And it’s not just broken legs and the like that put limits on the arms race. Economic limits are also important. Fast running muscles are costly to make. You need food to turn into muscle. That food could have been put into something else: into making milk for babies, for instance. Human arms races are also economically costly. The more money you put into bombers, the less money is available for fighters. Not to mention less money for hospitals and schools.
Think of the economic calculation that a plant, such as a potato, has to do. A plant is a good example, because while we might be tempted (wrongly) to think that a gazelle or a cheetah or a horse does calculations in its head, nobody could seriously imagine that a plant does sums. And doing calculations consciously is exactly what we are not talking about. The equivalent of calculations is done by natural selection over the generations. So, back to the potato plant. It has a limited amount of ‘money’ to play with. ‘Money’ here means the energy resources that ultimately come from the sun, turned into the currency of sugar and often stored as starch, for instance in a potato tuber. The plant needs to spend some money on leaves (to take in sunlight to make yet more money). It needs to spend some money on roots (to take in water and minerals). It needs to spend some money on underground tubers (to store money for next year). It needs to spend some money on flowers (to attract insects to pollinate other potato plants and spread the genes – including genes for getting the spending decisions right). Potato plants that get their ‘calculations’ wrong – perhaps not spending enough on tuber storage for next year – are less successful in passing on their genes. As the generations go by, plants that get their economic sums wrong become less numerous in the population. And that means that genes for getting economic sums wrong become less numerous. The population ‘gene pool’ becomes more and more full of genes for getting the economic sums right.
Having learned from the potato plant that we are not talking about conscious calculations, we can safely go back to gazelles and talk about how they get their economic balance right. The details are different from the potato but the principles are the same. Gazelles need to be cautious of cheetahs and lions. They need to be scared. They need to keep a watchful eye open. And a ‘watchful’ nose, for they often use smell to detect danger. But, importantly, they also need to spend a lot of time eating. Weight for weight, plant food is less nutritious than meat, so a herbivore – an animal that eats only plants – like a gazelle or a cow needs to keep eating almost all the time. A gazelle that was too scared would keep running away on the slightest suspicion of danger and wouldn’t have enough time to eat. On the African plains you can sometimes see antelopes and zebras grazing within sight of lions, knowing full well they are there. They keep a wary eye open in case the lions show signs of starting a hunt. But they go on grazing. Over the generations, natural selection has achieved a fine balance between being too scared (and therefore not getting enough to eat) and not being scared enough (and therefore getting eaten).
Evolution consists of changes in the proportions of genes in populations. What we see from outside is changes in bodies or behaviour as the generations go by. But what is really going on is that some genes are becoming more numerous in the population and others less numerous. Genes survive, or fail to survive, in the population as a direct result of their effects on bodies and behaviour, only some of which are visible to us. It’s not just cheetahs and gazelles, zebras and lions; it’s chameleons and squids, kangaroos and kakapos, buffaloes and butterflies, beech trees and bacteria, every animal and plant, every mushroom and every microbe – they all contain the genes that helped an unbroken line of ancestors to survive and pass those genes on.
You and I and the Prime Minister, your cat and the birds singing outside your window, every single one of us can look back at our ancestors and make the following proud claim: not a single one of my ancestors died young. Plenty of individuals died young, but they are not the ones that became ancestors. Not a single one of your ancestors fell over a cliff, or was eaten by a lion, or died of cancer, before living long enough to have at least one child. Of course that’s obvious when we think about it. But it’s really, really important. It means that every single one of us, every animal and plant and fungus and bacterium, every one of the seven billion people around the world, contains genes for being good at surviving and becoming an ancestor.
The details of what makes us good at surviving vary from species to species. For cheetahs it’s sprinting, for wolves it’s long-distance running, for grass it’s being good at absorbing sunlight and not minding too much about being cropped by cows (or lawnmowers), for cows it’s being good at digesting grass, for hawks it’s being good at hovering and spotting prey, for moles and aardvarks it’s being good at digging. For all living creatures, it’s getting the economic balance right. It’s being good at thousands and thousands of things, all working together through every corner and cranny of the body, through every one of billions of cells. The details vary hugely, but they all have one thing in common. They are all ways of being good at passing on genes to future generations. Passing on genes that make them good at surviving and passing the same genes on. Just different detailed ways of doing the same thing: surviving and passing on genes.
We agreed that an eye or any organ that’s complicated (like Paley’s watch) is too improbable to have just happened (like Paley’s stone). An excellent seeing device like a human eye cannot spring spontaneously into existence. That would be too improbable, like throwing a hundred pennies down and getting all heads. But an excellent eye can come from a random change to a slightly less excellent eye. And that slightly less good eye can come from an even less good eye. And so on back to a really rather poor eye. Even a very, very poor eye is better than no eye at all. You can tell the difference between night and day, and perhaps detect the looming shadow of a predator. And the same kind of thing is true not just of eyes but of legs and hearts and tongues and feathers and blood and hair and leaves. Everything about living creatures, no matter how complicated, no matter how improbable – as improbable as Paley’s watch – can now be understood. Whatever it is that you’re looking at, it didn’t spring into existence all at once. Instead, it came from something just a little bit different from what went before. Improbability dissolves away when you see it as arriving gradually, stealthily, step by tiny step, where each step brings about only a really small change. And the first step may not have brought about anything very good at all.
Improbable things don’t jump into the world suddenly. As I said before, that’s what improbable means. Paley was right about the watch. A watch can’t spring spontaneously into existence. It has to have a watchmaker. Watchmakers, too, don’t spring spontaneously into existence. They are born as complicated babies: human babies that grow into human adults, with human hands and brains and ability to learn a skill like watchmaking. Those human hands and brains evolved gradually from ape hands and brains; those apes evolved gradually from monkey-like ancestors; they in turn evolved by gradual, slow, painfully slow degrees from shrew-like ancestors; from fish-like ancestors before that; and so on. It was all gradual, slow, never sudden, never improbable like a watch spontaneously springing into existence at one go.
Designers need an explanation, just as watches do. Watchmakers have their explanation: being born from a woman, and before that by slow, gradual evolution through a very long chain of ancestors – the same explanation as for all living things. So where does that leave God, the alleged designer of everything? If you don’t think about it very hard, God seems to be a good explanation for the existence of improbable things like chameleons and cheetahs and watchmakers. But if we think about it more carefully, we can see that God himself is even more improbable than William Paley’s watch. Anything clever enough – complicated enough – to design things has to arrive late in the universe. Anything as complicated as a watchmaker must be the end product of a long, slow climb from earlier simplicity. Paley thought his watchmaker argument establish
ed the existence of God. But, when properly understood, the very same argument goes in exactly the opposite direction: in the direction of disproving God’s existence. Little did Paley know that he was eloquently and persuasively shooting himself in the foot.
Let’s go back to Archdeacon Paley’s watch and look more carefully at how it differs from his stone. You can do the scramble test on both. If you take a particular stone and scramble the bits a thousand times, you’d need a lot of luck to hit upon exactly the same stone again. So you might say the stone is as improbable as the watch. But all those randomly cobbled stones will still just be stones and there’ll be nothing special about any of them. Not so the watch. If you scramble the parts of the watch a thousand times, you’ll get a thousand random messes. But not one of them will tell the time or do anything useful (not unless your random scrambling is ridiculously lucky!). They won’t even be beautiful. That’s the key difference between watch and stone. Both are equally improbable in that they are a unique combination of parts which won’t just ‘happen’ by sheer luck. But the watch is unique in another, and more interesting way which separates it from all the random scramblings: it does something useful; it tells the time. Stones don’t have that kind of uniqueness. There is nothing to single out any one of those thousands of randomly scrambled stones from all the rest. They’re all just stones. Of all the thousands of ways the bits of a watch could come together, only one of those ways will be a watch. Only one will tell the time.
But now suppose, on your walk across the heath with Archdeacon Paley, you stubbed your toe on this:
Would you now be happy to say that this ‘just happened’, like Paley’s stone? I suspect not. I think you – and certainly Paley – might be tempted to think it was carefully made by a designer, an artist. It wouldn’t look out of place in a posh gallery, would it? A valuable work of art, fashioned by a famous sculptor. The shiny cubes seem so perfect, tastefully mounted in the rough stone base. For me it was a bombshell to discover that nobody crafted these beautiful objects. They just happened. Exactly like Paley’s stone. Indeed, they are a kind of stone.
They’re crystals. Crystals just grow, spontaneously. And some grow into precise geometric shapes which look, overwhelmingly, as though an artist had made them. These happen to be crystals of iron disulphide. There are many other crystals, spontaneously formed from different chemicals, which also look beautiful. Some are so beautiful – diamonds, rubies, sapphires, emeralds – that they command fabulous prices, and people wear them around their necks or on their fingers.
To repeat: nobody carved that beautiful iron disulphide ‘sculpture’. It just happened. Just grew. That’s what crystals do. Crystals of iron disulphide are called pyrite, or sometimes ‘fool’s gold’ because of their shiny colour. People who have dug them up have been fooled into thinking they were real gold and danced with joy, only to have their hopes cruelly dashed.
Crystals have pretty, geometrically precise shapes because their shape comes straight from the arrangement of their atoms. When water is cold enough it crystallizes into ice. The molecules in ice take up orderly positions next to each other. Like soldiers on parade, except that there are billions and billions of soldiers in even a small crystal: rank upon rank stretching off into the far distance in all directions. Unlike with soldiers, ‘all directions’ includes the up/down direction. The three-dimensional parade of molecules is called a lattice. Diamonds and other precious stones are also crystals, each with its own lattice pattern. Rocks, stones and sand are made of crystals, too, but often the crystals are so small and packed together that you can’t easily see them as separate crystals.
Crystals also form in another way: when a substance is dissolved, usually in water, and the water evaporates. You can easily do this with ordinary table salt, sodium chloride. Boil a cupful of salt in water to dissolve it, then leave the solution to evaporate in a wide, shallow dish. As the days go by, you can see new salt crystals forming in the water. Crystals of common salt can be cubes like iron pyrite, or larger structures built of cubes and looking like four-sided (‘ziggurat’) pyramids. What happens is that sodium and chlorine atoms recognize each other and link arms. The proper name for the ‘arms’ is bonds. (Actually, in this case they’re technically not atoms: they’re ions, sodium and chloride ions, but the difference isn’t important here.) Now, here’s how crystals grow. Sodium and chloride ions still floating around in the water happen to bump into an existing crystal. They recognize the chloride or sodium ions already there on the edge of the crystal and link arms with them – and that’s how the crystal grows. The reason crystals of common salt have square sides is that the ‘arms’ of the ions are at right-angles to each other. The crystal gets its shape from the right-angles of the files of ‘soldiers on parade’. Not all crystals are square-sided, and you’ve probably already guessed why. Their ‘arms’ point at angles other than right-angles, so their ‘soldiers on parade’ line themselves up at those other angles. That’s why fluorite crystals, for example, are octahedral – eight-sided.
Crystals can be large single stones with a nice geometric shape like a cube or an octahedron. But sometimes small crystals stick to each other to form more complicated shapes. The interior of each of the small building blocks of these complicated shapes betrays the underlying ‘parade-ground of soldiers’. But the ‘buildings’ are more elaborate. Snowflakes are an example. You’ve probably read that no two snowflakes are the same. In water ice the number of ‘arms’ is six, so the natural shape of each tiny ice crystal is six-sided. A snowflake is not just one of those tiny crystals. It’s a ‘building’, made of lots of tiny six-sided ‘bricks’. You’ll notice that the six-sided design is reflected in the shape of the ‘building’, as well as the shape of the bricks themselves. Every snowflake has six-way symmetry (the illustration opposite shows a few examples). But they are all different, and many of them are very beautiful.
It’s worth pondering why snowflakes are all unique. It’s because each has a unique history. Unlike crystals of salt, which grow at their margins in liquid water, snowflakes grow at their margins by adding tiny water crystals to the ‘building’ as they fall through clouds of water vapour. There are two ways in which they can grow. Which of the two predominates depends upon the ‘micro-climate’ in each tiny bit of cloud – how cold it is and how humid. Different micro-climates in the cloud vary in both temperature and humidity. Every snowflake experiences lots of different micro-climates as it floats down through the cloud: a unique moment-to-moment pattern of humidity change and temperature change. So the assembly of the ‘building’ follows a unique pattern and that particular snowflake ends up with a unique shape. It’s a kind of fingerprint of moment-to-moment history.*
And what makes them beautiful? As with the image in a kaleidoscope, it’s symmetry. All six sides, all six corners, all six points or sets of points, are symmetrical. And why are they symmetrical? Because they are so small that all parts of the growing ‘building’ experience the same ‘historical’ pattern of humidity and temperature changes. By the way, although all snowflakes are unique, some are less beautiful than others. It’s the beautiful ones that get pictured in books.
If we didn’t know better, we might have thought, ‘Oh look, snowflakes are so beautiful, and all unique. They must have been designed by a gifted creator with an ever-fertile mind able to think up so many millions of different designs.’ But, as we have just seen, snowflakes and other beautiful crystals are like Paley’s stone, not like Paley’s watch. Science gives us a full and complete explanation of their beautiful and complex symmetry, and it also explains why they are all unique. Like Paley’s stone, snowflakes ‘just happened’. When molecules – or things generally – spontaneously form themselves into particular shapes like this – when they ‘just happen’ – the process is called self-assembly. I think you can see why. Self-assembly is very important in living things, as we’ll soon see. This chapter is about self-assembly in life.
; My champion example of living self-assembly is pictured on the title page of this chapter. It’s a virus, the lambda bacteriophage. All viruses are parasites and this one, as the name ‘bacteriophage’ suggests, attacks bacteria. I think you’ll agree that it looks like a lunar lander. And it behaves like one, landing on the surface of a bacterium where it stands, firmly mounted on its ‘legs’. It then punches a hole through the bacterium’s cell wall and injects its genetic material, its DNA, via its central ‘tail’ – which might better be called its ‘hypodermic’. The machinery inside the bacterium can’t tell the difference between the virus DNA and its own. It has no choice but to obey the instructions coded in the virus’s DNA, and they tell it to manufacture lots more viruses which then burst out to land on, and re-infect, more bacteria. But what’s interesting for this chapter is that the virus’s ‘body’ self-assembles like a crystal. Or like a set of crystals. The head really looks like the sort of crystal you could wear round your neck (except it’s much too small). It, and all the other parts of the virus, self-assemble just like crystals, from molecules drifting about inside the bacterium and slotting into the already growing crystal.
When I started talking about crystals, I used the metaphors of ‘soldiers on parade’ and ‘linking arms’. We’re now going to need a slightly different metaphor: a jigsaw puzzle. You could think of a growing crystal as an unfinished jigsaw puzzle. Just as a jigsaw might, it grows outwards from the middle, as pieces are added to the edges. But unlike the ordinary flat puzzle that sits on a table, a crystal is a three-dimensional jigsaw puzzle.
Outgrowing God Page 14