THERE IS GRANDEUR IN THIS VIEW OF LIFE
UNLIKE his evolutionist grandfather Erasmus, whose scientific verse was (somewhat surprisingly, I have to say) admired by Wordsworth and Coleridge,
Charles Darwin was not known as a poet, but he produced a lyrical crescendo in the last paragraph of On the Origin of Species.
Thus, from the war of nature, from famine and death,[i] the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
There’s a lot packed into this famous peroration, and I want to sign off by taking it line by line.
‘From the war of nature, from famine and death’
Clear-headed as ever, Darwin recognized the moral paradox at the heart of his great theory. He didn’t mince words – but he offered the mitigating reflection that nature has no evil intentions. Things simply follow from ‘laws acting all around us’, to quote an earlier sentence from the same paragraph. He had said something similar at the end of Chapter 7 of The Origin:
it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its foster-brothers, – ants making slaves, – the larvae of ichneumonidae feeding within the live bodies of caterpillars, – not as specially endowed or created instincts, but as small consequences of one general law, leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die.
I’ve already mentioned Darwin’s revulsion – widely shared by his contemporaries – in the face of the female ichneumon wasp’s habit of stinging its victim to paralyse but not kill it, thereby keeping the meat fresh for its larva as it eats the live prey from within. Darwin, you’ll remember, couldn’t persuade himself that a beneficent creator would conceive such a habit. But with natural selection in the driving seat, all becomes clear, understandable and sensible. Natural selection cares naught for any comfort. Why should it? For something to happen in nature, the only requirement is that the same happening in ancestral times assisted the survival of the genes promoting it. Gene survival is a sufficient explanation for the cruelty of wasps and the callous indifference of all nature: sufficient – and satisfying to the intellect if not to human compassion.
Yes, there is grandeur in this view of life, and even a kind of grandeur in nature’s serene indifference to the suffering that inexorably follows in the wake of its guiding principle, survival of the fittest. Theologians may here wince at this echo of a familiar ploy in theodicy, in which suffering is seen as an inevitable correlate of free will. Biologists, for their part, will find ‘inexorably’ by no means too strong when they reflect – perhaps along the lines of my ‘red flag’ meditation of the previous chapter – on the biological function of the capacity to suffer. If animals aren’t suffering, somebody isn’t working hard enough at the business of gene survival.
Scientists are human, and they are as entitled as anyone to revile cruelty and abhor suffering. But good scientists like Darwin recognize that truths about the real world, however distasteful, have to be faced. Moreover, if we are going to admit subjective considerations, there is a fascination in the bleak logic that pervades all of life, including wasps homing in on the nerve ganglia down the length of their prey, cuckoos ejecting their foster brothers (‘Thow mortherer of the heysugge on y braunche’), slave-making ants, and the single-minded – or rather zero-minded – indifference to suffering shown by all parasites and predators. Darwin was bending over backwards to console when he concluded his chapter on the struggle for survival with these words:
All that we can do, is to keep steadily in mind that each organic being is striving to increase at a geometrical ratio; that each at some period of its life, during some season of the year, during each generation or at intervals, has to struggle for life, and to suffer great destruction. When we reflect on this struggle, we may console ourselves with the full belief, that the war of nature is not incessant, that no fear is felt,[ii] that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply.
Shooting the messenger is one of humanity’s sillier foibles, and it underlies a good slice of the opposition to evolution that I mentioned in the Introduction. ‘Teach children that they are animals, and they’ll behave like animals.’ Even if it were true that evolution, or the teaching of evolution, encouraged immorality, that would not imply that the theory of evolution was false. It is quite astonishing how many people cannot grasp this simple point of logic. The fallacy is so common it even has a name, the argumentum ad consequentiam – X is true (or false) because of how much I like (or dislike) its consequences.
‘The most exalted object which we are capable of conceiving’
Is ‘the production of the higher animals’ really ‘the most exalted object which we are capable of conceiving’? Most exalted? Really? Are there not more exalted objects? Art? Spirituality? Romeo and Juliet? General Relativity? The Choral Symphony? The Sistine Chapel? Love?
You have to remember that, for all his personal modesty, Darwin nursed high ambitions. On his world-view, everything about the human mind, all our emotions and spiritual pretensions, all arts and mathematics, philosophy and music, all feats of intellect and of spirit, are themselves productions of the same process that delivered the higher animals. It is not just that without evolved brains spirituality and music would be impossible. More pointedly, brains were naturally selected to increase in capacity and power for utilitarian reasons, until those higher faculties of intellect and spirit emerged as a by-product, and blossomed in the cultural environment provided by group living and language. The Darwinian world-view does not denigrate the higher human faculties, does not ‘reduce’ them to a plane of indignity. It doesn’t even claim to explain them at the sort of level that will seem particularly satisfying, in the way that, say, the Darwinian explanation of a snake-mimicking caterpillar is satisfying. It does, however, claim to have wiped out the impenetrable – not even worth trying to penetrate – mystery that must have dogged all pre-Darwinian efforts to understand life. But Darwin doesn’t need any defense from me, and I’ll pass over the question of whether the production of the higher animals is the most exalted object we can conceive, or merely a very exalted object.
What, however, of the predicate? Does the production of the higher animals ‘directly follow’ from the war of nature, from famine and death? Well, yes, it does. It directly follows if you understand Darwin’s reasoning, but nobody understood it until the nineteenth century. And many still don’t understand it, or perhaps are reluctant to do so. It is not hard to see why. When you think about it, our own existence, together with its post-Darwinian explicability, is a candidate for the most astonishing fact that any of us are called upon to contemplate, in our whole life, ever. I’ll come to that shortly.
‘Having been originally breathed’
I have lost count of the irate letters I have received from readers of a previous book, taking me to task for, as the writers think, deliberately omitting the vital phrase, ‘by the Creator’ after ‘breathed’? Am I not wantonly distorting Darwin’s intention? These zealous correspondents forget that Darwin’s great book went through six editions. In the first edition, the sentence is as I have written it here. Presumably bowing to pressure from the religious lobby, Darwin inserted ‘by the Creator’ in the second and all subsequent editions. Unless there is a very good reason to the contrary, when quoting On the Origin of Species I always quote the first edition. This is partly because my own copy of that historic print run of 1,250 is one of my most precious possessions, given me by my benefactor and friend Charles Simonyi. But it is also because the first edition is the most historically important. It is the one that thumped the Victorian solar plexus and drove out the wind of centuries. Moreover, later editions, especially the sixth, pandered to more than public opinion. In an attempt to respond to various learned but misguided critics of the first edition, Darwin backtracked and even reversed his position on a number of important points that he had actually got right in the first place. So, ‘having been originally breathed’ it is, with no mention of any Creator.
It seems that Darwin regretted this sop to religious opinion. In a letter of 1863 to his friend the botanist Joseph Hooker, he said, ‘But I have long regretted that I truckled to public opinion, and used the Pentateuchal term of creation, by which I really meant “appeared” by some wholly unknown process.’ The ‘Pentateuchal term’ Darwin is referring to here is the word ‘creation’. The context, as Francis Darwin explains in his 1887 edition of his father’s letters, was that Darwin was writing to thank Hooker for the loan of a review of a book by Carpenter, in which the anonymous reviewer had spoken of ‘a creative force . . . which Darwin could only express in Pentateuchal terms as the primordial form “into which life was originally breathed”’. Nowadays, we should dispense even with the ‘originally breathed’. What is it that is supposed to have been breathed into what? Presumably the intended reference was to some kind of breath of life,[iii] but what might that mean? The harder we look at the border between life and non-life, the more elusive does the distinction become. Life, the animate, was supposed to have some sort of vibrant, throbbing quality, some vital essence – made to sound yet more mysterious when dropped into French: élan vital.[iv] Life, it seemed, was made of a special living substance, a witch’s brew called ‘protoplasm’. Conan Doyle’s Professor Challenger, a fictional character even more preposterous than Sherlock Holmes, discovered that the Earth was living, a kind of giant sea urchin whose shell was the crust that we see, and whose core consisted of pure protoplasm. Right up to the middle of the twentieth century, life was thought to be qualitatively beyond physics and chemistry. No longer. The difference between life and non-life is a matter not of substance but of information. Living things contain prodigious quantities of information. Most of the information is digitally coded in DNA, and there is also a substantial quantity coded in other ways, as we shall see presently.
In the case of DNA, we understand pretty well how the information content builds up over geological time. Darwin called it natural selection, and we can put it more precisely: the non-random survival of information that encodes embryological recipes for that survival. Self-evidently it is to be expected that recipes for their own survival will tend to survive. What is special about DNA is that it survives not in its material self but in the form of an indefinite series of copies. Because there are occasional errors in the copying, new variants may survive even better than their predecessors, so the database of information encoding recipes for survival will improve as time goes by. Such improvements will be manifest in the form of better bodies and other contrivances and devices for the preservation and propagation of the coded information. On the ground, the preservation and propagation of DNA information will normally mean the survival and reproduction of bodies containing it. It was at the level of bodies, their survival and reproduction, that Darwin himself worked. The coded information within them was implicit in his world-view, but not made explicit until the twentieth century.
The genetic database will become a storehouse of information about the environments of the past, environments in which ancestors survived and passed on the genes that helped them to do so. To the extent that present and future environments resemble those of the past (and mostly they do), this ‘genetic book of the dead’ will turn out to be a useful manual for survival in the present and future. The repository of that information will, at any one moment, reside in individual bodies, but in the longer term, where reproduction is sexual and DNA is shuffled from body to body, the database of survival instructions will be the gene pool of a species.
Each individual’s genome, in any one generation, will be a sample from the species database. Different species will have different databases because of their different ancestral worlds. The database in the gene pool of camels will encode information about deserts and how to survive in them. The DNA in mole gene pools will contain instructions and hints for survival in dark, moist soil. The DNA in predator gene pools will increasingly contain information about prey animals, their evasive tricks and how to outsmart them. The DNA in prey gene pools will come to contain information about predators and how to dodge and outrun them. The DNA in all gene pools contains information about parasites and how to resist their pernicious invasions.
Information on how to handle the present so as to survive into the future is necessarily gleaned from the past. Non-random survival of DNA in ancestral bodies is the obvious way in which information from the past is recorded for future use, and this is the route by which the primary database of DNA is built up. But there are three further ways in which information about the past is archived in such a way that it can be used to improve future chances of survival. These are the immune system, the nervous system, and culture. Along with wings, lungs and all the other apparatus for survival, each of the three secondary information-gathering systems was ultimately prefigured by the primary one: natural selection of DNA. We could together call them the four ‘memories’.
The first memory is the DNA repository of ancestral survival techniques, written on the moving scroll that is the gene pool of the species. Just as the inherited database of DNA records the recurrent details of ancestral environments and how to survive them, the immune system, the ‘second memory’, does the same thing for diseases and other insults to the body during the individual’s own lifetime. This database of past diseases and how to survive them is unique to each individual and is written in the repertoire of proteins that we call antibodies – one population of antibodies for ‘experience’ with the proteins that characterize the pathogen. Like many children of my generation, I had measles and chickenpox. My body ‘remembers’ the ‘experience’, the memories being embodied in antibody proteins, along with the rest of my personal database of previously vanquished invaders. I have fortunately never had polio, but medical science has cleverly devised the technique of vaccination for planting false memories of diseases never suffered. I shall never contract polio, because my body ‘thinks’ it has done so in the past, and my immune system database is equipped with the appropriate antibodies, ‘fooled’ into making them by the injection of a harmless version of the virus. Fascinatingly, as the work of various Nobel Prizewinning medical scientists has shown, the immune system’s database is itself built up by a quasi-Darwinian process of random variation and non-random selection. But in this case the non-random selection is selection not of bodies for their capacity to survive, but of proteins within the body for their capacity to envelop or otherwise neutralize invading proteins.
The third memory is the one we ordinarily think of when we use the word: the memory that resides in the nervous system. By mechanisms that we don’t yet fully understand, our brains retain a store of past experiences to parallel the antibody ‘memory’ of past diseases and the DNA ‘memory’ (for so we can regard it) of ancestral deaths and successes. At its simplest, the third memory works by a trial-and-error process that can be seen as yet another analogy to natural selection.
When searching for food, an animal may ‘try’ various actions. Though not strictly random, this trial stage is a reasonable analogy to genetic mutation. The analogy to natural selection is ‘reinforcement’, the system of rewards (positive reinforcement) and punishments (negative reinforcement). An action such as turning over dead leaves (trial) turns out to yield beetle larvae and woodlice hiding under the leaves (reward). The nervous system has a rule that says, ‘Any trial action that is followed by reward should be repeated. Any trial action that is followed by nothing, or, worse, followed by punishment, for example pain, should not be repeated.
But the brain’s memory goes much further than this quasi-Darwinian process of non-random survival of rewarded actions, and elimination of punished actions, in the animal’s repertoire. The brain’s memory (no need for inverted commas here, because it is the primary meaning of the word) is, at least in the case of human brains, both vast and vivid. It contains detailed scenes, represented in an internal simulacrum of all five senses. It contains lists of faces, places, tunes, social customs, rules, words. You know it well from the inside, so there is no need for me to spend my words evoking it, except to note the remarkable fact that the lexicon of words at my disposal for writing, and the identical, or at least heavily overlapping, dictionary at your disposal for reading, all reside in the same vast neuronal database, along with the syntactic apparatus for arranging them into sentences and deciphering them.
Furthermore, the third memory, the one in the brain, has spawned a fourth. The database in my brain contains more than just a record of the happenings and sensations of my personal life – although that was the limit when brains originally evolved. Your brain includes collective memories inherited non-genetically from past generations, handed down by word of mouth, or in books or, nowadays, on the internet. The world in which you and I live is richer by far because of those who went before us and inscribed their impacts on the database of human culture: Newton and Marconi, Shakespeare and Steinbeck, Bach and the Beatles, Stephenson and the Wright brothers, Jenner and Salk, Curie and Einstein, von Neumann and Berners-Lee. And, of course, Darwin.
All four memories are part of, or manifestations of, the vast superstructure of apparatus for survival which was originally, and primarily, built up by the Darwinian process of non-random DNA survival.
‘Into a few forms or into one’
Darwin was right to hedge his bets, but today we are pretty certain that all living creatures on this planet are descended from a single ancestor. The evidence, as we saw in Chapter 10, is that the genetic code is universal, all but identical across animals, plants, fungi, bacteria, archaea and viruses. The 64-word dictionary, by which three letter DNA words are translated into twenty amino acids and one punctuation mark, which means ‘start reading here’ or ‘stop reading here’, is the same 64-word dictionary wherever you look in the living kingdoms (with one or two exceptions too minor to undermine the generalization). If, say, some weird, anomalous microbes called the harumscaryotes were discovered, which didn’t use DNA at all, or didn’t use proteins, or used proteins but strung them together from a different set of amino acids from the familiar twenty, or which used DNA but not a triplet code, or a triplet code but not the same 64-word dictionary – if any of these conditions were met, we might suggest that life had originated twice: once for the harumscaryotes and once for the rest of life. For all Darwin knew – indeed, for all anyone knew before the discovery of DNA – some existing creatures might have had the properties I have here attributed to the harumscaryotes, in which case his ‘into a few forms’ would have been justified.
Is it possible that two independent origins of life could both have hit upon the same 64-word code? Very unlikely. For that to be plausible, the existing code would have to have strong advantages over alternative codes, and there would have to be a gradual ramp of improvement towards it, a ramp for natural selection to climb up. Both these conditions are improbable. Francis Crick early suggested that the genetic code is a ‘frozen accident’, which, once in place, was difficult or impossible to change. The reasoning is interesting. Any mutation in the genetic code itself (as opposed to mutations in the genes that it encodes) would have an instantly catastrophic effect, not just in one place but throughout the whole organism. If any word in the 64-word dictionary changed its meaning, so that it came to specify a different amino acid, just about every protein in the body would instantaneously change, probably in many places along its length. Unlike an ordinary mutation, which might, say, slightly lengthen a leg, shorten a wing or darken an eye, a change in the genetic code would change everything at once, all over the body, and this would spell disaster. Various theorists have come up with ingenious suggestions for special ways in which the genetic code might evolve: ways in which, to quote one of their papers, the frozen accident might be ‘thawed’. Interesting as these are, I think it is all but certain that every living creature whose genetic code has been looked at is descended from one common ancestor. No matter how elaborate and different the high-level programs that underlie the various life forms, all are, at bottom, written in the same machine language.
Of course we cannot rule out the possibility that other machine languages may have arisen in yet other creatures that are now extinct – the equivalent of my harumscaryotes. And the physicist Paul Davies has made the reasonable point that we haven’t actually looked very hard to see if there are any harumscaryotes (he doesn’t use the word, of course) that are not extinct but still lurking in some extreme redoubt of our planet. He admits that it is not very likely, but argues – somewhat along the lines of the man who searches for his keys under a street lamp rather than where he lost them – that it is a lot easier and cheaper to look thoroughly on our planet than to travel to other planets and look there. Meanwhile, I don’t mind recording my private expectation that Professor Davies won’t find anything, and that all surviving life forms on this planet use the same machine code and are all descended from a single ancestor.
‘Whilst this planet has gone cycling on according to the fixed law of gravity’
Humans were aware of the cycles that govern our lives long before we understood them. The most obvious cycle is the day/night cycle. Objects floating in space, or orbiting other objects under the law of gravity, have a natural tendency to spin on their own axis. There are exceptions, but our planet is not one of them. Its period of rotation is now twenty-four hours (it used to spin faster) and we experience it, of course, as night follows day.
Because we live on a relatively massive body, we think of gravity primarily as a force that pulls everything towards the centre of that body, which we experience as ‘down’. But gravity, as Newton was the first to understand, has a ubiquitous effect, which is to keep bodies throughout the universe in semi-permanent orbit around other bodies. We experience this as the yearly cycle of seasons, as our planet orbits the sun.[v] Because the axis on which our planet spins is tilted relative to the axis of rotation around the sun, we experience longer days and shorter nights during the half of the year when the hemisphere on which we happen to live is tilted sunwards, the period that climaxes in summer. And we experience shorter days and longer nights during the other half of the year, the period that, at its extreme, we call winter. During our hemisphere’s winter, the sun’s rays, when they strike us at all, do so at a shallower angle. The glancing angle spreads a winter sunbeam more thinly over a wider area than the same beam would cover in summer. On the receiving end of fewer photons per square inch, it feels colder. Fewer photons per green leaf means less photosynthesis. Shorter days and longer nights have the same effect. Winter and summer, day and night, our lives are governed by cycles, just as Darwin said – and Genesis before him: ‘While the earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.’
Gravity mediates other cycles that also matter to life, although they are less obvious. Unlike other planets that have many satellites, often relatively small, Earth happens to have a single large satellite, which we call the moon. It is large enough to exert a significant gravitational effect in its own right. We experience this principally in the cycle of tides: not just the relatively fast cycle as tides come in and out daily, but the slower monthly cycle of spring tides and neap tides, which is caused by interactions between the sun’s gravitational effect and that of the monthly orbiting moon. These tidal cycles are especially important for marine and coastal organisms, and people have rather implausibly wondered whether some kind of species memory of our marine ancestry survives in our monthly reproductive cycles. That may be far-fetched, but it is a matter for intriguing speculation how different life would be if we had no orbiting moon. It has even been suggested, again implausibly in my opinion, that life without the moon would be impossible.
What if our planet didn’t spin on its axis? If it kept one face permanently towards the sun, as the moon does towards us, the half with permanent day would be a roasting hell, while the half with permanent night would be insufferably cold. Could life survive in the twilight hinterland between, or perhaps buried deep in the ground? I doubt if it would have originated in such unfriendly conditions, but if Earth gradually spun down to a halt there would be plenty of time to accommodate, and it is not implausible that at least some bacteria would succeed.
What if Earth spun, but on an axis that was not tilted? I doubt if that would rule life out. There would be no summer/winter cycle. Summer and winter conditions would be a function of latitude and altitude but not time. Winter would be the permanent season experienced by creatures living close to either of the two poles, or up high mountains. I don’t see why that should rule life out, but life without seasons would be less interesting. There would be no incentive to migrate, or to breed at any particular time of the year rather than any other, or to shed leaves or to moult or hibernate.
If the planet were not in orbit around a star at all, life would be completely impossible. The only alternative to orbiting a star is hurtling through the void – dark, close to absolute zero temperature, alone and far from the source of energy that enables life to trickle upstream, temporarily and locally, against the thermodynamic torrent. Darwin’s phrase ‘cycling on according to the fixed law of gravity’ is more than just a poetic device to express the relentless and unimaginably extended passage of time.
Being in orbit around a star is the only way a body can remain a relatively fixed distance away from a source of energy. In the vicinity of any star – and our sun is typical – there is a finite zone bathed in heat and light, where the evolution of life is possible. As you move away from a star into space, this habitable zone dwindles rapidly, following the famous inverse square law. That is, light and heat diminish not in direct proportion to the distance from the star, but in proportion to the square of the distance. It is easy to see why this must be so. Imagine concentric spheres of increasing radius centred on a star. The energy radiating outwards from the star falls on the inside of a sphere and is ‘shared’ evenly by every square inch of the internal area of the sphere. The surface area of a sphere is proportional to the square of the radius (ESK).[vi] So if sphere A is twice as far from the star as sphere B, the same number of photons has to be ‘shared’ over an area four times as great. This is why Mercury and Venus, the innermost planets of our solar system, are scorching hot, while the outer ones, such as Neptune and Uranus, are cold and dark, although still not as cold and dark as deep space.
The Second Law of Thermodynamics states that, although energy can be neither created nor destroyed, it can – must, in a closed system – become more impotent to do useful work: that is what it means to say that ‘entropy’ increases. ‘Work’ includes things like pumping water uphill or – the chemical equivalent – extracting carbon from atmospheric carbon dioxide and using it in plant tissues. As already spelled out in Chapter 12, both those feats can be achieved only if energy is fed into the system, for example electrical energy to drive the water pump, or solar energy to drive the synthesis of sugar and starch in a green plant. Once the water has been pumped to the top of the hill, it will then tend to flow downhill, and some of the energy of its downward flow can be used to drive a water wheel, which can generate electricity, which can drive an electric motor to pump some of the water uphill again: but only some! Some of the energy is always lost – though never destroyed. Perpetual motion machines (you can’t say it too dogmatically) are impossible.
In life’s chemistry, the carbon extracted from the air by sun-driven ‘uphill’ chemical reactions in plants can be burned to release some of the energy. We can literally burn it in the form of coal, which you can think of as stored solar energy, for it was put there by the solar panels of long-dead plants in the Carboniferous age and other past times. Or the energy may be released in a more controlled way than actual combustion. Inside living cells, either of plants or of animals that eat plants, or of animals that eat animals that eat plants (etc.), sun-made carbon compounds are ‘slow-burned’. Instead of literally bursting into flames, they give up their energy in a serviceable trickle, where it works in a controlled manner to drive ‘uphill’ chemical reactions. Inevitably, some of this energy is wasted as heat – if it were not, we’d have a perpetual motion machine, which is (you can’t say it too often) impossible.
Almost all the energy in the universe is steadily being degraded from forms that are capable of doing work to forms that are incapable of doing work. There is a levelling off, a mixing up, until eventually the entire universe will settle into a uniform, (literally) uneventful ‘heat death’. But while the universe as a whole is hurtling downhill towards its inevitable heat death, there is scope for small quantities of energy to drive little local systems in the opposite direction. Water from the sea is lifted into the air as clouds, which later deposit their water on mountaintops, from which it runs downhill in streams and rivers, which can drive water wheels or electric power stations. The energy to lift the water (and hence to drive the turbines in the power stations) comes from the sun. This is not a violation of the Second Law, for energy is constantly being fed in from the sun. The sun’s energy is doing something similar in green leaves, driving chemical reactions locally ‘uphill’ to make sugar and starch and cellulose and plant tissues. Eventually the plants die, or they may be eaten by animals first. The trapped solar energy has the opportunity to trickle down through numerous cascades, and through a long and complex food chain culminating in bacterial or fungal decay of the plants, or of the animals that prolong the food chain. Or some of it may be sequestered underground, fi rst as peat and then as coal. But the universal trend towards ultimate heat death is never reversed. In every link of the food chain, and through every trickle-down cascade within every cell, some of the energy is degraded to uselessness. Perpetual motion machines are . . . all right, that’s enough repetition, but I won’t apologize for quoting, as I have done in at least one previous book, the marvellous saying of Sir Arthur Eddington on the subject:
If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations – then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation – well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. When creationists say, as they frequently do, that the theory of evolution contradicts the Second Law of Thermodynamics, they are telling us no more than that they don’t understand the Second Law (we already knew that they don’t understand evolution). There is no contradiction, because of the sun!
The whole system, whether we are talking about life, or about water rising into the clouds and falling again, is fi nally dependent on the steady flow of energy from the sun. While never actually disobeying the laws of physics and chemistry – and certainly never disobeying the Second Law – energy from the sun powers life, to coax and stretch the laws of physics and chemistry to evolve prodigious feats of complexity, diversity, beauty, and an uncanny illusion of statistical improbability and deliberate design. So compelling is that illusion that it fooled our greatest minds for centuries, until Charles Darwin burst on to the scene. Natural selection is an improbability pump: a process that generates the statistically improbable. It systematically seizes the minority of random changes that have what it takes to survive, and accumulates them, step by tiny step over unimaginable timescales, until evolution eventually climbs mountains of improbability and diversity, peaks whose height and range seem to know no limit, the metaphorical mountain that I have called ‘Mount Improbable’. The improbability pump of natural selection, driving living complexity up ‘Mount Improbable’, is a kind of statistical equivalent of the sun’s energy raising water to the top of a conventional mountain.[vii] Life evolves greater complexity only because natural selection drives it locally away from the statistically probable towards the improbable. And this is possible only because of the ceaseless supply of energy from the sun.
‘From so simple a beginning’
We know a great deal about how evolution has worked ever since it got started, much more than Darwin knew. But we know little more than Darwin did about how it got started in the first place. This is a book about evidence, and we have no evidence bearing upon the momentous event that was the start of evolution on this planet. It could have been an event of supreme rarity. It only had to happen once, and as far as we know it did happen only once. It is even possible that it happened only once in the entire universe, although I doubt that. One thing we can say, on a basis of pure logic rather than evidence, is that Darwin was sensible to say ‘from so simple a beginning’. The opposite of simple is statistically improbable. Statistically improbable things don’t spontaneously spring into existence: that is what statistically improbable means. The beginning had to be simple, and evolution by natural selection is still the only process we know whereby simple beginnings can give rise to complex results.
Darwin didn’t discuss how evolution began in On the Origin of Species. He thought the problem was beyond the science of his day. In the letter to Hooker that I quoted earlier, Darwin went on to say, ‘It is mere rubbish, thinking at present of the origin of life; one might as well think of the origin of matter.’ He didn’t rule out the possibility that the problem would eventually be solved (indeed, the problem of the origin of matter largely has been solved) but only in the distant future: ‘It will be some time before we see “slime, protoplasm, etc” generating a new animal.’ At this point in his edition of his father’s letters, Francis Darwin inserted a footnote telling us,
On the same subject my father wrote in 1871: ‘It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc, present, that a proteine compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.’
Charles Darwin was here doing two rather distinct things. On the one hand he was presenting his only speculation on how life might have originated (the famous ‘warm little pond’ passage). On the other hand, he was disabusing present-day science of the hope of ever seeing the event replicated before our eyes. Even if ‘the conditions for the first production of a living organism’ are still present, any such new production would be ‘instantly devoured or absorbed’ (presumably by bacteria, we would today have good reason to add), ‘which would not have been the case before living creatures were formed’.
Darwin wrote this seven years after Louis Pasteur had said, in a lecture at the Sorbonne, ‘Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment.’ The simple experiment was the one in which Pasteur showed, contrary to popular expectation at the time, that broth sealed off from access by micro organisms would not spoil.
Demonstrations such as Pasteur’s are sometimes cited by creationists as evidence in their favour. The false syllogism runs as follows: ‘Spontaneous generation is never nowadays observed. Therefore the origin of life is impossible.’ Darwin’s 1871 remark was precisely designed as a riposte to that kind of illogicality. Evidently, the spontaneous generation of life is a very rare event, but it must have happened once, and this is true whether you think the original spontaneous generation was a natural or a supernatural event. The question of just how rare an event the origin of life was is an interesting one to which I shall return.
The first serious attempts to think about how life might have originated, those of Oparin in Russia and (independently) Haldane in England, both began by denying that the conditions for the first production of life are still with us. Oparin and Haldane suggested that the early atmosphere would have been very different from the present one. In particular, there would have been no free oxygen, and the atmosphere was thus – as chemists mysteriously call it – a ‘reducing’ atmosphere. We now know that all the free oxygen in the atmosphere is the product of life, specifically plants – obviously, not a part of the antecedent conditions in which life arose. Oxygen flooded into the atmosphere as a pollutant, even a poison, until natural selection shaped living things to thrive on the stuff and, indeed, suffocate without it. The ‘reducing’ atmosphere inspired the most famous experimental attack on the problem of the origin of life, Stanley Miller’s flask full of simple ingredients, which bubbled and sparked for only a week before yielding amino acids and other harbingers of life.
Darwin’s ‘warm little pond’, together with the witch’s brew concocted by Miller that it inspired, are nowadays often rejected as a preamble to advancing some favoured alternative. The truth is that there is no overwhelming consensus. Several promising ideas have been suggested, but there is no decisive evidence pointing unmistakably to any one. In previous books I have attended to various interesting possibilities, including the inorganic clay crystals theory of Graham Cairns-Smith, and the more recently fashionable view that the conditions under which life first arose were akin to the Hadean habitat of today’s ‘thermophilous’ bacteria and archaea, some of which thrive and reproduce in hot springs that are literally boiling. Today, a majority of biologists are moving towards the ‘RNA World theory’, and for a reason that I find quite persuasive.
We have no evidence about what the first step in making life was, but we do know the kind of step it must have been. It must have been whatever it took to get natural selection started. Before that first step, the sorts of improvement that only natural selection can achieve were impossible. And that means the key step was the arising, by some process as yet unknown, of a self-replicating entity. Self-replication spawns a population of entities, which compete with each other to be replicated. Since no copying process is perfect, the population will inevitably come to contain variety, and if variants exist in a population of replicators those that have what it takes to succeed will come to predominate. This is natural selection, and it could not start until the first self-replicating entity came into existence.
Darwin, in his ‘warm little pond’ paragraph, speculated that the key event in the origin of life might have been the spontaneous arising of a protein, but this turns out to be less promising than most of Darwin’s ideas. This isn’t to deny that proteins are vitally important for life. We saw in Chapter 8 that they have the very special property of coiling themselves up to form three-dimensional objects, whose exact shape is specified by the one-dimensional sequence of their constituents, the amino acids. We also saw that the same exact shape confers on them the ability to catalyse chemical reactions with great specificity, speeding particular reactions up perhaps a trillionfold. The specificity of enzymes makes biological chemistry possible, and proteins seem almost indefinitely flexible in the range of shapes that they can assume. That, then, is what proteins are good at. They are very, very good at it indeed, and Darwin was quite right to mention them. But there is something that proteins are outstandingly bad at, and this Darwin overlooked. They are completely hopeless at replication. They can’t make copies of themselves. This means that the key step in the origin of life cannot have been the spontaneous arising of a protein. What, then, was it?
The best-replicating molecule that we know is DNA. In the advanced forms of life with which we are familiar, DNA and proteins are elegantly complementary. Protein molecules are brilliant enzymes but lousy replicators. DNA is exactly the reverse. It doesn’t coil up into three-dimensional shapes, and therefore doesn’t work as an enzyme. Instead of coiling up it retains its open, linear form, and this is what makes it ideal both as a replicator and as a specifier of amino-acid sequences. Protein molecules, precisely because they coil up into ‘closed’ shapes, do not ‘expose’ their sequence information in a way that might be copied or ‘read’. The sequence information is buried inaccessibly inside the coiled-up protein. But in the long chain of DNA the sequence information is exposed and available to act as a template.
The ‘Catch-22’ of the origin of life is this. DNA can replicate, but it needs enzymes in order to catalyse the process. Proteins can catalyse DNA formation, but they need DNA to specify the correct sequence of amino acids. How could the molecules of the early Earth break out of this bind and allow natural selection to get started? Enter RNA.
RNA belongs to the same family of chain molecules as DNA, the polynucleotides. It is capable of carrying what amount to the same four code ‘letters’ as DNA, and it indeed does so in living cells, carrying genetic information from DNA to where it can be used. DNA acts as the template for RNA code sequences to build up. And then protein sequences build up using RNA, not DNA, as their template. Some viruses have no DNA at all. RNA is their genetic molecule, solely responsible for carrying genetic information from generation to generation.
Now for the key point of the ‘RNA World theory’ of the origin of life. In addition to stretching out in a form suitable for passing on sequence information, RNA is also capable of self assembling, like our magnetic necklace of Chapter 8, into three-dimensional shapes, which have enzymatic activity. RNA enzymes do exist. They are not as efficient as protein enzymes, but they do work. The RNA World theory suggests that RNA was a good enough enzyme to hold the fort until proteins evolved to take over the enzyme role, and that RNA was also a good enough replicator to muddle along in that role until DNA evolved.
I find the RNA World theory plausible, and I think it quite likely that chemists will, within the next few decades, simulate in the laboratory a full reconstruction of the events that launched natural selection on its momentous way four billion years ago. Fascinating steps in the right direction have already been taken.
Before leaving the subject, however, I must repeat the warning I have given in earlier books. We don’t actually need a plausible theory of the origin of life, and we might even be a little bit anxious if a too plausible theory were to be discovered! This glaring paradox arises from the famous ‘Where is everybody?’ question, which was posed by the physicist Enrico Fermi. Enigmatic as his question sounds, Fermi’s companions, fellow physicists at the Los Alamos Laboratory, were attuned enough to know exactly what he meant. Why haven’t we been visited by living creatures from elsewhere in the universe? If not visited in person, at least visited by radio signals (which is vastly more probable).
It is now possible to estimate that there are upwards of a billion planets in our galaxy, and about a billion galaxies. This means that, although it is possible that ours is the only planet in the galaxy that has life, in order for that to be true, the probability of life arising on a planet would have to be not much greater than one in a billion. The theory that we seek, of the origin of life on this planet, should therefore positively not be a plausible theory! If it were, life should be common in the galaxy. Maybe it is common, in which case a plausible theory is what we want. But we have no evidence that life exists outside this planet, and at very least we are entitled to be satisfied with an implausible theory. If we take the Fermi question seriously, and interpret the lack of visitations as evidence that life is exceedingly rare in the galaxy, we should move towards positively expecting that no plausible theory of the origin of life exists. I have developed the argument more fully in The Blind Watchmaker, and shall leave it there. My guess, for what it is worth (not much, because there are too many unknowns), is that life is very rare, but that the number of planets is so large (more are being discovered all the time) that we are probably not alone, and there may be millions of islands of life in the universe. Nevertheless, even millions of islands could still be so far apart that they have almost no chance of ever encountering one another, even by radio. Sadly, as far as practicalities are concerned, we might as well be alone.
‘Endless forms most beautiful and most wonderful have been, and are being, evolved’
I’m not sure what Darwin meant by ‘endless’. It could have been just a superlative, deployed to soup up ‘most beautiful’ and ‘most wonderful’. I expect that was part of it. But I like to think that Darwin meant something more particular by ‘endless’. As we look back on the history of life, we see a picture of never-ending, ever rejuvenating novelty. Individuals die; species, families, orders and even classes go extinct. But the evolutionary process itself seems to pick itself up and resume its recurrent flowering, with undiminished freshness, with unabated youthfulness, as epoch gives way to epoch.
Let me briefly return to the computer models of artificial selection that I described in Chapter 2: the ‘safari park’ of computer biomorphs, including arthromorphs and the conchomorphs that showed how the great variety of mollusc shells might have evolved. In that chapter, I introduced these computer creatures as an illustration of how artificial selection works and how powerful it is, given enough generations. Now I want to use these computer models for a different purpose.
My overwhelming impression, while staring into the computer screen and breeding biomorphs, whether coloured or black, and when breeding arthromorphs, was that it never became boring. There was a sense of endlessly renewed strangeness. The program never seemed to get ‘tired’, and nor did the player. This was in contrast to the ‘D’Arcy’ program that I briefl y described in Chapter 10, the one in which the ‘genes’ tugged mathematically at the coordinates of a virtual rubber sheet on which an animal had been drawn. When doing artificial selection with the D’Arcy program, the player seems, as time goes by, to move further and further away from a reference point where things made sense, out into a no-man’s-land of mis-shapen inelegance, where sense seems to decrease the further we travel from the starting point. I have already hinted at the reason for this. In the biomorph, arthromorph and conchomorph programs, we have the computer equivalent of an embryological process – three different embryological processes, all in their different ways biologically plausible. The D’Arcy program, by contrast, doesn’t simulate embryology at all. Instead, as I explained in Chapter 10, it manipulates the distortions by which one adult form may be transformed into another adult form. This lack of an embryology deprives it of the ‘inventive fertility’ that the biomorphs, arthromorphs and conchomorphs display. And the same inventive fertility is displayed by real-life embryologies, which is a minimal reason why evolution generates ‘endless forms most beautiful and most wonderful’. But can we go beyond the minimal?
In 1989 I wrote a paper called ‘The evolution of evolvability’ in which I suggested that not only do animals get better at surviving, as the generations go by: lineages of animals get better at evolving. What does it mean to be ‘good at evolving’? What kinds of animals are good at evolving? Insects on land and crustaceans in the sea seem to be champions at diversifying into thousands of species, parceling up the niches, changing costumes through evolutionary time with frolicsome abandon. Fish, too, show amazing evolutionary fecundity, so do frogs, as well as the more familiar mammals and birds.
What I suggested in my 1989 paper is that evolvability is a property of embryologies. Genes mutate to change an animal’s body, but they have to work through processes of embryonic growth. And some embryologies are better than others at throwing up fruitful ranges of genetic variation for natural selection to work upon, and might therefore be better at evolving. ‘Might’ seems too weak. Isn’t it almost obvious that some embryologies must be better than others at evolving, in this sense? I think so. It is less obvious, but nevertheless I think a case can be made, that there might be a kind of higher-level natural selection in favour of ‘evolvable embryologies’. As time goes by, embryologies improve their evolvability. If there is a ‘higher-level selection’ of this kind, it would be rather different from ordinary natural selection, which chooses individuals for their capacity to pass on genes successfully (or, equivalently, chooses genes for their capacity to build successful individuals). The higher-level selection that improves evolvability would be of the kind that the great American evolutionary biologist George C. Williams called ‘clade selection’. A clade is a branch of the tree of life, like a species, a genus, an order or a class. We could say that clade selection has occurred when a clade, such as the insects, spreads, diversifies and populates the world more successfully than another clade such as the pogonophora (no, you probably haven’t heard of these obscure, worm-like creatures, and there’s a reason: they are an unsuccessful clade!). Clade selection doesn’t imply that clades have to compete with each other. The insects don’t compete, at least not directly, with the pogonophora for food or space or any other resource. But the world is full of insects, and almost devoid of pogonophora, and we are rightly tempted to attribute the success of the insects to some feature that they possess. I am conjecturing that it is something about their embryology that makes them evolvable. In the chapter of Climbing Mount Improbable entitled ‘Kaleidoscopic Embryos’ I offered various suggestions for specific features that make for evolvability, including constraints of symmetry, and including modular architectures such as a segmented body plan.
Perhaps partly because of its segmentally modular architecture, the arthropod clade[viii] is good at evolving, at throwing up variation in multiple directions, at diversifying, at opportunistically filling niches as they become available. Other clades may be similarly successful because their embryologies are constrained to mirror-image development in various planes.[ix] The clades that we see peopling the lands and the seas are the clades that are good at evolving. In clade selection, unsuccessful clades go extinct, or fail to diversify to meet varying challenges: they wither and perish. Successful clades blossom and flourish as leaves on the phylogenetic tree. Clade selection sounds seductively like Darwinian natural selection. The seduction should be resisted, or should at least ring alarm bells. Superficial resemblances can be actively misleading.
The fact of our own existence is almost too surprising to bear. So is the fact that we are surrounded by a rich ecosystem of animals that more or less closely resemble us, by plants that resemble us a little less and on which we ultimately depend for our nourishment, and by bacteria that resemble our remoter ancestors and to which we shall all return in decay when our time is past. Darwin was way ahead of his time in understanding the magnitude of the problem of our existence, as well as in tumbling to its solution. He was ahead of his time, too, in appreciating the mutual dependencies of animals and plants and all other creatures, in relationships whose intricacy staggers the imagination. How is it that we find ourselves not merely existing but surrounded by such complexity, such elegance, such endless forms most beautiful and most wonderful?
The answer is this. It could not have been otherwise, given that we are capable of noticing our existence at all, and of asking questions about it. It is no accident, as cosmologists point out to us, that we see stars in our sky. There may be universes without stars in them, universes whose physical laws and constants leave the primordial hydrogen evenly spread and not concentrated into stars. But nobody is observing those universes, because entities capable of observing anything cannot evolve without stars. Not only does life need at least one star to provide energy. Stars are also the furnaces in which the majority of the chemical elements are forged, and you can’t have life without a rich chemistry. We could go through the laws of physics, one by one, and say the same thing of all of them: it is no accident that we see . . .
The same is true of biology. It is no accident that we see green almost wherever we look. It is no accident that we find ourselves perched on one tiny twig in the midst of a blossoming and flourishing tree of life; no accident that we are surrounded by millions of other species, eating, growing, rotting, swimming, walking, flying, burrowing, stalking, chasing, fleeing, outpacing, outwitting. Without green plants to outnumber us at least ten to one there would be no energy to power us. Without the ever-escalating arms races between predators and prey, parasites and hosts, without Darwin’s ‘war of nature’, without his ‘famine and death’ there would be no nervous systems capable of seeing anything at all, let alone of appreciating and understanding it. We are surrounded by endless forms, most beautiful and most wonderful, and it is no accident, but the direct consequence of evolution by non-random natural selection – the only game in town, the greatest show on Earth.
[i] Darwin told us that he derived his original inspiration for natural selection from Thomas Malthus, and perhaps this particular phrase of Darwin was prompted by the following apocalyptic paragraph, called to my attention by my friend Matt Ridley: ‘Famine seems to be the last, the most dreadful resource of nature. The power of population is so superior to the power in the earth to produce subsistence for man, that premature death must in some shape or other visit the human race. The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction, and often finish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague, advance in terrific array, and sweep off their thousands and ten-thousands. Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow, levels the population with the food of the world.’
[ii] I wish I could believe that.
[iii] Religious traditions have long identified life with breath. ‘Spirit’ comes from the Latin for ‘breath’. Genesis has God first making Adam and then firing him up by breathing into his nostrils. The Hebrew word for ‘soul’ is ruah or ruach (cognate ruh in Arabic), which also means ‘breath’, ‘wind’, ‘inspiration’.
[iv] The term was coined in 1907 by the French philosopher Henri Bergson. I’ve always treasured Julian Huxley’s sarcastic deduction that railway trains must be propelled by élan locomotif.
[v] It is with horrified fascination that I return, as if scratching an itch or pressing a toothache, to the poll, documented in the Appendix, suggesting that 19% of British people don’t know what a year is, and think the Earth orbits the sun once per month. Even of those who understand what a year is, a larger percentage has no understanding of what causes seasons, presuming, with rampant Northern Hemisphere chauvinism, that we are closest to the sun in June and furthest away in December.
[vi] ‘Every Schoolboy Knows’ (and every schoolgirl can prove it by Euclidean geometry).
[vii] It is no accident that Claude Shannon, when developing his metric of ‘information’, which is itself a measure of statistical improbability, lit upon exactly the same mathematical formula that Ludwig Boltzman had developed for entropy in the previous century.
[viii] Insects, crustaceans, spiders, centipedes, etc.
[ix] For example, a mutation in the leg of a millipede will be mirrored on both sides, and probably repeated the length of the body as well. Although it is a single mutation, embryological processes constrain it to be repeated many times left and right. It may at first seem paradoxical that a constraint should increase the evolutionary versatility of a clade. The reason is spelled out in the same chapter of Climbing Mount Improbable, ‘Kaleidoscopic Embryos.’