Chapter nine — THE LADDER OF CREATION

The theory of evolution by natural selection was put forward in the 1850s independently by two men. One was Charles Darwin; the other was Alfred Russel Wallace. Both men had some scientific background, of course, but at heart both men were naturalists. Darwin had been a medical student at Edinburgh University for two years, before his father who was a wealthy doctor proposed that he might become a clergyman and sent him to Cambridge. Wallace, whose parents were poor and who had left school at fourteen, had followed courses at Working Men’s Insti­tutes in London and Leicester as a surveyor’s apprentice and pupil teacher.

The fact is that there are two traditions of explanation that march side by side in the ascent of man. One is the analysis of the physical structure of the world. The other is the study of the processes of life: their delicacy, their diversity, the wavering cycles from life to death in the individual and in the species. And these traditions do not come together until the theory of evolution; because until then there is a paradox which cannot be resolved, which cannot be begun, about life.

The paradox of the life sciences, which makes them different in kind from physical science, is in the detail of nature everywhere. We see it about us in the birds, the trees, the grass, the snails, in every living thing. It is this. The manifestations of life, its expressions, its forms, are so diverse that they must contain a large element of the accidental. And yet the nature of life is so uniform that it must be constrained by many necessities.

So it is not surprising that biology as we understand it begins with naturalists in the eighteenth and nineteenth centuries: observers of the countryside, bird-watchers, clergymen, doctors, gentlemen of leisure in country houses. I am tempted to call them, simply, ‘gentlemen in Victorian England’, because it cannot be an accident that the theory of evolution is conceived twice by two men living at the same time in the same culture — the culture of Queen Victoria in England.

Charles Darwin was in his early twenties when the Admir­alty was about to send out a survey ship called the Beagle to map the coast of South America, and he was offered the unpaid post of naturalist. He owed the invitation to the professor of botany who had befriended him at Cambridge, though Darwin had not been excited by botany there but by collecting beetles.

I will give a proof of my zeal: one day, on tearing off some old bark, I saw two rare beetles, and seized one in each hand; then I saw a third and new kind, which I could not bear to lose, so that I popped the one which I held in my right hand into my mouth.

Darwin’s father opposed his going, and the captain of the Beagle did not like the shape of his nose, but Darwin’s Wedgwood uncle spoke up for him and he went. The Beagle set sail on 27 December 1831.

The five years that he spent on the ship transformed Darwin. He had been a sympathetic, subtle observer of birds, flowers, life in his own countryside; now South America exploded all that for him into a passion. He came home convinced that species are taken in different direc­tions when they are isolated from one another; species are not immutable. But when he came back he could not think of any mechanism that drove them apart. That was in 1836.

When Darwin did hit on an explanation for the evolution of species two years later, he was most reluctant to publish it. He might have put it off all his life if a very different kind of man had not also followed almost exactly the same steps of experience and thought that moved Darwin, and arrived at the same theory. He is the forgotten and yet the vital character, a sort of man from Porlock in reverse, in the theory of evolution by natural selection.

His name was Alfred Russel Wallace, a giant of a man with a Dickensian family history as comic as Darwin’s was stuffy. At that time, in 1836, Wallace was a boy in his teens; he was born in 1823, and that makes him fourteen years younger than Darwin. Wallace’s life was not easy even then.

Had my father been a moderately rich man ... my whole life would have been differently shaped, and though I should, no doubt, have given some attention to science, it seems very unlikely that I should have ever undertaken ... a journey to the almost unknown forests of the Amazon in order to observe nature and make a living by collecting.

So Wallace wrote about his early life, when he had had to find a way to earn his living in the English provinces. He took up the profession of land-surveying, which did not require a university education, and which his older brother could teach him. His brother died in 1846 from a chill he caught travelling home in an open third-class carriage from a meeting of a Royal Commission committee on rival railway firms.

Evidently it was an open-air life, and Wallace became interested in plants and insects. When he was working at Leicester, he met a man with the same interests who was rather better educated. His new friend astonished Wallace by telling him that he had collected several hundred different species of beetles in the neighbourhood of Leices­ter, and that there were more to be discovered.

If I had been asked before how many different kinds of beetles were to be found in any small district near a town, I should probably have guessed fifty ... I now learnt . . . that there were probably a thousand different kinds within ten miles.

It was a revelation to Wallace, and it shaped his life and his friend’s. The friend was Henry Bates, who later did famous work on mimicry among insects.

Meanwhile the young man had to make a living. Fortunately, it was a good time for a land-surveyor, because the railway adventurers of the 1840s needed him. Wallace was employed to survey a possible route for a line in the Neath Valley in South Wales. He was a conscientious technician, as his brother had been and as Victorians were. But he suspected rightly that he was a pawn in a power game. Most of the surveys were only meant to establish a claim against some other railway robber baron. Wallace calculated that only a tenth of the lines surveyed that year were ever built.

The Welsh countryside was a delight to the Sunday naturalist, as happy in his science as a Sunday painter is in his art. Now Wallace observed and collected for himself, with a growing excitement in the variety of nature that affectionately remained in his memory all his life.

Even when we were busy I had Sundays perfectly free, and used then to take long walks over the mountains with my collecting box, which I brought home full of treasures ... At such times I experienced the joy which every discovery of a new form of life gives to the lover of nature, almost equal to those raptures which I afterwards felt at every capture of new butterflies on the Amazon.

Wallace found a cave on one of his weekends where the river ran underground, and decided then and there to camp overnight. It was as if unconsciously he was already preparing himself for life in the wild.

We wanted for once to try sleeping out-of-doors, with no shelter or bed but what nature provided ... I think we had determined purposely to make no preparation, but to camp out just as if we had come accidentally to the place in an unknown country, and had been compelled to sleep there.

In fact he hardly slept at all.

When he was twenty-five, Wallace decided to become a full-time naturalist. It was an odd Victorian profession. It meant that he would have to keep himself by collecting specimens in foreign parts to sell to museums and collectors in England. And Bates would come with him. So the two of them set off in 1848 with £100 between them. They sailed to South America, and then a thousand miles up the Amazon to the city of Manaus, where the Amazon is joined by the Rio Negro.

Wallace had hardly been further than Wales, but he was not overawed by the exotic. From the moment of arrival, his comments were firm and self-assured. For example, on the subject of vultures, he records his thoughts in his Narrative of Travels on the Amazon and Rio Negro five years later.

The common black vultures were abundant, but were rather put to it for food, being obliged to eat palm-fruits in the forest when they could find nothing else.

I am convinced, from repeated observations, that the vultures depend entirely on sight, and not at all on smell, in seeking out their food.

The friends separated at Manaus, and Wallace set off up the Rio Negro. He was looking for places that had not been much explored by earlier naturalists; for if he was going to make a living by collecting, he needed to find specimens of unknown or at least of rare species. The river was swollen with rain, so that Wallace and his Indians were able to take their canoe right into the forest. The trees hung low over the water. Wallace for once was awed by the gloom, but he was also elated by the variety in the forest, and he speculated how it might look from the air.

What we may fairly allow of tropical vegetation is, that there is a much greater number of species, and a greater variety of forms, than in the temperate zones.

Perhaps no country in the world contains such an amount of vegetable matter on its surface as the valley of the Amazon. Its entire extent, with the exception of some very small portions, is covered with one dense and lofty primeval forest, the most extensive and unbroken which exists upon the earth.

The whole glory of these forests could only be seen by sailing gently in a balloon over the undulating flowery surface above: such a treat is perhaps reserved for the traveller of a future age.

He was excited and frightened when for the first time he went into a native Indian village; but it is characteristic of Wallace that his lasting feeling was pleasure.

The . . . most unexpected sensation of surprise and delight was my first meeting and living with a man in a state of nature — with absolute uncontaminated savages! . . . They were all going about their own work or pleasure which had nothing to do with white men or their ways; they walked with the free step of the independent forest-dweller, and . . . paid no attention whatever to us, mere strangers of an alien race.

In every detail they were original and self-sustaining, as are the wild animals of the forests, absolutely independent of civilization, and who could and did live their lives in their own way, as they had done for countless generations before America was discovered.

It turned out that the Indians were not fierce but helpful. Wallace drew them into the business of collecting speci­mens.

During the time I remained here (forty days), I procured at least forty species of butterflies quite new to me, besides a considerable collection of other orders.

One day I had brought me a curious little alligator of a rare species, with numerous ridges and conical tubercles (Caiman gibbus), which I skinned and stuffed, much to the amusement of the Indians, half a dozen of whom gazed intently at the operation.

Sooner or later, amid the pleasures and the labours of the forest, the burning question began to flicker in Wallace’s acute mind. How had all this variety come about, so alike in design and yet so changeable in detail? Like Darwin, Wallace was struck by the differences between neighbouring species, and like Darwin he began to wonder how they had come to develop so differently.

There is no part of natural history more interesting or instructive than the study of the geographical distribution of animals.

Places not more than fifty or a hundred miles apart often have species of insects and birds at the one, which are not found at the other. There must be some boundary which determines the range of each species; some external peculiarity to mark the line which each one does not pass.

He was always attracted by problems in geography. Later, when he worked in the Malay archipelago, he showed that the animals on the western islands resemble species from Asia, and on the eastern islands from Australia: the line that divides them is still called the Wallace line.

Wallace was as acute an observer of men as of nature, and with the same interest in the origin of differences. In an age in which Victorians called the people of the Amazon ‘savages’, he had a rare sympathy with their culture. He understood what language, what invention, what custom meant to them. He was perhaps the first person to seize the fact that the cultural distance between their civilization and ours is much shorter than we think. After he conceived the principle of natural selection, that seemed not only true but biologically obvious.

Natural selection could only have endowed savage man with a brain a few degrees superior to that of an ape, whereas he actually possesses one very little inferior to that of a philoso­pher. With our advent there had come into existence a being in whom that subtle force we term ‘mind’ became of far more importance than mere bodily structure.

He was steadfast in his regard for the Indians, and he wrote an idyllic account of their life when he stayed in the village of Javíta in 1851. At this point, Wallace’s journal breaks into poetry — well, into verse.

There is an Indian village; all around,

The dark, eternal, boundless forest spreads

Its varied foliage.

Here I dwelt a while, the one white man

Among perhaps two hundred living souls.

Each day some labour calls them. Now they go

To fell the forest’s pride, or in canoe

With hook, and spear, and arrow, to catch fish;

A palm-tree’s spreading leaves supply a thatch

Impervious to the winter’s storms and rain.

The women dig the mandiocca root,

And with much labour make of it their bread.

And all each morn and eve wash in the stream,

And sport like mermaids in the sparkling wave.

The children of small growth are naked, and

The boys and men wear but a narrow cloth.

How I delight to see those naked boys!

Their well-form’d limbs, their bright, smooth, red-brown skin,

And every motion full of grace and health;

And as they run, and race, and shout, and leap,

Or swim and dive beneath the rapid stream,

I pity English boys; their active limbs

Cramp’d and confined in tightly-fitting clothes;

But how much more I pity English maids,

Their waist, and chest, and bosom all confined

By that vile torturing instrument called stays!

I’d be an Indian here, and live content

To fish, and hunt, and paddle my canoe,

And see my children grow, like young wild fawns,

In health of body and in peace of mind,

Rich without wealth, and happy without gold!

The sympathy is different from the feelings that South American Indians aroused in Charles Darwin. When Darwin met the natives of Tierra del Fuego he was horrified: that is clear from his own words and from the drawings in his book on The Voyage of the Beagle. No doubt the ferocious climate had an influence on the customs of the Fuegians. But nineteenth-century photographs show that they did not look as beastly as they seemed to Darwin. On his voyage home, Darwin had published a pamphlet with the captain of the Beagle at Cape Town to recommend the work that missionaries were doing to change the life of savages.

Wallace spent four years in the Amazon basin; then he packed his collections and started home.

The fever and ague now attacked me again, and I passed several days very uncomfortably. We had almost constant rains; and to attend to my numerous birds and animals was a great annoyance, owing to the crowded state of the canoe, and the impossibility of properly cleaning them during the rain. Some died almost every day, and I often wished I had nothing whatever to do with them, though, having once taken them in hand, I determined to persevere.

Out of a hundred live animals which I had purchased or had had given to me, there now only remained thirty-four.

The voyage home went badly from the start. Wallace was always an unlucky man.

On the 10th June we left [Manaus], commencing our voyage very unfortunately for me; for, on going on board, after bidding adieu to my friends, I missed my toucan, which had, no doubt, flown overboard, and not being noticed by any one, was drowned.

His choice of a ship was most unlucky, since she was carrying an inflammable cargo of resin. Three weeks out, on 6 August 1852, the ship caught fire.

I went down into the cabin, now suffocatingly hot and full of smoke, to see what was worth saving. I got my watch and a small tin box containing some shirts and a couple of old note­books, with some drawings of plants and animals, and scrambled up with them on deck. Many clothes and a large portfolio of drawings and sketches remained in my berth; but I did not care to venture down again, and in fact felt a kind of apathy about saving anything, that I can now hardly account for.

The captain at length ordered all into the boats, and was himself the last to leave the vessel.

With what pleasure had I looked upon every rare and curious insect I had added to my collection! How many times, when almost overcome by the ague, had I crawled into the forest and been rewarded by some unknown and beautiful species! How many places, which no European foot but my own had trodden, would have been recalled to my memory by the rare birds and insects they had furnished to my collection!

And now everything was gone, and I had not one specimen to illustrate the unknown lands I had trod or to call back the recollection of the wild scenes I had beheld! But such regrets I knew were vain, and I tried to think as little as possible about what might have been and to occupy myself with the state of things which actually existed.

Alfred Wallace returned from the tropics, as Darwin had done, convinced that related species diverge from a com­mon stock, and nonplussed as to why they diverged. What Wallace did not know was that Darwin had hit on the explanation two years after he returned to England from his voyage in the Beagle. Darwin recounts that in 1838 he was reading the Essay on Population by the Reverend Thomas Malthus (‘for amusement’, says Darwin, meaning that it was not part of his serious reading) and he was struck by a thought in Malthus. Malthus had said that population multiplies faster than food. If that is true of animals, then they must compete to survive: so that nature acts as a selective force, killing off the weak, and forming new species from the survivors who are fitted to their environment.

‘Here then I had at last got a theory by which to work,’ says Darwin. And you would think that a man who said that would set to work, write papers, go out and lecture. Nothing of the kind. For four years Darwin did not even commit the theory to paper. Only in 1842 he wrote a draft of thirty-five pages, in pencil; and two years later expanded it to two hundred and thirty pages, in ink. And that draft he deposited with a sum of money and instructions to his wife to publish it if he died.

‘I have just finished my sketch of my species theory,’ he wrote in a formal letter for her dated 5 July 1844 at Downe, and went on:

I therefore write this in case of my sudden death, as my most solemn and last request, which I am sure you will consider the same as if legally entered in my will, that you will devote £400 to its publication, and further, will yourself, or through Hensleigh (Wedgwood), take trouble in promoting it. I wish that my sketch be given to some competent person, with this sum to induce him to take trouble in its improvement and enlargement.

With respect to editors, Mr (Charles) Lyell would be the best if he would undertake it; I believe he would find the work pleasant, and he would learn some facts new to him.

Dr (Joseph Dalton) Hooker would be very good.

We feel that Darwin would really have liked to die before he published the theory, provided after his death the priority should come to him. That is a strange character. It speaks for a man who knew that he was saying something deeply shocking to the public (certainly deeply shocking to his wife) and who was himself, to some extent, shocked by it. The hypochondria (yes, he had some infection from the tropics to excuse it), the bottles of medicine, the enclosed, somewhat suffocating atmosphere of his house and study, the afternoon naps, the delay in writing, the refusal to argue in public: all those speak for a mind that did not want to face the public.

The younger Wallace, of course, was held back by none of these inhibitions. Brashly he went off in spite of all adversities to the Far East in 1854, and for the next eight years travelled all over the Malay archipelago to collect specimens of the wild life there that he would sell in England. By now he was convinced that species are not immutable; he published an essay On the Law which has regulated the Introduction of New Species in 1855; and from then ‘the question of how changes of species could have been brought about was rarely out of my mind’.

In February of 1858 Wallace was ill on the small volcanic island of Ternate in the Moluccas, the Spice Islands, between New Guinea and Borneo. He had an intermittent fever, was hot and cold by turns, and thought fitfully. And there, on a night of fever, he recalled the same book by Malthus and had the same explanation flash on him that had struck Darwin earlier.

It occurred to me to ask the question. Why do some die and some live? And the answer was clearly, that on the whole the best fitted lived. From the effects of disease the most healthy escaped; from enemies, the strongest, the swiftest, or the most cunning; from famine, the best hunters or those with the best digestion; and so on.

Then I at once saw, that the ever present variability of all living things would furnish the material from which, by the mere weeding out of those less adapted to the actual conditions, the fittest alone would continue the race.

There suddenly flashed upon me the ideaof the survival of the fittest.

The more I thought over it, the more I became convinced that I had at length found the long-sought-for law of nature that solved the problem of the Origin of Species ... I waited anxiously for the termination of my fit so that I might at once make notes for a paper on the subject. The same evening I did this pretty fully, and on the two succeeding evenings wrote it out carefully in order to send it to Darwin by the next post, which would leave in a day or two.

Wallace knew that Charles Darwin was interested in the subject, and he suggested that Darwin show the paper to Lyell if he thought it made sense.

Darwin received Wallace’s paper in his study at Down House four months later, on 18 June 1858. He was at a loss to know what to do. For twenty careful, silent years he had marshalled facts to support the theory, and now there fell on his desk from nowhere a paper of which he wrote laconically on the same day,

I never saw a more striking coincidence; if Wallace had my MS sketch written out in 1842, he could not have made a better short abstract!

But friends resolved Darwin’s dilemma. Lyell and Hooker, who by now had seen some of his work, arranged that Wallace’s paper and one by Darwin should be read in the absence of both at the next meeting of the Linnean Society in London the following month.

The papers made no stir at all. But Darwin’s hand had been forced. Wallace was, as Darwin described him, ‘generous and noble’. And so Darwin wrote The Origin of Species and published it at the end of 1859, and it was instantly a sensation, and a best-seller.

The theory of evolution by natural selection was certainly the most important single scientific innovation in the nineteenth century. When all the foolish wind and wit that it raised had blown away, the living world was different because it was seen to be a world in movement. The creation is not static but changes in time in a way that physical processes do not. The physical world ten million years ago was the same as it is today, and its laws were the same. But the living world is not the same; for example, ten million years ago there were no human beings to discuss it. Unlike physics, every generalization about biology is a slice in time; and it is evolution which is the real creator of originality and novelty in the universe.

If that is so, then each one of us traces his make-up back through the evolutionary process right to the beginnings of life. Darwin, of course, and Wallace looked at behaviour, they looked at bones as they are now, at fossils as they were, to map points on the path by which you and I have come. But behaviour, bones, fossils are already complex systems in life, put together from units which are simpler and must be older. What could the simplest first units be?

Presumably they are chemical molecules that characterize life.

So when we look back for the common origin of life, today we look even more deeply, at the chemistry that we all share. The blood in my finger at this moment has come by some millions of steps from the very first primeval molecules that were able to reproduce themselves, over three thousand million years ago. That is evolution in its contemporary conception. The processes by which this has happened in part depend on heredity (which neither Darwin nor Wallace really understood) and in part on chemical structure (which, again, was the province of French scientists rather than British naturalists). The explanations flow together from several fields, but one thing they all have in common. They picture the species separating one after another, in successive stages — that is implied when the theory of evolution is accepted. And from that moment it was no longer possible to believe that life could be re-created at any time now.

When the theory of evolution implied that some animal species came into being more recently than others, critics most often replied by quoting the Bible. Yet most people believed that creation had not stopped with the Bible. They thought that the sun breeds crocodiles from the mud of the Nile. Mice were supposed to grow of themselves in heaps of dirty old clothes; and it was obvious that the origin of bluebottles is bad meat. Maggots must be created inside apples — how else did they get there? All these creatures were supposed to come to life spontaneously, without the benefit of parents.

Fables about creatures that come to life spontaneously are very ancient and are still believed, although Louis Pasteur disproved them beautifully in the 1860s. He did much of that work in his boyhood home in Arbois in the French Jura which he loved to come back to every year. He had done work on fermentation before that, particularly the fermentation of milk (the word ‘pasteurization’ reminds us of that). But he was at the height of his power in 1863 (he was forty) when the Emperor of France asked him to look into what goes wrong with the fermentation of wine, and he solved that problem in two years. It is ironic to remember that they were among the best wine years that have ever been; to this day 1864 is remembered as being like no other year.

‘The wine is a sea of organisms,’ said Pasteur. ‘By some it lives, by some it decays.’ There are two things striking in that thought. One is that Pasteur found organisms that live without oxygen. At the time that was just a nuisance to wine-growers; but since then it has turned out to be crucial to the understanding of the beginning of life, because then the earth was without oxygen. And second, Pasteur had a remarkable technique by which he could see the traces of life in the liquid. In his twenties he had made his reputation by showing that there are molecules that have a characteristic shape. And he had since shown that this is the thumbprint of their having been through the process of life. That has turned out to be so profound a discovery, and it is still so puzzling, that it is right to look at it in Pasteur’s own laboratory and his own words.

How does one account for the working of the vintage in the vat: of dough left to rise: or the souring of curdling milk: of dead leaves and plants buried in the soil and turning to humus? I must in fact confess that my research has long been dominated by the idea that the structure of substances from the point of view of left-handed and right-handedness (if all else is equal) plays an important part in the most intimate laws of the organization of living beings, and enters into the most obscure corners of their physiology.

Right hand, left hand; that was the deep clue that Pasteur followed in his study of life. The world is full of things whose right-hand version is different from the left — hand version: a right-handed corkscrew as against a left — handed, a right snail as against a left one. Above all, the two hands; they can be mirrored one in the other, but they cannot be turned in such a way that the right hand and the left hand become interchangeable. That was known in Pasteur’s time to be true also of some crystals, whose facets are so arranged that there are right-hand versions and left — hand versions.

Pasteur made wooden models of such crystals (he was adroit with his hands, and a beautiful draughtsman) but much more than that, he made intellectual models. In his first piece of research he had hit on the notion that there must be right-handed and left-handed molecules too; and what is true of the crystal must reflect a property of the molecule itself. And that must be displayed by the behav­iour of the molecules in any unsymmetrical situation. For instance, when you put them into solution and shine a polarized (that is an unsymmetrical) beam of light through them, the molecules of one kind (say, by convention, the molecules Pasteur called right-handed) must rotate the plane of polarization of the light to the left. A solution of crystals all of one shape will behave unsymmetrically towards the unsymmetrical beam of light produced in a polarimeter. As the polarizing disc is turned, the solution will look alternately dark and light and dark and light again.

The remarkable fact is that a chemical solution from living cells does just that. We still do not know why life has this strange chemical property. But the property establishes that life has a specific chemical character, which has maintained itself throughout its evolution. For the first time Pasteur had linked all the forms of life with one kind of chemical structure. From that powerful thought it follows that we must be able to link evolution with chemistry.

The theory of evolution is no longer a battleground. That is because the evidence for it is so much richer and more varied now than it was in the days of Darwin and Wallace. The most interesting and modern evidence comes from our body chemistry. Let me take a practical example: I am able to move my hand at this moment because the muscles contain a store of oxygen, and that has been put there by a protein called myoglobin. That protein is made up of just over one hundred and fifty amino acids. The number is the same in me and all the other animals that use myoglobin. But the amino acids themselves are slightly different. Between me and the chimpanzee there is just one difference in an amino acid; between me and the bush baby (which is a lower primate) there are several amino acid differences; and then between me and the sheep or the mouse, the number of differences increases. It is the number of amino acid differences which is a measure of the evolutionary distance between me and the other mammals.

It is clear that we have to look for the evolutionary progress of life in a build-up of chemical molecules. And that build-up must begin from the materials that boiled on the earth at its birth. To talk sensibly about the beginning of life we have to be very realistic. We have to ask a historical question. Four thousand million years ago, before life began, when the earth was very young, what was the surface of the earth, what was its atmosphere like?

Very well, we know a rough answer. The atmosphere was expelled from the interior of the earth, and was therefore somewhat like a volcanic neighbourhood any­where — a cauldron of steam, nitrogen, methane, ammonia and other reducing gases, as well as some carbon dioxide. One gas was absent: there was no free oxygen. That is crucial, because oxygen is produced by the plants and did not exist in a free state before life existed.

These gases and their products, dissolved weakly in the oceans, formed a reducing atmosphere. How would they react next under the action of lightning, electric discharges, and particularly under the action of ultra-violet light — which is very important in every theory of life, because it can penetrate in the absence of oxygen? That question was answered in a beautiful experiment by Stanley Miller in America round about 1950. He put the atmosphere in a flask — the methane, the ammonia, the water, and so on - and went on, for day after day, and boiled and bubbled them up, put an electric discharge through them to simulate lightning and other violent forces. And visibly the mixture darkened. Why? Because on testing it was found that amino acids had been formed in it. That is a crucial step forward, since amino acids are the building blocks of life. From them the proteins are made, and proteins are the constituents of all living things.

We used to think, until a few years ago, that life had to begin in those sultry, electric conditions. And then it began to occur to a few scientists that there is another set of extreme conditions which may be as powerful: that is the presence of ice. It is a strange thought; but ice has two properties which make it very attractive in the formation of simple, basic molecules. First of all, the process of freezing concentrates the material, which at the beginning of time must have been very dilute in the oceans. And secondly, it may be that the crystalline structure of ice makes it possible for molecules to line up in a way which is certainly important at every stage of life.

At any rate, Leslie Orgel did a number of elegant experiments of which I will describe the simplest. He took some of the basic constituents which are sure to have been present in the atmosphere of the earth at any early time: hydrogen cyanide is one, ammonia is another. He made a dilute solution of them in water, and then froze the solution over a period of several days. As a result, the concentrated material is pushed into a sort of tiny iceberg to the top, and there the presence of a small amount of colour reveals that organic molecules have been formed. Some amino acids, no doubt; but, most important, Orgel found that he had formed one of the four fundamental constituents in the genetic alphabet which directs all life. He had made adenine, one of the four bases in DNA. It may indeed be that the alphabet of life in DNA was formed in these sorts of conditions, and not in tropical conditions.

The problem of the origin of life centres not on the complex but on the simplest molecules that will reproduce them­selves. It is the ability to replicate working copies of the same molecule that characterizes life; and the question of the origin of life is therefore the question, whether the basic molecules that have been identified by the work of the present generation of biologists could have been formed by natural processes. We know what we are looking for at the beginning of life: simple, basic molecules like the so — called bases (adenine, thymine, guanine, cytosine) that compose the DNA spirals which reproduce themselves during the division of any cell. The subsequent course by which organisms have become more and more complex is then a different, statistical problem: namely, the evolution of complexity by statistical processes.

It is natural to ask whether self-copying molecules were made many times and in many places. There is no answer to this question except by inferences, which have to be based on our interpretation of the evidence provided by living things today. Life today is controlled by a very few molecules — namely the four bases in DNA. They spell out the message for inheritance in every creature that we know, from a bacterium to an elephant, from a virus to a rose. One conclusion that could be drawn from this uniformity in the alphabet of life is, that these are the only atomic arrangements that will carry out the sequence of replication of themselves.

However, there are not many biologists who believe that. Most biologists think that nature can invent other self-copying arrangements; the possibilities must surely be more numerous than the four we have. If that is right, then the reason why life as we know it is directed by the same four bases is because life happened to begin with them. On that interpretation, the bases are evidence that life only began once. After that, when any new arrangement came up, it simply could not link to the living forms that already existed. Certainly no one thinks now that life is still being created from nothing here on earth.

Biology has been fortunate in discovering within the span of one hundred years two great and seminal ideas. One was Darwin’s and Wallace’s theory of evolution by natural selection. The other was the discovery, by our own contemporaries, of how to express the cycles of life in a chemical form that links them with nature as a whole.

Were the chemicals here on earth at the time when life began unique to us? We used to think so. But the most recent evidence is different. Within the last years there have been found in the interstellar spaces the spectral traces of molecules which we never thought could be formed out in those frigid regions: hydrogen cyanide, cyano acetylene, formaldehyde. These are molecules which we have not supposed to exist elsewhere than on earth. It may turn out that life had more varied beginnings and has more varied forms. And it does not at all follow that the evolutionary path which life (if we discover it) took elsewhere must resemble ours. It does not even follow that we shall recognize it as life — or that it will recognize us.

Date: 2016-01-14; view: 813