Why do men have nipples?

Why do men have nipples? Chances are you’ve asked yourself this at some point in time, and that question remains one of the many unanswered mysteries about the human body.

That’s not to say that science hasn’t tried to explain why men have nipples, with the most popular theories involving thousands of years of evolution. According to these assumptions, men have nipples for one very simple reason–because women have nipples.

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Experts at Scientific American explain this as an evolutionary and developmental process of uncoupling between males and females. In simple terms, because men and women receive genetics from both parents, they inherit all the traits of those parents. It isn’t until a child becomes distinguished by gender that certain genes are silenced and others allowed to evolve. For men, nipples are there because humans have nipples, but only the female of the species develops them further as a means to nourish offspring.

“Their (nipples’) advantage in females, in terms of reproductive success, is clear,” explained Professor Andrew Simons of Scientific American. “But because the genetic “default” is for males and females to share characters, the presence of nipples in males is probably best explained as a genetic correlation that persists through lack of selection against them, rather than selection for them. Interestingly, though, it could be argued that the occurrence of problems associated with the male nipple, such as carcinoma, constitutes contemporary selection against them. In a sense, male nipples are analogous to vestigial structures such as the remnants of useless pelvic bones in whales: if they did much harm, they would have disappeared.”

While the logic behind this theory of male nipples is sound, there may be more to it than simple evolution. Research compiled by Live Science indicates that men have nipples so they may actually serve a purpose, but what that purpose is remains unclear. The fact of the matter is that men can actually lactate just like women, and this is true for humans and a number of other male mammals.

Both human males and females have breast tissue that contains hollow cavities called alveoli, which are lined with milk-secreting cells.

The only difference in women lactating versus men lactating is the presence of the hormone called prolactin which is responsible for milk production. In most situations healthy women, even when not pregnant, have double the amount of prolactin in their systems compared to men.

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But there are certain circumstances that will cause a man to lactate. According to research, starvation and liver damage can cause men to lactate as can abnormalities of the hypothalamus. While these situations seem to be the result of abnormal hormone regulation in men, they prove that men have nipples that are very functional.

Does this mean men will one day be an alternative option for breastfeeding children? It’s unlikely, but it does indicate that nipples are far more than just decorative when it comes to those not designed to bear children.