Sexual differentiation in humans any androgen can cause external masculinization. The most potent is dihydrotestosterone (DHT), generated from testosterone in skin and genital tissue by the action of 5α-reductase. A male fetus may be incompletely masculinized if this enzyme is deficient. In some diseases and circumstances, other androgens may be present in high enough concentrations to cause partial or (rarely) complete masculinization of the external genitalia of a genetically female fetus. The testes begin to secrete three hormones that influence the male internal and external genitalia. They secrete anti-müllerian hormone, testosterone, and Dihydrotestosterone. anti-Müllerian hormone (AMH) causes the paramesonephric ducts to regress. Testosterone, which
Fraternal birth order and male sexual orientation support a prenatal origin to sexual orientation development in men and indicate that the fraternal birth order effect is probably the result of the mother's body's “memory” for both male births as well as male gestations (i.e., every instance of being pregnant with a male fetus). So even if a male fetus was not carried to term, he still increases the likelihood of homosexuality in any subsequent male fetuses gestated by the same mother. The existence of the fraternal birth order effect on male sexual orientation has been confirmed many times. One approach for establishing the ubiquity of this effect