The origins of research intothe origins of lifeIris Fry

The Cohn Institute for the History and Philosophy of Science and Ideas, Tel Aviv University, Tel Aviv 69978, Israel

Most scientists at the end of the 19th and the beginning

of the 20th century chose to ignore the question of the

origin of life on Earth, regarding it as toomysterious and

complex to handle. Yet, in the early 1950s an exper-

imental field devoted to the study of the problem made

its first steps. The pioneering theories of several

scientists in the first decades of the 20th century played

a major role in this transformation, notably those of the

Russian biochemist Alexander I. Oparin and the British

geneticist and biochemist J.B.S. Haldane. The ideas of

the lesser-known American psycho-physiologist Leo-

nard Troland also made a significant contribution to

subsequent developments in origin-of-life research.

Therefore, it is well worth taking a look at the

professional, philosophical and ideological commit-

ments that shaped the approaches of the three scientists

to origin-of-life research.

Introduction

In the fall of 1951, Stanley Miller, a young doctoralstudent at the University of Chicago, was fascinated andinspired by a lecture delivered by the Nobel Laureatephysicist and chemist, Harold Urey. In his lecture, Ureydiscussed physical and chemical conditions that mighthave existed on the primordial Earth, and their potentialrelevance to the emergence of life. Miller convinced Ureyto let him try his hand at experimentally simulating theseconditions. In Miller’s simulated primordial atmosphereand ocean, contained in a glass apparatus that hedesigned with Urey, the synthesis of organic molecules,mainly amino acids – the building blocks of proteins, wasexperimentally demonstrated for the first time in thespring of 1953. The Miller–Urey experiment and manyothers that followed in the 1950s and 1960s led to thecreation of an experimental scientific field devoted to theelucidation of the origin of life on Earth.

Both the empirical setup of these experiments and thephilosophical assumptions underlying them can be tracedback to several theoretical developments in the early 20thcentury. In the 1920s and the 1930s, the Russianbiochemist Alexander I. Oparin and the British biochem-ist and geneticist J.B.S. Haldane described possiblescenarios for the emergence of life on Earth, the commonelements of which came later to be known as the Oparin–Haldane hypothesis [1]. However, this hypothesis and thetheory formulated by the American psycho-physiologist

Corresponding author: Fry, I. (iris.fry@gmail.com).

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Leonard Troland in the 1910s had to overcome an impassein scientific attitudes to the origin of life before they couldbe accepted by the scientific community (Figure 1).

Two key developments in the late 19th century played amajor part in creating this impasse [2]. Experimentsperformed in the 1860s by the French chemist LouisPasteur convinced most scientists that organisms, includ-ing microorganisms, originated only from their parentsand were not, as believed for ages, repeatedly andspontaneously generated from inanimate matter. Simul-taneously, Charles Darwin’s Origin of Species, publishedin 1859, focused attention on the primordial earth.Although it did not explicitly discuss the emergence oflife, the concept of Darwinian evolution led to the questionthat challenged Pastuer’s logic: how did primitive lifeforms originate in the first place?

By the beginning of the 20th century several otherfactors had exacerbated this intellectual quandary. Newcytological studies revealed the crucial function of thenucleus, which contrasted sharply with established viewsabout the homogeneity of the protoplasm and followingthe rise of biochemistry, enzymes were being discoveredand isolated. The realization that even the simplest of cellswas enormously complex convinced many scientists thatan ‘impassable abyss existed between the living and thedead’ [3].

Responding to this crisis, a so-called ‘neo-vitalistic’trend rejected any attempt to explain biological phenom-ena solely in terms of physics and chemistry, postulatinginstead a special active ‘living force’. Others adhered tothe idea of panspermia, literally ‘germs of life everywhere’[4]. Versions of the theory of panspermia sidestepped theorigin-of-life question by claiming that life is eternal in theuniverse and arrived on Earth from outer space. Likeseveral other well-known physicists, Hermann vonHelmholtz admitted to supporting this theory ‘because ofthe complete impossibility of explaining the origin of lifescientifically in any other way’ [5].

The Oparin–Haldane hypothesis

In 1924, Oparin challenged these dualistic views of lifeand matter, offering instead a detailed scenario for thenatural emergence of life in a pamphlet entitled TheOrigin of Life, which he expanded into a book – The Originof Life on Earth – in 1936. In 1929 Haldane independentlypublished a shorter and less-detailed paper, also entitledThe Origin of Life. Both men claimed that an abundantsynthesis of organic compounds was a necessary precursor

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. doi:10.1016/j.endeavour.2005.12.002

Figure 1. Key players in the development of origin of life research. (a) Alexander I. Oparin (right of photo, 1894–1980) at work in the laboratory. Image supplied by, and

reproduced with permission from, Novosti Photo Library/Science Photo Library; (b) the famous British biochemist and geneticist J.B.S. Haldane (1892–1964). Image supplied

by, and reproduced with permission from, the National Portrait Gallery, London (www.npg.org.uk); and (c) American psycho-physiologist Leonard Troland, taken in the

1920s during his time at Harvard. Image reproduced courtesy of the MIT Museum.

Review Endeavour Vol.30 No.1 March 2006 25

to the emergence of life on ancient Earth. They were thefirst to formulate specific hypotheses about the geophysi-cal conditions in the primordial environment and theconstituents of the early atmosphere that made suchorganic synthesis possible.

In his 1936 book Oparin concluded, based on develop-ments in geochemistry and astronomy, that a primordialatmosphere would have been devoid of oxygen (a claimmade by Haldane in 1929). The postulated constituents ofthis atmosphere were methane, ammonia, free hydrogenand water vapor. Whereas organic compounds tend todecompose in the presence of oxygen, the constituents ofthe so-called ‘reducing atmosphere’ could easily combineto form simple organic molecules under the influence ofenergy sources like heat, lightning and ultravioletradiation [6]. Furthermore, both Oparin and Haldanehypothesized that the organic compounds were sub-sequently dissolved in the primordial ocean that reached,in Haldane’s phrase, the consistency of a ‘hot dilute soup’[7]. Chemical evolution in the ‘soup’, aided by abundantenergy, led to the formation of increasingly complexorganic structures. As a consequence of natural selection,these molecules gradually evolved into primitiveliving systems.

Oparin and Haldane’s suggestion that organic com-pounds, synthesized from inorganic molecules, served asthe building blocks for primitive organisms (the so-calledheterotrophic origin-of-life theory) deviated radically fromthe then-prevalent autotrophic conception, which pro-posed that the first organisms produced their organicmaterial by photosynthesis from carbon dioxide andwater. By taking an intellectual leap, Oparin and Haldane

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recognized that independent organic synthesis could havetaken place on the primordial Earth prior to theemergence of organisms.

The empirical claims of the Oparin–Haldane hypoth-esis, made known to readers in the West mainly throughthe 1938 English translation of Oparin’s The Origin of Lifeon Earth, served as inspiration for the Miller–Ureyexperiment and similar studies that followed [8]. Miller’ssimulated atmosphere was reducing, consisting ofmethane, ammonia, hydrogen and water vapor. He usedelectrical discharges as an energy source to imitateprimordial lightning, and his simulated ocean turnedinto a ‘soup’ following the dissolution of organic molecules,notably amino acids. However, the significance of theOparin–Haldane hypothesis as a framework for origin-of-life research far transcended its empirical details,particularly because it led scholars to consider thepossibility of evolution prior to the existence of life.Philosophically, the hypothesis rejected the vitalisticoption – in which life and inanimate matter were twoseparate, unbridgeable categories – and went evenfurther. In the 1860s and 1870s, some Darwinians adopteda simplistic mechanistic-outlook regarding the origin oflife. Still failing to realize the enormous complexity of thesimplest of cells, they postulated an unproblematictransfer of inanimate matter into life. The Oparin–Haldane hypothesis also rejected this mechanistic con-ception, instead raising an evolutionary materialisticalternative and postulating not only continuity but alsonovelty. Life evolved naturally from inorganic matterthrough intermediate steps, and this process gave rise tounique biological properties.

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Alexander Oparin – biochemistry and dialectical

materialism

Oparin’s ideas on the prebiotic synthesis of organiccompounds were influenced by the mineral theory of theorigin of petroleum suggested in the late 19th century bythe famous Russian chemist Dmitry Medeleyev. However,Oparin’s origin-of-life scenario was first and foremostconceived in terms of the developing field of biochemistry.In the early 20th century, biochemists focused primarilyon the isolation and study of enzymes. Consequently, theytended to view life as a ‘self-regulating dynamic equili-brium of a system of catalytic reactions’ [9]. Restricted bythe power of the then-used light microscope, many cellularconstituents were seen as colloid gels – small droplets ofpolymers suspended in liquid. Enzymes were also charac-terized as ‘colloidal catalysts’ [10]. As a biochemist, Oparinfocused his experimental work on enzymology, particu-larly during his long career as the director of the famousBakh Institute of Biochemistry in Moscow. He regardedmetabolism, carried out by enzymatic reactions, as thedefining characteristic of life. It was through metabolism,Oparin claimed, that the cell could adapt to itschanging environment.

Based on colloid chemistry, he suggested that organicpolymers (resembling proteins and sugars) in theprimordial ocean formed a sort of colloidal solution. Oncethis solution reached a certain concentration, enclosedmicroscopic droplets separated from their aqueousenvironment. These so-called ‘coagulates’ or ‘coacervates’could selectively absorb material from the solution,perform primitive enzymatic reactions, grow in size andeventually divide. Such structures, viewed by Oparin aspossible ‘protocells’, were thus engaged in a primordialkind of reproduction, transferring from parent to offspringtheir internal organization that was responsible for theircapacity to metabolize. Primitive division and inheritanceformed the basis for primitive processes of naturalselection and thus for the evolution of more intricate andefficient metabolism. Because Oparin’s scenario washeterotrophic, he went on to account for the furtherevolution of autotrophic organisms capable of producingtheir own organic material through photosynthesis. Withthe establishment of molecular biology in the 1950s and1960s, Oparin also discussed the evolution of a geneticapparatus, claiming that such evolution could haveoccurred only within a metabolizing protocellularstructure [11].

Along with biochemistry and colloidal chemistry asscientific sources of inspiration, Oparin also had strongphilosophical and ideological commitments that shapedhis thinking on the origin of life. In his 1924 bookletOparin was motivated by traditional materialism,denouncing neo-vitalism and the panspermia theories,and attempting to demonstrate the similarities betweenbiological and physico-chemical systems. Such material-ism was no doubt compatible with the social and politicalclimate in the Soviet Union during the 1920s [12].

However, by the time he published his 1936 bookOparin had already departed from simplistic materialism.He became committed to the tenets of dialecticalmaterialism, relying heavily on the Dialectics of Nature

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by Friedrich Engels (the co-founder of Marxism), whichwas published in the Soviet Union in 1925. Oparin hadapplied the basic dialectical postulate to his origin-of-lifetheory, arguing that matter underwent changes andevolved from one level of organization to the next, witheach level being characterized by specific new laws,including ‘biological laws’. In 1936 Oparin emphasizedproperties he considered unique to life, especially complexorganization and the purposeful nature of biologicalprocesses – a clear distinction to his pamphlet of 1924.

Oparin’s prominent status within Soviet science andhis close association with the Communist Party and thepolitical establishment, notably his relationship with thepowerful agronomist Trofim Lysenko, have led to the claimthat his Marxist jargon reflected no more than politicalopportunism [13]. However, in spite of the unsavoryalliance between Oparin and Lysenko in the 1940s andearly 1950s, historian of Soviet science Loren Grahamargues that Oparin’s ideological views were more than justlip service; they stemmed from a truthful incorporation ofdialectical materialism into his scientific conception [14].

J.B.S. Haldane – the virus as analogue and phylogenetic

link

Haldane’s illustrious career was marked by his historiccontributions in the 1920s and 1930s to genetics and theelucidation of enzymatic activity. He was also instru-mental in the establishment of evolutionary genetics. Itwas, however, the emergence of genetics and the discoveryof viruses that provided the main inspiration for his 1929paper on the origin of life. He also relied on the 1927experiments of the English chemist E.C.C. Baly, whoproduced sugars and amino acids by applying ultravioletradiation to solutions of carbon dioxide and ammoniain water.

Haldane postulated that large, self-reproducingorganic molecules were the intermediate link betweeninanimate matter and life, constituting the ‘first living orhalf-living things’. These formed in the rich ‘soup’ underthe influence of ultraviolet radiation [15]. He was muchimpressed by viruses, particularly the discovery in 1917 ofthe bacteriophage, literally the ‘bacterium eater’. It ishighly significant that Haldane agreed with the Americangeneticist Herman Muller’s likening of the bacteriophageto a gene that copies itself within the cell. Haldaneenvisaged the virus, which was only capable of reprodu-cing itself within the supporting cellular surrounding, asan analogue of his primitive reproducing molecules thatdepended on the ‘vast chemical laboratory’ of the ‘soup’.However, for Haldane, the virus was more than just afunctional model or analogue. He suggested the possibilitythat life on Earth could have remained in ‘the virus stagefor many millions of years’ before the evolution of acellular structure [16] and that the virus might actually bea missing link in the development of life [17].

Thus, whereas Oparin regarded life first and foremostas a metabolizing multi-molecular system, Haldane sawits distinguishing characteristic as the ability to reproduceitself. Yet, in contrast to some future supporters of the‘replication-first’ view of life, Haldane pointed out that in atrue living system the function of any part, including

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genes, depended on the cooperation of all the other parts.Although an acknowledgement of an Oparin-like ‘bio-chemical view’, Haldane’s ideas could also been indebtedto the work of his father, the famous physiologist J.S.Haldane, who proclaimed an organicist conception of lifein the 1910s and 1920s. Moreover, this anti-mechanisticposition could be seen as anticipating J.B.S.’s conversionto dialectical materialism a few years later [18].

It is noteworthy that many of those who contributed tothe early-20th century philosophical breakthrough in thestudy of the origin of life were Marxists: notably Oparin,Haldane, the virologist N.W. Pirie and the Englishphysical chemist J.D. Bernal [19]. The significance of theMarxist philosophical–ideological commitment can begleaned from Oparin’s comment that ‘Dialectical materi-alism makes it possible to accept the material basis of lifewithout having to regard every phenomenon not includedin physics and chemistry as vitalistic or super-natural’ [20].

Leonard Troland – promoting the ‘genetic enzyme’

Troland’s remarkable ideas on the origin of life might haveremained obscure had his three papers on the subject(1914, 1916 and 1917) not been revisited and partlyadopted by the geneticist Herman Muller in the 1920s and1930s [21]. Troland was neither a biochemist nor ageneticist, but a psycho-physiologist. Until his death –by a mysterious accident at the age of 43 – he taughtpsychology at Harvard, concomitantly holding engineer-ing posts and being responsible for several inventions incolor cinematography, early television and laser develop-ment. His dismay with the state of biology under theassault of neo-vitalism led him to suggest a comprehensivetheory based on ‘a single physico-chemical conception’, ‘anenzyme or organic catalyst’ that could explain the‘fundamental mysteries of vital behavior’, among themthe origin of life [22].

Not sharing Oparin’s and Haldane’s professional back-ground, but still reliant on the discovery of enzymes andon the new findings in genetics, Troland was primarilypreoccupied by the logic of the origin-of-life situation.Regarding life as characterized by self-reproduction andself-organization achieved through selective catalysis andregulation, he strived to account for the emergence ofthese properties by physico-chemical means. UnlikeOparin’s and even Haldane’s, Troland’s was an abstractmodel relating to the sudden appearance in the primordialocean of a primitive molecule endowed with two remark-able catalytic abilities. This enzyme molecule was bothautocatalytic, catalyzing its own formation, and hetero-catalytic, catalyzing the formation of an envelopearound itself.

Reflecting the then lack of knowledge concerning boththe mechanism of enzyme action and the nature of thehereditary material, Troland first spoke of an ‘enzyme’ andthen of a ‘genetic enzyme’, before identifying in 1917 hisprimitive molecule with nucleic acids that combine withproteins in the nucleus [23]. In 1929, when HermanMuller adopted some of Troland’s ideas, he replaced‘genetic enzyme’ with ‘gene’ [24]. In attributing thecapability of both autocatalysis and heterocatalysis to

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his ‘genetic enzyme’, and moreover, in postulating theneed to combine gene and enzyme in the same molecule,Troland’s conception is a forerunner of the ‘ribozymes’,enzymatic RNA molecules. The ribozymes, hypothesizedin the 1960s and discovered in the 1980s, are consideredthe cornerstone of the RNA world, regarded by mostorigin-of-life scientists as a crucial stage in the emergenceof life [25]. Like present-day RNA-world supporters,Troland saw the autocatalytic aspect of his ‘geneticenzyme’ as its pivotal function.

Among Troland’s important contributions to the ‘repli-cation-first’ outlook on the origin-of-life was his clearanalysis of the presuppositions this conception implied,which was later repeated by other researchers [26]. Thesepresuppositions were spelled out in his response toaccusations that the sudden appearance of a double-actingenzyme was extremely improbable. First, he pointed outthat autocatalysis would produce many copies out of afirst, single molecule. Second, he argued that there was ahuge timeframe for this ‘lucky accident’ – the suddenformation of the first genetic enzyme – to occur. ‘Since onlyone event of this specific kind is required by the theoryduring a period of time covering many millions of years,objections based upon general consideration of probabilityhave practically no force,’ he wrote [27]. Furthermore, heclaimed that self-reproduction of the genetic enzyme alsoprovided the basis for mutations and evolution throughnatural selection.

Two rival traditions and a unifying theme

Oparin’s biochemical conception characterized life as amulti-molecular, multifunctional metabolic system,whereas Haldane and Troland’s genetic theories identifiedearly life with molecular self-reproduction. These twoconcepts later became the two main lines of research in theorigin-of-life field, and the conflict between their suppor-ters grew in intensity, especially with the establishment ofmolecular biology. Since the 1950s, the realization that theorganization of the most primitive cell already involvedtight interaction between metabolism and replication,between nucleic acids and proteins, has given rise to a‘chicken-and-egg’ dilemma in origin-of-life research: howcould nucleic acids or proteins emerge independently, andif they could, which came first? This led to variousattempted ‘metabolic’ and ‘genetic’ solutions; the latternotably producing the RNA-world theory. Addressingprocesses that took place billions of years ago alsoinevitably leads to debates about specific primordialconditions. These uncertainties are progressively beingovercome through the efforts of scientists in the variedfields of geology, astrophysics, planetary science, evol-utionary biology and chemistry. Data and theories from allthese fields contribute to the challenging interdisciplinaryproject focused on the emergence of life on Earth andpossibly on other planets, recently named astrobiology.

Debates and controversy being part of the study of theorigin of life, it should be emphasized nevertheless thatthe Oparin–Haldane hypothesis still provides a frame-work that unifies the various traditions and lines ofresearch. Although many doubts have been raised inrecent years regarding the existence of the reducing

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atmosphere and the primordial ‘soup’, the philosophicalsignificance of the hypothesis remains valid. The under-lying presupposition that living systems emerged frominanimate matter via natural processes is an inherentpart of the wider and strongly substantiated evolutionaryworldview. It is this presupposition that makes theempirical study of the origin of life possibleand worthwhile.

References

1 Oparin and Haldane met for the first time in 1963, at the SecondInternational Conference on the Origin of Life that was held inWakulla Springs, FL, USA. For details on this see Fox, W.S., ed. (1965)The Origins of Pebiological Systems: Proceedings of a ConferenceConducted at Wakulla Springs, Florida on 27–30 October 1963,Academic Press (New York, NY, USA), p. xv and p. 98

2 For an overview of these historical developments see Fry, I. (2000) TheEmergence of Life on Earth: A Historical and Scientific Overview,Rutgers University Press (New Brunswick, NJ, USA)

3 Oparin, A.I. (1967) The Origin of Life (Synge, A., trans.). In Bernal,J.D. The Origin of Life, pp. 199–234 (Appendix I), Weidenfeld andNicolson (London, UK), p. 203. This was the first time Oparin’s 1924pamphlet was published in English

4 Kamminga, H. (1982), Life from space – a history of panspermia.Vistas in Astronomy 26, pp. 67–86

5 Oparin, A.I. (1967), p. 206 (footnote)6 In his The Origin of Life, Haldane suggested that ultraviolet rays

could have easily penetrated the oxygen-deficient atmosphere owingto the absence of an ozone layer. Haldane, J.B.S. (1967) The Origin ofLife. In Bernal, J.D. The Origin of Life, pp. 242–249 (Appendix II),Weidenfeld and Nicolson. The 1929 paper was originally published inRationalist Annual, 3–10

7 Haldane, J.B.S. (1967), p. 2468 Oparin’s The Origin of Life on Earth, published in 1936, was

translated into English by Sergius Morgulis as Oparin, A.I. (1938)The Origin of Life, Macmillan (New York, NY, USA). It was thistranslation that was read by Harold Urey prior to the Miller–Ureyexperiment, reaffirming his views on the reducing nature of theprimordial atmosphere; Urey, H.C. (1952) On the early chemicalhistory of the Earth and the origin of life. Proceedings of the NationalAcademy of Sciences USA 38, pp. 351–363. The 1938 translation wasreprinted in 1953 as Oparin, A.I. (1953) The Origin of Life, DoverPublications Inc. (New York, NY, USA). Meanwhile Oparin hadrevised his original book and published a second edition of it in Russiain 1941. This new edition was translated into English by Ann Syngeand published as Oparin, A.I. (1957) The Origin of Life on the Earth,Academic Press (New York, NY, USA). Both the 1953 and the 1957editions were widely read by scientists in the West

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9 Kohler, E.R. (1973) The enzyme theory and the origin of biochemistry.Isis 64, pp. 181–196 (op. cit. p. 185)

10 Oparin, A.I. (1953), pp. 173–17511 Oparin, A.I. (1968) Genesis and Evolutionary Development of Life

(Maas, E., trans.), Academic Press12 See Graham, L.R. (1987) Science, Philosophy and Human Behavior in

the Soviet Union, Columbia University Press (New York, NY, USA),pp. 72–73. Furthermore, in his entry on Oparin in the Dictionary ofScientific Biography, historian Mark B. Adams notes that ‘in the early1920s many tracts were published [in the Soviet Union] as part of thegovernment’s campaign to support materialism and underminereligion, and popular pamphlets on Darwinism, human evolution,and experimental biology abounded.’ Adams, M.B. (1990) Oparin,Alexandr Ivanovich. In Dictionary of Scientific Biography (Vol. 18,supplement II) (Holmes F.L., ed.-in-chief), pp. 695–700, CharlesScribner’s Sons (New York, NY, USA)

13 See Adams, M.B. (1990), pp. 698–699; and Muller. H.J. (1966) Thegene material as the initiator and the organizing basis of life.American Naturalist 100, pp. 493–517 (op. cit. p. 494)

14 Graham, L.R. (1987), pp. 71, pp. 82–83, p. 90 and p. 10115 Haldane, J.B.S. (1967)16 Ibid., p.24717 Podolsky, S. (1996) The role of the virus in origin-of-life theorizing.

Journal of the History of Biology 29, pp. 79–126 (op. cit. p. 94)18 Haldane joined the Communist Party in 1936, soon after the outbreak

of the Spanish Civil War, and was chairman of the editorial board ofthe party organ, the Daily Worker. As noted by Podolsky, in the 1930s‘many left-intellectual scientists both politically advocated socialismor Marxism and epistemologically advocated dialectical materialism.’Podolsky, S. (1996), p. 107 (note 104)

19 See Graham, L.R. (1987), pp. 72–73; and Podolsky, S. (1996), pp. 79–126

20 Oparin, A.I. (1961) Life: Its Nature, Origin and Development,Academic Press, p. 5

21 Muller. H.J. (1966), p. 49422 Troland, L.T. (1914) The chemical origin and regulation of life. Monist

24, pp. 92–133 (op. cit. p. 92 and p. 102)23 Troland, L.T. (1917) Biological enigmas and the theory of enzyme

action. American Naturalist 51, pp. 321–350 (op. cit. p. 342)24 Muller, H. (1929) The Gene as the Basis of Life. In Proceedings of the

International Congress of Plant Sciences (Duggar, B.M., ed.), pp. 917–918, George Banta (Menasha, WI, USA)

25 Gilbert, W. (1986). The RNA world. Nature 319, p. 61826 See Dawkins, R. (1978) The Selfish Gene, Oxford University Press

(Oxford, UK), p. 16; and Dawkins, R. (1986) The Blind Watchmaker,Penguin Books (London, UK), pp. 140–163

27 Since Troland’s time, evaluations of the ‘tine window’ during which lifecould have emerged have changed considerably. In the 1950s and1960s scientists thought it could span billions of years, but in recentyears it has undergone a dramatic narrowing. See, Fry, I. (2000), pp.123–126; and Troland, L.T. (1914)