Human body and biology

25 to explore

• Watch What If? Lab What if everyone had the same fingerprints? The swirls and loops on your fingertips form before you are born, and no two people's are known to match, not even identical twins'. That's why fingerprints are used to tell people apart and to unlock phones. Imagine a world where everyone's fingerprints were exactly the same, and discover how they form, what they might be for, and what would change.
• Watch What If? Lab What if germs did not exist? We often think of germs as bad, but many of the tiny living things around us are harmless or even helpful. About as many microbes live in your body as you have body cells, and they help you digest food and help your immune system develop, and helpful bacteria turn milk into yogurt and cheese. Imagine a world with no microbes at all, and see what we would lose.
• Watch What If? Lab What if humans had tails? Many animals use their tails to balance, to signal to each other, or even to grab branches. People and apes have no tails, but we each have a small tailbone at the bottom of our spine. Imagine life with a tail, meet monkeys that hang by theirs, and discover what scientists learned in 2024 about how our ancestors lost their tails.
• Watch Try it What If? Lab What if you climbed Mount Everest? The higher you go, the thinner the air gets. In this lab, travel from sea level to 8.8 kilometers, near the top of Mount Everest, using a model of the atmosphere. Watch the air pressure fall to about a third, the temperature drop far below freezing, and water boil at under 70 °C.
• Watch What If? Lab What if you could hear like a bat? People hear sounds from about 20 to 20,000 vibrations a second. Bats can hear sounds up to about 100,000. They shout out high calls and listen for the echoes to find insects in the dark: that's echolocation. Imagine bat ears, and discover the hidden world of sound all around you.
• Watch What If? Lab What if you could not sweat? Sweat is your body's built-in cooler. When it dries off your skin, it carries heat away with it. Dogs can hardly sweat, so they pant instead. Imagine a body with no sweat, and discover the clever ways people and animals keep cool.
• Watch What If? Lab What if you could regrow a hand? Axolotls, salamanders from Mexico, can regrow whole legs, and even parts of their hearts and brains. Our bodies can heal too: skin grows back over a scrape and broken bones knit together. But we can't regrow a hand. Discover how axolotls do it, what our own bodies can regrow, and what scientists are learning.
• Watch What If? Lab What if you could remember everything? Imagine never forgetting anything: every lunch, every conversation, every page you ever read. A few people come close, remembering what they did on almost any date. But scientists think forgetting is useful too. Explore how memories form, why your brain lets some things fade, and tricks that help you remember what matters.
• Watch What If? Lab What if you could see in the dark? Your eyes need light to see. Cats need only about a sixth as much light as people, thanks to a shiny mirror layer at the back of their eyes. And special cameras can 'see' infrared light, the invisible glow of warm bodies. Imagine having night vision and find out how it really works.
• Watch What If? Lab What if you could see like an eagle? Some eagles can see about twice as much fine detail as people can. Their big eyes are packed with light-sensing cells, and many birds of prey have two extra-sharp spots in each eye where we have one. Imagine trading eyes with an eagle and find out what you would gain, and what eagles might not see at all.
• Watch What If? Lab What if you had gills? Fish don't breathe water itself: their gills take tiny amounts of oxygen gas out of the water. Air is about one fifth oxygen, but water holds only a few oxygen molecules in every million. Imagine growing gills, and find out how fish, and the smiling axolotl, get enough oxygen.
• Watch What If? Lab What if you had no bones? An adult has 206 bones. They hold the body up, guard the brain, heart and lungs, and give muscles something to pull on. Imagine a body with no bones, then meet animals like the octopus that really do live without them.
• Watch What If? Lab What if you had no sense of balance? Deep inside each ear are tiny loops filled with fluid. They tell your brain when your head turns and tilts, and together with your eyes and the touch sensors in your legs, they keep you steady. Imagine losing that sense, then discover why spinning makes you dizzy and how astronauts relearn their balance back on Earth.
• Watch What If? Lab What if you had no sense of smell? Your nose does more than you think. Much of what you call taste is really smell, and smell can warn you about smoke or food that has gone bad. Imagine a day with no sense of smell, then meet a dog, whose nose has up to 300 million smell receptors.
• Watch What If? Lab What if you had no teeth? Your teeth cut, tear and grind food into small pieces so you can swallow it. Imagine eating with no teeth at all! Find out what each kind of tooth does, how baby teeth make way for adult teeth, and how birds manage without any teeth, using a muscly stomach called a gizzard.
• Watch What If? Lab What if you had no thumbs? Your thumb is special: it can swing across your hand and touch the tip of every finger. That move lets you pinch, grip, write and use tools. Imagine a day without thumbs, then meet chimpanzees that grip with thumbs like ours and giant pandas that grasp bamboo with a clever 'pseudo thumb.'
• Watch What If? Lab What if you lived on a space station? On the International Space Station, astronauts and everything around them float. That sounds fun, but without the steady pull of gravity to work against, bones and muscles get weaker. That's why astronauts exercise for about two hours every day. Imagine moving in, and find out how they stay strong.
• Watch What If? Lab What if you never blinked? You blink about 15 times a minute, mostly without noticing. Each blink spreads a thin layer of tears across your eyes to keep them moist and wash away dust. Imagine never blinking again, then discover what tears do, why eyes feel dry, and how fish and snakes manage with no eyelids that close.
• Watch What If? Lab What if you never got hiccups? A hiccup is a sudden twitch of your diaphragm, the dome-shaped muscle under your lungs that helps you breathe. Then your vocal cords snap shut and make the 'hic' sound. Imagine never hiccuping again, and discover what scientists have found out about hiccups, from babies before they are born to the tricks people try.
• Watch What If? Lab What if you never slept? You spend about a third of your life asleep. While you sleep, your brain is busy sorting the day's memories and, scientists think, tidying itself up. Imagine never sleeping, then meet birds and dolphins that can rest one half of the brain at a time.
• Watch Try it What If? Lab What if your arm muscle joined farther from your elbow? Your forearm works like a lever, with your elbow as the pivot. Your biceps muscle pulls on it just a few centimeters from the elbow, so it has to pull much harder than the weight in your hand. Move the muscle's attachment in a lever model and discover the trade between strength and speed.
• Watch Try it What If? Lab What if your eyes were underwater? The clear front of your eye, the cornea, does most of its focusing by bending light as it passes from air into the eye. In this lab, shine a beam from air into an eye-like material, then from water into it, and see the bend almost vanish. That's why things look blurry when you open your eyes underwater.
• Watch What If? Lab What if your heart were as small as a mouse’s? A resting mouse's heart can beat more than 550 times a minute; yours beats about 60 to 100 times. A blue whale's heart has been measured as slow as 2 beats a minute. Explore why small animals have racing hearts and big animals slow ones, and why your heart is just the right size for you.
• Watch Try it What If? Lab What if your legs were as long as a giraffe’s? When you walk, each leg swings forward like a pendulum hanging from your hip. Longer pendulums swing more slowly. A giraffe's legs are about 1.8 meters long. Make a model leg twice as long and find out how much slower it swings, and why long legs still cover ground faster.
• Watch What If? Lab What if your skin could make food from sunlight? Plants catch sunlight and turn it into food, a process called photosynthesis. Imagine if your skin could do the same. Would you be able to skip meals? We'll compare how much energy your body needs with how much sunshine could give, and meet a real sea slug that keeps borrowed plant parts working inside its body.