Information

Do male mammals other than humans have nipples?

Do male mammals other than humans have nipples?


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

vi fM Ou hN vb gb uC gD NL AM QP Bi YZ MG WX DF dX

When I grew rabbits, I had a pair, one male and one female. And while the female's nipples were quite prominent, especially after giving birth, I don't remember the male having any nipples at all.

Do males of other mammal species, have nipples like human males, or is it a trait that's unique to Humans?


At the very least, I know that male primates also have nipples like female, though they are very close relatives to human. On the other hand, in some of my dissection labs, I noticed that male pigs also have nipples just like the female ones. It seems to be the case that most male mammals have nipples, which probably has to do with mammals being breast-feeder and their developmental pattern.

There is a page on Wikipedia that I found about this topic: http://en.wikipedia.org/wiki/Nipple#In_male_mammals


Most mammalian males have nipples. The duck-billed platypus does not have nipples but you begin to see development of nipples in marsupials (Park and Lindberg 2004) like the opossum and kangaroo. Development of a complete nipple begins in the eutherian (placental) mammals.

The mammary glands develop early in the embryo along a pair of ridges called the mammary ridge, mammary lines, or milk line (shown in an adult human in the figure below, taken from Wikipedia). The nipples form along this line. In humans, this happens during the fifth week of development. Within a few days, nipples begin to form. The number of nipples pairs that form is characteristic of the species (e.g., 1 pair in humans to 9 pairs in pigs). The development of nipples occurs before sexual differentiation begins which, in humans, is during the sixth week of development. That's why both males and females have nipples. This same order of develop occurs in other mammals, revealing our common ancestry.

However, because the process is under genetic control, mistakes can happen. Occasionally, humans (and other mammals) can develop extra nipples, the so-called supernumerary nipple(s). The most common places that humans develop one or more supernumerary nipples are identified by the circles in the figure above. The actor Mark Wahlberg is not shy about showing his.

For a general overview of mammary gland development, Dr. Jacqueline Veltmaat has a nice web page that highlights her research in this area. For those interested in the more technical genetic aspects of mammary gland development, a paper by Watson and Khaled (2007) reviews the genetic processes that regulate development of the mammary gland in mammals, based on the mouse model system. The article covers all stages of mammary gland development, from the embryo through puberty to pregnancy. Their Figure 1 shows one row of embryonic mammary buds (labeled MB1 - MB5) in the embryonic mouse. In the case of the mouse, all of the mammary buds will develop into fully functioning mammary glands. Another paper by Robinson (2007) discusses the signalling pathways during development of the mammary glands.

Literature Cited

Park, C.S. and G.L. Lindberg. 2004. The mammary gland and lactation. pp. 720-741 in Dukes' Physiology of Domestic Animals, W.O. Reece, ed. (Publisher not identified.)

Robinson, G.W. 2007. Cooperation of signalling pathways in embryonic mammary gland development. Nature Reviews Genetics 8: 963-972.

Watson, C.J. and W.T. Khaled. 2008. Mammary development in the embryo and adult: a journey of morphogenesis and commitment. Development 135: 995-1003.


When people hear the word "nipple," most often their minds picture a woman&aposs. Nipples and breasts just seem to go together in most people&aposs minds.

But of course, men have nipples, too. Even though men&aposs are the only nipples we are allowed to see in public, they are oddly mysterious, overlooked and ignored. What are they even for?

What is a nipple?

The nipple and areola are two different things. Think of a bullseye: The nipple is at the center and the areola is the darker skin that surrounds it.

Why do men have nipples?

During early development, just after fertilization, male and female embryos start out alike, with the same genetic material. In the first four to five weeks, nipples start to develop, but it isn&apost until after six or seven weeks that the sex chromosomes (XX for female or XY for male) assert any differences. So most humans have nipples in common.

But why would a body go through the effort of growing nipples if they have no use? Actually, male nipples do serve a purpose, although it&aposs one people don&apost often discuss. According to one study, for almost 52% of men, nipple stimulation enhances sexual arousal. So a majority of men report erogenous uses for their nipples.

Still, male nipples are relatively mysterious. Here are # things you might not know about them.


Why Do Boys Have Nipples?

The reason that males have nipples is that during development in the fetus, everyone first develops as a female and the human chest and nipples develop before the Y chromosome is introduced into the fetus. The Y chromosome is the chromosome responsible for coding a fetus to be a male baby. By this time, the nipple has already fully been developed, and there’s no removing it at this point.

This is not exclusive to humans, though. Most male mammals also have nipples, as they go through the same stages of development in the womb.

Fun trivia fact : The only mammals don’t have nipples are monotremes! Male lab mice, some male house mice, and even male horses also join the no-nipple club.


9 thoughts on &ldquo Why Do Men Have Nipples? &rdquo

That’s crazy to think about. Men breastfeeding babies? LOL. Reminds me of an episode of Family Guy. Link provided: https://www.youtube.com/watch?v=6OkcucXIuVI
But in all seriousness, I think since all humans have chests to protect their heart and lungs and insides, it would look very odd if only males didn’t have nipples on their chests. Maybe its just the way we’re made regardless of evolution.

This is really an interesting blog. I’ve always wondered why men have nipples because they literally have no purpose on men except for the fact we would look weird without them. I always thought it was an evolution type thing but i could never really figure out what we used to use them for.

I’ve always wondered this! I knew that embryos all started off as female, but I didn’t realize that nipples grew so early on in the process. There has to be a biological explanation for it, some reason why it was useful in the past, but I guess we’ll have to wait and see if they disappear completely in many many years, or if they become useful. It would be so weird to see men without nipples one day.

This is a very interesting blog. I’ve never thought about why men have nipples. Its really a funny concept when you think about it. Do other males animals have nipples? or just male humans?

I’ve never really about it but nipples truly serve no purpose. I guess we would just look weird without them. It makes sense that we have them if you believe in evolution because apes have nipples but if you do not believe in evolution it may be a pretty confusing topic.

Why do you think men have nipples? I know from my view I believe men have nipples because of how you said men start off as women until our chromosomes change. But if you look at other animals that are male they do not have nipples. So then again that may not be the reason because if my dog max has nipples, then something is not right.

So, the idea that you said men have nipples because nipples because previously we were able to breast feed could be true. But why do male monkeys have nipples? Ok, you can say that we were developed from chimps. But if that was true from chimps then why are there still chimps. But let us just pretend that it was proven that we did develop from them, doesn’t evolution calls for a species to enhance itself to survive. Then how come we did not lose that trait of having nipples because they seem to not have any use for them either.

Thus, I will conclude that both theories may be wrong and there may be another reason why we may have them. So far like you said there is no proven theory so “Why do males have nipples,” for right now we still do not know

It’s definitely an interesting concept that males either in the past or the present had nipples to breast feed. I agree with Genevieve when she says that since we are descendants of apes it makes sense that we also have nipples. The thought of males being able to breast feed isn’t a ridiculous idea but I don’t think the world will see that happening anytime even in the remote future.

This is a really entertaining blog. And no I have actually never wondered that in my head. But now I know why next time I sit down and begin to wonder why guys would have nipples if they have almost no purpose. But this is actually quite interesting due to the fact that now you answered the question I wanted the answer. And it would probably be insane if men were able to breast feed in the future. I am having such a hard time buying that it will actually happen.

I think the question of “why do men have nipples” might be extended into “why do male mammals have nipples?” Being that we are evolutionary descendants of apes, it makes sense that our males would have nipples just like their males do. In fact, many mammal fetuses look similar during the early stages of gestation. At conception, the zygote looks no different than that of a rat or a dog, only through time do we see the key differences. If nipples develop early enough in gestation, then we might be able to assume that male humans have nipples because the first male mammals had nipples. Perhaps the answer lies in an entirely different species than our own.


Why Do Male Cats Have Nipples?

Unfortunately, I couldn’t think of a more tactful way to start this article but writing about nipples on male cats is certainly worthwhile as I’ve spoken with dozens (and dozens) of cat owners who are honestly confused about the subject.

So why do male cats have nipples? Just like many other mammals, nipples on male cats are a result of an evolutionary quirk. Nipples are developed before the actual gender of the fetus is determined even if male cats don’t actually need them.

You can learn more about the details of feline fetal development in this article from PawPeds but just like in humans nipples on male cats vestigial structures that don’t actually serve any purpose.

But that’s usually only the first question that gets asked about nipples on male cats.

Let’s dig a little deeper and cover everything you ever wanted to know about male cat nipples…but were afraid to ask!

Wait A Second…Cats Have Nipples?

Yes! All cats have nipples! In fact, almost all mammals have nipples so they can nurse their young with milk. While there are some notable exceptions (looking at you platypus) to the mammalian nipple rule, most male mammals have nipples too.

But if you’ve never noticed nipples on any cat don’t be surprised. You’re not the only one.

Obviously, cats have plenty of fur that can obscure and hide their nipples but another factor is whether or not your female cat has been spayed. When female cats are spayed at a young age and never have a litter their nipples don’t develop in the same way. As a result, they can be very difficult to actually see.

Can Male Cats Produce Milk?

Even though male cats have nipples they can’t actually produce milk. They may have the nipples (and even mammary glands) but just like all other male mammals they can’t actually produce the milk.

In other words, your male cat’s nipples are all for show!

How Many Nipples Do Cats Have?

Here’s one of the most interesting feline nipple factoids…cats actually have a varying amount of nipples! It’s usually between 6 to 8 nipples in pairs along the abdomen but it’s completely normal for this number to vary between cats. That’s true for both male and female cats!

There is even the rare case of a cat breaking the rules and having an odd number of nipples!

If you want to take a moment to stop reading this article and count your cat’s nipples, I totally understand. After all, your cat might be one of the rare felines to have an odd number!

How Many Nipples Do Male Cats Have?

Male cats have the same number of nipples as female cats which is usually between 6 to 8 nipples in pairs alongside their abdomen. But just like female cats, some cats may have an odd number of nipples!

Can Male Cats Get Breast Cancer?

Yes, it is possible but luckily it’s quite rare. Feline specialist Dr. Arnold Plotnick explains that “Males rarely develop breast cancer. In fact, less than 1% of cats that develop mammary cancer are males.”

It’s also worth noting that you can greatly reduce the risk of breast cancer in female cats by spaying them, too. Dr. Plotnick explains “Intact cats are at an increased risk of breast cancer. Spaying a cat, especially before their first heat, greatly reduces this risk. A hormonal influence is known to exist in dogs, and it is clear that estrogen and progesterone play a similar role in tumor development in cats, although this role is not as well understood.”

It’s just another reason to always spay your cat!

Where Are Your Cat’s Nipples?

I’m sure you already know that your cat’s nipples are on their tummy.

But finding out where they are exactly can be a little tricky. You can find your cat’s nipples to the left or right of the middle of your cat (also called your cat’s midline). This picture of a mom cat nursing her kittens will give you a good idea of where to look.

You might have to move some fur around to find them. It can actually be easier to feel for them first then part the hair to find them. Cats that are pregnant or nursing will have much more prominent nipples which makes them easier to find.

So what does a cat nipple feel like?

Cat’s that are spayed or haven’t been pregnant will have smaller nipples that feel like a bug bite with a distinct point (that’s the nipple). They’re generally pretty soft at the edge and a little firm in the middle.

So What Does a Cat Nipple Look Like?

Most people would describe them as a small, pink, and slightly raised bump. It almost has the same volcano-style shape that a pimple does. One male cat or females without litters they’re quite small.

It’s also worth noting that if you notice something that feels like a nipple where it shouldn’t be make sure to consult your veterinarian.

How Exactly Do Nipples Work?

Nipples allow milk to be transported from a complex system within your cat’s mammary tissue directly into the mouth of her kittens. After millions and millions of years of evolution kittens instinctively know to find a nipple and suck on it to get food. In other words, it’s not something they have to learn.

But they aren’t exactly the most precise little creatures either! Kittens are very quick to suckle anything that could even remotely resemble a nipple including your finger or a littermate’s foot! Sadly, kittens nursing on their littermates is a big problem especially when kittens are taken away from their mother too early. That just shows you how strong of an instinct it is for kittens to suckle!

Cat You Tell The Difference Between Genders Based On Nipples?

In most cases, you can’t determine the gender of a cat strictly based on their nipples. However, if a female cat has a litter of kittens she’ll most likely have larger nipples for the rest of her life after the pregnancy and nursing process. Not only does your cat’s breast tissue become engorged with milk but having a pack of hungry kitten nursing multiple times a day permanently changes the size of your cat’s nipples.

Still, this isn’t a reliable method since a female cat that’s been spayed early will have very similar nipples to a male cat. If you need to determine the gender of a cat you should rely on checking thier genitalia from the back. This post from Washington State University has a great description of what to look for.

That’s It On Nipples In Male Cats!

Okay, I think we’ve covered just about everything there is to know about nipples in male cats.

Did you know there was so much to talk about when it comes to nipples in male cats?!

Logan has always loved everything about cats! Growing up with a family full of pets and a lifelong passion for animals he pursued work in the veterinary industry. After 10 years, he started BetterWithCats.net to help cat owners learn more about their feline friends.

Wondering why cats chatter? Let's talk about 4 reasons to explain this cute but strange feline behavior.

Wondering why your cat is making weird mouth movements? We've got 11 possible reasons to explain this strange feline behavior.


Do all mammals have teats?

They can have more than two teats, and all of the teats may or may not be productive of milk. Recent research has shown that mammals conform to what is known as the one-half rule, in other words, their typical litter size is equal to one half the typical number of teats the animal has.

Subsequently, question is, what male animals do not have nipples? First of all, the most evident group is monotremes (platypus and echidnas), because even females don't have nipples (they secrete milk through some openings in their skin). Another male mammal without nipples is the brown rat, or Rattus norvegicus (the typical laboratory rat).

Similarly, you may ask, why do all mammals have nipples?

Many male mammals, humans included, have nipples. Scientists believe that the reason behind this is the result of natural genetic selection &ndash- or lack thereof. Male and female animals start out life almost identical in utero, complete with nipples.

Do all male mammals have mammary glands?

All male and female mammals have mammary glands, which is the organ that produces milk. When mammary glands mature fully in females during puberty, they develop into a state where a hormonal spike&mdashmost notably of prolactin&mdashcan easily induce lactation. For males, the gland generally doesn't mature to that level.


Why do men even have nipples?

If you feel silly for wondering why men have nipples you can feel a bit better knowing that Darwin asked himself the same question. What is the point of having nipples if men can’t breastfeed?

Darwin’s idea was that both men and women used to be able to breastfeed their children. Then men who breastfed passed some disadvantage on to their offspring, such as being able to raise fewer of them than women, and the ability was inactivated over time due to disuse. However, the answer to this question actually lies in human development rather than evolution.

Spoiler alert: it all happens when you’re an embryo. Image credits: Anatomist90.

As the embryo starts to grow within the mother’s womb, it is a generic human being. If it continues to grow undisturbed it will be born as a female. At week 4 of development, milk lines develop they are stripes of tissue that extend from the armpits to the thighs and later regress to form two nipples. Sometimes, extra nipples can be left along this pathway (that’s how Mark Wahlberg got a 3 rd nipple).

However, if a Y chromosome is present, the embryo will sexually differentiate to become male by producing factors which block the development of female structures. Sexual differences appear in week 7, with the gonads differentiating into a testis or ovary. So nipples are present before the sex of an embryo is fixed.

A man with extra nipples. Image credits: Thomas Godard.

Nipples in men do not pose a disadvantage so they are not evolutionarily selected against, as Darwin thought, so men continue to have nipples. It is difficult to lose an organ if it is not harmful, even if it is no longer useful. For example, humans still have tailbones and appendixes although neither is useful anymore.

Men having nipples may cause you to wonder:

Can men breastfeed?

If you’ve tried this at home, you’ll know that the answer is no. However, there is a rare condition called galactorrhea where affected men can lactate. This condition is often brought on by a testosterone deficiency or imbalance. Alcoholism, severe starvation, or other liver stress can cause male lactation because the liver usually controls the release of prolactin, which is a hormone that regulates milk production.

Can men get breast cancer?

It is rare but some men do get breast cancer. Only about 0.001% of men get it. Men have a small amount of breast tissue, an amount that is similar to a girl before puberty and is still vulnerable to cancer-causing mutations.

Do other male mammals have nipples?

Most other mammals have nipples the word mammal even comes from the Latin “mamma” which means teat. However, there are exceptions. Monotreme (egg-laying mammals) males, such as platypuses, do not have nipples but then again neither do the females they excrete milk through modified sweat glands. Other exceptions are male horses and some male rodents, which do not have nipples either.

On the other end of the spectrum, two species of bats, dayak fruit bats and masked flying foxes, have milk-producing males — although it is not known what role, if any, that they have feeding offspring. Some male goats have also been found to produce milk. Theoretically, lactating males should evolve in animals with one monogamous partner, unreliable food sources, and when both parents care for the offspring.


16 facts about nipples

Although both males and females have nipples, the functions of this body part differ. For both sexes, nipples can be an erogenous zone. However, the postpartum function of the female nipple is to aid in breastfeeding.

In this article, we look at some more interesting facts about nipples.

Share on Pinterest Nipples come in many shapes, colors, and sizes, and they can change shape during pregnancy.

Here are some facts about nipples:

1. The nipples can be an erogenous zone for both sexes.

According to a 2020 article , nipple stimulation plays an important role in the sexual satisfaction of about 80% of females. The authors concluded that using a topical formulation that stimulates the nipples 30 minutes before sexual activity can improve orgasmic satisfaction, strength, and pleasure.

Although male breasts are less well-studied, a 2017 article states that nipples are an erogenous zone for males.

2. Nipples can be hairy.

According to Planned Parenthood, it is normal to have hairs around the nipples.

Hair can be present around the nipples in both males and females.

3. Why do males have nipples?

In mammals, once an embryo has formed, it has the potential to become either male or female.

The nipples form very early in gestation, which is why males also have nipples.

The genes responsible for the development of reproductive organs do not become activated until a later stage.

4. Accessory nipples exist.

Sometimes, a person may have an extra nipple or set of nipples.

According to the Genetic and Rare Diseases Information Center, these are known as supernumerary nipples, and they are a common congenital abnormality. They most frequently occur along the embryonic milk lines, just like in other mammals.

One 2016 article estimates that roughly 1–5% of the population has a supernumerary nipple.

Although most people have just one extra nipple, there have been at least two cases of people with seven nipples.

5. Nipples can occur anywhere on the body.

Although accessory nipples typically occur along the mammary crests, or milk line, they can appear anywhere on the body.

There has been a case of an accessory nipple occurring on the foot, for example.

6. Some people are born without nipples at all.

Known as athelia, this is a rare condition in which a person is born without any nipples.

7. A set of nipples holds a Guinness World Record.

According to the Guinness World Records, in 2013, a person used their nipples to lift 71.87 pounds.

8. There are different types of nipples.

Nipples can be flat, protruding, or inverted.

According to the Center for Young Women’s Health, roughly 10–20% of females have an inverted nipple on at least one breast.

Although this will not affect a person’s health, it is important to keep inverted nipples clean.

9. Breastfeeding is still possible with inverted nipples.

Although inverted nipples can make it more difficult to breastfeed, they do not make it impossible.

According to the World Health Organization (WHO) , an inverted nipple can sometimes be nonprotractile, meaning that it does not stretch out when a person pulls it. Instead, the tip goes inward.

In these cases, it is often more difficult for the baby to attach to the nipple. However, protractility often improves during pregnancy and in the first week or so after a baby is born. Otherwise, there are alternative ways to breastfeed successfully with inverted nipples.

10. Breastfeeding females can spontaneously leak milk if they hear babies crying.

This effect is called the let-down reflex.

The let-down reflex occurs when the nerves in a person’s breast send signals that release the milk to the milk ducts so that it can start to come out of the nipples.

This mechanism is important for breastfeeding or expressing milk, but it can also happen at other times. For instance, it can happen when a female hears their baby crying or even thinks about their baby. It can also sometimes happen when another baby cries.

11. Bumps on the areolae are normal.

The small bumps on areolae are also known as the Montgomery glands.

These glands secrete oil to cleanse the nipple opening and prevent the chapping and cracking of the nipple that often occurs due to breastfeeding.

According to an older study , there is also evidence to suggest that this secretion may attract newborns to the nipples.

Although these bumps are normal, a person should see a doctor if they become inflamed or secrete brown fluid.

12. Breast milk can come out of multiple places.

There are between 10 and 20 perforations in the skin of the nipples, called nipple pores, from which the milk exits the body.

When breast milk is pumped, it can either look like a single stream or be visibly coming from different “holes” in the nipple.

13. Nipples can change shape during pregnancy.

One study demonstrated that during pregnancy, nipple length and width, as well as areola width, could increase significantly.

However, if a person notices that their nipples have changed drastically, and they are not pregnant, it is important that they visit their doctor.

The Centers for Disease Control and Prevention (CDC) advise that changes to the nipples could be a sign of breast cancer.

14. Nipple cancer is a rare form of cancer, but it can happen.

Nipple cancer, also known as Paget’s disease, is a rare condition associated with breast cancer. It affects the nipple and the areola.

According to the National Cancer Institute, about 1–4% of breast cancer cases involve Paget’s disease.

This condition can also affect males, but it is much more common among females.

Although doctors do not entirely understand what causes Paget’s disease of the breast, they do have theories.

The most widely accepted theory is that cancer cells from a tumor inside the breast travel through the milk ducts to the nipple and areola. This theory would explain why this cancer is so rare in males.

15. People can get nipple tattoos.

During a mastectomy, the surgeon may sometimes need to remove the nipple too.

After undergoing this procedure, some people may opt for nipple reconstruction. The options include using a nipple prosthetic, a skin graft, or a tattoo.

16. Nipple stimulation can induce labor.

Stimulating the nipples may help the onset of labor.

According to a 2018 study , oxytocin can help induce labor. Nipple stimulation produces oxytocin.

In the same study, 3 days of breast stimulation caused oxytocin levels to increase.

Other research has shown that nipple stimulation can also have an effect on the duration of labor. A 2015 study found that stimulating the nipples during labor shortened the first stage of labor to an average of 3.8 hours.


Why do men have nipples?

By Susan McCarthy
Published June 8, 1999 4:00PM (EDT)

Shares

Why do men have nipples? To prove they're mammals, obviously. The
distinguishing features of mammals, from whales to mice, are two:
having hair and suckling their offspring. This gives us the
notorious sentence that demonstrates why our pronouns need
overhauling: "Man is an animal who suckles his young."

Clearly, if men didn't have nipples, to demonstrate their
theoretical membership in the La Leche League, we could only
identify them as mammals by their hairiness. And where would that
leave bald guys? What are they, reptiles?

There are some male mammals without nipples, a fact I was alerted
to by Aristotle, who wrote "Such, for instance, is the case with
horses, some stallions being destitute of these parts."

Since Aristotle's medical facts were sometimes a bit wobbly -- he
said cabbage cures hangovers -- I called an equine veterinarian. "I
have never seen a stallion with nipples," she declared flatly. "And
I have looked around down there." As far as I know, she's never
seen a bald stallion, either, so that's how they avoid being called
reptiles.

The veterinarian pointed out that a mare's two nipples are located
toward the tail end of the body, as opposed to the chic head-end
location in humans. This, she daintily hinted, might be why
stallions don't exhibit nipples. "There's no room."

These shocking facts sent me on a quest for other data on animal
nipples or, as medical types have long preferred to say, mammae.
Male nipples? Mammae masculinae. (If you need to be even more
obscure you can also call a nipple a mamilla or a thelium.)

My mother, when I told her of my research, may have been hinting
that there were more hard-hitting stories I could be working on by
bringing up the folk analogy "as useless as tits on a boar hog." My
research appears to indicate that boar hogs do in fact have tits.
Which they are not known to use.

Not only do male platypuses not have nipples, neither do females.
The milk simply flows out through pores and is licked up by baby
platypuses. And while platypuses are not actually categorized as
reptiles, you'll notice that people are always talking about how
"primitive" they are and making fun of their noses.

I would have assumed that nipples were only available in even
numbers had I not learned that female possums, for example, have
between seven and 25 nipples. The delightful Virginia opossum, which
inhabits the middles of American roads and highways, usually has
13, efficiently arranged in an open circle with one in the center.
This information should not tempt you to snicker and point the next
time you see a possum: They also have 50 teeth.

Most mammals, however, stick to even numbers of nipples, and often
the males get to have them too. In addition to boar hogs, dogs,
cats, all primates and many other animals feature the mamma
masculina.

It seems that human embryos develop mammary tissue before they
bother to check on whether they're going to be male or female and
start modifying the basic plan with surges of this or that hormone.
After only a few weeks, milk ridges form -- two stripes of tissue
that start in the armpits, curve out over the chest, go straight
down the stomach and then veer in toward the groin, ending
somewhere high on each thigh. Later the milk ridges regress to some
extent, usually leaving us with just two nipples.

Quite a few people end up with an extra, or supernumerary nipple
somewhere along the trail of the milk ridge, however. (One man had
five.) Sometimes they can't be mistaken for anything but a nipple,
and other times they look like a mole. In fact, many people with
supernumerary nipples don't know they have them until some
officious and informative person starts examining their moles.
Extras often run in families -- Darwin cites two brothers who each
had a supernumerary nipple. Anyone who thinks that's weird should
immediately leave the room and go check his or her torso for moles. How
do you know you're not head-to-foot extra nipples and we've all
just been too polite to mention it?

What of male nipples as erogenous zones? You know they are, or why
would they be banished from the chest of Ken? (To avoid inflaming
Barbie.) I have looked into the matter of G.I. Joe: I never owned a
G.I. Joe, though I recall liking his accessories, particularly the
canteen. (Don't take that the wrong way. Sometimes a canteen is
just a canteen.)

I asked a friend, who indicated with some annoyance that her
childhood G.I. Joes were just as smooth-chested as Ken. But it
seems that over the years G.I. Joe bulked up, and from being an
average Joe with an average physique became an eerily burly
muscle man who apparently never leaves the gym except to go to the
rifle range. Somewhere along the line some G.I. Joes acquired
nipples to go with their superior muscle definition and popping
veins. The effect is not particularly erotic: I suspect they're
just there to give the viewer a reassuring landmark among all the
unfamiliar ripples of the bodybuilder's torso caused by out-of-control delts, pecs, abs, intercostals and other oddities.

(In addition to the mute testimony of dolls, many actual men state
emphatically that male nipples are erogenous zones.)

Of course, the principal reason for the nipple's enduring
popularity is its function as a food delivery device. Ask any baby.
Ask any father who has held his child in his arms and suddenly had
said infant jerk its head to the side and latch optimistically onto
a nipple. After a moment, the baby gives the father the reproachful
look of an innocent child betrayed: You're no fun!

Darwin, who thought about everything, naturally wondered about
nipples. He collected case reports of men and women with extra
nipples (which he called mammae erraticae), including the case of
a woman who allegedly nourished a child via an extra nipple on her
thigh. (Why? Why not use the ones on her chest? Pure showboating,
that's my guess.) This led him to suspect that we are descended
from creatures with more than just the two mammae.

He also pondered male nipples. In "The Descent of Man," Darwin
suggests the possibility that "long after the progenitors of the
whole mammalian class had ceased to be androgynous, both sexes
yielded milk, and thus nourished their young and in the case of
marsupials, that both sexes carried their young in marsupial
sacks."

Darwin defended mammae masculinae: "The mammary glands and nipples,
as they exist in male mammals, can indeed hardly be called
rudimentary they are merely not full developed, and not
functionally active." He suggested that ancestral males gave up the
practice of nursing, after a prolonged period, perhaps because
litters were smaller. When "the males ceased to give this aid,
disuse to the organs during maturity would lead to their becoming
inactive and . this state of inactivity would probably be
transmitted to the males at the corresponding age of maturity. But
at an earlier age these organs would be left unaffected, so that
they would be almost equally well developed in the young of both
sexes."

Surely this is why everybody loves Darwin. Who else was thinking up
ancestral father animals suckling pouches full of thirsty babies?

I asked mammalogist Douglas Long, collections manager for
ornithology and mammalogy at the California Academy of Sciences,
whether there's any new thinking on this particular suggestion of
Darwin's. "Unfortunately, the fossil record doesn't give much of
a clue at all," Long said. "It's very intriguing."

While there's no evidence to refute or support Darwin's hypothesis,
Long points out that of the thousands of species of living mammals,
"Not a single one has a male that is able to lactate in any way."
Why all the male nipples, then? Long cites the embryologic process
that creates mammary tissue and also notes that, evolutionarily
speaking, "It's a lot more difficult to lose an organ than develop
an organ . It could be that males still have nipples because
there's nothing deleterious about nipples. There's no real need to
get rid of them. Why do we still have toenails, for example? Other
animals use them for digging, scratching or fighting, but we
don't. They're useless but at the same time they don't distract
from the business of living."

Pigeons and a couple of species of fish do something similar to
suckling their young, a task they split down the middle. Male and
female pigeons and doves feed their nestlings "pigeon's milk," a
cheesy substance they manufacture in their crops. Discus and orange
chromide fish feed their young with a nutritious mucus from the
sides of their bodies.

(Which reminds me. I do not want to hear about the breast being
just a modified sweat gland one more time, OK? That was a long
time ago and it was a pretty radical modification. Milk isn't
sweat. Do you ever hear people say "the sweat of human kindness,"
"She rode a sweat-white horse" or "got sweat?" There's a reason:
Milk is different from sweat. Until I hear you describe your hand
as a modified flipper, there will be no more talk of sweat glands.)

Male humans look pretty unhelpful next to pigeons. Newborn babies,
still pumped full of maternal hormones, usually lactate slightly,
producing a few drops of "witch's milk." Medical conditions like
acromegaly (excess growth hormone) can induce male lactation.

Dr. Miriam Stoppard, author of "The Breast Book," agrees with
Darwin that male nipples are more than rudimentary, cheerfully
suggesting that "men could develop fully functional breasts given
the right hormonal conditions."

That's right. If men would just submit themselves to an intense
barrage of hormone therapy, affecting every organ system of the
body in unknown ways, maybe they would be able to suckle their
young and throw off the charge of reptilianism once and for all.
But where is the research? Where is the funding? Where is the will?

Whither the male nipple? Is it ever likely to stomp off in an
evolutionary snit over not getting any respect ("Enough about boar
hogs!") and leave male humans as smooth-chested as stallions or
bulls? It seems unlikely. They've managed to hang in there all
these millennia, and many guys speak well of their nipples and
would clearly vote to retain them. Ask any boar hog and he'll
tell you the same.

Susan McCarthy

Susan McCarthy is a San Francisco freelance writer and the author, with Jeffrey Masson, of "When Elephants Weep: The Emotional Lives of Animals."


Why Does it Matter?

Understanding how mammals develop, and how both genetics (hardwired code) and epigenetics (how that code expresses) affect us, can help us to better understand mammalian, and particularly human nature regarding sex, gender, and sexuality.

The above phenomena help explain the similarities between male and female genitals and orgasms it explains why men have nipples, and may also explain why sex, sexual identity, and sexual preference are spectrums rather than binary either/or things. [10]

  • Why do Men have Nipples? We all start life as a blank slate, thus there are many parts that are common to both sexes, including nipples. Nipples develop before the Y gene is expressed in males, and the Y gene goes on to suppress breast development in “males.” The process begins before any hormones are released, adding to the blank slate theory, but continue before the Y gene expresses (thus there is a female quality). This does not mean that one should attribute nipples to “starting as female” (that is arguably an under-simplification of the truth). [11]
  • Why is it thought that some people are born gay or born transgender? We all start life as being the same sex (essentially a blank slate that can become either sex based on genetic code and other factors). As we grow and our genes express, a wide spectrum of influences affects fetal development and the neonate. Many of these factors have to do with the Y chromosome and hormones, which affect the brain. Since a wide variety of influences impact the blastocyst and fetus, it is reasonable to expect a wide spectrum of results in the neonate. Androgens and Estrogen are present in both sexes, this and a host of other factors (some noted above and some not) offer solid supporting evidence to the argument for intersex (and transgender and even potentially other aspects of LGBT). This is however its own issue with much to discuss.

We all have very specific hardwired code from our parents when we start life as a single fertilized egg (zygote), from there it is a matter of gene expression. When the Y gene expresses males become males, until then, only the X gene expresses and we are all essentially females (if you judge female / male by sex organ rather than genetic code).

  1. X chromosome
  2. X chromosome
  3. XY sex-determination system
  4. Sexual differentiation
  5. Stanford’s The Genetics of Sex Determination: Rethinking Concepts and Theories for a modern take on sexual differentiation
  6. Sex Determination and Differentiation. USBC.edu.
  7. This is what Intersex Means
  8. Babies (fetuses) start as females?
  9. Stages of Development of the Fetus
  10. Why do men have nipples?
  11. Development of the Human Breast

"All Mammals Start as Female" is tagged with: Cells, DNA, Evolution, Sex. Gender. and Sexuality