48 facts, each with a source
Human body facts
Human body facts about the one you are sitting in. Roughly 8% of your DNA came from ancient viruses, you almost certainly have mites living on your face, and a newborn can breathe and swallow at the same time. Every fact links to the reference behind it.
Brain
- Damage to one side of the brain can erase the concept of the opposite side of space.
- Immune cells prune your brain. They eat synapses whole.
- Your brain burns about a fifth of your energy, and concentrating hard barely moves the number.
- You became you by deletion. Billions of connections cut.
- Your brain cannot feel pain.
- You forget almost every dream within minutes.
- Your brain runs on less power than a fridge bulb.
Heart
- Across mammals, a lifetime works out at roughly a billion heartbeats whether you are a shrew or an elephant.
- Your heart contains its own small nervous system — tens of thousands of neurons that keep it beating and adjusting after every nerve from the brain has been cut.
- You make two million red blood cells every second.
- Your blood vessels would wrap around the planet twice.
- Deoxygenated blood is dark red, never blue.
Senses
- Your eyes jump several times a second and you go briefly blind during each jump.
- A muscle in your middle ear tightens a fraction of a second before you speak.
- Smell is the only sense that does not route through the brain's central relay station first.
- The tongue map with sweet at the tip and bitter at the back came from a mistranslated German paper.
- Your taste buds are completely replaced every ten days.
- Your cornea has no blood supply.
- There is a hole in your vision and your brain paints over it.
- Everyone needs reading glasses eventually.
Immune System
Digestion
- Your stomach acid can dissolve a razor blade.
- Your gut runs on its own nerve network of several hundred million neurons, roughly what a cat carries in its whole brain.
- Your appendix is not useless.
- Most of your serotonin is made in the gut, not the brain — and it cannot cross into the brain from there.
Muscles
- About one person in seven is missing a forearm muscle.
- One bone in your body touches no other bone.
- Bone is stronger than concrete.
- Enamel is the hardest thing your body makes and it never grows back.
- Babies have no kneecaps in the usual sense.
- Babies are born with 300 bones and lose nearly 100 of them.
- The tiny muscles that raise goosebumps are useless for warmth on a nearly hairless animal, but they anchor the stem cells that grow new hair.
- You are wearing a skeleton you did not have ten years ago.
- You are about a centimetre taller in the morning.
Aging
More human body facts
- Roughly 8% of human DNA came from ancient viruses.
- Cells cross the placenta in both directions during pregnancy.
- You almost certainly have mites living on your face.
- Human body temperature has been falling for 150 years.
- You are more closely related to a mushroom than a mushroom is to a plant.
- You leave a personal cloud of bacteria in every room.
- Your fingerprints were made by random pressure in the womb.
- You cannot hum while holding your nose.
- Starve a cell and it eats itself. Neurons included.
- You are glowing in the dark right now.
- You are only about half human.
- One nostril is doing most of your breathing right now.
- Your left lung is smaller than your right.