The Ascent of Man

by Jacob Bronowski

  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 note-books, 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 idea of 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 inno
vation 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 generalisation 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 characterise 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 recreated 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 ‘pasteurisation’ 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 organisation 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 polarised (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 polarisation 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 polarising 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.

  Right hand, left hand; that was the deep clue that Pasteur followed in his study of life.

  Pasteur’s wooden models of right-handed and left-handed tartrate crystals.

  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.