Why do men have nipples?

All humans square measure engineered to identical basic feminine arrange with the vertebrate developing as feminine or male looking on whether or not it's XX or XY sex chromosomes and thence totally different hormones. androgen causes a erectile organ to grow into a member and labia to become a pocket. The mystery is that in several mammals male nipples square measure small, whereas in men they're totally fashioned with blood vessels and nerves. Quite why this could be no-one appears to grasp.