Because they grow them!
More specifically, because nipples appear to be a sexually unlinked gene. Nipples develop around week 3-4 in the womb while sex hormones begin to assert themselves several weeks later. While doing my customary three minute internet search for the answer to this query, I stumbled upon something called Galactorrhea. It may sound like a zero gravity digestive malefaction, but trust me, it’s even better. (I don’t know if ‘better’ is the right word…maybe more interesting) especially when it occurs in infants.
Picture yourself in the 1700’s. I don’t really care what you’re doing there. Maybe you’re a blacksmith or a housewife wearing one of those cute bonnets. Then imagine how terrified you are of witches. (trust me..this is going somewhere). You’re really terrified of witches. They stir pots full of blood and frogs and hair. They cackle and have gross warts on their faces. They’re mean and like to abduct children.
Ok. The scene is set for me to introduce Galactorrhea. Some children, both male and female, (approximately 5%) are born with enough of their mother’s hormones in their bodies to have fully functioning milk glands and ducts. Milk seeps from their nipples at the moment of birth (and can for several months after) It is not so fondly referred to, as witch’s milk. Believed to be the sustenance craved by the familiars of witches. As a 1700’s citizen, you’re probably pretty nervous that your son’s nipple seepage is in high demand by creepy ladies with imaginary friends. Right?
Just keep in mind, it’s totally normal. It’s also medically inadvisable to ‘manually express’ the milk. Don’t laugh. In some cultures it is still thought that if parents don’t manually express (aka ‘milk their babies’) daily, that witches will find their children and suckle them, leaving a curse. Interesting article summary : Here.
If you’re disappointed with the lack of real information regarding male nipples contained within this blog post, I recommend visiting this Scientific America article.