AMazinG BiOloGy fACts

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(a serious medical condition in which the appendix becomes inflamed and painful). 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.