Why do men have nipples (just like many other male mammals), even though they lack the milk-producing equipment that goes with them?
The answer is simple!
During the first several weeks, male and female embryos follow the same blueprint, which includes the development of nipples. This blueprint has the potential to produce either male or female anatomy.
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. At this point the sex is defined, but by then, the nipples are already formed!