The immune system has a difficult task ‘deciding’ what is ‘foreign’ and therefore to be fought (a ‘suspected’ parasite), and what it should accept as part of the body itself. This can be particularly tricky, for example, when a woman is pregnant. The baby inside her is ‘foreign’ (babies are not genetically identical to their mothers because half their genes come from the father). But it is important for the immune system not to fight against the baby. This was one of the difficult problems that had to be solved when pregnancy evolved in the ancestors of mammals. It was solved – plenty of babies do manage to survive in the womb long enough to be born. But there are also plenty of miscarriages, which perhaps suggests that evolution had a hard time solving it and that the solution isn’t quite complete. Even today, many babies survive only because doctors are on hand – for example, to change their blood completely as soon as they are born, in some extreme cases of immune-system overreaction.
Another way in which the immune system can get it wrong is to fight too hard against a supposed ‘attacker’. That is what allergies are: the immune system needlessly, wastefully and even damagingly fighting harmless things. For example, pollen in the air is normally harmless, but the immune system of some people overreacts to it – and that’s when you get the allergic reaction called ‘hay fever’: you sneeze and your eyes water, and it is very unpleasant. Some people are allergic to cats, or to dogs: their immune systems are overreacting to harmless molecules in or on the hair of these animals. Allergies can sometimes be very dangerous. A few people are so allergic to peanuts that eating a single one can kill them.
Sometimes an overreacting immune system goes so far that a person is allergic to himself! This causes so-called auto-immune diseases (autos is Greek for ‘self’). Examples of auto-immune diseases are alopecia (your hair falls out in patches because the body attacks its own hair follicles) and psoriasis (an overactive immune system causes pink scaly patches on the skin).
It is not surprising that the immune system sometimes overreacts, because there’s a fine line to be trodden between failing to attack when you should and attacking when you shouldn’t. It’s the same problem we met over the antelope trying to decide whether to run away from the rustle in the long grass. Is it a leopard? Or is it a harmless puff of wind stirring the grass? Is this a dangerous bacterium, or is it a harmless pollen grain? I can’t help wondering whether people with a hyperactive immune system, who pay the penalty of allergies or even auto-immune diseases, might be less likely to suffer from certain kinds of viruses and other parasites.
Such ‘balance’ problems are all too common. It is possible to be too ‘risk averse’ – too jumpy, treating every rustle in the grass as danger, or unleashing a massive immune response to a harmless peanut or to the body’s own tissues. And it is possible to be too gung-ho, failing to respond to danger when it is very real, or failing to mount an immune response when there really is a dangerous parasite. Treading the line is difficult, and there are penalties for straying off it in either direction.
Cancers are a special case of a bad thing that happens: a strange one, but a very important one. A cancer is a group of our own cells that have broken away from doing what they are supposed to do in the body and have become parasitic. Cancer cells are usually grouped together in a ‘tumour’, which grows out of control, feeding on some part of the body. The worst cancers then spread to other parts of the body (that’s called metastasis) and eventually often kill it. Tumours that do this are called malignant.
The reason cancers are so dangerous is that their cells are directly derived from the body’s own cells. They are our own cells, slightly modified. This means the immune system has a hard time recognizing them as foreign. It also means it is very difficult to find a treatment that kills the cancer, because any treatment you can think of – like a poison, say – is likely to kill our own healthy cells as well. It is much easier to kill bacteria, because bacterial cells are different from ours. Poisons that kill bacterial cells but not our own cells are called antibiotics. Chemotherapy poisons cancer cells, but it also poisons our healthy cells because they are so similar. If you overdo the dose of the poison, you may kill the cancer, but not before killing the poor patient.
We’re back to the same problem of striking a balance between attacking genuine enemies (cancer cells) and not attacking friends (our own normal cells): back to the problem of the leopard in the long grass again.
Let me end this chapter with a speculation. Is it possible that auto-immune diseases are a kind of byproduct of an evolutionary war, over many ancestral generations, against cancer? The immune system wins many battles against pre-cancerous cells, suppressing them before they have a chance to become fully malignant. My suggestion is that, in its constant vigilance against pre-cancerous cells, the immune system sometimes goes too far and attacks harmless tissues, attacks the body’s own cells – and we call this an auto-immune disease. Could it be that the explanation of auto-immune diseases is that they are evidence of evolution’s work-in-progress on an effective weapon against cancer?
What do you think?
12
WHAT IS
A MIRACLE?
IN THE FIRST chapter of this book I talked about magic, and separated supernatural magic (casting a spell to turn a frog into a prince, or rubbing a lamp to conjure up a genie) from conjuring tricks (illusions, such as silk handkerchiefs turning into rabbits, or women being sawn in half). Nobody nowadays believes in fairytale magic. Everybody knows that pumpkins turn into coaches only in Cinderella. And we all know that rabbits come out of apparently empty hats only by trickery. But there are some supernatural tales that are still taken seriously, and the ‘events’ they recount are often called miracles. This chapter is about miracles – stories of super-natural happenings that many people believe, as opposed to fairy-tale spells, which nobody believes, and conjuring tricks, which look like magic but we know are faked.
Some of these tales are ghost stories, spooky urban legends or stories of uncanny coincidence – stories like, ‘I dreamed about a celebrity whom I hadn’t thought about for years, and the very next morning I heard that he’d died in the night.’ Many more come from the hundreds of religions around the world, and these in particular are often called miracles. To take just one example, there is a legend that, about 2,000 years ago, a wandering Jewish preacher called Jesus was at a wedding where they ran out of wine. So he called for some water and used miraculous powers to turn it into wine – very good wine, as the story goes on to tell us. People who would laugh at the idea that a pumpkin could turn into a coach, and who know perfectly well that silk handkerchiefs don’t really turn into rabbits, are quite happy to believe that a prophet turned water into wine or, as devotees of another religion would have it, flew to heaven on a winged horse.
Rumour, coincidence and snowballing stories
Usually when we hear a miracle story it’s not from an eye witness, but from somebody who heard about it from somebody else, who heard it from somebody else, who heard it from somebody else’s wife’s friend’s cousin … and any story, passed on by enough people, gets garbled. The original source of the story is often itself a rumour that began so long ago and has become so distorted in the retelling that it is almost impossible to guess what actual event – if any – started it off.
After the death of almost any famous person, hero or villain, stories that somebody has seen them alive start rushing around the globe. This was true of Elvis Presley, of Marilyn Monroe, even of Adolf Hitler. It’s hard to know why people enjoy passing on such rumours when they hear them, but the fact is that they do, and that is a big part of the reason why rumours spread.
Here’s a recent example of how such a rumour gets started. Soon after Michael Jackson died in 2009, an American television crew was given a guided tour of his famous mansion called Neverland. In one scene of the resulting film, people thought they saw his ghost at the end of a long corridor. The recording is very unconvincing – however, it was e
nough to start wild rumours flying around. Michael Jackson’s ghost is at large! Copycat sightings soon emerged. For example, there is a photograph that a man took of the polished surface of his car. To you and me, especially when we compare the ‘face’ with the other clouds on either side, what we are looking at is obviously the reflection of a cloud. But to the overheated imagination of the devoted fan it could only be the ghost of Michael Jackson, and the picture on YouTube has received more than 15 million hits!
Actually, there’s something interesting going on here, which is worth mentioning. Humans are social animals, the human brain is pre-programmed to see the faces of other humans even where there aren’t any. This is why people so often see faces in the random patterns made by clouds, or on slices of toast, or in damp patches on walls.
Spine-tingling ghost stories are fun to tell, especially if they are really scary, and even more so if you claim that they are true. When I was eight, my family lived briefly in a house called Cuckoos, about 400 years old, with wonky black Tudor beams. Not surprisingly, the house had a legend about a long-dead priest hidden in a secret passage. There was a story that you could hear his footsteps on the stairs, but with the twist that you could hear one step too many – spookily explained by the fact that the staircase was said to have had an extra step in the sixteenth century! I remember the pleasure I took in passing the story on to my schoolfriends. It never occurred to me to ask how good the evidence was. It was enough that the house was old, and my friends were impressed.
People get a thrill from passing on ghost stories. The same applies to miracle stories. If a rumour of a miracle gets written down in a book, the rumour becomes hard to challenge, especially if the book is ancient. If a rumour is old enough, it starts to be called a ‘tradition’ instead, and then people believe it all the more. This is rather odd, because you might think they would realize that older rumours have had more time to get distorted than younger rumours that are close in time to the alleged events themselves. Elvis Presley and Michael Jackson lived too recently for traditions to have grown up, so not many people believe stories like ‘Elvis seen on Mars’. But maybe in 2,000 years’ time …?
What about those strange stories people tell of having a dream about somebody they haven’t seen or thought of for years, then waking up to find a letter from that person waiting on the doormat? Or waking up to hear or read that the person died in the night? You may have had such an experience yourself. How do we explain coincidences like that?
Well, the most likely explanation is that they really are just that: coincidences, and nothing more. The key point is that we only bother to tell stories when strange coincidences happen – not when they don’t. Nobody ever says, ‘Last night I dreamed about that uncle I haven’t thought of for years, and then I woke up and found that he hadn’t died in the night!’
The more spooky the coincidence, the more likely the news of it will spread. Sometimes it strikes a person as so remarkable that he fires off a letter to a newspaper. Perhaps he dreams, for the first time ever, of a once famous but long forgotten actress from the distant past, then wakes to discover that she died in the night. A ‘farewell visit’ in a dream – how spooky! But just think for a moment what has actually happened. For a coincidence to be reported in a newspaper, it only has to be experienced by one person among the millions of readers who might write to the paper. If we just take Britain alone, about 2,000 people die every day, and there must be a hundred million dreams every night. When you think of it like that, we’d positively expect that from time to time somebody will wake up and discover that the person they had been dreaming of had died in the night. They are the only ones who would send their stories to the papers.
Another thing that happens is that stories grow in the telling and re-telling. People enjoy a good story so much that they embellish it to make it a bit better than it was when they heard it. It is such fun giving people goose-pimples that we exaggerate the story – just a little, to make it a bit more colourful – and then the next person to pass the story on exaggerates a bit more, and so on. For example, having woken up to find that a famous person had died in the night, you might make enquiries to discover exactly when she died. The answer might come back, ‘Oh, it must have been approximately 3 a.m.’ Then you work out that you could well have been dreaming about her somewhere around 3 a.m. And before you know where you are, the ‘approximately’ and the ‘somewhere around’ get left out of the story as it does the rounds until it becomes: ‘She died at exactly 3 a.m., and that is exactly the moment when my cousin’s friend’s wife’s granddaughter was dreaming about her.’
Sometimes we can actually pin down the explanation of a weird coincidence. A great American scientist called Richard Feynman tragically lost his wife to tuberculosis, and the clock in her room stopped at precisely the moment she died. Goose-pimples! But Dr Feynman was not a great scientist for nothing. He worked out the true explanation. The clock was faulty. If you picked it up and tilted it, it tended to stop. When Mrs Feynman died, the nurse needed to record the time for the official death certificate. The sickroom was rather dark, so she picked up the clock and tilted it towards the window in order to read it. And that was the moment at which the clock stopped. Not a miracle at all, just a faulty mechanism.
Even if there had been no such explanation, even if the clock’s spring really had wound down to a stop at exactly the moment when Mrs Feynman died, we shouldn’t be all that impressed. No doubt at any minute of every day or night, quite a lot of clocks in America stop. And quite a lot of people die every day. To repeat my earlier point, we don’t bother to spread the ‘news’ that ‘My clock stopped at exactly 4.50 p.m., and (would you believe it?) nobody died.’
One of the charlatans I mentioned in the chapter on magic used to pretend he could restart watches by the ‘power of thought’. He would invite his large television audience to go and fetch any old broken-down watch in the house and clutch it in their hand while he tried to start it remotely with the power of thought. Almost immediately the phone in the studio would ring, and a breathless voice at the other end would announce, in awed tones, that their watch had started.
Part of the explanation may have been similar to that in the case of Mrs Feynman’s clock. It’s probably less true of modern digital watches, but in the days when watches had springs, simply picking up a stopped watch could sometimes restart it as the sudden movement activated the hairspring balance wheel. This can happen more easily if the watch is warmed up, and the heat from a person’s hand can be enough to do that – not often, but it doesn’t have to be often when you have 10,000 people, all over the country, picking up their stopped watches, perhaps shaking them, and then clutching them in warm hands. Only one of the 10,000 watches has to start in order for the owner to phone through the news in great excitement and impress the entire television audience. We never hear about the 9,999 watches that didn’t restart.
A good way to think about miracles
There was a famous Scottish thinker in the eighteenth century called David Hume who made a clever point about miracles. He began by defining a miracle as a ‘transgression’ (or breaking) of a law of nature. Walking on water, or turning water into wine, or stopping or starting a clock by the power of thought alone, or turning a frog into a prince, would be good examples of breaking a law of nature. Miracles like that would be very disturbing indeed to science, for the reasons discussed in the chapter on magic. Disturbing if they ever happened, that is! So how should we respond to stories of miracles? This was the question Hume turned to; and his answer was the clever point I mentioned.
If you want to know Hume’s actual words, here they are, but you have to remember that he wrote them more than two centuries ago, and English style has changed since then.
No testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous than the fact which it endeavours to establish.
Let’s put Hume’s point into oth
er words. If John tells you a miracle story, you should believe it only if it would be even more of a miracle for it to be a lie (or a mistake, or an illusion). For example, you might say, ‘I would trust John with my life, he never tells a lie, it would be a miracle if John ever told a lie.’ That’s all well and good, but Hume would say something like this: ‘However unlikely it might be that John could tell a lie, is it really more unlikely than the miracle that John claims to have seen?’ Suppose John claimed to have watched a cow jump over the moon. No matter how trustworthy and honest John might normally be, the idea of his telling a lie (or having an honest hallucination) would be less of a miracle than a cow literally jumping over the moon. So you should prefer the explanation that John was lying (or mistaken).
That was an extreme and imaginary example. Let’s take something that really happened, to see how Hume’s idea might work in practice. In 1917, two young English cousins called Frances Griffiths and Elsie Wright took photographs, which they said were of fairies. To modern eyes, the photographs are obvious fakes, but at the time, when photography was still quite a new thing, even the great writer Sir Arthur Conan Doyle, creator of the famously un-foolable Sherlock Holmes, was taken in by it, and so were quite a lot of other people. Years later, when Frances and Elsie were old women, they came clean and admitted that the ‘fairies’ were nothing more than cardboard cut-outs. But let’s think like Hume, and work out why Conan Doyle and the others should have known better than to fall for the trick. Which of the following two possibilities do you think would be the more miraculous, if it were true?