A Nature review that begins with the pronouncement that an experiment “has quashed” major objections to the RNA world of prebiotic origins (Ref 1) is bound to raise a few eye-brows. It is a bold pronouncement indeed and one that must be accompanied by a water-tight set of evidences. In his review of the work of John Sutherland and others at the University of Manchester, science writer Richard Van Noorden promised just that by declaring to his readers that these same scientists had achieved the ‘never-before-performed’ feat of making a ribonucleotide- one of the components of RNA- in the lab (Ref 1). Key to the success of the experiment was the presence of a phosphate group that, in addition to serving as one of the final reactants in the ribonucleotide synthesis process, also functioned as a catalyst earlier on in the reaction (Refs 1-3). This result was the culmination of twelve long years of laboratory-based research during which simple molecules had been shown to be the “unwitting choreographers” of ribonucleotide synthesis (Ref 1).
Sutherland’s work fell squarely within the boundaries of the popular ‘RNA world’ hypothesis which posits that RNA preceded DNA in the prebiotic processes that later brought about life. In contrast New York University chemist Robert Shapiro maintained his position on the ‘Non-RNA-World’ rostrum by voicing his concerns over the assertion that Sutherland’s laboratory experiment had really provided a justifiable representation of the chemical maelstrom of the early earth (Ref 1). Ten years ago Shapiro laid out the ground work for what he saw as the implausible order of events that would have had to ensue if ribonucleotides were to have existed in sufficient quantities for the formation of RNA. In Shapiro’s assessment
“An isolated lagoon or other body of sea water would have to undergo extreme concentration, to perhaps 10-5 of its initial volume. This reduction in volume would be needed to bring urea from a concentration of 10-4 to 10-5 M assumed for many substances in a prebiotic ocean to that necessary for the reaction. It would further be necessary that the residual liquid be held in an impermeable vessel……The concentration process would have to be interrupted for some decades (assuming a temperature near 25°C) with the urea concentration near saturation, to allow the reaction to occur. At this point, the reaction would require quenching (perhaps by evaporation to dryness) to prevent loss by deamination. At the end, one would have a batch of urea in solid form, containing some cytosine (and uracil). This sequence cannot be excluded as a rare event on early Earth, but it cannot be termed plausible.” (Ref 4)
University of California chemist David Deamer and colleagues likewise contended that conditions on early earth would have been “inconsistent with moving beyond the initial stages of generating monomers and perhaps random polymers” (Ref 5) while former Yale biochemist Harold Morowitz famously wrote of the RNA world as “an environment that is impossibly improbable”(Ref 6). The rich specter of energy sources that would have decimated biologically-relevant molecules such as RNA led physicist Paul Davies to similarly question a naive reliance on prebiotic soup scenarios in general:
“A watery soup is a recipe for molecular disassembly, not self-assembly… The same energy sources that generate organic molecules also serve to destroy them. To work constructively, the energy has to be targeted at the specific reaction required. Uncontrolled energy input, such as simple heating, is far more likely to prove destructive than constructive. The situation can be compared to a workman laboriously building a brick pillar by piling bricks one on top of another. The higher the pillar goes, the more likely it is to wobble and collapse…As a general rule, if you simply heat organics willy-nilly, you end up not with delicate long chain molecules but with a tarry mess, as barbecue owners can testify.” (Ref 7, pp. 89-90).
To be sure, these same arguments ring as true today as they did when they were originally published regardless of which energy source is under study. Several alternative ‘Origins’ hypotheses have of course been put forward (Ref 5-8). Writing in the Proceedings of the National Academy of Sciences, the late Salk Institute biochemist and RNA World champion Leslie Orgel considered the notion of some self-organizational principle through which chemical cycles might have originated on the early earth (Ref 8). As Orgel pointed out, organic chemists have been successful in generating very simple chemical cycles- that is cycles that include perhaps one or two intermediate stages. Yet such an achievement is a far cry from the labyrinthine biochemical cycles that exist in even the simplest forms of life (Ref 8). In Orgel’s own words,
“To postulate one fortuitously catalyzed reaction, perhaps catalyzed by a metal ion, might be reasonable, but to postulate a suite of them is to appeal to magic.” (Ref 8 )
With the prebiotic earth reduced to a tarry barbecue mess upon which magic is the best we can come up with for explaining the origin of life’s biochemistry, one may rightly ask how much of what is under discussion falls within contemporary limitations over what is definable as science. As astronomer Guillermo Gonzalez and philosopher Jay Richards are quick to note, science today has become “applied naturalism” defined broadly as, “the conviction that the material world is all there is, and that chance and impersonal natural law alone explain, indeed must explain, its existence” (Ref 9, p.224). In his review of Sutherland’s experiments, Access Research Network correspondent David Tyler re-instated intelligent design as a viable alternative for explaining the origins of information-rich molecules such as RNA (Ref 10).
1. Richard Van Noorden (2009), RNA world easier to make, Nature, 13 May 2009, See http://www.nature.com/news/2009/090513/full/news.2009.471.html
2. Matthew W. Powner, Béatrice Gerland & John D. Sutherland (2009), Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions, Nature 459, 239-242
3. Kate Ravilious (2009), Molecule of life emerges from laboratory slime, New Scientist, 13th May, 2009, Online Access http://www.newscientist.com/article/mg20227084.200-molecule-of-life-emerges-from-laboratory-slime.html
4. Robert Shapiro (1999), Prebiotic cytosine synthesis: A critical analysis and implications for the origin of life, Proc Natl Acad Sci U S A. 1999 April 13; 96 (8): 4396-4401
5. David Deamer, Jason Dworkin, Scott Sandford, Max Bernstein, Louis Allamandola (2002), The First Cell Membranes, Astrobiology Volume 2 pp. 371-381
6. Richard Robinson (2005), Jump-Starting a Cellular World: Investigating the Origin of Life, from Soup to Networks, PLoS Biol 3(11): e396
7. Paul Davies (1999) The Fifth, Miracle, The Search for the Origin and the Meaning of Life Published by Simon and Schuster, New York
8. Leslie E. Orgel (2000), Self-organizing biochemical cycles, PNAS Vol 97, pp. 12503-12507
9. Guillermo Gonzalez and Jay Richards (2004), The Privileged Planet, How Our Place In The Cosmos is designed for Discovery, Regnery Publishing Inc, Washington D.C, New York, p.39
10. David Tyler (2009), Ribonucleotides and the revival of the “warm little pond” scenario, ARN, 19th May, 2009, See http://www.arn.org/blogs/index.php/literature/2009/05/19/ribonucleotides_and_the_revival_of_the_