Generally speaking, we can roughly identify the gender of a fetus based on the different shapes of its external genitalia when it is separated from the mother\’s body. Those who have a \”small penis\” are boys, and those who don\’t have a \”small penis\” are naturally girls. In fact, when did the real distinction between men and women begin to form? In fact, it is doomed the moment the sperm and egg combine to become a fertilized egg. The embryo needs to go through a long 10 months (about 40 weeks) of differentiation and development in the mother\’s body before it can come to the human world. Under normal circumstances, when the embryo develops to 8-10 weeks, testicles appear in the male fetus and begin to secrete androgens. Androgens cause the fetus\’s external reproductive organs to develop and change in the male direction; fetuses without testicles, due to the lack of androgen effects, the external genitalia It naturally goes in the female direction.