Why do men have nipples?

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Welcome to Stuff You Should Know, from HowStuffWorks.com.

Hey, and welcome to the podcast.  I’m Josh Clark.  There’s Charles W. “Chuck” Bryant and we’re doing this.  We’re doing it.

Whether you like it or not.

Yeah, we’re recording our podcast, Stuff You Should Know.  You probably know because you tuned in.

Yes.

So, welcome –

– And if it was an accident, hey, welcome to the party.

Talk about serendipity.

You’re about to learn about male nipples.

Yeah, you are.

Talk about a party.

Yeah.  You got them.  I got them.

We all do.

Do you wanna talk about chromosomes for a second?

Sure.

Okay, Chuck.  You and I each have 23 chromosomes in our body.  We talked a little bit in Designer Children, I think, about –

– Yeah.

– a little genetics over here; we’re not gonna go into that now, but the 23 chromosomes, if you put a man and a woman side-by-side, or their chromosomes side-by-side –

Yeah.

– 22 of the 23 chromosomes are gonna be exactly alike.  It’s that 23rd that gets you.  The 23rd chromosome either has a pair of Xs or an X and a Y.  A pair of Xs equals a woman.  XY equals a man, okay?

We’re not that far apart.

We’re really not, and that becomes very, very clear when we’re in utero because sexual dimorphism, which is the inward and outward differences between genders – between male and female –

Uh-huh?

Like hoo-hoos, and ha-has, and that kinda stuff.

Pee-pees and cuckoos.

Sure.  Those are all hammered out in the course of our development on the 23rd chromosome, right?

Yeah.

A lot of it, you come out with, right?  You were born with a vagina or a penis.

Yeah, or both.

Right, but a lot of it is also set up to be kicked in when puberty happens.

That’s right.

But still, there’s differences.  There’s changes and it’s all because of this 23rd chromosome.

Some of the things, though, can go either way.  And, depending on what happens when puberty comes along, either nothing is going to happen to these – to this equipment, I guess you could call it.

Yeah.

Or a lot of crazy things happen to it and one of those – the good examples of this – are nipples.

Yeah.

There’s a really great question.  Why do men have nipples, Chuck?

Yeah, I have a funny little story about this.  My sister and I were hanging out probably about 15 years ago and I was – they had a male dog, and I was rubbing the belly, and the dog had very like just pronounced nipples – more so than you would usually see on a male dog.

Okay.

And I guess I never noticed before and I was just like – I was kinda grossed out.  I was like, “God, why does your dog have nipples?”  And she’s like, “You have nipples.”  And then, it just like – it was an awakening.

It blew your mind.

Blew my mind.

Yeah.

It’s like, “Wow, you’re right I do.  Why?”  And I never really researched things like this back then, and now I know why.

Now, we know why.

Yeah.

And we should say, this is the generally-accepted explanation; it’s not necessarily scientific fact, but it is – this is pretty much why.

Yeah, most mammals, in fact – most male mammals – have nipples.  I think mice, stallions, and –

– Platypi.

Yeah, the male platypus is among the handful of animals that – of mammals that – where the boys are born nipple-free.

Which is weird because, as Conger points out – Cristen Conger from Stuff Mom Never Told You –

Yeah.

She wrote this article and she points out that you can make the case that mice are more evolved, in that respect, than human males.

Yeah, ours could be a flaw.

Yeah.  We’ll get to that, but let’s talk about this.

So, back in 1999, right before Y2K – it’s Y2K Fever – Yale University researchers released a study that say, “Hey, we’ve gotten to the bottom of this mystery of why or how male mice don’t grow nipples.”  They’re just complete – seriously.  Go out in your yard right now.  Trap a mouse.  Pick it up by its tail and examine its –

– Little belly.

– no nipples.  Nothing.

Or, if it’s got nipples, that means it’s a little lady.

Exactly, that’s the way you tell.

That’s right.

– One of the ways you tell with mice.

And it’s because of a protein.

Um-hum.

PTHrP.

Yeah.

It’s always so exciting when they give them names like this.

After mice are – after their mammary tissue starts to form, it produces this protein and, in male mice, it signals the cells to form male hormone receptors and it basically destroys the tissue like in utero, correct?

Yes, because boy mice and male – and female mice are all – they all develop mammary tissue, which gives you all the equipment for nipples, and breasts, and milk ducts, and all that stuff.

They just destroy theirs before they’re born.

Yeah, that protein signals it – for it to be destroyed in male mice.

Prepare for the mind-blower now.  Boys and girls, as humans, undergo a very similar process in utero as well.

Yep.

Before that sexual dimorphism that’s really carried out by the 23rd chromosome begins, we both – both genders – start to develop mammary tissue and develop all the equipment.  It’s called milk lines.

Yeah, Conger –

– They’re kinda like –

Conger calls it the plumbing.  We have the same plumbing.

Right, exactly.

Which is kinda funny and true.

Yeah, we develop this plumbing before it’s decided or before we start to develop sexual traits.

Right.

So, it’s almost like, if you look at timeline of sexual development, the nipples come first.

Yeah.

So that they’re not associated as far as the – I guess – nature is concerned with male or female in humans.

– Right, nope.  It’s the same thing.

Yeah, so, we don’t have a protein that takes care of this – the nipples in males.  So, men are – and boys and girls are born with pretty much exactly the same set-up until puberty.

That’s right, and that’s when the hormones kick in; estrogen in girls is going to cause breast growth and mammary gland development.

Yeah.

And that’s when things diverge.

You know what really stood out to me on this?  That means that our – nature’s default setting, as far as humans are concerned, is female.

Yeah.

I think that’s pretty neat.

That is pretty neat.  Well, you know, women are the seed of everything.

Sure.

Seed of life.

That’s right.

So –

– That’s what everybody calls them.

The seed of life?

Yeah.

So, the simple answer then is the reason we have nipples is because we’ve always had nipples, and through the years, evolution never said, “You know what?  You don’t need nipples.”

No, and the – I think the case has been made that the reason men still have nipples is because nipples are so vital to female reproductive success that there’s no – Conger points out, there’s no – adaptive pressure to select nipples out of men.

Yeah, it’s such a vital function.

Right.

Yeah.

So, it’s like, “Ah, we don’t wanna possibly mess with anything.”

Right.

“So, everybody gets nipples, okay?  Just live with it.”

– Yeah, yeah.

Yeah, but that’s why men have nipples – because default setting for humans is girls.

Yeah, and that’s interesting.  And I love my little my nipples.  I’ll just come out and say it.

You do.

Well, I think it would be odd to not have them.

I don’t think so.

It’d look so weird.

– It’d be – it’d take a little getting used to, but I think it would not look odd.

You know, we did our Barbie podcast.  Has that come out already?

Yeah.

And there are people on the Web that will teach you how to make nipples for your Barbie dolls.

I saw that.

– Or your Ken dolls.

Yeah.

Yeah.

Like very realistic-looking ones.

Very realistic, but yeah, you’d look like a Ken doll.  It would just be weird.

I don’t think Ken looks abnormal without nipples.

That’s because it’s a doll and he also doesn’t look abnormal without a penis.

– Yeah, that’s true.

You know?

Yeah.

I think you would be a little distressed if you woke up one day without nipples.  Or maybe you’d love it.  Maybe it’s a new lease on life for you.

Yeah, I’d be like –

– You’d just go bare-chested everywhere.

“This is great!  I’m a freak!”

Yeah.

Yeah.  So, we said, Chuck, something that’s kinda interesting, if you ask me.  If you take a six-year-old boy and a six-year-old girl – a prepubescent boy and prepubescent girl –

Yeah.

– and you compared their mammary glands, the whole mammary operation they’ve got going on, they’re virtually the same.  And it’s not until estrogen comes along that the differences really change.  The fat develops so the breasts get bigger.  These milk ducts develop.  You’ve got all this process that just kinda takes these things that are almost latent and turns them into functioning breasts, right?

– Yeah.

If – we found – if you expose a man to estrogen, he could, conceivably, lactate himself.  That’s Part 2 of this.  We didn’t even put that in the title because we didn’t want to blow your minds right out of the gate.

Yeah.

But the point is, is men have nipples because girls have nipples, and men can lactate because women can lactate.

Yeah, and in fact, as little babies, you and I might have lactated.  Who knows?  When – the hormone, prolactin, is what facilitates breast milk production in new moms.  When – they can actually pass this along, in utero, to their fetus and that little baby can come out – if they get enough of that passed along –

Yeah?

– with the ability to lactate, both little boys and little girls, and it’s called witch’s milk.  It only lasts a couple of weeks, usually.

Yeah, I’ll bet it’s a distressing couple of weeks if you’re the parent.  Like, “What is going on?”

– Do you think?  Well, I’m sure it’s explained.  There’s all sorts of weird things that can happen right away that you’re like, “What?!”

Yeah.

And I think, usually, doctors are like, “Don’t worry.  That – little fontanelles.  The brain will grow together.”  Or not the brain, the skull will grow together at some point.  Don’t worry about the soft spot.

– Yeah, just don’t pat it on the head that hard.

So, that – yeah, witch’s milk, it occurs.  And I don't know how rare it is; she didn’t say, but I got the impression –

– It’s rare-ish.

Is it?

Yeah, even rarer is spontaneous lactation in adult men.

Yes.

And that’s called galactorrhea, which does not sound very pleasant.

No, it doesn’t.

But, essentially, if you lack enough testosterone that your estrogen levels are comparatively high, you can suffer galactorrhea, which basically is male lactation – spontaneous male lactation.

Yeah, but Conger points out, it could be, you know, the cause of alarm though if you’re an older man, correct?  Is that just because of the testosterone deficiency?

Right.

Okay.

Yeah.

But Darwin thinks, “Hey, maybe early man breastfed –” like full-on breastfed.

Um-hum.

And who knows?  Maybe they did.

Who’s to say?  Are we to say?  No.

Charles Darwin.

Yeah, so, you’ve got – galactorrhea is a possibility; witch’s milk is a possibility – two ways that human males can spontaneously lactate.

And we’re not the only ones who do.  There is a type of bat that was discovered to lactate spontaneously and a surprising amount of animals, over the course of the last century or two –

– Oh, yeah?

– have been exposed to all sorts of different tests to make them spontaneously lactate.

Hmm.

Steer was made to lactate.  Do you know how surprised that steer must have been?

Yeah.

But we’ve found that if you can increase estrogen levels, and trigger the release of prolactin, you can make men produce milk.

Right.

And it happens sometimes.  So, the prolactin is produced by the thyroid gland, right?

Yeah.

– Or pituitary?

Yeah, and women, when they have a little baby, they – it really ramps up, like ten times as much.

Exactly.  So, what they found is that after a baby is born, dads suffer – I guess “suffer” is not the right word.  Dads experience an increase in prolactin production, too.  Normally, it’s not enough to cause lactation, but they suspect you can make it happen if you are – okay, so this is really strange.  If you hold a baby to your breast – your nipple – and you’re a man, and you’re the father, so you’re already kinda like prolactin-high –

Sure.

– you could, conceivably, trigger the production of milk if you did that repeatedly over the course of, like, a couple weeks.

Yeah, it’s a physiological response and biological, I guess, sorta all wrapped up into one, and you can have like sympathy lactation almost.

Yeah, and it’s happened.  2002, in Sri Lanka, right?

Yeah, I didn’t actually get to look this guy up, so I don't know a whole lot about him, other than the fact that he breastfed his daughters after his wife died.

Yeah, his wife died during childbirth and he took over.

Wow, that’s amazing.

It is.  But another way to lactate is if you’re starving, Chuck.

Oh, really?

Yeah, there was this one POW camp, Japanese POW camp, and in just one, there was 500 cases of men lactating spontaneously.

For each other?  To live on or –?

– No, you would think.

Oh.

Actually, what happened is – so, your pituitary gland produces prolactin and your liver is typically charged with eating up excess hormones, right?  When you’re starving, both of them kinda slow down, but when you start to eat normally again, your pituitary gland starts functioning quicker than your liver.

Oh.

So, you have higher levels of hormones, including prolactin; hence, you have starving men who lactate.

Wow.  That’s a reality show – some sorta island.  Lactation Island.  I don't know.

And there’s a tribe, the Aka, a pygmy tribe in Africa.  There’s about 20,000 of them, and this dude – it was documented that they – men breastfeed their children, and this dude – went and lived with them.  And not only that, it’s amazing.  They’re known as the best fathers in the world because they spend 47 percent of their time – 47 percent of the time, their babies are within arm’s reach of the father.

Oh, that’s neat.

Which is, far and away, more than any other culture in the history of the world.

Right.

Forty-seven percent.  And the gender roles in this Aka tribe are completely interchangeable.  Like, sometimes, the men go out and hunt and the women take care of things; sometimes, the women go out and hunt and the men wash the clay pots and take care of the children.

Huh.

And it’s just – they don’t know gender roles like that.

Wow.

It’s just completely interchangeable.  It’s pretty cool.

That is very cool.

– Yeah.

And that’s a – that was a question that kinda Darwin raised.  Like, “Well, wait a minute.  Maybe we used to breastfeed.  Men used to breastfeed and that’s why we have this,” which would make it vestigial, right?

Right.

Like wisdom teeth or appendix – it’s something that we used to use that we don’t any more, so it’s superfluous.

Sure.

Or it’s possible that we can, in a pinch, which would not make it vestigial because we could still, conceivably use it like the dad in Sri Lanka or the Aka.

– Right.

The – I guess the big question that it underlines is, “Why?”  If men can do it, why aren’t we?

Yeah.

Why wouldn’t you do that?  Especially if we live in generally monogamous cultures?

Well, I think, probably because of evolution – because women did it for tens of thousands of years only.

Right.

Like if we had kept doing it, if early man did do that, and they just kept doing that, then today, you and I might – it might be like, “Hey, I’ll pump and dump today, honey.”

Exactly.

“Don’t worry about it.”

So, let me ask you this.  If we stopped – if we used to do it – even if we didn’t used to do it –

– Right.

– but the very fact that we’re equipped to do it, like under the right conditions, under the right chemical balance, you and I could lactate right now.

– Yeah.

Right?

Let’s have a party.

As our culture has become more and more monogamous, and it’s – we get further and further away from males going around and spreading their DNA with as many mates as possible, and instead, pair up, then it’s entirely possible that, 10,000 years from now, men and women will both breastfeed.  We’ve got the equipment; it’s possible that it’ll just get easier and easier for us to do it, and then, we will breastfeed as well.

Interesting.

It is.

Well, it’s, apparently, quite a bonding experience between mother and child, and so, I’d do it.  Jeri just laughed.  I was not breastfed, however.

Oh, you weren’t.

Nah, man, I was the Child No. 3 and –

Your mom was over it?

Yeah, she’s just like, “No more.”  So, I’ve never looked into the ramifications of that – psychologically, if that matters.

It seems like you turned out okay.

No comment.

So, before we sign off, I guess we should raise the point that because we do have a lot of the same anatomy underneath, men can get breast cancer.

Right.

It’s not rare, but it’s not super common.  I think, in 2012, about 2,200 American men were diagnosed with breast cancer.

Yeah.

And so, it happens.  You never hear about it.  There’s nothing to be ashamed of, guys.

That’s a high-enough rate to say – for some to say – like, “Well, then, that means that nipples should be selected out in men and probably will –”

– Right.

“– eventually.”

Well, therein lies what we mentioned earlier – is the fact that it could be just a flaw.

Yeah.

An adaptive flaw over the years.

Yeah, what about third nipples?  Additional nipples?  Did you know that they happen most frequently in males and on the left side?

– Yeah, that’s interesting.

One in 40 newborns has an extra nipples.

Yeah, a lot of – I mean, have you ever seen these?

Yeah, they don’t usually look like a full-on nipple.

Yeah, sometimes, they’ll look like a birthmark or something like that.

It has a tooth growing in it.

But yeah, Chandler had the third nipple on Friends, right?

Yeah, right.  It’s the superfluous – so did Krusty the Clown.

Oh, really?

Yeah.

I don’t think I knew that.

Yeah, one in 40.  That’s way more common than I think.  That means that I know a few dudes that have a third nipple; they probably just hadn’t told me.

I don’t think I know 40 people.

You’re so weird.

You got anything else?

Nope.

Okay, well, if you wanna learn more about male nipples, male lactation, evolution, vestigial stuff, you can type in, “Why do men have nipples?” in the search bar at HowStuffWorks.com, and it’ll bring up this article, and I said search bar, which means it’s time for listener mail.

Whoa, whoa, whoa.  I guess I need to stop myself.

Stop.

We have a television show coming out where I play Josh, you play Chuck, and the television show is called Stuff You Should Know.

That’s right.

And it’s coming out on The Science Channel, January 19th, Saturday, at 10:00 and 10:30 p.m.  Two episodes for the big debut.

That’s right and we are debuting after the Season 3 premiere of Idiot Abroad with Ricky Gervais and Karl Pilkington.

Yes.

Which we’re excited about.  That’s a great lead-in for us.  And, if you don’t have cable and you don’t Science Channel –

– Or even if you do, and you’re like, “I love that and I wanna see it 800 times –”

You can get it on iTunes, we’re told, now.  They are making these shows available on iTunes for purchase the day after the episode airs and Episode 1 is free, dudes and dudettes.

Yeah, so every Saturday, when we have a new episode, the following day on iTunes, you’ll be able to buy it.

That’s right.

So, January 19th is the big premiere.  I’m already wearing a dickey, and a bowtie, and little cuffs right now.  How do I look?

You look great.

I’m getting ready, slowly but surely.

That’s right.

That’s 10:00 p.m. on Science Channel, Stuff You Should Know, the television show.  It’s going to be great.

January 19th.

That’s right.

All right.  Now listener mail?

Yeah.

I’m gonna call this Mustache Woman.  Remember, during one of the November plugs I think, we said something about ladies: of course, you don’t have the moustache, but blah, blah, blah?  It can happen and this is probably a pretty good podcast to mention this.

Okay.

This is from Kayla.

“Hi, guys.  I was listening to what will happen when we reach the singularity and Chuck said men – I guess women – if you can grow a moustache, more power to you.  I immediately stopped the podcast so I could e-mail.

I suffer from a condition known as Polycystic Ovarian Syndrome, PCOS, which is a leading cause of infertility and affects about 12 percent of women.  Many women don’t know what it is or that they have it, but symptoms include infrequent or no menstruation cycles, acne, weight gain, diabetes and insulin-resistance, and hirsutism.”

– Hirsu –

– Hirsutism.

Like, “Her suit.”

Yeah.

Her-suit-ism, yeah.

“Which is excess hair.”

Yeah.

“It can lead to women growing hair where no woman should: on the face, excessive arm hair, legs, and even hair on the nipples.  Luckily, I am not affected by this particular symptom, but some women report having to shave several times a day, including sneaking razors into work to shave their faces.”

Aw.

“Needless to say, this is a devastating reality and can have huge impacts on a woman’s confidence and emotional well-being.  One lady with PCOS is participating in Mowvember to raise money for men’s health –”

– That’s awesome.

“– and to promote PCOS awareness.”

That is really awesome.

Very cool.  “So, I’d love it if you could read this on the air and raise some awareness around this condition.  You can find more information through the Polycystic Association of Australia via Twitter at POSAA.  I’m Australian.  Please, don’t do an impersonation.”

Are you going to?

No.  That’s terrible.  “I would really appreciate the plug.  Big fan of you guys.  This is Kayla.”

Awesome, Kayla.  Thank you very much for writing in and thank you to the woman who grew a moustache for Mowvember.

That’s pretty awesome.

Hats off to you.

If you want to let us know about something that we obviously don’t know about because we made some weird reference to it, you can tell us all about it on Twitter at SYSKPodcast.  You can join us on Facebook.com/StuffYouShouldKnow.  You can send us a good, old-fashioned e-mail to StuffPodcast@Disovery.com.

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24 minutes