by Andrew Brown
Miller elegantly demonstrated that the organic building blocks of life could have arisen as a result of electrical excitation of the primitive atmosphere (he thought that ultraviolet light from the Sun would be an equally effective source of energy but could not test that idea in his glass apparatus). His two-page report in Science cited just three references – by Oparin, Urey and Bernal. Miller’s experiment transformed the whole subject of the origin of life from armchair speculation into a new branch of experimental science, in a flash.
While Miller had shown that the Oparin–Haldane hypothesis was plausible, he could not prove that these chemical reactions were actually taking place in the prebiotic phase of life. Bernal thought it was ‘now indisputable’ that organic molecules could have arisen in this way and ‘their presence in organisms is strong presumptive evidence for the pre-existence of the reducing atmosphere from which Miller synthesized them’.28 Sage also interpreted the appearance of red-coloured substances, capable of absorbing light, in Miller’s experiment as opening the way to photosynthesis. He remained concerned about the problem of concentration of the primitive molecules necessary for their chemical interaction – the issue that had led him to propose clay as a means of absorbing organic molecules and holding them in close quarters. It now appeared to him that if polymers consisting of a thousand atoms or so could be achieved, they would bind layers of water molecules ‘provoking the formation of macroscopic colloidal aggregates… The water held in this way has properties intermediate between those of ice and of ionic solution. It possesses mechanical rigidity, but ions and even small molecules such as sugars can diffuse through it except for the portion within one or two water molecule diameters of the particle… Protein molecules are particularly suited for the formation of such waterholding colloids and it seems to me that the evidence is still strong that they or some smaller polypeptides were the first substances in the evolution of life fitted for this role’.29
Pirie, as one might expect, was far less impressed than Sage with the significance of Miller’s report. He believed that the set of chemical reactions observed in that experiment were of relevance only if the currently accepted model of the physical creation of the Earth and its subsequent development held sway. He had little confidence in that model because, in his words, ‘Every few years a new theory of the origin of the earth appears and with it new probabilities about the primitive atmosphere… some suggest an oxidizing and some a reducing atmosphere. Until substantial unanimity has been reached and maintained on this point, we can only speculate about the types of molecule that would have been present in the surface layers, because the factors that lead to different conclusions about the atmosphere lead also to different conclusions about the surface… The attitude of mind that leads people to erect a new dogma on the “Stop Press” news from astronomy and physics is similar to that of the child who, seeing copyists at work in an art gallery, said ‘What do they do with the old pictures when the new ones are finished?’30
Pirie’s essay also contained a few more gibes against Sage, who was given the right of reply. While not attempting to conceal his differences with Pirie, he seemed to be tiring of their argument.
Pirie is certainly entitled to have another crack at me and I can only object at misrepresentation. I am not quite so ignorant as he makes me out to be, only more wrong-headed. Ancient authorities impress him more than they do me… Nor do I think science is really like painting. The new pictures in science may or may not be so well painted as the old, but they have something in them that the old simply did not have. Our art should consist in fitting the new facts in, not rejecting them out of hand. With his positive propositions I am, however, in almost complete agreement, particularly with his ideas on the evolution of molecules. I would not try to limit biopoesis [Pirie’s term for the making of life] to our particular brand, but I think we are more likely to find out this kind first as we know something of the beginning from geochemistry and the end from biochemistry.31
The point Bernal was making in the last sentence was that emerging evidence from astronomers and geochemists as to the mode of formation of the planet from condensation of cosmic dust, together with the chemical composition and likely temperature of its surface, should act as a guide to the chemical reactions that could have taken place initially. At the other end, biochemical processes of present-day life and the cellular organelles such as nuclei, mitochondria and membranes where they take place, should have precursors in primitive life forms. Indeed ‘we should look for close relations between chemical processes likely to take place on the surface of a newly formed planet and those occurring in organisms, particularly the most common processes which are also likely to be the oldest’.32
Pirie thought Sage’s line of reasoning was sophistry. He believed that the uniformity of present-day organisms in their chemical composition and metabolism was often exaggerated, and what were the dominant biochemical pathways now might have completely replaced the earliest, primitive, mechanisms. He summarized his position thus:
Every biopoesis on Earth starts with the same Geochemistry; my contention is that they may have used different aspects of it. [Pirie thought one of his greatest contributions was to add an s to origin.] The final result is present-day Biochemistry; but my contention is that we may be emphasizing the wrong aspects of it. Alongside the now well-understood protein and carbohydrate mechanisms there are many that we look on as bizarre and unusual. It may well be that these resemble the primitive mechanisms; the commonly made assumption that those mechanisms which are quantitatively most important now, are the primitive ones, is wholly arbitrary. The facts of Geochemistry and Biochemistry do not define any particular route between the beginning and the present position.
Fortunately for Sage, he was not restricted to an exclusive debate with Pirie on the origin of life. Other scientists were now attracted to the subject, encouraged no doubt by Miller’s successful experiment. Bernal received word from Oparin that he was planning an international conference in Moscow in the summer of 1957. Sage gave some thought to what he might speak about, and decided that he should give two papers. The first would be a general paper on ‘Ideas on the principles of the study of the origin of life’. In this lecture, he would emphasize the critical importance of physical coherence as expressed in gels and coacervates (featureless blobs of jelly proposed by Oparin as precursors of living cells); the origin and place of polymer formation; the mutual biochemical reactions of nucleic acids, purines, sugars and fats; and finally the role of the different kinds of molecules in producing the structures observable in viruses and cells. He would attempt to relate the above with aspects of geochemical and geophysical evolution.33 The second lecture would concentrate more on geometric structure of macromolecules related to the origin of life. Sage also made some suggestions about scientists Oparin should invite: John Randall from King’s College, Rosalind Franklin, Dorothy Hodgkin, Crick and Watson amongst them.
Sage had a chance to rehearse his lectures at Oparin’s institute during a visit to the USSR in September 1956. It was an unsettling time for Stalinists – the waves from Khrushchev’s sudden indictment of the cult of personality and of the Stalin-era state crimes were rocking the previously unshakable Soviet edifice. Sage was joined on this trip by Alan Mackay, who remembers that their official translator, a lecturer in English at Moscow University, had a distinctly cockney accent. Although Bernal was still treated as an honoured guest, he commented to Mackay that his lavish suite of rooms at the Hotel Moskva was poor compared to the accommodation on his previous visits, when his sitting room had not only contained a grand piano, but a stuffed bear proffering a box of matches.34
The first international symposium on ‘The origin of life on the earth’ attracted more than forty scientists from sixteen countries to Moscow in August 1957. Bernal addressed them in the first session and proposed a schema for the stages by which life might have begun. He did not believe that his framework was ‘the correct one or that it may not r
equire drastic modification, but I do urge that it is better in such a Congress to have before it some pattern than none’.35 He reiterated his belief in the principle proposed by Sir Charles Lyell, the Victorian geologist and friend of Darwin, who ‘tells us to search in the present world for processes which may have occurred in the past’. In the context of the origin of life, Bernal thought that this meant more than just searching for the origin of the materials of the organic world in the inorganic, but that there should also be continuity of the basic chemical processes like oxidation–reduction and hydrolysis–condensation reactions. As to the materials, he was struck that the commonest, stable, elements of the earth’s crust such as silicon and aluminium play almost no role in biochemistry, whereas the soluble simple ions such as potassium and magnesium and the labile atoms of sulphur, phosphorus and iron are key.
While accepting Pirie’s point that there may have been other radically different forms of life, now long extinct, Bernal thought that this just meant scientists were restricted to studying the origin of the one form of life that now existed on Earth. In his opinion, this could be traced only by working backwards: attempting to work forwards from any initial inorganic origins would be futile because there were too many possible lines to be followed.
There may well be potential biochemical cycles that would have solved the problems of the formation of life and reproduction of organisms as well as, and even better than, those actually evolved. But biochemical evolution differs from that of organisms in that variant forms, if not actually incorporated in the common biochemical pattern, became absolutely extinct. There is only one dominant chemical pattern of life.36
With Pirie in the audience, Sage now even proposed a working definition of life: the embodiment within a certain volume of self-maintaining chemical processes. The problem confronting them was how such a system could establish itself, starting from available inorganic materials and subsequently reproduce and evolve. He sub-divided this large question into four interrelated but distinct problems:
The problem of the external source of free energy to keep the system going;
The problem of the facilitation of the energy interchanges within the system, where an isothermal condition implies some catalysis; [biochemical processes take place without the input of heat that would be necessary in the absence of enzymes]
The problems of the means of holding the system together and in the more complicated cases, such as bacterial and nucleated cells, of how all parts of the organism can maintain their individuality while being in constant chemical relation with each other;
The problems of reproduction with its almost, but never quite exact, duplication of organisms as shown in evolving species, pose the further problem of the normal transference, with occasional modification, of specific guiding patterns.
Sage gave the audience reasons to be optimistic: the exact composition of the Earth’s original atmosphere did not have to be known before considering the emergence of organic molecules; the efficiency of primitive protoenzymes was probably extremely low; and the first natural polymers would not need to have a high degree of regularity to permit the formation of colloidal proto-cells.
Pirie, in his presentation,37 came close to agreement on some points with Sage – for example, he did not think discussions on biopoesis should wait for more accurate data on the original composition of the Earth’s surface. He was also ready to concede that it seemed likely that all present life-forms were protein-based, although he still thought this irrelevant to any discussion about the origins of life. He introduced a novel idea, illustrated by two cones joined apex to apex (like a narrow-wasted egg-timer), that in the beginning there was chemical diversity and structural simplicity. As inefficient chemical processes disappeared, there was a point of maximal simplicity (the narrow waist) where life originated and thereafter the biochemistry became simplified as protein-based organisms ascended, resulting in morphological complexity and chemical uniformity.
So struck was Pirie with his own picture of biopoesis that it took pride of place in a summary of the Moscow symposium that he wrote for Nature. Nor could he resist a clever dig at Sage: ‘Argument about evolution presents many intellectual pitfalls for the imprudent. J.D. Bernal fell into some of them with consequent inversion. This was the position in which, according to Engels, Marx found Hegel. Marx put Hegel on his feet and put posterity in his debt by making the Dialectic useful. I would like to perform a like service for my friend.’38 His friend reacted as follows:
N.W. Pirie’s characteristic and entertaining account of the symposium in Moscow on the origin of life mainly consists of an exposition of his views on the subject and a metaphysical criticism of a minor part of my own contribution to the discussion.39
Where Pirie had made his familiar complaint that the Victorian intellectuals like Huxley and Tyndall ‘had a clearer grip on the nature of the problem’, Sage was encouraged that ‘so many distinguished and active scientists in fields ranging from astrophysics to genetics… had come together to discuss a subject of such wide scope and importance’. In his single-page report, Sage was able to give Nature’s readership a much fuller and more detailed account of the meeting than Pirie managed in more than double the number of words. Sage ended by saying ‘I hope these remarks may do something to enlarge Pirie’s view of the symposium, but they still are far from doing justice to the wealth of information presented and the interesting discussions that ensued.’40
Pirie’s familiar name was ‘Bill’, bestowed by his parents after ‘Kaiser Bill’ in recognition of their son’s youthful belligerence and nonconformist ways. He never outgrew these traits and took pride in his ‘distrust of authority and majority opinion’.41 At times, this scepticism meant he rejected new facts such as Franklin’s structure of TMV or the genetic code, and his prickliness caused unease among the younger molecular biologists. Sage was an established figure, who was not threatened by Pirie’s sniping, and did not take offence at the personal insults – although he would have preferred a more cerebral debate. He regretted that the controversy with Pirie was not very productive because it was ‘largely due to a difference in temperament’.42 Pirie wrote over forty articles on the origins of life over a sixty-year period, and ultimately came to regard them as ‘extremely repetitive’.43
At Bedford School, Bernal’s housemaster gave him the title of ‘Astronomer Royal’, and as a schoolboy he wrote his first scientific paper on the theory of comets.44 The paper was lost and never published, but gave Bernal a general feeling for reciprocal space that helped him to develop so rapidly as an X-ray crystallographer. His astronomical interests were reawakened in connection with the origins of life in the early 1960s, when some American scientists announced that they had identified biogenic hydrocarbons, similar to animal products like butter, in the carbonaceous material of a meteorite that had fallen to earth nearly a century before in France. The Orgueil meteorite had been carefully examined at the time by Pasteur himself, who attempted to culture any indigenous microorganisms from its interior and found none. Naturally the conclusion of the American scientists (Nagy, Meinschein and Hennessy) ‘that biogenic processes occur and that living forms exist in regions of the universe beyond the earth’ caused an enormous amount of public excitement. Although the trio were reliable scientists, Bernal, writing in Nature, could see a disadvantage to the amount of publicity they received.
There is a danger that this [publicity] will, in serious scientific circles, cause the observations of the three authors to be overlooked, which would be a great mistake, for whatever the interpretation put on them they are of cardinal importance to science… The major question that arises, therefore, is as to the interpretation of the results. Though the mass spectroscopic evidence indicates a composition of meteoritic hydrocarbons within the range of those given by material of organic origin on the Earth, from this it only follows that the meteorite material may be of organismal origin and not that it must be so… If the material is derived from lif
e, this must have occurred on the planetary parent body from which by general consensus we believe meteorites to have been derived by fragmentation.45
Soon after the original announcement about long hydrocarbon molecules in the Orgueil meteorite came another, even more astonishing, discovery. Bart Nagy, a chemist, had brought a microbiologist, George Claus, into the research and they found evidence of microscopic particles in the Orgueil meteorite and a second meteorite, the Ivuna, which resembled fossilized algae.46 These organized elements showed some staining with biological agents and appeared to Claus to have some morphological structures like the double membrane of a cell wall. A group from Chicago tried to replicate the findings of the New York team and did find similar round particles which ‘appeared to possess a clear double wall, as described by Claus and Nagy, but since the thickness of this wall could be changed by slight adjustment of the focus, the “wall” may be an optical illusion’.47 They carried out a detailed chemical analysis of the particles and found that their composition was ‘strikingly different from that of any known fossil or living organism’. The discovery of fossils in meteorites had been announced once before in the late nineteenth century, and the Chicago group were unimpressed by the morphological evidence which depended on ‘a great deal of subjective judgement’. To them a purely inorganic mode of origin for the organized elements seemed perfectly possible.