Why do men have nipples? That strange bodily question has baffled so many that it even has become the title of a book by Mark Leyner and Billy Goldberg. Interestingly, solving this puzzle has more to do with understanding your embryonic development than your evolutionary past.
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Hi everyone. Cara Santa Maria here. Why do men have nipples? I mean, people are mammals who evolved from other mammals. If you go back far enough in the evolutionary chain, our ancestors were no longer all that mammal-ish, but that was over 200 million years ago. So, ever since we mammals had mammary glands, it's been the females of the species who needed the nipples. You know, to feed their young. So then, why do men have nipples? Why would they've ever evolved them to begin with?
Ah, but we're thinking inside the evolutionary box. Have you ever heard the phrase "ontogeny recapitulates phylogeny?" Ever wondered what it means?
Ontogeny refers to the development of a single organism in utero. phylogeny is the evolutionary history of an entire species. So where do nipples fit into this? Well, back in the 1800s, some scientists noticed that changes an embryo goes through in the womb seemed to mimic the whole evolutionary history of that animal. And although this hypothesis kinda seems like it sorta looks like it might be true, turns out it doesn't really hold water. See, we shouldn't be thinking about nipple phylogeny, what about nipple ontogeny?
Well, in the womb, we go through different developmental stages: zygote, embryo, fetus. And if you remember, females have two X chromosomes, while males have an X and Y. It's that Y chromosome that makes a man a man. But as an embryo, we all kind of start out, I dunno, unisex. At about the sixth week of pregnancy, a special part of the Y chromosome, called the SRY gene, gets activated, and it tells the male embryo to start developing manly hormones and eventually, you know, manly bits. See, this starts at six weeks, but nipples develop at five and a half weeks, thus...men have nipples.
And sometimes men end up with more than the two nipples we've grown to know and love. Women can too, but it's almost three times more common in men to have what are called supernumerary nipples. They occur in lines below the normal two, just like you'd see in a mammal that has multiple pairs. Go ahead and check. Do you have any moles or freckles in line with your nipples?
Don't worry, you're not alone. One in 18 men have supernumerary nipples. It's just one of those random flukes of development. It's not dangerous at all. Having extra nipples just makes you extra manly.
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