7 Surprising Facts About the Chin

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The human body is an amazing thing. For each one of us, it’s the most intimate object we know. And yet most of us don’t know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

The humble chin, that bony protrusion at the bottom of your face, is a mysterious little body part that is a surprising source of controversy among researchers. Though popular culture derives great meaning out of how "strong" or "weak" chins are, very little science backs that up. Here, however, are seven actually scientific facts, which Mental Floss learned from experts, about the chin.

1. RESEARCHERS DISAGREE ABOUT THE PURPOSE OF A CHIN.

The most interesting thing about the chin, according to Faisal Tawwab, a family practice doctor with Multicare Physicians in Orlando, Florida, is that there is no precise answer as to why we even have one. "Prevailing theories include assistance with speech, to protect the jaw from chewing, as a way to measure attractiveness when seeking a partner, or a combination of all three," he tells Mental Floss. "Research to find the true purpose of the chin is ongoing. There are critiques around all of the current prevailing theories."

2. IT MIGHT HELP THE JAW STRESS LESS.

The chin may have evolved to protect the jaw from the unique stresses of shaping our mouths to form language, according to a 2007 study in the journal Medical Hypotheses. Your chin may help bear some of the muscle load of chewing and speaking (a valid reason to want a strong one).

3. THE CHIN IS CRITICAL TO CHEWING.

"The most important function of the chin is mastication [chewing] and lip continence," Francesco Gargano, a board certified plastic surgeon with The Plastic Surgery Center in New Jersey, tells Mental Floss. "Several muscles insert into the chin and are part of the occlusal plane," the space between your teeth when the mouth is closed. Research supports this theory, suggesting that the chin "helps buttress the jaw against certain mechanical stresses," including chewing, which produces a great deal of force.

4. CHINS MAY HAVE HELPED OUR ANCESTORS CHOOSE A MATE.

A more recent theory is that our chins helped us choose mates. "Males tend to have longer chins with a square appearance and flat base. Females tend to have narrower and rounder chins," says Gargano. A 2010 study in the American Journal of Physical Anthropology argues that there would be no difference in chin shape if it weren't related to sexual attraction because there's no functional difference; males and females ostensibly eat and talk the same way. Not everyone agrees. (See #7.)  

5. WE'RE THE ONLY ANIMALS WITH CHINS. 

While humans may share some things in common with animals, chins are not one of them. "Elephants are the only other creature with a body part similar to the chin," Tawwab says. But the elephant's "chin" is actually caused by a lack of lower teeth and a big lower lip. It's not a bony protrusion, which is a real chin—and a feature that's ours alone. The human chin is considered a cladistic apomorphy, Tawwab says: a feature or body part not found in the earliest forms of a clade (group of organisms sharing a common ancestor). In short, it's evidence of our species's evolution—and one of our defining physical characteristics.

6. DOES HAVING A CHIN CLEFT IMPROVE YOUR DATING PROSPECTS? 

"Historically, numerous cultures have assigned meanings to being born with a cleft chin, usually pertaining to luckiness in love," Tawwab says. The reality is much more mundane. "The current theory suggests that a cleft chin is actually caused by an incomplete fusion of the jaw bones before birth." There are several types of clefts, as well: vertical furrows, Y-shaped furrows, and round dimples. 

7. A CHIN MAY SIMPLY BE WHERE EVOLUTION STOPPED.

A chin may not have anything to do with withstanding pressure or attracting a mate, according to Nathan Holton, an anthropologist at the University of Iowa. His research suggests that the Homo genus (including humans, Neanderthals, and other relatives) simply evolved smaller faces—and Homo sapiens most of all. The lower jaw is the last part of the face to stop growing, which causes it to be more prominent as compared to other parts of the face. The prominent chin "is a secondary consequence of faces getting smaller," Holton writes.

14 Facts About Feet

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iStock/pepifoto

The foot is one of the most overworked, under-appreciated parts of the human body. Think about it: In a single day, the average person takes 8000 to 10,000 steps. That works out to be four trips around the world over a lifetime, putting a lot of wear and tear on your intricate foot bones. The foot may be humble, but its design is essential to how we walk upright, and hoofing it on two feet is a defining feature of humanity. Here are some fun—and a few funky—facts about the human foot.

1. FOOT BONES MAKE UP ABOUT A QUARTER OF ALL THE BONES IN OUR BODIES.

There are 26 foot bones in each of your feet—one less than in each hand. When we’re born, those foot bones are mostly cartilage. They only completely harden around age 21.

2. HUMANS HAVE WORN SHOES FOR A VERY LONG TIME.

When did humans begin wearing shoes, anyway? About 40,000 years ago, according to research from Washington University in St. Louis that analyzed foot bones from Neanderthals and early humans. Older specimens had thicker, stronger toes, likely from gripping the ground as they walked barefoot. That’s around the same time that the archaeological record shows a burst of artistic and technological advancements among early humans, including the first stone tools, which may have aided in the production of shoes. The oldest preserved shoe, incidentally, is 5500 years old and was found in an Armenian cave, buried in sheep dung.

3. THE BIG TOE USED TO BE A KIND OF FOOT THUMB.

This grasping toe helped our predecessors climb trees and, when young, grip onto their mothers. Thanks to modern science, if you lose your thumb, you can now replace it with a toe: toe-to-thumb transplants are a surprisingly common procedure these days.

4. FOOT BONES HOLD BIG CLUES ABOUT THE EVOLUTION OF BIPEDALISM.

Scientists are studying Homo naledi, a specimen discovered in a South African cave in 2013 that many researchers believe is a new human relative. H. naledi had very human-like feet, but with somewhat curved toe bones that suggest it climbed trees. It could be that H. naledi was beginning to experiment with walking. 

5. THERE WAS A FOOT CHEESE EXHIBITION IN IRELAND.

Warm, sweaty feet make a perfect home for bacteria, which feed on our dead skin cells and produce gases and acids that emit those arresting foot odors. They're apparently also good at cultivating cheese. An exhibition in Dublin in 2013 displayed a variety of cheeses made with bacteria samples obtained from real people’s feet, armpits, and belly buttons. Delicious. (No one actually ate any of the cheeses.)

6. FEET ARE ONE OF THE MOST TICKLISH PARTS OF THE BODY.

There’s a good reason for that: Humans have nearly 8000 nerves in our feet and a large number of nerve endings near the skin. Having ticklish feet can be a good sign: Reduced sensitivity can be an indicator of peripheral neuropathy (numbness in the feet caused by nerve damage). 

7. FOOT NUMBNESS CAN CAUSE BIG PROBLEMS FOR DIABETICS.

Complications of diabetes include poor circulation and foot numbness that can lead to serious skin ulcers, which sometimes require amputation of toes or feet. In 2010 alone, 73,000 lower-limb amputations were performed on diabetics.

8. FOOT SIZES AND WIDTHS IN THE U.S. AND UK ARE INCREASING.

Feet are spreading to support extra weight as our populations pack on the pounds. According to a 2014 study by the College of Podiatry in the UK, the average foot has increased two sizes since the 1970s. As people have grown taller and heavier, feet respond by growing. It appears many people are still in denial about their expanding feet: Though retailers are starting to respond by making larger and roomier shoes, half of women and a third of men reported they buy poorly fitting shoes. Podiatrists say ill-fitting shoes are to blame for a significant portion of foot problems, especially among women.

9. MANY GLAMOROUS CELEBRITIES HAVE BIG FEET.

From the bound feet of female Chinese elites to Cinderella and Barbie, freakishly small feet are often celebrated as more feminine. But plenty of glamorous women both past and present have had larger than average feet, among them Jacqueline Kennedy, Oprah Winfrey, Uma Thurman, and Audrey Hepburn (size 10, 11, 11, and 10.5, respectively).

10. WOMEN HAVE FOUR TIMES AS MANY FOOT PROBLEMS AS MEN.

That painful fact is often attributed to wearing heels. Ironically, Western women started wearing heels to effect a more masculine look: European men adopted the look from Persian warriors in the 17th century, and women soon followed suit.

11. THE AVERAGE PERSON WALKS ABOUT 100,000 MILES IN A LIFETIME. 

That’s a lot of stress on our feet. It’s not surprising, then, that lower back pain, headaches, indigestion, and spine misalignment are often related to foot problems. Some runners blow way past this mark: They've logged at least 100,000 in running miles alone. One committed runner, Herb Fred, has run a whopping 247,142 miles.

12. FOOT SIZE HAS ZERO TO DO WITH PENIS SIZE.

In a study published in 2015, researchers synthesized data from 17 previous studies that included the penis measurements of more than 15,000 men from around the world. The results: There is little evidence that penis size is linked to height, body mass, or shoe size.

13. THERE'S A REASON GRANDPA'S TOENAILS LOOK LIKE THAT.

Ever heard someone describing their toenails as “horse hooves”? As we get older, our toenails tend to thicken, making them hard to trim. This happens because toenails grow more slowly as we age, causing the nail cells to accumulate. Stubbing toes, bad shoes, and dropping things on your feet can also cause thickening, as can fungal infections and peripheral arterial disease, which narrows arteries and reduces the blood flow to limbs.

14. THERE'S A GUINNESS WORLD RECORD FOR MOST FEET AND ARMPITS SNIFFED.

Odds are you don’t have any job-related tasks nearly as revolting as this one: In the 15 years that Madeline Albrecht worked for an Ohio lab that tests Dr. Scholl products, she sniffed more than 5600 feet and untold numbers of armpits. Albrecht currently holds the Guinness World Record for—yes, this is a category—the number of feet and armpits sniffed.

11 Insightful Facts About Eyes

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iStock.com/Paffy69

There are a lot of myths and misconceptions about the eyes. No, sitting too close to the TV won't damage your vision, and reading in dim light won’t hurt either. It’s understandable that various parts of the eye are so little understood, though. Each eye has more than a million optic nerve cells and over 106 million photoreceptor cells, making it one of the most complex organs we have. Here are a few more things you should know about your “windows to the soul.”

1. Newborn babies see the world in black and white—and red.

“It is a myth that babies see in black and white,” Anna Franklin, leader of the University of Sussex's Baby Lab, told The Guardian. While newborns do see black, white, and shades of gray, they can also detect red objects against a gray backdrop, Franklin says. The reason why they can’t see more colors is because the cones in their eyes—the photoreceptor cells responsible for picking up colors—are too weak to detect them. Those cells quickly get stronger, though. After about two months, babies can distinguish between red and green, and a few weeks later they can tell the difference between blue and yellow.

2. Your eyeballs grow as you age.

Another common misconception is that your eyes remain the same size from birth to adulthood. As a newborn, your eyes measure about three-fifths of an inch from front to back, compared to a little under an inch in adults. Your eyes actually grow a great deal in the first two years of life, and another growth spurt occurs when you go through puberty. The confusion likely stems from the fact that your eyes as a 6-month-old infant are two-thirds the size they will be when you’re an adult.

3. The length of your eye partly determines how well you'll be able to see.

If your eyeball is too long or too short, you might end up having problems with your vision. Nearsighted people have eyes that are longer than average, while farsighted people have eyes that come up a little short. If you were to magically add or remove a millimeter of length from your eye, it would completely change your prescription. Aside from eye length, the shape of your cornea (the outer part of the eye where contact lenses are placed) and lens (the part of the eye located behind the iris and pupil) are other key factors that determine the quality of your vision. That's because both of these parts work together to refract light.

4. Contact lenses can't really get lost behind your eye.

Although it may feel like a dislodged contact lens is stuck behind your eye, that isn’t exactly what’s happening. The thin membrane covering the white part of your eye and the underside of your eyelid—called the conjunctiva—forms a pouch and prevents objects from getting behind your eyeball. If a contact lens gets shifted out of place to the point where you can no longer see it, it’s just stuck underneath your upper eyelid, which isn’t nearly as scary.

5. Blue-eyed people share a common ancestor.

Originally, everyone in the world had brown eyes. It wasn’t until around 6000 to 10,000 years ago that the first blue-eyed person was born as a result of a genetic mutation, according to a 2008 study. That mutation of the OCA2 gene essentially “turned off the ability to produce brown eyes” and diluted the color to blue, Professor Hans Eiberg of the University of Copenhagen said in a statement.

6. Parts of the eye can get sunburned.

There’s a good reason you should wear sunglasses when it’s bright outside. Too much exposure to UV rays can damage the surface of the cornea and conjunctiva, causing a condition akin to sunburn called photokeratitis. Symptoms include pain, red or swollen eyes, the sensation of a foreign body in the eyes, blurred vision, headaches, and seeing halos around lights. While the discomfort is temporary and tends to go away within 48 hours, longer exposure to UV rays can have a long-term effect on your vision and lead to macular degeneration (deterioration of the retina, which is often age-related) and cataracts (clouding of the eye's lens, which reduces the amount of light coming in).

7. Your eye muscles are the fastest muscle in your body.

Extraocular muscles are what let you look around in all directions. You have six of these muscles in each eye, and many of the motions they make are involuntary. This lets you flick your eyes to one side and notice something in your peripheral vision without consciously looking in that direction. When both of your eyes move in the same direction, the movement is called a saccade, which comes from the French word for “jerk” (the verb, not the person). These jerky movements are extremely rapid, lasting about 50 to 60 milliseconds per saccade, according to Dr. Reza Shadmehr, professor of biomedical engineering and neuroscience at Johns Hopkins University. “Saccadic eye movements are the fastest voluntary movements that we can make. The eyes move at around 500 degrees per second or more,” Shadmehr tells Mental Floss.

8. Your eye movements might give away your next move.

Shadmehr and other researchers conducted an experiment in 2015 to test the relationship between saccades and decision-making. Participants were placed in front of a computer and asked to choose between two options that appeared on the screen: an immediate reward and a delayed reward. For instance, one option might be “get $10 today,” while the other might be “wait 30 days and get $30.” Their eye movements were tracked the entire time, and researchers discovered that these movements gave away the choice they were about to make before they made it. At the last minute, their eyes would move at a faster velocity towards the option that they preferred.

“What’s interesting is that as the saccades are being made, the velocity of the eyes starts out being equal between these two stimuli, but then right before you decide ‘I like A better than B,' the saccade that you make toward A has a higher velocity than the one you make toward B,” Shadmehr explains. “The idea is that the way you’re evaluating things is reflected in the way you move toward them.”

In another experiment, Shadmehr found a correlation between faster eye movements and impatient and impulsive behaviors. Similarly, other studies have shown that our eye movements are linked to moral decisions and even our political temperament.

9. You can tell some animals' place in the food chain by looking at a part of their eye.

In 2015, vision scientist Martin Banks and his colleagues looked at the eyes of 214 species in an attempt to answer the question, “Why do animal eyes have pupils of different shapes?” By the end of their study, they noticed a few patterns. Predatory animals like big cats and snakes tend to have pupils in the shape of vertical slits. This particular shape gives them the advantage of being able to accurately judge the distance separating them and their prey, so they'll know exactly how far they have to pounce. On the other hand, horizontal pupils are more common in goats, deer, cattle, and other herbivores. This shape improves an animal’s panoramic vision, which helps them look out for predators.

10. An eye condition may have been partly responsible for Leonardo da Vinci's artistic genius.

Visual neuroscientist Christopher Tyler argued in a recent paper that the master artist behind Mona Lisa had strabismus, a disorder where the eyes are misaligned. Essentially, one of his eyes turned outwards, and he was able to use both of his eyes separately (monocular as opposed to binocular vision). Tyler believes this actually aided his art by improving his ability to render three-dimensional images on a flat canvas. “The condition is rather convenient for a painter, since viewing the world with one eye allows direct comparison with the flat image being drawn or painted,” Tyler said. We’ll never know for sure whether or not this was true for Leonardo, but it’s an intriguing theory.

11. SURGEONS HOPE TO BE PERFORMING WHOLE EYE TRANSPLANTS BY 2026. 

Currently, only cornea transplants to improve vision are possible, but a team of Pittsburgh-based transplant surgeons said in 2016 that they hoped to be performing whole eye transplants in humans within the next decade. Transferring an eye from a deceased donor to a recipient certainly won’t be easy, though. A complicated network of muscles, blood vessels, and nerves connects the eyes to the brain via the optic nerve. However, further studies into the optic nerve and recent advances in immunosuppressive drugs and surgical techniques have brought them several steps closer to achieving this goal. If successful, the surgery could restore vision to people who have suffered severe eye injuries. Their research is backed by the Department of Defense, which is concerned about the number of soldiers who sustain eye injuries in combat.

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