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12 Facts About the Penis

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Of all the body parts, none may elicit more questions—and myths—than the penis. One of the male sexual organ's main roles is to make procreation happen, but the penis also has cultural significance. Here are 12 facts to clear up the confusion.

1. THE PENIS HAS TWO PRIMARY FUNCTIONS.

The penis has two main biological roles, according to Michael Reitano, a physician-in-residence and an expert in sexual health and wellness for Roman Health. One is the elimination of waste in the form of urine; the second is the means for transferring semen, which carries sperm from the testes out of the body to somewhere else, such as the vagina for procreation. Another of its functions is, of course, sexual pleasure.

2. IT DEVELOPS FROM A CLITORIS-LIKE ORGAN.

All mammalian embryos start life as female in presentation, before the chromosome process is activated, with an external, undifferentiated clitoris-like structure. Eventually, embryos with XX chromosomes will develop a clitoris, labia, and vagina, while those with XY chromosomes will grow a penis and testes.

3. THE PENIS IS COMPOSED OF THREE TUBES.

The penis may look like one long tube, but there are actually three columns of tissue that run along the inside of the penis. Two are corpus cavernosum columns, which extend from the base to the end of the penis and fill with blood to allow for erection. The other is the corpus spongiosum; it surrounds the urethra, the tube through which urine and semen passes. The corpus spongiosum also fills with blood during erection, but remains pliable to keep the urethra open.

4. HUMANS MAY HAVE THE LARGEST PENIS OF ALL PRIMATES ...

When girth is considered, the human penis is quite a bit larger than those of its primate cousins. "A gorilla, for example, has a penis just 2 inches long. Human males walk upright, and it is thought that larger genitalia might have acted as a sexual attractant in competitive situations," Reitano says. But according to the Center for Academic Research and Training in Anthropogeny, chimpanzees and bonobos' penises are more slender but comparable to the length of an average human penis (which is 5.16 inches long and 4.59 inches around when erect, 3.61 inches and 3.66 inches around when not). Scientists theorize that our unique proportions are a result of natural selection through female mate choice.

5. ... AND THOSE PENISES MAY ONCE HAVE BEEN BARBED.

The human penis is most definitely among the smoothest in the animal kingdom. "In the distant past, it probably had sharp barbs, like some of our primate cousins, to make sex with another partner soon after coitus unlikely," Reitano says. Chimp penises still have small barbs that "hold the female in place, and when the penis is removed, it irritates the female's vagina so she avoids other chimps who might want to mate with her," he explains. (Let's not get started on the exploding corkscrew penis of the Muscovy duck, which looks like it makes for some irritating coitus.)

6. IN THE 15TH CENTURY, MEN FEARED WITCHES WHO COULD STEAL THEIR PENISES.

One of many bizarre beliefs put forth in the Malleus Maleficarum, a 15th-century German witch-hunting manual by Heinrich Kramer and Jacob Sprenger, was the opinion that witches could steal men's penises. Kramer wrote that witches "can take away the male organ." He didn't mean Lorena Bobbitt-style, clarifying, "not indeed by despoiling the human body of it, but by concealing it with some glamour."

In a 2002 paper published in the Journal of Folklore Research, Moira Smith pointed to male sexual insecurity as a driver of the witch hunts. "Many of the crimes (maleficia) attributed to witches concerned sexuality: copulation with incubus devils, procuring abortions, causing sterility and stillbirth, and impeding sexual relations between husbands and wives," she wrote.

7. ERECTIONS ARE MORE COMPLICATED THAN THEY SEEM.

Achieving an erection is one of the most complex functions to happen in a man, Reitano says: "For starters, hormones must be released on demand, arteries need to carry six times more blood to the penis with perfect efficiency, the nervous system must transmit its signals without a hitch, and the mind must be working in perfect harmony with the body."

The ability to get and sustain an erection, he says, depends upon "a body that is perfectly tuned physically, psychologically, and emotionally." The inability to achieve an erection, a.k.a. erectile dysfunction, is usually the first sign of poor health, according to Reitano.

8. UNLIKE OTHER MAMMALS, HUMANS LACK A PENIS BONE …

Many mammals, including gorillas and chimpanzees, have a penis bone or "baculum," says Arash Akhavein, a urologist at Cedars-Sinai in Los Angeles. In some animals, like whales, the baculum hangs back inside the abdomen until mating time, and then it slides into the penis to help maintain an erection. Instead of relying on this kind of structure, the human penis requires blood flow and engorgement for erection.

9. … AND YET IT'S POSSIBLE TO "FRACTURE" A PENIS.

Unfortunately, the penis can be fractured during sex, Reitano says. While penile fracture is relatively uncommon, it can happen when the thick sheath called the tunica albuginea, which gives an erect penis its rigidity, is injured by blunt force. "When it fractures, there is usually a clear popping sound, extreme pain, and the rapid loss of erection," Reitano says.

And yes, researchers have studied the sexual positions associated with the problem in heterosexual couples. A 2014 study in Advances in Urology found that the woman being atop the man was the primary position associated with penile fracture; the man being behind the woman was the second most commonly linked. A 2017 study in the International Journal of Impotence Research found that man-behind-woman was most often associated with fracturing a penis, followed by man-atop-woman.

10. MASTURBATION FEARS MAY HAVE DRIVEN MASS CIRCUMCISION.

In an uncircumcised penis, the glans (head) of the penis is covered by skin known as the foreskin, which can be pulled back from the glans. Circumcision, the removal the foreskin, is an ancient surgical practice performed for religious reasons and to prevent issues stemming from poor hygiene.

One thing circumcision doesn't prevent is masturbation. But in English-speaking countries in the 19th century, a general attitude against sexual profligacy, fueled by religious ideology, led to fears about the effects of masturbation and a spike in circumcision. Religious leaders and physicians warned people to avoid "self-abuse" for fear it could cause physical and mental disorders such as tuberculosis, memory loss, and epilepsy. As Tom Hickman writes in his book God's Doodle: The Life and Times of the Penis, "What made circumcision common among the proliferating 19th-century middle classes on both sides of the Atlantic was the hysteria about masturbation; removing the foreskin helped its prevention, doctors declared, and also cured bed-wetting and other conditions."

11. ADULT MEN GET CIRCUMCISED, TOO.

It's most common for boys to be circumcised as newborns, and in some cultures as adolescents, but there are a number of reasons why adult men may choose to have a later-in-life circumcision, Akhavein says. These include tears in the skin where the tip of the penis attaches to the foreskin; when the foreskin is too tight to be retracted easily, a condition called phimosis; and a buildup of smegma, a whitish waxy substance made up of dead skin cells and oils. Men who had an incomplete circumcision (too little skin removed) in childhood would also be good candidates.

12. ICELAND HAS A PENIS MUSEUM.

In 1974, an Icelandic history teacher named Sigurður Hjartarson received a cattle whip made out of a bull penis, which apparently gave him the idea to collect other penises, because hey, why not? The result is the Icelandic Phallological Museum, which holds a collection of more than 238 penises and penile parts from nearly all the fauna in Iceland. Yes, including Homo sapiens.

The largest penis on hand, from a sperm whale, stands at 6 feet tall and weighs nearly 150 pounds. "You’ll learn that as with everything in nature, the diversity in this department is as great as in any other; even within the same species the difference in size and shape is often quite remarkable," Hjartarson told Mental Floss in 2015.

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Pierluigi Luceri, Flickr // CC BY-NC-ND 2.0
Two Human Toes Were Stolen From an Anatomy Exhibit
Pierluigi Luceri, Flickr // CC BY-NC-ND 2.0
Pierluigi Luceri, Flickr // CC BY-NC-ND 2.0

A 28-year-old New Zealand man walked into an anatomy exhibition with 10 toes and walked out with 12. We don't know why or how he did it, but the man stole two human toes from a Body Worlds display in Auckland last month, The New Zealand Herald reports.

The unnamed man appeared in court Monday and pleaded guilty to improperly interfering with the corpse "of an unknown person" and purloining two toes, which alone are valued at about $3800. The motivation for the human remains heist wasn't stated. (Fulfilling a dare seems a likely explanation, or maybe he's just a fan of The Big Lebowski.)

Whatever the reason may be, the story has a happy ending, at least: The digits have since been returned to their rightful place in the "Vital" exhibit, which explores the human body in motion. "Vital," which will remain open in Auckland until July 13, is one of several traveling exhibitions curated by Body Worlds. Two other Body Worlds exhibits are currently on view in the U.S., including "RX" (showcasing the effects of disease) in Toledo, Ohio, and "Animal Inside Out" (an "anatomical safari") in Richmond, Virginia.

The bodies, all of which are donated for exhibition purposes, are preserved via plastination, a process that "replaces bodily fluids and soluble fat in specimens with fluid plastics that harden after vacuum-forced impregnation," according to the Body Worlds website. More than 16,000 people around the world have signed up to donate their bodies after their deaths.

[h/t The New Zealand Herald]

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Illustration by Mental Floss / Images: iStock
11 Facts About the Appendix
Illustration by Mental Floss / Images: iStock
Illustration by Mental Floss / Images: iStock

Despite some 500 years of study, the appendix might be one of the least understood structures in the human body. Here's what we know about this mysterious organ.

1. THE ANCIENT EGYPTIANS CALLED IT THE "WORM" OF THE BOWEL.

The human appendix is small, tube-shaped, and squishy, giving ancient Egyptians, who encountered it when preparing bodies for funerary rites, the impression of a worm. Even today, some medical texts refer to the organ as vermiform—Latin for "worm-like."

2. THE APPENDIX SHOWS UP IN LEONARDO DA VINCI’S DRAWINGS.

The earliest description of a human appendix was written by the Renaissance physician-anatomist Jacopo Berengario da Carpi in 1521. But before that, Leonardo da Vinci is believed to drawn the first depiction of the organ in his anatomical drawings in 1492. Leonardo claimed to have dissected 30 human corpses in his effort to understand the way the body worked from mechanical and physiological perspectives.

3. IT'S ABOUT THE SIZE OF A PINKY FINGER.

The appendix is a small pouch connected to the cecum—the beginning of the large intestine in the lower right-hand corner of your abdomen. The cecum’s job is to receive undigested food from the small intestine, absorb fluids and salts that remain after food is digested, and mix them with mucus for easier elimination; according to Mohamad Abouzeid, M.D., assistant professor and attending surgeon at NYU Langone Health, the cecum and appendix have similar tissue structures.

4. CHARLES DARWIN THOUGHT IT WAS A VESTIGIAL ORGAN …

The appendix has an ill-deserved reputation as a vestigial organ—meaning that it allegedly evolved without a detectable function—and we can blame Charles Darwin for that. In the mid-19th century, the appendix had been identified only in humans and great apes. Darwin thought that our earlier ancestors ate mostly plants, and thus needed a large cecum in which to break down the tough fibers. He hypothesized that over time, apes and humans evolved to eat a more varied and easier-to-digest diet, and the cecum shrank accordingly. The appendix itself, Darwin believed, emerged from the folds of the wizened cecum without its own special purpose.

5. … BUT THE APPENDIX PROBABLY EVOLVED TO HELP IMMUNE FUNCTION.

The proximity and tissue similarities between the cecum and appendix suggest that the latter plays a part in the digestive process. But there’s one noticeable difference in the appendix that you can see only under a microscope. “[The appendix] has a high concentration of the immune cells within its walls,” Abouzeid tells Mental Floss.

Recent research into the appendix's connection to the immune system has suggested a few theories. In a 2015 study in Nature Immunology, Australian researchers discovered that a type of immune cells called innate lymphoid cells (ILCs) proliferate in the appendix and seem to encourage the repopulation of symbiotic bacteria in the gut. This action may help the gut recover from infections, which tend to wipe out fluids, nutrients, and good bacteria.

For a 2013 study examining the evolutionary rationale for the appendix in mammal species, researchers at Midwestern University and Duke University Medical Center concluded that the organ evolved at least 32 times among different lineages, but not in response to dietary or environmental factors.

The same researchers analyzed 533 mammal species for a 2017 study and found that those with appendices had more lymphatic (immune) tissue in the cecum. That suggests that the nearby appendix could serve as "a secondary immune organ," the researchers said in a statement. "Lymphatic tissue can also stimulate growth of some types of beneficial gut bacteria, providing further evidence that the appendix may serve as a 'safe house' for helpful gut bacteria." This good bacteria may help to replenish healthy flora in the gut after infection or illness.

6. ABOUT 7 PERCENT OF AMERICANS WILL GET APPENDICITIS DURING THEIR LIFETIMES.

For such a tiny organ, the appendix gets infected easily. According to Abouzeid, appendicitis occurs when the appendix gets plugged by hardened feces (called a fecalith or appendicolith), too much mucus, or the buildup of immune cells after a viral or bacterial infection. In the United States, the lifetime risk of getting appendicitis is one in 15, and incidence in newly developed countries is rising. It's most common in young adults, and most dangerous in the elderly.

When infected, the appendix swells up as pus fills its interior cavity. It can grow several times larger than its average 3-inch size: One inflamed appendix removed from a British man in 2004 measured just over 8 inches, while another specimen, reported in 2007 in the Journal of Clinical Pathology, measured 8.6 inches. People with appendicitis might feel generalized pain around the bellybutton that localizes on the right side of the abdomen, and experience nausea or vomiting, fever, or body aches. Some people also get diarrhea.

7. APPENDECTOMIES ARE ALMOST 100 PERCENT EFFECTIVE FOR TREATING APPENDICITIS.

Treatment for appendicitis can go two ways: appendectomy, a.k.a. surgical removal of the appendix, or a first line of antibiotics to treat the underlying infection. Appendectomies are more than 99 percent effective against recurring infection, since the organ itself is removed. (There have been cases of "stump appendicitis," where an incompletely removed appendix becomes infected, which often require further surgery.)

Studies show that antibiotics produce about a 72 percent initial success rate. “However, if you follow these patients out for about a year, they often get recurrent appendicitis,” Abouzeid says. One 2017 study in the World Journal of Surgery followed 710 appendicitis patients for a year after antibiotic treatment and found a 26.5 percent recurrence rate for subsequent infections.

8. AN INFECTED APPENDIX DOESN’T ACTUALLY BURST.

You might imagine a ruptured appendix, known formally as a perforation, being akin to the "chestbuster" scene in Alien. Abouzeid says it's not quite that dramatic, though it can be dangerous. When the appendix gets clogged, pressure builds inside the cavity of the appendix, called the lumen. That chokes off blood supply to certain tissues. “The tissue dies off and falls apart, and you get perforation,” Abouzeid says. But rather than exploding, the organ leaks fluids that can infect other tissues.

A burst appendix is a medical emergency. Sometimes the body can contain the infection in an abscess, Abouzeid says, which may be identified through CT scans or X-rays and treated with IV antibiotics. But if the infection is left untreated, it can spread to other parts of the abdomen, a serious condition called peritonitis. At that point, the infection can become life-threatening.

9. SURGEONS CAN REMOVE AN APPENDIX THROUGH A TINY INCISION.

In 1894, Charles McBurney, a surgeon at New York's Roosevelt Hospital, popularized an open-cavity, muscle-splitting technique [PDF] to remove an infected appendix, which is now called an open appendectomy. Surgeons continued to use McBurney's method until the advent of laparoscopic surgery, a less invasive method in which the doctor makes small cuts in the patient's abdomen and threads a thin tube with a camera and surgical tools into the incisions. The appendix is removed through one of those incisions, which are usually less than an inch in length.

The first laparoscopic appendectomies were performed by German physician Kurt Semm in the early 1980s. Since then, laparoscopic appendectomies have become the standard treatment for uncomplicated appendicitis. For more serious infections, open appendectomies are still performed.

10. AN APPENDIX ONCE POSTPONED A ROYAL CORONATION.

When the future King Edward VII of Great Britain came down with appendicitis (or "perityphlitis," as it was called back then) in June 1902, mortality rates for the disease were as high as 26 percent. It was about two weeks before his scheduled coronation on June 26, 1902, and Edward resisted having an appendectomy, which was then a relatively new procedure. But surgeon and appendicitis expert Frederick Treves made clear that Edward would probably die without it. Treves drained Edward's infected abscess, without removing the organ, at Buckingham Palace; Edward recovered and was crowned on August 9, 1902.

11. THE WORLD'S LONGEST APPENDIX MEASURED MORE THAN 10 INCHES.

On August 26, 2006, during an autopsy at a Zagreb, Croatia hospital, surgeons obtained a 10.24-inch appendix from 72-year-old Safranco August. The deceased currently holds the Guinness World Record for "largest appendix removed."

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