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Bones are the unsung heroes of biology. Always working beneath the surface, they’re the ossified architecture that makes our bipedal existence possible — not to mention the existence of thousands of other species. And their amazing durability gives archaeologists and paleontologists an unparalleled glimpse into early human history and beyond. Here are seven amazing facts about bones to shine some much-needed light on these building blocks of our bodies.

Less Than 5% of Animal Species on Earth Are Vertebrates

All animals on Earth fall into one of two categories: vertebrates or invertebrates. This distinction is based on whether an animal has a spinal column. (Those that do, including humans, are the former; those that don’t are the latter.) Although all mammals, reptiles, amphibians, birds, and fish are vertebrates, they’re vastly outnumbered by invertebrates, which include worms, sea sponges, arthropods, and jellyfish (not really fish, despite their name). In fact, of the estimated 1.37 million surviving species on Earth, according to the International Union for the Conservation of Nature, only 66,800 have a spine. It turns out that a backbone is a bit of a biological rarity.

The largest invertebrate group by far is that of the class Insecta, which includes around 900,000 known living species (about 80% of the species on Earth) and millions more that have not yet been described by science. (Some estimates put the number of unnamed insect species as high as 30 million, though it’s likely less than that.) Insects don’t have spinal columns; instead, they have exoskeletons, which, while lacking a backbone, do have some spine-like features. And speaking of spines…

Pythons Have Nearly 20 Times More Vertebrae Than Humans

The average human is born with 33 distinct vertebrae, which are connected to one another through flexible joints called facets. Birds, meanwhile, have anywhere from 39 to 63 vertebrae. But even they can’t compete with snakes, especially large species of snakes like pythons. The Australian Oenpelli python (Morelia oenpelliensis), for example, may have as many as 600 vertebrae. That’s nearly three times as many bones as an adult human has in their entire body — though only two times as many as that same human has at birth. Which brings us to the next fact…

Human Babies Have More Bones Than Adults

Babies pack a lot of bones in their tiny bodies — around 300, in fact, which is nearly 100 more than adult humans have. The reason for this is biologically genius: These extra bones, many of which are made entirely or partly of cartilage, help babies remain flexible in the womb and (most crucially) at birth, making it easier for them to pass through the birth canal. As a baby grows into childhood and eventually early adulthood, the cartilage ossifies while other bones fuse together. This explains the “soft spots” in a baby’s skull, where the bones have yet to fuse completely.

It also explains why kids may be more susceptible to injury — fracture rates are high around the ages of 11 to 15, when many young people experience growth spurts due to puberty. This is because children’s bones have growth plates, which are particularly sensitive to trauma. Those growth plates eventually close as we age, and a child’s bone count decreases until it settles at 206. Our bones continue to change in a process called “bone remodeling” throughout our lives, but the number typically remains stable once we reach adulthood.

Half the Bones in Our Bodies Are in Our Hands and Feet

Perhaps surprisingly, the lion’s share of those 206 bones in the human body are in our hands and feet. Each foot contains 26 bones, and each hand contains 27, for a grand total of 106 bones in just those four extremities. Interestingly (but perhaps not surprisingly), the hand and foot are similar in terms of bone structure. On our hands, for example, each finger has three bones — the distal, middle, and proximal phalanges — except for the thumb, which has two (just the distal and proximal). Our feet are the same, with three phalanges in each of the smaller toes, and two in the big toe. The five metacarpals — that is, the bones that make up the palm of your hand — are also arranged similarly to the five metatarsals in your foot. The hand, however, has an extra bone called the pisiform, which is located on the outside edge of the wrist and attaches to various tendons and ligaments.

The Femur Is the Longest and Strongest Human Bone

The bones in our hands and feet are relatively small, though not as small as the stapes, the smallest bone in the human body, found in the middle ear. On the other end of the spectrum is the femur, notable for being the longest and strongest bone. The average adult femur — named for the Latin for “thigh,” where it’s located — stretches to about 18 inches in length and can support as much as 30 times the weight of your body. Because of this, it plays a crucial role in our ability to stand and move. It also connects to many muscles, tendons, and ligaments in our hips and knees.

Only One Bone Isn’t Connected to Another Bone in the Human Body

Bones provide necessary skeletal scaffolding, and that means they’re usually connected to other bones via joints woven together with ligaments and tendons. However, there is one notable exception in the human body — one bone that is not connected to any other bone nearby. That exception is the hyoid, a small U-shaped bone in the neck, at the root of the tongue. Instead of connecting to other bones, the hyoid is linked only to muscles, ligaments, and cartilage, making it something of a “free-floating” loner. That’s not to say it’s superfluous, though. The hyoid aids in the very vital human activities of talking, chewing, and swallowing, so it’s actually pretty important.

Your “Funny Bone” Is Not a Bone

Your “funny bone,” named as such for its location near the humerus bone — “humorous,” get it? — is not really a bone at all. Rather, it’s part of the ulnar nerve, which runs from your neck all the way to your hand. Nerves are usually protected by bone, muscle, and fat, so they can perform their bioelectrical functions undisturbed, but a small part of the ulnar nerve in the back of the elbow is a little more exposed. There, the nerve is protected only by a tunnel of tissue, known as the cubital tunnel, so when you hit your “funny bone,” the ulnar nerve presses against the medial epicondyle (one of the knobby ends of the humerus bone), which in turn sends a painful sensation throughout your lower arm and hand. And because the nerve gives feeling to the pinky and ring fingers, those two digits may feel particularly sensitive compared to your other three fingers.

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When it comes to teeth, there’s always something new to learn. Innovations like fillings and toothbrushes had a long and rich history before they reached our mouths, and cultural norms can vary wildly — or be oddly similar — throughout place and time.

Which famous author became a tooth-removal evangelist? What animals have far more teeth than you’d expect? What kinds of small creatures gather baby teeth in the night?

Smile big and read on for eight facts that just might change the way you think about your pearly whites.

Tooth Enamel Is the Hardest Substance in the Human Body

Move over, bones! The outer layer protecting our teeth is the hardest thing in our bodies. The next layer down, dentin, is also stronger than bone. The trade-off is that teeth have a very limited ability to heal themselves, unlike bones. You can’t put a cast on a cavity, after all.

Snails Have Thousands of Teeth

Each unassuming snail hides a microscopic secret: between 1,000 and 12,000 tiny teeth protruding from its tongue. They use these teeth to break down parts of their food, and since the teeth are not especially durable, they need to be replaced pretty frequently. This tooth-covered tongue is called a radula, and it’s not exclusive to snails. Slugs have them, too, along with some squids.

Not all radula are the same, though. Some predatory snails have venomous radula, and the terrifying-looking Welsh ghost slug has razor-sharp (and teeny-tiny!) teeth for eating worms.

The Earliest Toothbrushes Came From China

Tooth-cleaning goes back thousands of years, with methods including abrasive powder, cloth, and frayed sticks. Bristle toothbrushes emerged in China during the Tang dynasty (618–907 CE); the handles were made from ivory or bamboo. These brushes didn’t catch on in Europe until the 17th century, first in France and later in England.

While toothbrushes evolved in design throughout the 18th and 19th centuries, the materials stayed largely the same. Plastic handles came along in the early 1900s, and nylon bristles followed in 1938.

It Took a While to Get Americans to Brush Their Teeth

It sounds gross, but it’s true: Toothbrushing didn’t become a standard, everyday part of American life until the 1940s. That doesn’t mean all people didn’t brush their teeth — it just wasn’t the standard practice it is today.

The tide started to change in the decades prior, though. In the 1910s, schools started implementing dental hygiene programs like toothbrush drills, in which children practiced brushing their teeth with their teachers. Similar programs visited factories to care for workers’ teeth. This wasn’t just benevolence: Employers hoped their workers would miss fewer days of work due to tooth infections.

With dental hygiene already becoming normalized, one thing set it over the edge: American soldiers during WWII were required to brush their teeth every day, and brought the habit back home with them.

The Oldest Known Dental Filling Is Made of Beeswax

In 2012, scientists used the jaw of a Neolithic man to test out some new X-ray equipment — and in the process, made an exciting discovery. The man, who lived 6,500 years ago in modern-day Slovenia, had a filling made out of beeswax.

Drilling goes back even further than filling, though; archaeologists have found drill holes in teeth from more than 7,500 to 9,000 years ago in a graveyard in Pakistan.

Tooth Pulling Used to Be a Public Spectacle

Before modern dentistry existed, the task of tooth extraction in Britain fell to a strange assortment of professions, including blacksmiths, wigmakers, and a very specific kind of sideshow entertainer. Like snake-oil salesmen, charlatan tooth-drawers traveled to fairs and marketplaces wearing silly hats and sometimes even strings of teeth, eager to rip out teeth for curious spectators. They typically made a grand entrance, sometimes on horseback or with a team of assistants. Loud noises were a key part of the act, both to draw a crowd and to drown out the screams of their “patients.” This continued into the 1800s.

The alternatives, for what it’s worth, weren’t great either. In the 18th and 19th centuries, you could see a “barber-surgeon” (or later, just a surgeon) to get your painful tooth removed with a tooth key, a clawed device that looks a little like a broken corkscrew. All in all, it was not a great time to have bad teeth.

Tooth Fairy? More Like Tooth Mousie

Today, the most common American version of the tooth fairy is a small, whimsical figure, typically female, who checks under our pillows at night for lost baby teeth. But the tooth fairy is an early-20th-century invention, and that particular image rose to prominence right as Disney was releasing animated films featuring kind, gentle, feminine fairies.

The fairy is likely layered on top of a much longer tradition of offering baby teeth to rats and mice — the hope being that the child’s permanent teeth would grow in as strong as a rodent’s. While this practice appears throughout the world, it’s perhaps most common today in Spanish-speaking households. In fact, a specific tooth mouse named Ratoncito Perez emerged in Spanish lore in the 1800s, and spread throughout Latin America in children’s stories. A similar tooth mouse, La Petite Souris, goes back to 1600s France. In some countries, children make it more convenient for the rodent by placing their teeth in or near mouseholes.

The core concept — giving children money in exchange for teeth — dates back to at least the 12th or 13th century, and appears in Norse and Northern European tradition, while other lost-tooth rituals are common throughout the world’s history.

Roald Dahl Had All His Teeth Removed — Voluntarily — at 21

Famed author Roald Dahl was strange in many ways, including his strong opinions about teeth. When he was 21 years old and working at Shell Oil, he decided having teeth was just too much trouble, so he visited a highly regarded dentist in London to have them all taken out and an artificial set created. Five years later, he treated himself to extra-fancy new teeth with the sales from Shot Down in Libya, his first piece of paid writing.

This wasn’t especially unusual for British people at the time, but it gets weirder: Dahl became a teeth-removal evangelist. He convinced his mother to have all of hers removed. Then he turned to his four living siblings, none of whom actually went for it; this made him impatient and “foul-mouthed,” according to biographer Donald Sturrock. Finally, he convinced his brother-in-law to go — but to Dahl’s surprise, he never got false teeth to replace them.

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While there’s a lot happening on Earth, the sun is the real star of our show — pun intended. Hanging out at an average 93 million miles away from Earth, the sun is a perfect mixture of hydrogen and helium that spit-roasts our planet just right as we travel around its bright, glowing body. But although the sun is central to our survival, there’s still a lot we don’t know about it. For decades, space agencies have been sending missions to explore the sun and find answers; in 2021, NASA’s Parker Solar Probe became the first spacecraft to “touch” the sun by entering its upper atmosphere (still some 4 million miles away from its surface). Based on research from these missions and more, here are some of the most interesting things we’ve learned about the sun — and some of our best guesses at what its future might look like.

The Sun Is Middle-Aged

The sun seems eternal — an ever-present, life-giving fireball in the sky — but not even it can escape the wear and tear of time. Some 4.6 billion years ago, the sun formed from a solar nebula, a spinning cloud of gas and dust that collapsed under its own gravity. During its stellar birth, nearly all of the nebula’s mass became the sun, leaving the rest to form the planets, moons, and other objects in our solar system. Even today, the sun makes up 99.8% of all mass in the solar system.

Currently in its yellow dwarf stage, the sun has about another 5 billion years to go before it uses up all its hydrogen, expands into a red giant, and eventually collapses into a white dwarf. So at 4.6 billion years old, the sun could be best described as “middle-aged” — but we don’t think it looks a day over 3 billion.

1.3 Million Earths Could Fit Inside the Sun

The Earth is big, but the sun is bigger — way bigger. Measuring 338,102,469,632,763,000 cubic miles in volume, the sun is by far the largest thing in our solar system, and some 1.3 million Earths could fit within it. Even if you placed Earth in the sun and maintained its spherical shape (instead of squishing it together to fit), the sun could still hold 960,000 Earths. Yet when it comes to stars, our sun is far from the biggest. For instance, Betelgeuse, a red giant some 642.5 light-years away, measures nearly 700 times larger and 14,000 times brighter than our sun.

It Takes a Long Time for Light to Escape the Sun

The sunlight that reaches your eyes is older than you might think. It takes a little over eight minutes for photons from the surface of the sun to reach Earth, meaning every time you glimpse the sun (hopefully with sunglasses!), it actually looks as it appeared eight minutes ago. However, this photon blazing at the speed of light is at the end of a very long journey. Once a photon enters the sun’s “radiative zone,” the area between the core and the convective zone (the final layer which stretches to the surface), energy is absorbed after a very short distance into another atom, which then shoots that energy into yet another direction. The overall effect is what scientists call a “random walk,” and the result is that it can take a single photon thousands of years — up to 100,000 years — to escape the sun. As our knowledge of the sun grows, scientists will likely refine this number, but for now it’s safe to say that it takes “a long time.”

The Sun’s Atmosphere Is Much Hotter Than Its Surface

As you travel farther from the surface of Earth, things usually get colder and colder. Planes traveling at 35,000 feet, for example, travel through the stratosphere and experience temperatures around -60 degrees Fahrenheit. However, the sun’s atmosphere works in exactly the opposite way. While the surface of the sun hovers around 10,000 degrees Fahrenheit, the atmosphere (or corona) of the sun is hundreds of times hotter, with temperatures reaching up to 3.6 million degrees Fahrenheit.

Scientists aren’t exactly sure why the sun’s atmosphere is so much hotter than the surface. One leading theory is that a series of explosions called “nanoflares” release heat upwards of 18 million degrees Fahrenheit throughout the atmosphere. Although small when compared to the sun, these nanoflares are the equivalent of a 10 megaton hydrogen bomb, and approximately a million of them “go off” across the sun every second. Another theory is that the sun’s magnetic field is somehow transferring heat from its core, which rests at a blazing 27 million degrees Fahrenheit, to its corona.

Different Parts of the Sun Rotate at Different Speeds

The sun doesn’t rotate like your typical planet. While the Earth’s core does rotate ever so slightly faster than the planet’s surface, it mostly moves as one solid mass. The sun? Not so much. First of all, it’s a giant ball of gas rather than a rigid sphere like Earth. The gases at the sun’s core spin about four times faster than at its surface. The sun’s gases also spin at different speeds depending on their latitude. For example, the gases at the sun’s equator rotate much faster than the areas at higher latitudes, closer to the poles. A rotation that takes 25 Earth days at the sun’s equator takes 35 days to make the same journey near the poles.

The Sun Completes Its Own Galactic Orbit Every 250 Million Years

Picture a grade-school model of the solar system, and it’s easy to forget that the sun is on its own galactic journey. While the Earth orbits the sun, the sun is orbiting the center of the Milky Way galaxy. On its orbiting journey, it travels roughly 140 miles per second, or about 450,000 miles per hour (by comparison, the Earth travels around the sun at only 67,000 miles per hour). Although blazing fast by Earth standards, it still takes our star roughly 230 million years to complete a full revolution.

In About 1 Billion Years, the Sun Will Kill All Life on Earth …

In 5 billion years, the sun will enter its red giant phase and engulf many of the inner solar system planets, including Earth. However, Earth will lose its ability to sustain life much earlier than that, because the sun is steadily getting hotter as it ages. Scientists estimate that anywhere between 600 million and 1.5 billion years from now, the Earth will experience a runaway greenhouse effect induced by our warming sun that will evaporate all water on Earth and make life on our blue marble impossible (except for maybe some tiny microorganisms buried deep underground). Eventually, Earth will resemble Venus, a hellish planet warmed beyond habitability due to its thick atmosphere and proximity to the sun. Luckily, humanity has at least several hundred million years to figure out a plan B.  

… But Life Only Exists Because of the Sun in the First Place

You can’t get too mad at the sun for its warming ways, because life couldn’t exist without it. Earth is perfectly placed in what astronomers call a star’s “goldilocks zone,” where the sun isn’t too hot or too cold but just right. This advantageous distance has allowed life to flourish on Earth, with the sun bathing our planet in life-giving warmth. The sun also gives plants the light they need to grow and produce oxygen, which in turn forms the bedrock of the web of life — and it’s all thanks to the middle-aged, hydrogen-burning, massively huge star at the center of our solar system.

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While many inventions are the outcome of tireless effort and incredible insight, a little luck never hurts. Some inventions — from Post-it Notes to penicillin — are amazing examples of good fortune as well as curiosity and tenacity. After all, it’s not enough for an accident to reveal some incredible new advancement; it also needs to be witnessed by an inquisitive person prepared to understand its significance. Here are seven world-changing inventions that were discovered by accident, by people who made sure that these serendipitous moments didn’t go unnoticed.

Post-Its

In 1968, scientist Spencer Silver was working at the Minnesota Mining and Manufacturing Company, also known as 3M. Founded in 1902, 3M quickly evolved beyond mining, and by the mid-20th century, the company had expanded into the adhesives game. At the time, Silver was trying to make “bigger, tougher, stronger” adhesives, and thus considered one of his creations, known as acrylate copolymer microspheres, a failure. These microspheres could retain their stickiness but could also be removed easily — not exactly big, tough, or strong.

While Silver believed this light-hold adhesive could have some sort of use (he patented it just to be safe), he couldn’t put a finger on what that use was, exactly, until one day when fellow 3M scientist Art Fry was in search of a bookmark that could stick to pages without damaging the paper. Fry immediately thought of Silver’s microspheres, and the two scientists soon found themselves writing each other messages around the office on the world’s first Post-it Notes. “What we have here isn’t just a bookmark,” Fry once said. “It’s a whole new way to communicate.”

Microwave Ovens

Today 90% of American households have a microwave oven — and it’s all thanks to magnetron expert Percy Spencer. In the mid-1940s, Spencer was working at the aerospace and defense company Raytheon when he took a step in front of an active radar set. To his surprise, the candy bar in his pocket melted. Spencer conducted a few more experiments, using popcorn kernels and eggs, and realized that microwaves could vibrate water molecules, causing them to produce heat and cook food. Raytheon patented the invention in 1945, and released the first microwave oven, called the “Radarange,” the next year. It weighed 750 pounds and cost $5,000 (about $52,000 today). It wasn’t until the 1970s that both the technology and price reached that consumer sweet spot, and microwave ovens became a must-have appliance in every U.S. home.

Penicillin

If you ever need to stress to your boss the importance of vacation, share the tale of penicillin. On September 3, 1928, Scottish physician Alexander Fleming returned to his laboratory at St. Mary’s Hospital in London after a vacation of more than a month. Sitting next to a window was a Petri dish filled with the infectious bacteria known as staphylococcus — but it’s what Fleming found in the dish alongside the bacteria that astounded him.

Inside the Petri dish was a fungus known as penicillium, or what Fleming at the time called “mould juice.” Whatever the name, this particular fungus appeared to stop staphylococcus from spreading, and Fleming pondered whether this fungus’s bacteria-phobic superpowers could be harnessed into a new kind of medicine. Spoiler: It could, and in the coming years, Fleming developed the world’s first antibiotic, winning the Nobel Prize for medicine in 1945 for his accidental yet world-changing discovery. “I did not invent penicillin. Nature did that,” Fleming once said. “I only discovered it by accident.”

X-Rays

In November 1895, German scientist Wilhelm Conrad Röntgen was hard at work studying cathode radiation in his Würzburg laboratory when a chemically coated screen 9 feet away began to glow. What followed was seven weeks of what Röntgen’s wife, Bertha, later described as a “dreadful time.” Röntgen worked tirelessly, obsessed with discovering the secrets of the phenomenon he called “X-rays” (named because the rays were unknown, as in “solving for x”) — often coming home in a bad mood, and eating silently before immediately retreating back to his lab. Eventually, he even moved his bed to his lab so he could work around the clock. As Röntgen would later put it, “I didn’t think; I investigated.”

The result of this investigation was a paper published in late December that same year, titled “On a New Kind of Rays.” The work detailed how these X-rays could penetrate objects, and the medical applications for such an invention were immediately apparent. Within a month or two, the first clinical uses of X-rays occurred in Hanover, New Hampshire, and Röntgen became the recipient of the first Nobel Prize in physics in 1901.

Vulcanized Rubber

On its own, natural rubber isn’t immensely useful — it melts in warm weather, cracks in the cold, and adheres to basically everything. But once rubber undergoes a process known as “vulcanization,” in which natural rubber is mixed with sulfur (or some other curative) and heated to between 140 to 180 degrees Celsius, it gains immense tensile strength and becomes resistant to swelling and abrasion.

Although creating this kind of tough rubber is a relatively complicated process, evidence suggests that an ancient Mexican people known as the Olmecs (which means “rubber people”) used some type of vulcanization. But modern vulcanization didn’t arrive until 1839, when American inventor Charles Goodyear accidentally dropped India rubber mixed with sulfur on a hot stove. Recognizing that the rubber held its shape and also gained strength and rigidity, Goodyear soon patented his discovery. Alas, protecting those patents from infringement proved impossible, and Goodyear died in 1860 some $200,000 in debt.

However, Goodyear still saw his life as a success, once writing: “I am not disposed to complain that I have planted and others have gathered the fruits. A man has cause for regret only when he sows and no one reaps.” Thirty-eight years later, American entrepreneur Frank Seiberling started a company to supply tires for the nascent automobile industry. Because creating tires capable of handling the rough terrain of dirt roads relied entirely on the process of vulcanization, Seiberling named his enterprise after the man who made it all possible — calling it the Goodyear Tire & Rubber Company.

Velcro

Amazing inventions come to curious minds, and that’s certainly the case for Swiss engineer George de Mestral. While on a walk in the woods with his dog, de Mestral noticed how burrs from a burdock plant stuck to his pants as well as his dog’s fur. Examining the burrs under a microscope, de Mestral discovered that the tips of the burr weren’t straight (as they appeared to the naked eye), but instead contained tiny hooks at the ends that could grab hold of the fibers in his clothing. It took nearly 15 years for de Mestral to recreate what he witnessed under that microscope, but he eventually created a product that both stuck together securely and could be easily pulled apart. In 1954, he patented a creation he dubbed “Velcro,” a portmanteau of the French words velours (“velvet”) and crochet (“hook”).

Synthetic Dye

For most of human history, dyes and pigments were sourced from natural resources such as metals, minerals, and even bat guano. It was an expensive process, and one of the most costly colors to create was purple, which had to be sourced from a particular mollusk along the coast of Tyre, a city in modern Lebanon. In fact, the dye was so expensive that the color was reserved for royalty, with monarchs like Queen Elizabeth even passing laws to ensure as much.

Then came 18-year-old British chemist William Henry Perkin. In 1856, Perkin was working in a lab, where he was trying (and failing) to produce a synthetic form of quinine, a compound found in the bark of cinchona trees and used to treat malaria. While washing out the brown sludge of one failed experiment with alcohol, the mixture turned a brilliant purple. Calling his creation “mauveine,” Perkin soon realized that not only was this dye cheap to produce, but it also lasted longer than dyes derived from natural sources, which tended to fade quickly.

Perkin’s discovery kick-started a chain reaction of chemical advances that brought cheap, colorful dyes to the fashion industry. Within six years of Perkin’s happy accident, even Queen Victoria herself began wearing colorful garments of bright mauveine.