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The Scientific Mystery of ‘Male Nipples’

Their presence is evidence that human beings are more alike than they are different

People have been raising questions about Andrew Cuomo’s nipples and their alleged accoutrements since April. But long before the debate about whether or not the New York governor has nipple rings started, Twitter users, evolutionary biologists, Robert De Niro and Aristotle have all pondered a much bigger question: What’s up with “male nipples” to begin with?

The answer requires a somewhat basic review of genetics. Human infants inherit one gene from each of their parents, which is how people wind up with traits of both parents regardless of their biological sex. At around five weeks of gestation, embryos start to produce different hormones that cause external sex organs to grow. The catch is that nipples start to develop long before that differentiation takes place — at just 10 days of gestation. As a result, the nipples of those assigned male at birth aren’t fueled by the same composition of estrogen and prolactin that aid in breastfeeding. And so, they just sit there, doing nothing. 

“Nipples are part of being a mammal and not based on our sex. As a result of our sex chromosomes, ‘female nipples’ will have the ability to later grow into structures that produce milk,” explains Tanya Kormeili, a Santa Monica-based dermatologist. “Since male hormones don’t induce such a chemical signal, they stay small, similar to other mammals that are male.”

There are a few exceptions, of course. Male mice and horses don’t have nipples at all, whereas in certain breeds of bats, males are able to nurse their offspring. But since nipples pose no universal threats to humans — other than very rarely becoming cancerous — scientists suspect that there was never an evolutionary reason for natural selection to phase them out in cisgender men. Andrew Simons, a professor of biology at Carleton University in Canada, compared them to remnants of useless pelvic bones in whales for Scientific American: “If they did much harm, they would have disappeared.” 

According to sociologist and sexologist Carol Queen, part of the reason the question of why cis men have nipples keeps coming back up is because of a deeply ingrained cultural belief that biological sex is more rigidly differentiated than it really is. On an unconscious level, we don’t want to accept that men have nipples simply because women have nipples. “We start out undifferentiated, and that’s why essentially everybody has nipples,” Queen, the author of The Sex & Pleasure Book: Good Vibrations Guide to Great Sex for Everyone, tells me. Similar to how penises and clitorises begin the same in utero and alter in appearance and function from hormones, “other parts all have comparable matches in the so-called ‘opposite sex,’ a term I really find problematic,” Queen adds. “So asking what men’s nipples are for is a sidestep from the reason they are there.” 

Conflating the question of the purpose of men’s nipples with why they exist at all can spiral into TERF (or Trans-Exclusionary Radical Feminist) territory all too quickly, where males and females have distinct jobs that can never overlap — an oversimplification of the biology. Instead, the presence of “male nipples” is evidence that human beings are more alike than they are different regardless of sex, which occurs on a broad spectrum. 

Hormonal imbalances from medications and underlying medical conditions can cause men to unintentionally form breasts and even lactate. Trans and nonbinary parents and some cis fathers will simulate nursing regardless if anything comes out as a way to bond through skin-to-skin contact and provide comfort to their babies. And when trans women first start taking hormones, their breasts grow the same as they would for a teenage girl going through puberty, because, “again, there is the same basic tissue, and the differentiation is the function of the hormones on bodily tissue,” Queen explains. 

In short, we all have the same basic underlying machinery, nips included.

Still, if cis male nipples have any overarching purpose, maybe it’s a sexual one. Though nipples aren’t an erogenous zone for everyone, they are for a lot of people, and some guys completely miss out on that. “Some men are so attached to gender stereotypes that they think it’s ‘feminine’ to have sensitive nipples,” Queen says. “It’s not. Everyone has nerves, and not all women have sensitive nipples.”

Cuomo might, though. Yes, he’s made plenty of mistakes — selling out New Yorkers, ordering nursing homes to admit coronavirus-positive patients, talking about his mom and motorcycle too much for any adult — but if he got his nipples pierced at some point, that’s not one of them.

“Nipple piercings can do two main things: 1) enhance the nipple’s attractiveness to those who find this attractive; and 2) enhance sensation, including potentially playing a part in BDSM activities,” Queen explains. “When we see a person with nipple piercings, we don’t know the role they play for that person unless they tell us.”

So while some men’s nipples may not have a job to do per se, at least they have a hobby. And as much as evolution hasn’t had a good reason to phase them out, maybe it’s time for this question to go extinct. 

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