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 studies have demonstrated that the fraternal birth order effect does not operate through social or postnatal (e.g., learning or rearing or environmental) mechanisms; rather it is biological in nature and operates prenatally. It is also known that the fraternal birth order effect on male sexual orientation is unaffected by family dynamics, living with older brothers or learning. Fraternal birth order and male sexual orientation A correlation between fraternal birth order and male sexual orientation has been suggested by research. Ray Blanchard identified the association and referred to it as the fraternal birth order effect. In several studies, the observation is