Facts about human body
Your own body is a reliable source of surprises. It replaces cells by the million every second, keeps bacteria that outnumber human cells, and runs sensory tricks that make the world feel smoother than the raw signal ever is. The facts collected here stick to mainstream physiology, avoid the wellness myths that circulate alongside them, and explain the underlying mechanism rather than just quoting a startling number.
Babies are born with around 270 bones. Adults have 206.
Many of a newborn's bones are separate pieces of cartilage and bone that fuse together as the child grows. The skull alone starts as several plates with soft gaps between them.
Your gut has its own nervous system with hundreds of millions of neurons.
The enteric nervous system lines the digestive tract and can run digestion on its own, without instructions from the brain. It is sometimes called the second brain.
Fingernails grow about twice as fast as toenails.
A fingernail grows roughly 3.5 millimetres a month and takes around six months to replace itself completely. A toenail grows about 1.6 millimetres a month and needs over a year.
The femur is the longest and strongest bone in the body, and it is stronger than concrete by weight.
The thigh bone makes up about a quarter of a person's height. It routinely handles forces of several times body weight when you run or jump.
The human eye can distinguish roughly ten million different colours.
Colour vision comes from just three types of cone cells, sensitive to red, green and blue light. The brain compares their signals to produce the millions of shades we can tell apart.
You are about a centimetre taller in the morning than in the evening.
During the day, gravity squeezes water out of the discs between your vertebrae, and the spine compresses slightly. Overnight, lying down, the discs soak up fluid again.
Your heart pumps roughly 7,000 litres of blood every day.
At rest the heart moves about five litres per minute, which is your entire blood supply once every minute. Over a lifetime that adds up to well over 150 million litres.
Goosebumps are a leftover reflex from when our ancestors had fur.
Tiny muscles at the base of each hair pull it upright when you are cold or frightened. On a furry animal this traps a layer of warm air or makes the animal look bigger; on human skin it just makes bumps.
Your nose may be able to tell apart a trillion different smells.
A 2014 study estimated that humans can discriminate at least one trillion odours, far more than the 10,000 that textbooks had claimed for decades. The exact number is still debated, but the old figure was certainly far too low.
Tooth enamel is the hardest substance in the human body, but it cannot heal.
Enamel is about 96 percent mineral, harder than bone and able to withstand decades of chewing. Unlike bone, it contains no living cells, so once it is worn or damaged the body cannot rebuild it.
Identical twins share the same DNA but have different fingerprints.
Fingerprint ridges form in the womb between about the tenth and sixteenth week. Genes set the general pattern, but the fine details are shaped by tiny differences in pressure, position and growth.