Defeminization and masculinization
Defeminization and masculinization are the processes that a fetus goes through to become a male. It has often been said by biologists that in sexual differentiation in mammals, the female is the "default" developmental pathway, in the sense that elimination of any of several gene actions necessary for formation of male genitalia leads to the development of external female genitalia (though development of functional ovaries requires effective action of several less understood sex-specific genes). Two processes: defeminization, and masculinization, are involved in producing male typical morphology and behavior. Defeminization involves the suppression of the development of  female typical morphology (development of the Müllerian ducts into the fallopian tubes, uterus and vagina) and behavioural predispositions. Masculinization involves the production of male typical morphology (development of the Wolffian ducts into male reproductive structures) and behavioural predispositions. Both defeminization and masculinization are required for a mammalian zygote to become a fully reproductively functional male. A brief version of the female default paradigm can be stated as follows: History. This paradigm dates back to the 1950s. Even stronger versions were commonly stated in the 1960s and 1970s. One version, perhaps most associated with John Money, (who termed it the "Adam  principle"), held that additional steps in the cascade to male identity were the recognition by parents and doctor that the external genitalia were male, which resulted in a male sex assignment, which in turn resulted in a male sex of rearing by parents and society, which in turn (coupled with the reinforcing appearance of male genitalia) resulted in a male gender identity. At least by implication, female gender identity simply required a female sex of rearing and lack of an obvious penis.