Once again, this is obviously bad design, but it makes perfect sense if you look at the history. Our ancestors were fish. Fish have no neck. The fishy equivalent of the recurrent laryngeal nerve is not recurrent. It supplies one of the gills. The most direct route from the brain to the gill is behind the equivalent artery. It’s not a detour at all. Later in history, when the neck started to lengthen, the nerve needed to make a slight detour. The neck got steadily longer as the generations passed. And the detour too got longer and longer. Even when the detour became absurdly long in the ancestors of the giraffe, because of the way evolutionary change works (as we’ll see in the next chapter) it carried on just getting longer rather than changing the route altogether to jump over the artery. A designer would have taken one look at the nerve, as it passes within inches of the larynx on its way down the long, long neck, and said, ‘Wait a minute, that’s ridiculous.’ Again, a Helmholtz would have sent it back. It’s the same with the tube that carries our sperm from the testes to the penis. Instead of going by the most direct route, it travels up into the abdomen and loops over the tube carrying urine from the kidney to the bladder. Again, the detour makes sense only if you look at the evolutionary history.
I like the phrase ‘History written all over us’. When we get cold, we get goosebumps. That’s because our ancestors were hairy. When they got cold, each hair rose to thicken the layer of air trapped by the hairs that would keep us warm. Like putting on another sweater. We are no longer hairy all over our bodies. But the little hair-erecting muscles are still there. And they still – uselessly – respond to cold by raising non-existent hairs. Our hairy history is written all over our bare skin. Written in goosebumps.
To round off this chapter, I want to return to the cheetah and the gazelle. If God made the cheetah, he evidently put a lot of effort into designing a superb killer: fast, fierce, keen-eyed, with sharp claws and teeth, and with a brain dedicated to ruthlessly killing gazelles. But the same God put an equal amount of effort into making the gazelle. At the same time as he designed the cheetah to kill gazelles, he was busy designing the gazelle to be expert at escaping from cheetahs. He made both fast, so each could thwart the speed of the other. You can’t help wondering, whose side is God on? He seems to be piling on the agony for both. Does he enjoy the spectator sport? Wouldn’t it be horrible to think that God enjoys watching a terrified gazelle running for its life, then being knocked over and throttled by a cheetah gripping its throat so tightly that it can’t breathe? Or that he likes watching a cheetah that fails to kill starve slowly to death, along with its pathetically whimpering cubs?
Of course, for an atheist none of that presents a problem because we don’t believe in gods anyway. We are still at liberty to feel pity for the terrified gazelle or the starving cheetah and her cubs. But we don’t find their situations difficult to explain. Darwinian evolution by natural selection explains it – and everything else about life – perfectly well. As we shall see in the next three chapters.
The previous chapter was filled with amazing examples of animals beautifully built, displaying uncannily perfect colour patterns, or doing apparently clever things to assist their survival. After each story, I asked: must there not have been a designer, a creator, a wise god who thought it all out and made it happen? What exactly is it about those examples – and you could tell similar stories for every animal and plant that ever lived – that makes people think there had to have been a designer? The answer is improbability, and I now need to explain what I mean by that.
When we say something is improbable we mean it’s very unlikely to just happen by random chance. If you shake ten pennies and toss them on the table, you’d be surprised if all ten came up heads. It could happen but it’s very unlikely. (If you enjoy arithmetic you might like to work out just how unlikely, but I’m content to say ‘very’.) If somebody did the same thing with a hundred pennies it’s still just possible they’d all come up heads. But it’s so very very very improbable that you’d suspect a trick, and you’d be right. I’d bet everything I have that it was a trick.
With tossing pennies it’s easy – well, straightforward, at least – to calculate the odds against a particular outcome. For something like the improbability of the human eye, or the cheetah’s heart, we can’t calculate it exactly just by using arithmetic, like we can with the pennies. But we can say that it’s very very improbable. Things like eyes and hearts don’t just happen by luck. It’s this improbability that tempts people to think they must have been designed. And my task in this chapter and the next ones is to show that this thinking is mistaken. There was no designer. The improbability remains, whether we are talking about the improbability of an eye or the improbability of a creator capable of designing an eye. There has to be some other solution to the problem of improbable things. And that solution was provided by Charles Darwin.
For a living body, the equivalent of tossing pennies might perhaps be to scramble the bits of an eye, say, at random. The lens could end up at the back of the eye instead of the front. The retina could be in front of the cornea instead of behind the lens. The iris diaphragm could close when it’s dark and open when it’s light, instead of the sensible way round. Or open when you hear a trumpet and close when you smell an onion. The lens could be pitch black and not let any light through, instead of clear and transparent. Even having a retina or an iris diaphragm at all wouldn’t happen if you scrambled the bits of them at random.
Or imagine a randomly scrambled cheetah. It could have all four legs on one side, so it keeps toppling over sideways. The rear legs could be stuck on backwards, so they gallop in the opposite direction to the front legs and the cheetah doesn’t move either forwards or backwards but tries to tear itself in half. The heart could be connected to the windpipe, so it pumps air instead of blood. The cheetah could have teeth in its backside instead of in its mouth. And a totally scrambled cheetah wouldn’t have legs or heart or teeth at all. It would be a jumbled mess: a puréed cheetah smoothie.
This is just silly, as I’m sure you realize. There’s an infinite number of ways you could scramble the bits of a cheetah, and only a tiny number of them could run. Or see. Or smell. Or have babies. Or indeed stay alive. There’s an infinite number of ways you could scramble the bits of a chameleon, and only a tiny number of them could shoot a tongue out at an insect. It’s completely obvious that animals and plants do not come about by random chance. Whatever else is the explanation for cheetahs and gazelles, the lightning-fast chameleon tongue, the chromatophores and iridophores and leucophores of a squid, it cannot be random chance. Whatever is the true explanation for all the millions of animals and plants, it cannot be luck. We can all agree about that. So, what is the alternative?
Unfortunately, at this point many people go straight down the wrong path. They think the only alternative to random luck is a designer. If that is what you think, you’re in good company. It’s what almost everybody thought until Charles Darwin came along in the middle of the nineteenth century. But it’s wrong, wrong, wrong. It isn’t just a wrong alternative: it’s no alternative at all.
The wrong argument was most famously expressed by the Reverend William Paley in his 1802 book Natural Theology. Imagine you’re out for a walk on a heath, Archdeacon Paley said, and you happen to kick a stone. You are not impressed by the stone. It just happens to be there, and it just happens to have the rough, irregular, knobbly shape it has. A stone is just a stone. It doesn’t stand out from all the other stones. But now, says Paley, suppose you stumbled over not a stone but a watch.
A watch is complicated. Open up the back and you see lots of cogwheels, springs, delicate little screws. (In Paley’s time, of course, this wouldn’t have been a modern digital wristwatch: it would have been a mechanical time-piece, a pocket watch with a beautifully and expertly crafted movement.) And all those tiny interlocking parts work together to do something useful: in this case, tell the time. Unlike the stone, the watch couldn’t have just ha
ppened by luck. It had to have been deliberately designed and put together by a skilled watchmaker.
Of course, you can easily see where Paley was going with this. Just as the watch must have had a watchmaker, the eye must have had an eye-maker, the heart must have had a heart-maker. And so on. It’s possible you are now even more persuaded by Paley’s point than you were before. Even more reluctant to hear that it’s wrong and that there really is no need for a creator god.
The scrambling argument shows that whatever else the explanation of the beautiful improbability of living things may be, it certainly can’t be random luck. That’s pretty much what improbability means. But now here’s a little twist to the argument. It may be little, but it’s very important: the Darwinian twist. Suppose that, instead of scrambling all the bits of a cheetah at random and making a horrible mess, we change just one little bit of the animal, again in a random direction. The key point is that we change it only a very small amount. Suppose a cheetah is born with claws just a tiny bit longer than in the previous generation. Now we don’t have a horrible mess of scrambled cheetah. We still have a proper living, breathing, running cheetah. It has changed at random, but only very slightly. Now it is quite likely that this tiny change makes the cheetah a little bit worse at surviving. Or perhaps a bit better. Perhaps longer claws give the cheetah a better grip on the ground, and this helps it to run just that little bit faster. Like the spiked running shoes that athletes wear. So it catches a gazelle that would otherwise have narrowly escaped. Or perhaps the claws give the cheetah a better grip on the prey when it’s caught, so it has less chance of wriggling free.
And how did that cheetah get its slightly longer claws? Somewhere in the cheetah genome, there is a gene that affects claw length. A baby cheetah always inherits its genes from its parents. But we’re now talking about a new baby in which one gene, a gene which affects the claws, isn’t quite the same as the parental version. It changed at random. The gene has ‘mutated’. The process of mutation itself is random – it is not specifically guided towards improvement. Most mutant genes, in fact, make things worse. But some – as in our example of the slightly longer claws – happen to make things better. And in that case, the animals (or plants) that possess them are more likely to survive, and pass on their genes, including the mutant ones. That’s what Darwin called natural selection (although he didn’t use the word ‘mutation’).
A random mutation could make the claws blunter instead of sharper. And maybe less good at running or gripping prey. The smaller the change, the closer the probability gets to 50 per cent that it’s an improvement. To see why, imagine that the change is very large. Say the mutant claws are a foot long. That’s bound to make the cheetah less successful. It’ll trip over its monstrous claws and they’ll break when they try to grip anything. The same will be true of a big change in either direction. If the legs suddenly become two yards long or only six inches long, the cheetah will perish swiftly. Now think about a very small change, again in either direction. Imagine a mutation that is so small as to have almost no effect at all on the cheetah’s body. A change like that will have hardly any effect on the animal’s success, either way. A very small change, so small that it is almost – but not quite – zero, will have an approximately 50 per cent chance of being an improvement. The larger the mutation, in any direction, the greater the likelihood that it will damage the animal’s performance. Large mutations are bad. Small mutations approach a 50 per cent chance of being good.
Darwin realized that successful mutations are nearly always small. But the mutations that scientists study are usually large, for the obvious reason that small ones are hard to detect. And because large mutations, in any direction, are almost always bad, this has led some people to doubt evolution because they think all mutations are bad for survival. It may be true that all the mutations big enough to be easily studied in the lab are bad for survival. But it’s the small ones that matter in evolution.
Darwin persuaded his readers of the power of selection by first pointing to domestication. Humans have changed wild horses into dozens of different breeds. Some, like carthorses and medieval chargers, are larger than wild horses. Others, like Shetland ponies and Falabellas, are much smaller. We (that is, our human ancestors) made carthorses, by choosing to breed from the largest individuals in successive generations. We made Falabellas by breeding from the smallest. Generation by generation, we made all the breeds of dogs from wolf ancestors. We made Great Danes and Irish Wolfhounds by breeding from the largest as the generations went by. We made Chihuahuas and Yorkies by breeding consistently from the smallest. Starting with the wild cabbage, which is an ordinary, nondescript wild flower, we made Brussels sprouts, cauliflowers, kale, broccoli, kohlrabi and the mathematically elegant Romanescos (see this page). All were made by humans practising artificial selection. Farmers and gardeners, dog-breeders and pigeon-fanciers have known about the power of selection for centuries.
What Darwin brilliantly realized is that you don’t need the human selector. Nature does the job all by itself, and has been doing it for hundreds of millions of years. Some mutant genes help animals to survive and reproduce. Those genes become more frequent in the population. Other mutant genes make it harder for them to survive and reproduce, and so become less frequent in the population until they disappear altogether. It only takes a few centuries to turn a wolf into a whippet or a Weimaraner. Just think how much change could be achieved in a million centuries. Since our ancestors were fish crawling out of the sea, three million centuries have gone by. That’s an awful lot of time – a huge opportunity for change – step by step down the generations. The key point about mutation, to return to it, is that successful mutations, though random, are small. The mutant animal is not a randomly scrambled mess. Each random change makes it only a little bit different from the previous generation.
Let’s go back to our cheetah to see how nature does the job of a farmer or gardener or dog-fancier. The cub with the mutant gene grows up, and its slightly longer claws help it to run just that little bit faster. So it catches more prey, which means that its cubs are better fed and are more likely to survive and have cubs of their own. Some of these new cubs – grandchildren of the mutant – inherit the mutated gene, so they too grow up with slightly longer claws. They too run extra fast because of it and they too therefore have more cubs – great-grandchildren of the original mutant. And so on. It’s as though a human breeder systematically chose the fastest individuals to breed from. But there is no human breeder. Survival does the job instead. You can see what’s going to happen. As the generations go by, the mutated gene becomes more and more common in the population. Eventually a time comes when almost the entire population of cheetahs has the mutated gene. And they are all running just a little bit faster than their ancestors did.
This now puts extra pressure on the gazelles. Not all gazelles can run equally fast. None can run as fast as a cheetah, but some gazelles can run faster than other gazelles and they are the ones more likely to escape being eaten. This makes them more likely to survive to have babies. And their babies will inherit the genes for running fast. Genes for running slowly are more likely to end up in the bellies of cheetahs, lions or leopards, and consequently less likely to end up in future generations of gazelles. If, again by a random change in an existing gene, a new mutant gene were to arise which helps gazelles to run faster, it would spread through the gazelle population. Just like the cheetah mutation. It could be a change in the hooves. Or a change in the heart. Or some deeply buried change in the chemistry of the blood. The details don’t matter here. If any gene helps gazelles to survive, by any means whatsoever, it’ll get passed on to their children. So, like the cheetah gene, it will eventually spread until it becomes universal in the population. As the generations go by, both cheetahs and gazelles, hunters and hunted, have become just a little bit faster. We say there has been an evolutionary change on both sides.
I like the metaphor of the arms ra
ce. Of course, an individual cheetah and an individual gazelle literally run a race against each other. But that’s not an arms race. That’s just a race, and it ends rather swiftly in victory for either the cheetah (a meal) or the gazelle (escape). Arms races are run more slowly, in evolutionary time rather than individual cheetah/gazelle time. The arms race is between the gazelle species and the cheetah species (also lion species, leopard species, hyena species, Cape hunting dog species). And the result of the arms race is improvement, over the slow evolutionary time-scale. Improvement in equipment for survival: improvement in running speed as the generations go by; improvement in legs, stamina, dodging skill, sense organs to detect predators, or prey; improvement in blood chemistry to get oxygen to muscles fast.
Just like in human life, nothing is free. Improvements have to be paid for. Improved running speed demands longer legs with less heavy bones. And that is paid for in increased likelihood of broken legs. Human artificial selection has bred racehorses to run faster than natural selection ever did. But racehorses’ long, slender legs are consequently more likely to break. Imagine what would have happened to wild horses, if they had been driven by the arms race against sabretooth tigers to run as fast as modern racehorses. The fastest individuals might have been more likely to outrun the sabretooth, with their longer legs and lighter bones. But they’d also have been more likely to break a leg. Then they’d have been easy meat for the sabretooth. So in practice we’d expect the arms race to lead to a compromise: wild horses would run fast, but not quite as fast as a human-bred racehorse. And that’s what actually happened. Not surprisingly, modern racehorses often do break their legs. And tragically have to be shot.
Outgrowing God Page 13
