The phenomenon of life remains even today the biggest mystery and challenge to human intellect. Life and death can be defined only in conjunction with the Quranic revelations (see post 4 at http://quranscienceblog.blogspot.com). How to define life is a sweeping question that affects the whole branches of biology. According to Cleland and Chyba: “There is no broadly accepted definition of ‘life’. Suggested definitions face problems, often in the form of robust counter-examples.” [1]. In spite of the fact that biologists do not have any idea of what life is, it would seem ironical that several theories have been advanced to explain its origin. These can be broadly categorized into four namely, prebiotic soup theory, gene-first model, metabolism-first model [2] and panspermia theory.
Prebiotic soup theory
It was hypothesised that in the beginning, the earth was very hot and did not possess an atmosphere. But as it cooled, an atmosphere began to develop from the gas emitted from the rocks. The early atmosphere was without oxygen, the vital gas required for higher forms of life. Only primitive forms of life could have survived then. By chance combination of atoms, macromolecules were formed from which self-reproducing structures were formed. The reactions leading to their formation took place when the earth had been sufficiently cooled. The lowering of temperature would have also caused the condensation of steam into water creating large water bodies like oceans, seas, etc., on the planet. Several chemical elements particularly carbon, hydrogen, nitrogen and oxygen present in the primitive atmosphere combined to form amino acids from which proteins were formed. Stanley L. Miller and Harold Urey of the University of California, San Diego U.S.A., demonstrated that simple amino acids and several complex organic compounds could be formed in a closed system containing hydrogen, ammonia, methane and water vapour under the influence of electric discharge [3]. These results were considered strong evidence to suggest that a similar reaction might have taken place in the early atmosphere under the influence of lightning, resulting in the formation of amino acids and from them, the proteins. These organic substances might have accumulated in the soupy sea. In a discussion of the origin of life, George Wald concluded that life arose in the sea [4]. It was also hypothesized that random encounters of molecules could have led to the production of molecules of life. “The suggestion that random chemistry could produce the molecules of life “held the field for a long time.” But later calculations appeared to show that the early atmosphere contained much more carbon dioxide and much less hydrogen than Miller's model required, and correcting these concentrations cast doubt on the likelihood that complex molecules would form in abundance. Where, then, might organic precursors have come from? There is some, albeit scant, evidence for their arrival on comets colliding with the earth, but there is little enthusiasm for this as a solution. Finally, there is no geologic evidence, in either sediments or metamorphic rocks that such a soup ever existed.” [2].
Gene-first model
This theory suggests that DNA is the precursor of life. The model is however handicapped by the chicken-and-egg problem associated with DNA and protein. Since DNA codes for protein, it is required for the production of protein while protein is required for the synthesis of DNA as catalyst. The role of DNA in the prebiotic scenario thus became suspect. The importance shifted to RNA as it can function as temporary information carrier and catalyst. According to the RNA world hypothesis, the first living system was a polymer(s) of catalytic RNA capable of self-replication that subsequently evolved the ability to encode more versatile peptide catalysts [5]. Mineral-catalyzed reactions, followed by a series of fractionations, have been suggested to offer the most plausible route to RNA [6, 7]. According to Smith et al., a stable cell wall is required to protect the first primitive organism. The first cell wall might have been an internal mineral surface, from which the cell developed a protective biological cap emerging into a nutrient-rich “soup”. Ultimately, the biological cap might have expanded into a complete cell wall, allowing mobility and colonization of energy-rich challenging environments [8].
Metabolism-first model
Even while the RNA world hypothesis was seriously considered, Günther Wächtershäuser proposed a radical alternative theory of the origin of life based on iron sulfide. Iron disulfide (pyrite) can catalyze a variety of crucial biochemical reactions. According to him the earliest living system was not a nucleotide-based replicator but a mineral-based metabolizer converting simple and abundant inorganic compounds like carbon dioxide and hydrogen sulfide into more complex organic ones on the surface of a pyrite crystal [9, 10, 2]. Wächtershäuser’s theory of auto-origin suggests pyrite formation as the earliest energy source for life based on surface metabolism and autocatalytic reproduction cycle. Essentially it is a theory of carbon fixation from an archaic, pyrite-pulled version of the reductive citric acid cycle [9, 10]. Another view is that life on the earth might have begun in rocks on the ocean floor more than four billion years ago. Hot springs
Panspermia theory
The idea that life originated from non-life on this planet by chance received a jolt when a new theory called ‘directed panspermia’ was proposed in 1973 [15]. According to this theory, spores of life might have been sent to the earth in an unmanned spaceship by a more advanced civilization evolved billions of years ago on a planet of another star.
Problems with the theories
All attempts to assemble an integrated scheme of physicochemical processes have significant weaknesses [16]. Problems occur with hypotheses of the earliest molecules with the properties commonly associated with life. These include the unlikelihood of formation of complex self-replicating molecules such as RNA by chance encounters even over geological time; the difficulty of protecting such molecules following their formation from dilution and destruction by high temperatures, hydrolysis and ultraviolet radiation; and finally the difficulty of imagining how self-organization alone could lead to encapsulation of a complex hierarchy of biochemical reactions in a membrane to form the simplest unicellular organism [16]. The “RNA world” theory is not a feasible proposition and is losing ground. The theory is appealing because of the supposed dual roles played by RNA – both as genetic material and as a catalytic molecule in the protobiological evolution. However this concept encounters considerable difficulties for the fact that RNA is chemically fragile and difficult to synthesise abiotically. The known range of its catalytic activities is rather narrow, and the origin of an RNA synthetic apparatus is not clear [17].
A high temperature origin of life (80o to 110oC) was widely favoured because hyperthermophiles which grow at temperatures between 80o and 110oC are claimed to be the oldest organisms on the earth, although there are dissenting opinions [18]. The atmospheric models depicting an early warm (approximately 85o to 110oC) earth support this theory. Still higher temperature origin (350oC in submarine vents) was also proposed. However, the instability of nucleobases (adenine, uracil, guanine, cytosine and thymine) at temperatures much above 0oC would make them unlikely to accumulate on the early Earth. Since these compounds are essential for the formation of the first genetic material in the pre-RNA and RNA world, a low-temperature origin of life and atmospheric models suggesting a cool early earth (about 0oC) rather than a warm one (around 85o to 110oC) can only be considered, if origin of life involving these nucleobases is assumed [18].
Many of the theories of origin of life including those relating to the origin of the genetic code have been tested in laboratory experiments on the assumption that the protocol used in those experiments shall provide suitable proxy for a prebiotic environment [19]. A pre-RNA world would have come first, during which some substance, RNA-like polymer carried out the genetic functions later taken over by RNA. Although the hypothesis required the existence of a nucleotide soup in which RNA molecules performed the catalytic activities to assemble themselves, the experimental evidence does not appear to support the existence of such a soup [20].
Another serious problem is explaining the chirality. “To date, none of the models have proposed a solution to one of the more vexing origin problems: chirality. Three-dimensional molecules such as sugars and amino acids can exist in two mirror-image forms, like left and right hands (chiros is Greek for hand). Any nonbiological synthesis of such molecules, as would have occurred before life arose, produces equal amounts of each type. Nonetheless, modern cells use exclusively left-handed amino acids and right-handed ribose sugars, and interference from the wrong kind shuts down biological reactions. How could chiral life arise in the presence of so much interference?” [2]. According to Freeman Dyson, the popular accounts of the origin of life side step the issue of the origin of the complex cooperative schema worked out between proteins and nucleic acids – the controlled production of self-replicating catalytic systems of biomolecules. Instead they focus on other hurdle, i.e., producing amino acids and nucleotides, and getting them to polymerase into proteins and nucleic acids (typically RNA). All the scenarios that have been proposed for producing RNA under plausible natural conditions lack experimental demonstration and this includes the RNA world, clay crystals and vesicle accounts. No one has been able to synthesize RNA without the help of protein catalysts or nucleic acid templates, and on top of this problem, there is the fragility of the RNA molecule to contend with [21]. It seems very unlikely that minerals played an important part in prebiotic chemistry, both as simple adsorbents and as catalysts. It is also unlikely that a single mineral would have functioned as a specific catalyst for several unrelated reactions. Even if the members of a suite of minerals could each catalyze one step in a complex cycle, it does not seem likely that the cycle would self-organize on their surfaces [22]. All these hypotheses were proposed believing that life is material phenomenon. Anybody can suggest theory of this kind; not one but any number.
The experiments hitherto conducted on the origin of life show that life can arise only from life. Chemists have been able to make complex organic molecules such as proteins, amino acids, DNA, RNA and other complex building blocks of life in the laboratory but no one has been able to synthesize a cell or put together simple structures such as mitochondria or chloroplasts from its constituents [23]. At present we have the knowledge and technology required to produce any ‘gene’ (DNA molecule) in the laboratory. Molecular biologists have been synthesizing genes, and recently a research group at the J. Craig Venter Institute, USA. has artificially produced the complete genome of an organism. The organism is Mycoplasma genitalium, a parasitic bacterium with the smallest genome for any free-living cell. The group constructed synthetically the genome of the organism and named it Mycoplasma genitalium JCVI-1.0. It contained all genes of the organism except the gene MG408, which was disrupted to block pathogenicity [24]. This is a landmark achievement in biology for two reasons: one is that scientists could synthesize the genome (which according to them is genetic program) of a living organism. Secondly, it proved that genome cannot produce life. It is this unwelcome finding that is more important than the former. This would mean that even if a genome (identical to that of a living organism) had been produced through chance combination of molecules in the prebiotic soup as scientists assume, it would not have sprung to life. The failure of the synthetic genome to spring to life questions the very assumption that life is material phenomenon and it originated on Earth from non-life. It is pertinent to note that any claim of creating life from non-life should be based on chemical synthesis without involving a living cell or organism at any stage during the experiment. Instead of synthesizing a cell in the laboratory from scratch, researchers could as well use a dead cell as the starting material. A dead cell is identical to a prosthetic cell containing all the chemical structures including genome. They only have to restore life to it. Efforts so far made to synthesize life from non-life have failed indicating that there is no experimental evidence yet to establish that life is a material phenomenon. In other words, the experimental failures support the assertion that life is nonmaterial phenomenon (proving the Quranic revelation of nonmaterial rooh as the cause of life in verses15:28-29). Further none of the so-called ‘theories of origin of life’ proposes how life originated.
Literature on the origin of life leads us nowhere. Panspermia is not a theory of origin of life at all. It does not address the question of origin of life but hypothesizes that life descended to Earth from elsewhere. In effect, it only shifts the venue of origin from the earth to another region in the cosmos. It is silent about how life originated in the first place. Research papers published on the question of “origin of life” are mere views of the scientists about the likely scenarios that might have occurred prior to the origin of life, and nothing more! They all still remain in the province of non-life. In that condition they are neither theories of origin of life nor scientific facts. This will be made amply clear from the following conclusions drawn from a study of the origin of life (italics added): “A CO-dominant atmosphere may have existed when life originated. This atmosphere could have produced a variety of bioorganic compounds with yields comparable to those obtained from a strongly reducing atmosphere. A small amount of CO2 could have allowed the primitive Earth to freeze. This could mean that CO would have been more stable in the atmosphere than previously thought because of the reduced vapor pressure of water. Methane and ammonia would have been also more stable and could have contributed to the synthesis of bioorganic compounds. CO2 is likely to have been present, but it might not have been significantly involved in the synthesis of bioorganic compounds” [25]. The conclusions drawn from this study exemplify the kind of information being spewed out from research on origin of life. Biologists only construct storylines to enhance the credibility of the false assumption that life originated from non-life! It is such thought experiments on which these theories are founded! In fact there is not an iota of evidence to hypothesize life’s origin from non-life!
The biggest joke is none of these theories suggests how life originated! They all stay in the non-life domain. They do not even qualify as scientific theories as they are neither testable nor falsifiable directly or indirectly through their predictions. These theories do not yield any predictions also. Yet they are considered as scientific theories! Does anyone including their authors and publishers consider these stories as science? If not, why these stories are published and promoted as science to mislead the public?
References
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2. Robinson, R. 2005. Jump-starting a cellular world: Investigating the origin of life, from Soup to networks. PLoS Biol 3(11): e396.
3. Miller, S.L. and Urey, H.C. 1953. Production of some organic compounds under possible primitive Earth conditions. J. Amer. Chem. Soc. 77:2351.
4. Wald, G. 1979. The origin of life. In Life: Origin and Evolution, Readings from Scientific American, W.H. Freeman & Co., San Francisco, p. 47-56.
5. Gilbert, W. 1986. Nature (London
6. Joyce, G.E. and Orgel, L.E. 1993. in The RNA World, eds. Gesteland, R.F. and Atkins, J.F. Cold Spring Harbor Lab. Press, Plainview, NY, pp. 1-25.
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12. Bernal, J.D. 1967. The Origin of Life. Weidenfeld and Nicholson, London
13. Cairns-Smith, A.G. 1982. Genetic Takeover and the Mineral Origins of Life. Cambridge Univ. Press, New York
14. “Clays aided first life”. Astrobiology Magazine, http://www.astrobio.net/news/ Topic3.html.
15. Crick, F.H.C. and Orgel, L.E. 1973. Directed panspermia. Icarus 19:341.
16. Smith, J.V. 1998. Biochemical evolution I.
17. Devincenzi, D. ed. Final Report, Astrobiology Workshop at NASA Ames
18. Levy, M. and Miller, S.L. 1998. The stability of the RNA bases: Implications for the origin of life. Proc. Natl. Acad. Sci. USA 95:7933-7938.
19. Landweber, L.F. 1999. Testing ancient RNA-protein interactions. Proc. Natl. Acad. Sci. USA 96:11067-11068.
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21. http://www.astrobio.net/news/article428.html. Accessed April 25, 2003.
22. Orgel, L.E. 2000. Self-organizing biochemical cycles. Proc. Natl. Acad. Sci. USA 97(3):12503-12507.
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24. Gibson, D.G. et al. 2008. Complete chemical synthesis, assembly and cloning of a Mycoplasma genitalium genome. Science 319 (5867):1215-1220.
25. Miyakawa, S., Yamanashi, H., Kobayashi, K., Cleaves, J.H. and Miller, S.L. 2002. Prebiotic synthesis from CO atmospheres: Implications for the origins of life. Proc. Natl. Acad. Sci. USA 99(23): 14628-14631.
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