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Authors: Richard Dawkins

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BOOK: The Magic of Reality
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The divide between the South American plate and the African plate runs right down the middle of the South Atlantic, miles from either continent. Remember that the plates include the bottom of the sea, and that means hard rock. So how could South America and Africa have nestled together 150 million years ago? Wegener would have had no problem here, because he thought the continents themselves drifted about. But if South America and Africa once snuggled
, how does plate tectonics explain all the undersea hard rock that nowadays separates them? Have the undersea parts of the rocky plates somehow managed to grow?

Sea-floor spreading

Yes. The answer lies in something called ‘sea-floor spreading’. You know those moving walkways that you see at large airports to help people with luggage cover the long distances between, say, the entrance to the terminal and the departure lounge? Instead of having to walk all the way, they step on a moving belt and are carried along to some point where they have to start walking again. The moving walkway at an airport is only just wide enough for two people to stand side by side. But now imagine a moving walkway that is thousands of miles wide, stretching most of the way from the Arctic to the Antarctic. And imagine that, instead of moving at walking pace, it moves at the speed with which fingernails grow. Yes, you’ve guessed it. South America, and the whole South American plate, is being carried away from Africa and the African plate, on something like a moving walkway that lies deep under the sea bed and stretches from the far north to the far south of the Atlantic Ocean, moving very slowly.

What about Africa? Why isn’t the African plate moving in the same direction, and why doesn’t it keep up with the South American plate?

The answer is that Africa is on a different moving walkway, one that is travelling in the opposite direction. The African moving walkway goes from west to east, while the South American moving walkway goes from east to west. So
is going on in the middle? Next time you are at a big airport, stop just before you step on the moving walkway and watch it. It wells up out of a slit in the floor, and moves away from you. It is a belt, going round and round, travelling forwards above the floor and coming back towards you under the floor. Now imagine another belt, welling out of the same slit but going in exactly the opposite direction. If you put one foot on one belt and the other foot on the other belt you’d be forced to do the splits.

The equivalent of the slit in the floor at the bottom of the Atlantic Ocean runs all along the deep sea floor from the far south to the far north. It is called the mid-Atlantic ridge. The two ‘belts’ well up through the mid-Atlantic ridge and head off in opposite directions, one carrying South America steadily westwards, the other carrying Africa away to the east. And, like the belts at the airport, the great belts that move the tectonic plates roll around and come back deep within the Earth.

Next time you are at an airport, get on the moving walkway and let it carry you, while you imagine you are Africa (or South America if you prefer). When you get to the other end of the walkway and step off, watch the belt dive underground, ready to make its way back to where you’ve just come from.

The moving belts at an airport are driven by electric motors. What drives the moving belts that carry the great plates of the Earth with their cargo of continents? Deep beneath the Earth’s surface there are what are called convection currents. What’s a convection current? Maybe you have an electric convector heater in your house. Here’s how it
to heat a room. It heats air. Hot air rises because it is less dense than cold air (that’s how hot-air balloons work). The hot air rises until it hits the ceiling, where it can’t rise any more and is forced sideways by the fresh hot air pushing up from beneath. As it travels sideways, the air cools down, whereupon it sinks. When it hits the floor, it again moves sideways, creeping along the floor until it gets caught up in the heater and rises again. That explanation is a bit too simple, but the basic idea is all that matters here: under ideal conditions a convector heater can get the air moving round and round – circulating. This kind of circulation is called a ‘convection current’.

The same thing happens in water. In fact, it can happen in any liquid or any gas. But how can there be convection currents under the Earth’s surface? It isn’t liquid down there, is it? Well, yes, it is – sort of. Not liquid like water, but sort of half liquid like thick honey or treacle. That’s because it is so hot that everything is melting. The heat comes from deep down. The centre of the Earth is very hot indeed, and it goes on being hot until much closer to the surface. Occasionally the heat bursts out through the surface at a place we call a volcano.

Driven by heat

The plates are made of hard rock, and, as we’ve seen, most of them is under the sea. Each plate is several miles thick. This thick layer of armour plating is called the lithosphere, which literally means ‘sphere of rock’. Under the sphere of rock is an even thicker layer, if you can believe it, which isn’t actually
the sphere of treacle but probably should be (it’s actually the upper mantle). The hard rocky plates of the sphere of rock could be said to ‘float’ on the sphere of treacle. Deep heat beneath and within the sphere of treacle causes agonizingly slow, grinding convection currents in the treacle, and it is those convection currents that carry the great rocky plates floating above.

Convection currents follow pretty complicated paths. Just think about all the different ocean currents, and even the winds, which are sort of high-speed convection currents. So it’s no wonder that the various plates on the Earth’s surface are carried in all sorts of directions, rather than round and round as if they were all on a simple merry-go-round. No wonder the plates bump into each other or tear rendingly away from each other, dive one under the other or grate sideways against each other. And no wonder we feel these titanic forces – grinding, wrenching, roaring, scraping forces – as earthquakes. Terrible as earthquakes can be, the wonder is that they aren’t even more terrible.

Sometimes a moving plate slides underneath a neighbouring plate. This is called ‘subduction’. Part of the African plate, for example, is being subducted under the Eurasian plate. This is one reason why there are earthquakes in Italy, and it is one reason why Mount Vesuvius erupted in ancient Roman times and destroyed the towns of Pompeii and Herculaneum (because volcanoes tend to sprout along the edges of the plates). The Himalayan mountains, including Mount Everest, were forced up to their great height as the Indian plate was steadily subducted under the Eurasian plate.

We began with the San Andreas Fault, so let’s end there. The San Andreas Fault is a long, rather straight ‘slippage’ line between the Pacific plate and the North American plate. Both plates are moving north-west, but the Pacific plate is moving faster. The city of Los Angeles lies on the Pacific plate, not the North American plate, and is steadily creeping up on San Francisco, most of which is on the North American plate. Earthquakes are constantly to be expected in this whole region, and experts are predicting that there will be a big one within the next ten years or so. Fortunately, California, unlike Haiti, is well equipped to deal with the terrible plight of earthquake victims.

One day, parts of Los Angeles might end up in San Francisco. But that is a long way off, and none of us will be around to see it.




things happen? After a dreadful disaster such as an earthquake or a hurricane, you’ll hear people saying things like this:

‘It’s so
. What did those poor people ever do to deserve such a fate?’

If a really good person gets a painful disease and dies, while a really bad person remains in the best of health, once again we cry, ‘Unfair!’

Or we say, ‘Where’s the justice in that?’

It is hard to resist this feeling that, somehow, there ought to be a kind of natural justice. Good things should happen to good people. Bad things, if they must happen at all, should only happen to bad people. In Oscar Wilde’s delightful play
The Importance of Being Earnest
, an elderly governess called Miss Prism explains how, long ago, she wrote a novel. When she is asked whether it ended happily, she replies: ‘The good ended happily, and the bad unhappily. That is what fiction means.’ Real life is different. Bad things do happen, and they happen to good people as well as bad. Why? Why is real life not like Miss Prism’s fiction? Why do bad things happen?

Lots of peoples believe that their gods intended to create
perfect world but unfortunately something went wrong – and there are almost as many ideas about what that something was. The Dogon tribe of West Africa believe that at the beginning of the world there was a cosmic egg from which two twins hatched. All would have been well if the twins had hatched at the same time. Unfortunately, one of them hatched too soon, and spoiled the gods’ plan of perfection. That, according to the Dogon, is why bad things happen.

There are lots of legends about how death came into the world. All over Africa, different tribes believe that the chameleon was given the news of everlasting life and told to carry it to humans. Unfortunately the chameleon walked so slowly (they do, I know: as a child in Africa I had a pet chameleon called Hookariah) that the news of death, carried by a nippier lizard (or other faster animal in other versions of the legend), arrived first. In one West African legend, the news of life was brought by a slow toad, unfortunately overtaken by a fast dog bringing the news of death. I must say I’m a bit puzzled why
the order in which news arrives
should matter so much. Bad news is still bad, whenever it arrives.

Disease is a special kind of bad thing, and it has spawned plenty of myths of its own. One reason is that for a long time diseases were rather mysterious. Our ancestors faced other dangers – from lions and crocodiles, from enemy tribes, from the threat of starvation – but you could see them coming, and understand them. Smallpox, on the other hand, or the Black Death, or malaria, must have seemed to pounce from nowhere, without warning, and it wasn’t obvious how to guard against these assaults. It was a terrifying mystery. Where
diseases come from? What did we do to deserve this painful death, this agonizing toothache or these hideous spots? No wonder people resorted to superstition when desperately trying to understand disease, and even more desperately trying to protect themselves from it. In many African tribes, until quite recently, anybody who got ill, or had a sick child, would automatically look around for an evil magician or witch to blame.

If my child has a high fever, it must be because an enemy paid a witch doctor to cast a spell on her. Or maybe it is because I couldn’t afford to sacrifice a goat when she was born. Or perhaps it is because a green caterpillar walked across the path in front of me and I forgot to spit out the evil spirit.

In ancient Greece, sick pilgrims would spend the night in a temple dedicated to Asclepius, the god of healing and medicine. They believed the god would either heal them himself or reveal the cure in a dream. Even today, a surprisingly large number of sick people travel to places like Lourdes, where they plunge into a sacred pool in the hope that the holy water will heal them (actually, one might suspect that they are more likely to catch something from all the other people who have bathed in the same water). About 200 million people have made the pilgrimage to Lourdes during the past 140 years, hoping for a cure. In many cases there is not much wrong with them, and thankfully they mostly get better – as they would have anyway, with or without the pilgrimage.

Hippocrates, the ancient Greek ‘father of medicine’ who gives his name to the oath of good conduct that all doctors are
to observe, thought that earthquakes were important causes of disease. In the middle ages, many people believed that diseases were caused by the movements of the planets against the backdrop of stars. That’s part of a system of beliefs called astrology, which, ridiculous as it may seem, still has quite a few followers to this day.

The most persistent myth about health and disease, lasting from the fifth century
right up to the eighteenth century
, was the myth of the four ‘humours’. When we say, ‘He’s in a good humour today,’ that’s where the word comes from, although people don’t believe in the idea behind it any more. The four humours were black bile, yellow bile, blood and phlegm. Good health was thought to depend on a good ‘balance’ between them, and you can still hear something a bit similar from quack ‘healers’ today who will wave their hands over you in order to ‘balance’ your ‘energies’ or your ‘chakras’.

The theory of the four humours certainly couldn’t help doctors to cure illnesses, but it might have done no great harm except that it led to the practice of ‘bleeding’ patients. This involved opening a vein with a sharp instrument called a lancet, and drawing off quantities of blood into a special basin. This, of course, made the poor patient even sicker (it contributed to George Washington’s death) – but the doctors believed so strongly in the ancient myth of the humours that they did it again and again. What’s more, people didn’t only get bled when they were ill. Sometimes they asked the doctor to do it in advance of getting ill, in the hope that it would ward off sickness.

Once, when I was at school, our teacher asked us to
about why diseases happen. One boy put his hand up and suggested that it was because of ‘sin’! There are many people, even today, who think something like that is the cause of bad things generally. Some myths suggest that bad things happen in the world because our ancestors did something wicked long ago. I’ve already mentioned the Jewish myth of the founding ancestors Adam and Eve. You’ll remember that Adam and Eve did a simply terrible thing: they allowed themselves to be persuaded by the snake to eat the fruit of a forbidden tree. This mythical crime has reverberated down the ages and is still regarded by some people as responsible for all the bad things that happen in the world to this day.

Lots of myths talk about a conflict between good gods and bad gods (or devils). The bad gods are responsible for the bad things that happen in the world. Or there may be a single spirit of evil, called the Devil or something similar, who fights with the good god or gods. If only there wasn’t this tussle between devils and gods, or good gods and bad gods, bad things wouldn’t happen.

Why do bad things happen

Why does
happen? That’s a complicated question to answer, but it is a more sensible question than ‘Why do
things happen?’ This is because there is no reason to single out bad things for special attention unless bad things happen more often than we would expect them to, by chance; or unless we think there should be a kind of natural justice, which would mean that bad things should only happen to bad people.

Do bad things happen more often than we ought to expect by chance alone? If so, then we really do have something to explain. You may have heard people refer jokingly to ‘Murphy’s Law’, sometimes called ‘Sod’s Law’. This states: ‘If you drop a piece of toast and marmalade on the floor, it always lands marmalade side down.’ Or, more generally: ‘If a thing can go wrong, it will.’ People often joke about this, but at times you get the feeling they think it is more than a joke. They really do seem to believe the world is out to get them.

I do a certain amount of filming for television documentaries, and one of the things that can go wrong in filming ‘on location’ is unwanted noise. When an aircraft drones in the distance, you have to stop filming and wait for it to go, and this can be extremely irritating. Costume dramas of life in earlier centuries are ruined by even a trace of aircraft noise. Film people have a superstition that aircraft deliberately choose moments when silence is most important to fly overhead, and they invoke Sod’s Law.

Recently, a film crew I was working with chose a location where we felt sure there should be a minimum of noise, a huge empty meadow near Oxford. We arrived early in the morning to make doubly sure of peace and quiet – only to discover, when we arrived, a lone Scotsman practising the bagpipes (perhaps banished from the house by his wife). ‘Sod’s Law!’ we all proclaimed. The truth, of course, is that there is noise going on most of the time, but we only
it when it is an irritation, as when it interferes with filming. There is a bias in our likelihood of noticing annoyance, and this makes us think the world is out to annoy us deliberately.

In the case of the toast, it wouldn’t be surprising to find that it really does fall marmalade side down more often than not, because tables are not very high, the toast starts marmalade side up and there is usually time for one half-rotation before it hits the ground. But the toast example is just a colourful way to express the gloomy idea that ‘if a thing can go wrong it will.’

Perhaps this would be a better example of Sod’s Law: ‘When you toss a coin, the more strongly you want heads, the more likely it is to come up tails.’ That, at least, is the pessimistic view. There are optimists who think that the more you want heads, the more likely the coin is to come up heads. Perhaps we could call that ‘Pollyanna’s Law’ – the optimistic belief that things usually turn out for the good. Or it could be called ‘Pangloss’s Law’, after a character invented by the great French writer Voltaire. His ‘Dr Pangloss’ thought that ‘All is for the best in this best of all possible worlds.’

When you put it like that, you can quickly see that Sod’s Law and Pollyanna’s Law are both nonsense. Coins, and slices of toast, have no way of knowing the strength of your desires, and no desire of their own to thwart them – or fulfil them. Also, what is a bad thing for one person may be a good thing for another. Rival tennis players may both pray fervently for victory, but one has to lose! There is no special reason to ask, ‘Why do bad things happen?’ Or, for that matter, ‘Why do good things happen?’ The real question underlying both is the more general question: ‘Why does

Luck, chance and cause

People sometimes say, ‘Everything happens for a reason.’ In one sense this is true. Everything
happen for a reason – which is to say that events have causes, and the cause always comes before the event. Tsunamis happen because of undersea earthquakes, and earthquakes happen because of shifts in the earth’s tectonic plates, as we saw in Chapter 10. That is the true sense in which ‘everything happens for a reason’, the sense in which ‘reason’ means ‘past cause’. But people sometimes use reason in a very different sense, to mean something like ‘purpose’. They will say something like ‘The tsunami was a punishment for our sins’ or ‘The reason for the tsunami was to destroy the strip clubs and discos and bars and other sinful places.’ It is amazing how often people resort to this kind of nonsense.

Maybe it is a hangover from childhood. Child psychologists have shown that very young children, when asked why certain rocks are pointy, reject scientific causes as an explanation and prefer the answer: ‘So that animals can scratch themselves when they get itchy.’ Most children grow out of that kind of explanation for the pointy rocks. But quite a lot of adults seem unable to shake off the same kind of explanation when it comes to major misfortunes like earthquakes, or good fortune such as lucky escapes from earthquakes.

What about ‘bad luck’? Is there such a thing as bad luck, or indeed good luck? Are some people luckier than others? People sometimes talk of a ‘run’ of bad luck. Or they will say, ‘So many bad things have happened to me lately, I’m due for
piece of really good luck.’ Or they may say, ‘So-and-so is such an unlucky person, things always seem to turn out badly for her.’

‘I’m due for a piece of good luck’ is an example of a widespread misunderstanding of the ‘Law of Averages’. In the game of cricket, it often makes a big difference which team bats first. The two captains toss a coin to decide who gets the advantage, and each team’s supporters very much hope their captain will win the toss. Before a recent match between India and Sri Lanka, a Yahoo web page posed the question:

‘Will Dhoni [the Indian captain] be lucky once again with the toss?’

Of the answers they received, the following was chosen as ‘Best Answer’:

‘I firmly believe in the law of averages, so my bet is on Sangakkara [the Sri Lanka captain] being lucky and winning the much hyped toss.’

Can you see what rubbish this is? In a series of previous matches, Dhoni had won the toss every time. Coins are supposed to be unbiased. So the misunderstood ‘Law of Averages’ ought to see to it that Dhoni, having been lucky so far, should now lose the toss,
to redress the balance
. Another way to put this would be to say that it was now Sangakkara’s
to win the toss. Or that it would be
if Dhoni won the toss yet again. But the reality is that, no matter how many times Dhoni has won the toss before, the chances that he will win it again this time are
50:50. ‘Turns’ and ‘fairness’ simply don’t come into it.
may care about fairness and
, but coins don’t give a toss! Nor does the universe at large.

BOOK: The Magic of Reality
7.89Mb size Format: txt, pdf, ePub

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