Amazing Facts About The Human Body

1 APPENDIX TO LIFE

The appendix gets a bad press. It is usually treated as a body part that lost its function millions of years ago. All it seems to do is occasionally get infected and cause appendicitis. Yet recently it has been discovered that the appendix is very useful to the bacteria that help your digestive system function. They use it to get respite from the strain of the frenzied activity of the gut, somewhere to breed and help keep the gut's bacterial inhabitants topped up. So treat your appendix with respect.

2 SUPERSIZED MOLECULES

Practically everything we experience is made up of molecules. These vary in size from simple pairs of atoms, like an oxygen molecule, to complex organic structures. But the biggest molecule in nature resides in your body. It is chromosome 1. A normal human cell has 23 pairs of chromosomes in its nucleus, each a single, very long, molecule of DNA. Chromosome 1 is the biggest, containing around 10bn atoms, to pack in the amount of information that is encoded in the molecule..

3 ATOM COUNT

It is hard to grasp just how small the atoms that make up your body are until you take a look at the sheer number of them. An adult is made up of around 7,000,000,000,000,000,000,000,000,000 (7 octillion) atoms.

4 FUR LOSS

It might seem hard to believe, but we have about the same number of hairs on our bodies as a chimpanzee, it's just that our hairs are useless, so fine they are almost invisible. We aren't sure quite why we lost our protective fur. It has been suggested that it may have been to help early humans sweat more easily, or to make life harder for parasites such as lice and ticks, or even because our ancestors were partly aquatic.

But perhaps the most attractive idea is that early humans needed to co-operate more when they moved out of the trees into the savanna. When animals are bred for co-operation, as we once did with wolves to produce dogs, they become more like their infants. In a fascinating 40-year experiment starting in the 1950s, Russian foxes were bred for docility. Over the period, adult foxes become more and more like large cubs, spending more time playing, and developing drooping ears, floppy tails and patterned coats. Humans similarly have some characteristics of infantile apes – large heads, small mouths and, significantly here, finer body hair.

5 GOOSEBUMP EVOLUTION

Goosepimples are a remnant of our evolutionary predecessors. They occur when tiny muscles around the base of each hair tense, pulling the hair more erect. With a decent covering of fur, this would fluff up the coat, getting more air into it, making it a better insulator. But with a human's thin body hair, it just makes our skin look strange.

Similarly we get the bristling feeling of our hair standing on end when we are scared or experience an emotive memory. Many mammals fluff up their fur when threatened, to look bigger and so more dangerous. Humans used to have a similar defensive fluffing up of their body hairs, but once again, the effect is now ruined. We still feel the sensation of hairs standing on end, but gain no visual bulk.

6 SPACE TRAUMA

If sci-fi movies were to be believed, terrible things would happen if your body were pushed from a spaceship without a suit. But it's mostly fiction. There would be some discomfort as the air inside the body expanded, but nothing like the exploding body parts Hollywood loves. Although liquids do boil in a vacuum, your blood is kept under pressure by your circulatory system and would be just fine. And although space is very cold, you would not lose heat particularly quickly. As Thermos flasks demonstrate, a vacuum is a great insulator...

In practice, the thing that will kill you in space is simply the lack of air. In 1965 a test subject's suit sprang a leak in a Nasa vacuum chamber. The victim, who survived, remained conscious for around 14 seconds. The exact survival limit isn't known, but would probably be one to two minutes.

7 ATOMIC COLLAPSE

The atoms that make up your body are mostly empty space, so despite there being so many of them, without that space you would compress into a tiny volume. The nucleus that makes up the vast bulk of the matter in an atom is so much smaller than the whole structure that it is comparable to the size of a fly in a cathedral. If you lost all your empty atomic space, your body would fit into a cube less than 1/500th of a centimetre on each side. Neutron stars are made up of matter that has undergone exactly this kind of compression. In a single cubic centimetre of neutron star material there are around 100m tons of matter. An entire neutron star, heavier than our sun, occupies a sphere that is roughly the size across of the Isle of Wight.

8 ELECTROMAGNETIC REPULSION

The atoms that make up matter never touch each other. The closer they get, the more repulsion there is between the electrical charges on their component parts. It's like trying to bring two intensely powerful magnets together, north pole to north pole. This even applies when objects appear to be in contact. When you sit on a chair, you don't touch it. You float a tiny distance above, suspended by the repulsion between atoms. This electromagnetic force is vastly stronger than the force of gravity – around a billion billion billion billion times stronger. You can demonstrate the relative strength by holding a fridge magnet near a fridge and letting go. The electromagnetic force from the tiny magnet overwhelms the gravitational attraction of the whole Earth...

9 STARDUST TO STARDUST

Every atom in your body is billions of years old. Hydrogen, the most common element in the universe and a major feature of your body, was produced in the big bang 13.7bn years ago. Heavier atoms such as carbon and oxygen were forged in stars between 7bn and 12bn years ago, and blasted across space when the stars exploded. Some of these explosions were so powerful that they also produced the elements heavier than iron, which stars can't construct. This means that the components of your body are truly ancient: you are stardust.

10 THE QUANTUM BODY

One of the mysteries of science is how something as apparently solid and straightforward as your body can be made of strangely behaving quantum particles such as atoms and their constituents. If you ask most people to draw a picture of one of the atoms in their bodies, they will produce something like a miniature solar system, with a nucleus as the sun and electrons whizzing round like planets. This was, indeed, an early model of the atom, but it was realised that such atoms would collapse in an instant. This is because electrons have an electrical charge and accelerating a charged particle, which is necessary to keep it in orbit, would make it give off energy in the form of light, leaving the electron spiralling into the nucleus.

In reality, electrons are confined to specific orbits, as if they ran on rails. They can't exist anywhere between these orbits but have to make a "quantum leap" from one to another. What's more, as quantum particles, electrons exist as a collection of probabilities rather than at specific locations, so a better picture is to show the electrons as a set of fuzzy shells around the nucleus.