The Greatest Show on Earth: The Evidence for Evolution

by Richard Dawkins

‘Evolution, the Greatest Show on Earth, the Only Game in Town’.

They may think God had a hand in starting the process off, and perhaps didn’t stay his hand in guiding its future progress. They probably think God cranked the universe up in the first place, and solemnized its birth with a harmonious set of laws and physical constants calculated to fulfil some inscrutable purpose in which we were eventually to play a role. But, grudgingly in some cases, happily in others, thoughtful and rational churchmen and women accept the evidence for evolution.

Influential philosophers tell us we can’t prove anything in science. Mathematicians can prove things – according to one strict view, they are the only people who can – but the best that scientists can do is fail to disprove things while pointing to how hard they tried. Even the undisputed theory that the moon is smaller than the sun cannot, to the satisfaction of a certain kind of philosopher, be proved in the way that, for example, the Pythagorean Theorem can be proved. But massive accretions of evidence support it so strongly that to deny it the status of ‘fact’ seems ridiculous to all but pedants.

‘We may all have come into existence five minutes ago,3 provided with ready-made memories, with holes in our socks and hair that needed cutting.’

WHY DID IT take so long for a Darwin to arrive on the scene? What delayed humanity’s tumbling to that luminously simple idea which seems, on the face of it, so much easier to grasp than the mathematical ideas given us by Newton two centuries earlier – or, indeed, by Archimedes two millennia earlier?

The Platonist regards any change in rabbits as a messy departure from the essential rabbit, and there will always be resistance to change – as if all real rabbits were tethered by an invisible elastic cord to the Essential Rabbit in the Sky. The evolutionary view of life is radically opposite. Descendants can depart indefinitely from the ancestral form, and each departure becomes a potential ancestor to future variants.

Breeders are almost like modellers with endlessly malleable clay, or like sculptors wielding chisels, carving dogs or horses, or cows or cabbages, to their whim.

Mutations are the random changes in genes that constitute the raw material for evolution by non-random selection.

Michelangelo took a single chunk of marble, and then subtracted marble from it to reveal David lurking inside. Nothing was added. Gene pools, on the other hand, are continually added to, for example by mutation, while at the same time non-random death subtracts.

This chapter embarks on a step-by-step seduction of the mind as we pass from the familiar territory of dog breeding and artificial selection to Darwin’s giant discovery of natural selection, via some colourful intermediate stages.

Nectar is sugary syrup, and it is manufactured by plants specifically and only for paying, and fuelling, bees, butterflies, hummingbirds, bats and other hired transport. It is costly to make, funnelling off a proportion of the sunshine energy trapped by the leaves, the solar panels of the plant.

Of course, the relationship between insects and flowers is a two-way street, and we mustn’t neglect to look in both directions. Insects may ‘breed’ flowers to be more beautiful, but not because they enjoy the beauty.fn4 Rather, the flowers benefit from being perceived as attractive by insects. The insects, by choosing the most attractive flowers to visit, inadvertently ‘breed for’ floral beauty.

One way to put it is Darwin’s way: ‘sexual selection’. But another way – and the one that better suits my primrose path – is ‘selective breeding by females of males’. Bright colours may indeed attract predators, but they attract female pheasants too. Generations of hens chose to mate with bright, glowing males, rather than the dull brown creatures that the males would surely have remained but for selective breeding by females.

It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages, and then so imperfect is our view into long past geological ages, that we see only that the forms of life are now different from what they formerly were.

Perfection in one department must be bought, in the form of a sacrifice in another department.

A body is a patchwork of compromises.

What happens under domestication is that animals are artificially shielded from many of the risks that shorten the lives of wild animals. A pedigree dairy cow may yield prodigious quantities of milk, but its pendulously cumbersome udder would seriously impede it in any attempt to outrun a lion.

It is easy for us to overlook the dangers of being too risk-averse.

Even more interesting, however, were the unexpected side-effects of the selective breeding for tameness. These were truly fascinating and genuinely unforeseen. Darwin, the dog-lover, would have been entranced. The tame foxes not only behaved like domestic dogs, they looked like them. They lost their foxy pelage and became piebald black and white, like Welsh collies. Their foxy prick ears were replaced by doggy floppy ears.

The intimate relationship between flowers and their pollinators is a lovely example of what is called co-evolution – evolution together.

Co-evolution often occurs between organisms that have something to gain from each other, partnerships in which each side contributes something to the other, and both gain from the cooperation.

The measured age of our planet is about 4.6 billion years, or about 46 million centuries. The time that has elapsed since the common ancestor of all today’s mammals walked the Earth is about two million centuries. A century seems a pretty long time to us. Can you imagine two million centuries, laid end to end? The time that has elapsed since our fish ancestors crawled out of the water on to the land is about three and a half million centuries:

But all this presupposes that we know the age of the Earth, and of the various landmark points in the fossil record. This is a book about evidence, so I can’t just assert dates but must justify them. How, actually, do we know the age of any particular rock? How do we know the age of a fossil? How do we know the age of the Earth? How, for that matter, do we know the age of the universe? We need clocks, and clocks are the subject of the next chapter.

Chemistry is a dance of electrons. It is all about the interactions of atoms via their electrons.

It enters the food web via photosynthesis, which is the process whereby green plants take in carbon dioxide molecules from the atmosphere and use energy from sunlight to combine the carbon atoms with water to make sugars. All the carbon in ourselves and in all other living creatures comes ultimately, via plants, from carbon dioxide in the atmosphere. And it is continually being recycled back to the atmosphere: when we breathe out, when we excrete, and when we die.

All living creatures, whether plants or animals, have approximately the same ratio of carbon-12 to carbon-14, which is the same ratio as you’ll find in the atmosphere.

Although the vast majority of evolutionary change took place before any human being was born, some examples are so fast that we can see evolution happening with our own eyes during one human lifetime.

This is where the story starts to get quite complicated so, if it is late at night, it might be an idea to resume reading tomorrow …

Lenski’s research shows, in microcosm and in the lab, massively speeded up so that it happened before our very eyes, many of the essential components of evolution by natural selection: random mutation followed by non-random natural selection; adaptation to the same environment by separate routes independently; the way successive mutations build on their predecessors to produce evolutionary change; the way some genes rely, for their effects, on the presence of other genes. Yet it all happened in a tiny fraction of the time evolution normally takes.

Any fool can see that it is not plausible to describe a bacterium as clever. Even if there were clever bacteria, why would stopping prematurely make any difference to the learning prowess of a clever bacterium? But as soon as you start thinking in terms of natural selection, it makes perfect sense.

One of the nice things about science is that it is a public activity. Scientists publish their methods as well as their conclusions, which means that anybody else, anywhere in the world, can repeat their work. If they don’t get the same results, we want to know the reason why. Usually they don’t just repeat previous work but extend it: carry it further.

But madam, you did it yourself. And it only took you nine months.

We may be ‘wonderfully developed’ but we are not ‘wonderfully made’.

Bottom-up design works completely differently. I never believed this, but there used to be a myth that some of the finest medieval cathedrals in Europe had no architect. Nobody designed the cathedral. Each mason and carpenter would busy himself, in his own skilled way, with his own little corner of the building, paying scant attention to what the others were doing and no attention to any overall plan. Somehow, out of such anarchy, a cathedral would emerge. If that really happened, it would be bottom-up architecture.

What you would want is a computer simulation of starling flocks; and, as any programmer will tell you, there’s a right way and a wrong way to do it. Don’t try to choreograph the whole ballet – that would be terribly bad programming style for this kind of task. I need to talk about the better way to do it because something like it is almost certainly how the birds themselves are programmed, in their brains. More to the point, it is a great analogy for how embryology works.

Don’t try to program the behaviour of a whole flock, as an earlier generation of computer programmers might have done. Instead, clone the single computer starling you have programmed. Make a thousand copies of your robo-bird, maybe all the same as each other, or maybe with some slight random variation among them in their rules. And now ‘release’ thousands of model starlings in your computer, so they are free to interact with each other, all obeying the same rules.

The key point is that there is no choreographer and no leader. Order, organization, structure – these all emerge as by-products of rules which are obeyed locally and many times over, not globally. And that is how embryology works. It is all done by local rules, at various levels but especially the level of the single cell. No choreographer. No conductor of the orchestra. No central planning. No architect. In the field of development, or manufacture, the equivalent of this kind of programming is self-assembly.

‘It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.’

One such process is shown in action here

Every species is a cousin of every other. Any two species are descended from an ancestral species, which split in two.

My attention was first thoroughly aroused,6 by comparing together the numerous specimens, shot by myself and several other parties on board, of the mocking-thrushes, when, to my astonishment, I discovered that all those from Charles Island belonged to one species (Mimus trifasciatus); all from Albemarle Island to M. parvulus; and all from James and Chatham Islands (between which two other islands are situated, as connecting links) belonged to M. melanotis.

that the tortoises differed from the different islands,7 and that he himself could with certainty tell from which island any one was brought. I did not for some time pay sufficient attention to this statement, and I had already partially mingled together the collections from two of the islands. I never dreamed that islands, about fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted.

mean the fact that we can talk about ‘the’ mammalian skeleton at all: the fact that such a complicatedly interlocking thing is so gloriously different across the mammals, in all its parts, while simultaneously being so obviously the same thing throughout the mammals.

And ten million is not the most extravagant estimate of the number of surviving species. It’s well worth downloading the Hillis tree from his website4 (see endnotes), and then printing it as a wall hanging, on a piece of paper which, they recommend, should be at least 54 inches wide (even bigger would be an advantage).

The important point is that this whole story of the detour is a splendid example of how very far living creatures are from having been well designed.

When we look at animals from the outside, we are overwhelmingly impressed by the elegant illusion of design. A browsing giraffe, a soaring albatross, a diving swift, a swooping falcon, a leafy sea dragon invisible among the seaweed, a sprinting cheetah at full stretch after a swerving, pronking gazelle – the illusion of design makes so much intuitive sense that it becomes a positive effort to put critical thinking into gear and overcome the seductions of naïve intuition.

When we look inside, the impression is opposite. Admittedly, an impression of elegant design is conveyed by simplified diagrams in textbooks, neatly laid out and colour-coded like an engineer’s blueprint. But the reality that hits you when you see an animal opened up on a dissecting table is very different. I think it would be an instructive exercise to ask an engineer to draw an improved version of, say, the arteries leaving the heart.

And this brings us face to face with the difference between a designed economy and an evolutionary economy. In a designed economy there would be no trees, or certainly no very tall trees: no forests, no canopy. Trees are a waste. Trees are extravagant. Tree trunks are standing monuments to futile competition – futile if we think in terms of a planned economy.

You could say, as the Red Queen said to Alice, that they have to run as fast as they can just to stay in the same place.

This race is particularly keen when an old tree dies and leaves a vacant slot in the canopy. The echoing crash of an old tree falling is the starting gun for a race, in real time (although a slower real time than we animals are accustomed to), between saplings that have been waiting for just such a chance. And the winner is likely to be an individual tree that is well equipped, by genes that prospered through ancestral arms races in evolutionary time, to grow fast and high.