By the way, that same catapult trick, storing energy from slow muscles in quick-release elastic, is also used by jumping insects like grasshoppers and fleas. Their ‘rubber’ is a wonderful substance called resilin. Resilin is even more efficient than rubber as an elastic. That means that a higher proportion of the stored energy is available for eventual release. Efficient is a technical term meaning that little energy is lost as heat. Inevitably some is lost, according to the unbreakable laws of thermodynamics – but there’s no space to deal with those laws here. Most spectacularly of all, the elastic storage ‘crossbow’ trick is used by mantis shrimps to pack a punch which is utterly astounding in an animal only a few centimetres long. A pair of front limbs have evolved to become hammers or clubs, which batter prey at a speed of 50 mph. The acceleration is equivalent to that of a bullet from a .22 pistol. And that – unlike the bullet – is under water! To repeat, it is achieved using elastically stored energy. Direct muscle power couldn’t possibly achieve such speed.
There’s a bit more to the story of the chameleon’s tongue. For instance, the hyoid spike itself moves forward to help the flying tongue on its way. It’s as if, bow in hand, you run towards your target like a fast bowler in cricket, and then launch the arrow while still running. But I’ve already probably said enough to make you think: ‘Surely somebody must have designed the whole amazing apparatus?’ Again, you’d be wrong. Why do I keep saying this, and saying that it will all be explained in later chapters? Because this chapter is setting up the problem of what needs to be explained. And it’s a big problem. I don’t want to make light of it, which is why I devote this whole chapter to the problem itself, before we even start on the solution. As we’ll see, only evolution by natural selection is a big enough theory to solve such a big problem.
Although chameleons have wondrous tongues and swivelling turret eyes, they are even more famous for something else: their ability to change colour to match their background. A politician who keeps changing his mind to blend in with prevailing opinion is sometimes teased as a ‘political chameleon’. In their colour-changing skill chameleons are equalled by some flatfish, like plaice. But both are massively outclassed by octopuses and their kin. Chameleons and flatfish change colour slowly, over a time-scale of minutes. Octopuses, squids and cuttlefish, collectively called cephalopods, change colour from second to second.
Cephalopods are about as close to aliens as anything you’ll find on this planet. They have eight (octopuses) or ten (squids and cuttlefish) arms surrounding their beak of a mouth. The arms are capable of astonishing feats of finely controlled, continuously bendy movement, which is especially remarkable since they contain no skeleton. They are the only animals that have true jet propulsion, and they use it to swim backwards, especially in sudden escape. And – which is why they come into this chapter – they can change colour very fast and in highly complex patterns. Tantalizingly, the way they do it is similar to how modern colour televisions work.
Switch on your television and look closely at the screen with a powerful magnifying glass. Unless it’s an old-fashioned type (which has horizontal lines), you’ll notice that the whole screen is covered with millions of tiny coloured dots, called ‘pixels’. Every pixel is either red, blue or green, and every pixel can be turned on or off, brightened or dimmed, under the control of the TV set’s electronics. The pixels are too small to be seen when you’re sitting back watching television. But every colour, however subtle, that you see from your sofa is made by some mixture of pixel brightnesses. If you examine with your lens a bright white part of the picture, you’ll see that all three colours of pixels, red, blue and green, are brightly lit. In a red part of the picture – not surprisingly – only red pixels are brightly lit. Similarly for blue and green parts of the scene. Yellow is made by switching on the red and green pixels together, purple by mixing red and blue, brown by a more complicated mixture. Grey is like white, with all three colours switched on – but weakly. The electronic apparatus of the television makes the entire moving picture by rapidly controlling the brightness of every single one of the millions of pixels. Computer screens work in the same way.
And – wondrous to report – so does the skin of an octopus, squid or cuttlefish. Its whole skin is a living TV screen. The pixels are not controlled electronically, however. Instead, each pixel is a tiny bag of coloured pigment. There are three different colours, just like in the TV screen, except that they aren’t red, blue and green, they’re red, yellow and brown. But, as with TV pixels, the three types are independently controlled, to vary the patterns of colour over the skin surface.
The cephalopod pixels are much bigger than the TV screen ones. They’re bags of pigment, after all, and you can’t make bags that small. How are they controlled? Each bag lies inside an organ called a chromatophore. Fish have chromatophores too, but they work in a different way. In cephalopods, the wall of the bag is elastic (interesting how elasticity keeps cropping up). There are muscle cells attached to the chromatophore. The muscles are arranged like the arms of a starfish, except that there are about twenty arms instead of only five. When the muscles contract, they stretch the walls of the bag so that a larger area of pigment is splayed out, and the chromatophore takes on the colour of the pigment. When the muscles relax, the bag shrinks to a dot because of its elastic walls, so its colour becomes invisible from a distance. Because the colour-change is controlled by muscles, and the muscles by nerves, it’s fast: about one-fifth of a second to change. Not as fast as a television screen, but a lot faster than a chameleon’s skin, where the chromatophores are controlled by hormones – substances that travel, inevitably slowly, through the blood.
The muscle contractions tugging at the chromatophores are controlled by nerves, and the nerves are controlled by cells in the brain. Nerves are fast (although not as fast as the electronic components in a television). Theoretically, if we could hook up a squid’s brain cells to a computer, we could play Charlie Chaplin movies on its skin. Nobody’s ever done that, although the squid itself comes close, with lovely waves of colour-change like speeded-up clouds wafting across the sky. Dr Roger Hanlon of the Woods Hole Marine Biology Laboratory kindly read early drafts of this chapter for me. And when he read my Charlie Chaplin suggestion he told me this. He and some colleagues took a dead squid and hooked up a nerve in its fin to an iPod. Of course the fin couldn’t hear, but the wire pulsed electricity in time with the music’s strong beat, and this stimulated the chromatophore muscles. The result was pretty crazy, like a disco light show. Search for ‘Insane in the Chromatophores’ on YouTube.
The story of cephalopod colour gets better still. First, you need to know that there are two ways things can get colourful. One is by pigment (ink, dye, paint), which absorbs some of the colour out of the sunlight and reflects the rest. The other way is by what is called ‘structural coloration’ or ‘iridescence’. Iridescence doesn’t work by absorbing sunlight. It reflects it, and it produces colours that vary depending on the angle from which they’re seen and the angle at which the light hits the surface. Soap bubbles with their wonderful shimmering rainbow colours (Iris was the Greek rainbow goddess) are iridescent, and you may have seen the same thing in thin layers of oil on water. Iridescence is how peacocks make their lovely colours. Also the shining blue tropical butterflies called morphos.
Well, squids don’t miss a trick, and structural coloration is another of the tricks they don’t miss. Underneath the chromatophores is another layer of so-called ‘iridophores’. Iridophores don’t change their shape like chromatophores, but they glisten colourfully like a morpho’s wing. Often a shining blue or green, which the chromatophores, being red, yellow or brown, can’t do. And some, though not all, of these iridophores can change their colour, too – and they do it in a different way from chromatophores.
The iridophores lie in a separate layer underneath the chromatophores. So they form a colourfully glowing background which may be covered up, to a greater or lesser ex
tent, by the winking chromatophores above them. In addition to the chromatophores and iridophores, and in yet another layer below the iridophores, there are so-called leucophores. These are white. Like snowflakes, they are white because they reflect light of all wavelengths: not neatly and tidily like mirrors, but scattered in all directions.
What do cephalopods use their changing skin colours and patterns for? Mostly camouflage. They can manipulate their chromatophores almost instantaneously to mimic their background. This trick is visible in a lovely film, shot by Roger Hanlon while he was diving in the Caribbean Sea off Grand Cayman Island. This page shows a pair of stills from the film. As Dr Hanlon swam towards a clump of brown seaweed, to his amazement and delight part of the ‘seaweed’ turned a ghostly, threatening white. This made it seem to ‘emerge’ from the background, at which point it emitted a cloud of dark brown ink to obscure the view of any would-be predator and swam off. It’s well worth looking up the movie. Search for ‘Roger Hanlon octopus camouflage change’.
What’s especially remarkable is that cephalopods manage to mimic the colour of their background even though their eyes are colour-blind. How do they know what colour the background is? Nobody knows for sure, but there is suggestive evidence that they have some kind of seeing organs all over the skin, or at least in several patches of skin. These organs are not true eyes. They can’t form images. It’s more like having a retina distributed over the skin. And a retina is all they’d need to form a workable picture of the colour of the background.
Camouflage isn’t the only thing for which cephalopods use their astonishing powers of colour-change. Sometimes they use them to threaten enemies, or to court a mate. In another piece of film footage, Roger Hanlon captured a species of squid that uses white to threaten rival males, and stripy brown to court females (see this page). In his film a male squid achieves the amazing feat of colouring his right side white, to ward off other males, while at the same time colouring his left side stripy brown to please the female by his side. It’s well worth watching. Search for ‘Roger Hanlon’ ‘Signaling with skin patterns’ (note, it’s the American spelling, ‘signaling’). You can see the male change colour instantaneously. A few seconds later, the female moves to the other side of the male, and he reverses his colour accordingly so that she sees only his courtship pattern. Cephalopods can also change the texture of their skin, puckering it up in ridges, spikes or protrusions.
If you do a web search for ‘animal camouflage’ you will find hundreds more examples of creatures using spectacular (in one sense; the opposite in another) camouflage to protect themselves: spiders, frogs, fish, birds and, above all, insects (this page shows a few examples). It’s the attention to detail that is so shattering. Each one looks like the work of a sublimely skilled creative artist. And that word ‘creative’ brings me back to the main point of this chapter. Everything about an animal or plant, every detail of every one, looks overwhelmingly as though somebody designed and created it. And through the centuries people have – wrongly – given the credit to one or other of the countless gods we met in Chapter 1. Or to no god in particular but some unnamed creator.
For me, even more impressive than camouflage is the sheer complexity of living bodies. We got a taste of this with the eye. Your brain is even more amazing. It contains about 100 billion nerve cells – straggly branching tree-rooty things (see the illustration below) – wired up to each other in such a way that you can think, hear, see, love, hate, plan a barbecue, imagine a giant green hippopotamus or dream of the future.
On this page is a diagram of the chemical reactions that go on in a single cell of your body (you have more than 30 trillion cells altogether). The little blobs are chemical substances. The lines connecting them indicate chemical reactions between them. Don’t bother with the detailed labels. But if the chemical reactions they indicate stopped, you’d die.
Now think of just one molecule from your body, haemoglobin. It’s what makes your blood red, and it’s vitally important for carrying oxygen from the lungs to wherever it’s needed, for example the pounding leg muscles of a sprinting cheetah or gazelle. More than six thousand million million million haemoglobin molecules are surging round in your blood at this moment. I once calculated for an earlier book (it seems a ridiculously high figure, but nobody has contradicted it) that haemoglobin molecules are springing into existence in a human body at a rate of four hundred million million every second, and others are being destroyed at the same rate.
Awe-inspiring complexity. Once again, it seems to demand a master designer. And once again, later chapters will show that it doesn’t. That’s quite a challenge; and the purpose of this chapter, to repeat it, is to show how big the challenge is. Before we step up to answer it.
Beauty raises the same kind of challenge. The glowing beauty of a peacock’s tail – mostly achieved by structural, iridescent coloration – serves to attract peahens. We might even say it’s beauty for beauty’s sake. But beauty can also be ‘functional’: useful. I think airliners are beautiful, and their beauty comes from their streamlined shape. Flying birds are beautiful for the same reason. So are running cheetahs – although I don’t suppose gazelles think so.
This chapter might have left you with the impression that living ‘designs’ are perfect. Not just beautiful but ideally fit for purpose, whether that purpose is seeing, changing colour, running fast to catch prey, running fast to avoid becoming prey, looking exactly like tree bark, looking irresistible to peahens or whatever. If it has, I have to disappoint you, just a little. Especially if you look under the skin of living things, you’ll see flaws, and they are very revealing. What they reveal is evolutionary history. They are very much not what you’d expect to see if the animals had been intelligently designed. In fact, some are just the opposite.
Various species of fish make their living on the sea floor, and their bodies are flat. There are two ways of being flat. The obvious way is to lie on your belly and flatten the body from the top, so it spreads out sideways. That’s what skates and rays have done. You could think of them as sharks that have fallen victim to a garden roller. But plaice, sole and flounders have done it differently. They lie on one side. Sometimes the left side, sometimes the right. But they never lie on the belly like skates.
It will have occurred to you that there’s a problem with lying on your side if you’re a fish. One of your eyes is against the bottom of the sea and is therefore pretty useless. That problem doesn’t arise for skates and rays. Their eyes are on top of their flattened heads and both are useful for seeing things.
So, what did the plaice and flounders do about it? They grew a distorted, twisted skull, so that both eyes look upwards instead of one being flat against the sea bottom. And I do mean twisted and distorted (see this page). No sensible designer would have produced an arrangement like that. It makes no sense from a design point of view, but it has history written all over its Picasso-like face. Unlike the shark ancestors of skates and rays, the ancestors of these flatfish were shaped like a herring, a vertical blade. The left eye looked to the left and the right eye looked to the right. Symmetrically, as a good designer might wish. When they changed their way of life to live on the bottom, they couldn’t go back to the drawing board, in the way that a designer would. Instead they had to modify what was already there. Hence the distorted head.
Here’s another famous example of a revealing flaw: the retina of your eye. It’s back to front. It’s the same for all vertebrates. I’ve already described the retina as a screen of photocells. The photocells are hooked up to the brain by nerve cells. The sensible way to hook them up is the one used by cephalopods like octopuses. Their ‘wires’ connecting the photocells to the brain leave from the back of the retina in a sensible manner.
Not so the equivalent wires from the vertebrate retina. Here the photocells are wired backwards. Each photocell points away from the light. So how do the wires – the nerve cells – leading from the photocells manage to
reach the brain? They travel over the surface of the retina, taking information from the photocells, and converge on a circular patch in the middle of the retina where they dive through and then head back to the brain (see the diagram overleaf). The place where they dive through is called the ‘blind spot’. Because, not surprisingly, it is blind. What a ridiculous arrangement! The famous German scientist Hermann von Helmholtz (he was both a medical doctor and a pioneering physicist) once said that if a designer had presented him with the vertebrate eye he would have sent it back. Actually, although he would be perfectly justified in doing so, it works pretty well, as we can all see! The layer of nerve cells running over the surface of the retina is thin, and they are transparent enough to let light through.
My favourite example of bad design is the recurrent laryngeal nerve. The larynx is the voice box, in the throat. It’s supplied by two nerves from the brain called the laryngeal nerves. One of these, the superior laryngeal, is sensibly wired up directly from the brain to the voice box. The other one, the recurrent laryngeal, is crazy. It goes down the neck from the brain, shoots straight past the larynx (the place where it is supposed to end up), way down into the chest. There it loops around one of the main arteries attached to the heart, then whizzes straight back up the neck and finally ends up in the larynx, where it should have stopped on the way down. In a giraffe, that’s quite some detour. I saw this vividly when I assisted for a television programme in the dissection of a giraffe which had unfortunately died in a zoo.
Outgrowing God Page 12
