We now recognize that the direction of that development is largely determined by hormones from the fetal testis. In the agonadal state, the basic developmental trend is female; the fetal testes act to impose masculinity and to suppress femininity through their secretion of Mullerian-inhibiting substance and testosterone. Vital clues about these events have been provided by patients with various disorders of sexual differentiation. It is more than fitting that these insights have led to the development of techniques for the rapid diagnosis of infants born with ambiguous genitalia, and to specific forms of therapy which, if applied early and rationally, can prevent needless physical and psychological damage.
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