The Second Book of General Ignorance (10 page)

It’s old woodsman’s lore that moss always grows on the north side of the trees, but it doesn’t.

Mosses prefer shady places but they can grow on the south, west and east of trees (as well as the north), if there’s enough moisture to sustain them. The presence of moisture depends as much on the direction of the prevailing wind as on being out of the sun. And, although a tree in isolation tends to have more shade on its northern side, trees in wooded areas throw shade on one another, making it perfectly possible for the south side to be the mossy one.

Can you tell which way is north from the sun? If you face the sunrise in the east, north is 90° to your left, isn’t it?

This isn’t foolproof either. The sun only rises
exactly
in the east on two days a year, at the spring and autumn equinoxes, when night and day are of equal length. (
Equinox
is Latin for ‘equal night’.) In Britain, as a general rule, the sun rises in the south-east and sets in the south-west in winter; and rises in the north-east and sets in the north-west in the summer.

A more reliable method is to wait for nightfall and use the stars. Find the constellation of Ursa Major (Latin for ‘Great Bear’), better known as the Plough or Big Dipper. It looks a like a pan with a handle. Make a line between the two stars on the side of the pan opposite the handle and follow it upwards.
Polaris – the North Star – is the next bright star you find along that line. It’s not
exactly
north; but it’s good enough for someone hopelessly lost in a forest.

Unfortunately, this doesn’t work so well in the southern hemisphere. The nearest star to the celestial South Pole, sometimes called
Polaris Australis
, or the ‘Southern Pole star’, is Sigma Octantis in the constellation Octans, but it’s barely visible without a telescope.

The North Star isn’t always due north, either. This is because Earth wobbles as it spins. Think of the Earth as a ball, spinning round an imaginary stick that passes through each pole. Because of the gravitational pull of the Sun and Moon, the stick moves slightly over time, slowly tracing a circle in the sky. This means that the end of the stick isn’t always pointing directly at Polaris: it’s either moving slowly towards or away from it.

You don’t need to worry about that for a while yet, though. The movement is
very
slow: each rotation of that circle takes 25,765 years to complete. For our Bronze Age ancestors in 3000
BC
, the star Thuban in the constellation of Draco was closer to north. In 12,000 years time it will be Vega in the constellation Lyra. Polaris will be back in pole position again by
AD
27800.

Meanwhile, a neat trick is to use your watch. Point the hour hand at the sun. Taking the middle of the angle formed between that and the number twelve gives a fairly good approximation to south.

They don’t, as you may have heard, ‘dislocate their jaws’: they stretch them.

Most of the bones in a snake’s head – including the two halves of the jaw – are not locked in position, as in mammals, but are attached by a flexible ligament.

One of these bones links the snake’s lower jaw to its upper jaw in a double-jointed hinge. It’s called the quadrate bone because it is connected at four points.

We have this quadrate bone too, but it’s no longer attached to our jaw. Instead, it has migrated up into the ear and shrunk down in size to become the incus, or ‘anvil’, bone. This
combines with two other bones called the malleus (or ‘hammer’) and the stapes (‘stirrup’), to produce the miracle of efficiency that is the human middle ear.

The three-bone arrangement amplifies sound and is capable of much more acute hearing than the reptile system, where the eardrum is connected directly to the inner ear by just the single ‘stirrup’ bone. So, while we can’t swallow a goat whole, we can at least hear much better than snakes can.

Despite their big mouths, snakes sometimes bite off more than they can chew.

In 2005 the remains of a 1.8-metre (6-foot) alligator were found in the Florida Everglades National Park, protruding from the stomach of a 4-metre (13-foot) Burmese python. The python had tried to swallow the alligator whole and had then exploded. The alligator is thought to have clawed at the python’s stomach from the inside, leading it to burst.

Burmese pythons come from South-East Asia and are one of the six largest snakes in the world. In their natural habitat, they can grow to more than 6 metres (20 feet) long. They now infest the Everglades: all of them are pets that have been abandoned by, or escaped from, their owners.

In 1999 a study at Cornell University estimated that the control of invasive species cost the US a staggering $137 billion a year. In the following five years 144,000 more Burmese pythons were blithely imported into the United States.

In 2010 Florida finally passed a law banning the importation of Burmese pythons, but too late. They thrive in the hot, wet climate of the local swamps (along with dozens of other non-native species like monitor lizards and vervet monkeys). Fights between alligators and Burmese pythons are a not uncommon sight and are a popular tourist attraction. The result is quite often a draw.

You might think a snake is just one long tail with a head at one end, but in fact only about 20 per cent of a snake is tail.

The word
vertebra
is Latin for ‘joint’. Human beings have thirty-three vertebrae, which form the spinal column and the bones in the neck. Depending on the species, snakes can have over ten times as many. The great majority of these sprout a pair of ribs. Just as with people, snakes don’t have ribs in their head. And, at the other end (also as with people), where the ribs stop, the tail begins. The human ‘tail’ is called the coccyx; in a snake, its tail starts after its cloaca.

All reptiles, birds and amphibians have a cloaca. It’s named after the Cloaca Maxima, an early sewage system that ran through the Forum in ancient Rome. In snakes the cloaca is a small, flexible vent on its underside: the reptilian equivalent of a bottom. So a snake’s tail starts, just like a lizard’s or a pheasant’s, behind its behind.

Although controlled by a sphincter muscle, as in mammals, it differs from a mammal’s anus by providing a common passage for the removal of both urine and faeces. It’s also used
for mating and egg laying. Stored inside a male snake’s tail are his two penises (known as hemipenes or ‘half-penises’). To mate, he turns each one inside out, so that they poke out of his cloaca. They look rather like exotic varieties of mollusc, adorned with various knobs, spines and protuberances. Each is inserted, in turn, into the female’s cloaca, which is of a matching design to deter interlopers from other snake species.

Recent studies have shown that, while a snake can’t be referred to as ‘right-handed’, they are definitely ‘right-penised’: the hemipenis on the right side tends to be larger and is the one inserted first. Another use for the cloaca in some snake species is ‘popping’. This is where air is expelled from it in a series of sharp bursts, indistinguishable in timbre and volume from high-pitched human farts. The foul smell (and surprise value) helps keep predators at bay.

If a snake is kept in too small a space, it may attack and eat its own tail, thinking it’s a rival. Some snakes have been known to choke on their own tails.

The Ouroboros (Greek for ‘tail-eater’) is an ancient symbol of a snake swallowing its own tail. It appears in Egyptian, Greek, Norse, Hindu and Aztec mythology and represents the cyclical nature of things. In the
Timaeus
(360
BC
), Plato credited the origin of life in the universe to such a circular, self-consuming creature and the Swiss psychologist Carl Jung (1875–1961) believed it was an archetype, a concept hard-wired into our unconscious.

The Ouroboros unlocked one of the great scientific puzzles of the nineteenth century: the chemical structure of benzene. Found in crude oil, benzene is a powerful solvent used in the manufacture of dyes and plastics. First isolated in 1825, it was used as paint stripper, aftershave and to decaffeinate coffee before it was discovered to be dangerously toxic. Though its chemical formula, C
₆
H
_6,
was known, its atomic structure baffled everyone until the German chemist August
Kekulé (1829–96), after years of work, had the sudden insight that it was a ring of six carbon atoms. These were attached to each hydrogen atom with a single bond, but to each other with alternating single and double bonds.

Kekulé’s solution transformed organic chemistry. The breakthrough came to him in a daydream, when the image of a snake with its tail in its mouth suddenly came to mind.