"Basically, males and females are all built from the same genetic blueprint,
During the first several weeks, male and female embryos follow the same blueprint, which includes the development of nipples. However, at about six to seven weeks of gestation, a gene on the Y chromosome induces changes that lead to the development of the testes, the organ that makes and stores sperm and produces testosterone
After the testes are formed, the male fetus begins producing testosterone at about nine weeks of gestation, changing the genetic activity of cells in the genitals and brain. But by then, those nipples aren’t going anywhere