Don’t PNA in our OOL
Evolutionary theories for the origin of life (OOL) are in a bit of a crisis, unable to imagine how something as complex as a replicating cell (the necessary unit for Darwinian natural selection) could come into existence. Richard Robinson, a freelance science writer, surveyed the scene in PLoS Biology,1 and agreed: “The short answer is that they can’t, yet.” The word “yet” hinted that hope remains: “But this question may be a little closer to being answered as new money enters the field, and two new discoveries provide support for two competing models of prebiotic evolution.”
The two competing models are the “genetics first” model, that a replicating molecule bearing genetic information arose first, and the “metabolism first” model, that a metabolic cycle emerged that was later co-opted by information-bearing molecules. We’ll examine the two new discoveries he spoke of shortly.
Indeed, all may eventually prove wrong, and the real solution may lie hidden in some discovery yet to be made.
Robinson brought his readers up-to-date on the history of origin of life studies in a lighthearted manner. He pointed out that funding is a big issue among researchers in the field. He surveyed the Miller experiment (05/02/2003) and subsequent milestones from the 1950s to the present day, quoting Harold Morowitz (George Mason U) that “The initial Miller experiment was earth-shaking,” even though Morowitz himself discounts its relevance today, since in subsequent years researchers realized the initial conditions were wrong.
Robinson discussed the leading “RNA World” scenario (11/01/2002, 07/11/2002), but acknowledged that assuming RNA would emerge is like the “assume a can opener” joke (see prior commentary). Some have suggested a simpler polymer, like peptide nucleic acid (PNA), preceded RNA:
The case for PNA is weak, though. While modern cells still bear traces of a catalytic RNA world within them, “there is absolutely nothing that I know of to suggest there is evidence for PNA or other such molecules in present cells,”says [Leslie] Orgel [Salk Institute]. If they ever contributed to the development of life, all traces of their existence appear to have been wiped clean.
Apparently there was no PNA in the OOL, in other words. Robinson also discussed the problem of chirality, that is, how life selected only one hand out of mirror-image molecules (see online book). Robinson paid particular attention to the hypothesis by Michael Russell (12/03/2004) and William Martin that life began as a self-perpetuating chemical cycle in minerals around hydrothermal vents, but acknowledged again that this model also depends on RNA. Amidst the bad news, Robinson announced two recent discoveries he thinks provide new hope for the two competing theories.
In the beginning, hydrogen: The Miller experiment is not down for the count, he encouraged: “in June of 2005, the prebiotic soup got a new lease on life.” New calculations appear to show that there was considerably more hydrogen in the early atmosphere than once thought” (06/16/2005). Orgel thinks this could resurrect Miller’s chemistry, although “there is still an enormous way to go” to get all the precursor molecules for RNA.- Jumpstarting the bootstrap on piggyback: The other discovery, announced by Morowitz in support of the “metabolism first” scenario, is that “small organic molecules, such as amino acids, can catalyze the formation of other small organic molecules, such as nucleic acids.” The catalysis of sugars by amino acids was announced in Chemistry this past August, for instance. Coupled with new ideas about molecular networks (10/05/2005), Morowitz finds such results dramatic and filled with potential:
“What has emerged is a very strong self-organizing principle,” says Morowitz. In this view, while iron sulfide may have been the original catalyst, it did not remain the only one for long. As products of the original reactions catalyzed new reactions, metabolic networks quickly arose. Feedback loops developed when two molecules regulated one another’s synthesis. “The system can piggyback its way upward,” he says.
Robinson acknowledged that both scenarios, genetics-first and metabolism-first, have serious problems; “It is still unclear how, or whether, these competing models will fit together, and whether they will lead to a robust scenario for life’s origin” he said. “Indeed, all may eventually prove wrong, and the real solution may lie hidden in some discovery yet to be made.” Such speculations may not be practical, but the fascination lies in tackling the big questions. “You’re going to make a philosophical impact,” Morowitz said. Jack Szostak, another OOL researcher, added, “These are the big questions. Anybody who thinks has to be grabbed by these.”
1Richard Robinson, “Jump-Starting a Cellular World: Investigating the Origin of Life, from Soup to Networks,” Public Library of Science, Biology, Vol 3, issue 11, Nov 2005, DOI: 10.1371/journal.pbio.0030396.
Evolutionary OOL is a faith ministry, funded by charitable contributions from the federal government. It survives purely on hope – hope that somehow, somewhere, scientists may find the holy grail of a purely naturalistic origin of life. Evolutionists often chide creationists for believing in a “God of the gaps” – attributing to divine action what science has not yet explained. Yet here we see a naturalism of the gaps, as philosopher of science J. P. Moreland (Biola) quips. Putting God in a gap such as the origin of life by attributing it to design, he says, is justifiable when the gaps have been getting wider for a long time. The design inference is not a mere God-of-the-gaps retreat, he also argues, because there is positive evidence for design, not just lack of evidence for a natural explanation. Evolutionists lack both of these qualifiers for dealing with gaps. They cannot coax intractable molecules to fill in a gap that molecules do not naturally wish to fill, and there is no evidence nor requirement that chance and natural law could, would or should fill it.
Robinson’s article illustrates how evolutionary hope springs eternal despite pitiful snippets of evidence to bridge a widening canyon with disconnected bits of wet tissue paper. This hope is evident also in a 2005 lecture series on the Origin of Life by Dr. Robert Hazen (George Mason University) published by The Teaching Company. Hazen is a good teacher and storyteller; the listener can learn some organic chemistry and geology, and hear some interesting anecdotes about personalities in the field. But throughout the 24 lectures, Hazen was frank and honest about the difficulties, which as yet have no solution. The glue that holds all the bad news together is hope that a naturalistic explanation for OOL can be found. Never did he consider that other scientific explanations, like intelligent design, might have a better explanation, nor did he explain why scientists should be permitted to contradict the evidence of chemistry and physics indefinitely, just to maintain a philosophical preference for naturalism.
We need to remind such People of Frothy Faith that the science is against them. RNA is an extremely intractable molecule; it thrives in cells because there are genes and protein machines that manufacture it according to specifications written in DNA, and repair it or dispose of it when it breaks. Hazen admitted openly that no plausible natural environment produces the phosphates, the ribose sugars, the bases, or can assemble them into nucleotides, even if the building blocks formed somehow. Nor could the nucleotides plausibly link themselves into an RNA strand. Amino acids (a requirement for PNA), similarly, do not naturally link together – they dissolve in water. Furthermore, the chirality problem is serious. Hazen and Orgel sweep it away with whimsical speculations, but the probability is against them (see online book). The metabolism-first scenario (which Hazen and Morowitz favor), must face the eventuality of needing a genetic, information-carrying molecule. Without it, there is no hope of a Darwinian mechanism to preserve any gains. If PNA or TNA (threose nucleic acid, another hypothetical precursor to RNA) were to arise, there is the difficulty of imagining any plausible “genetic takeover” by RNA or DNA (11/05/2005). These are just a few of the show-stoppers. It only takes one show-stopper to stop a show.
Meanwhile, the gap between “top-down” and “bottom-up” approaches (02/06/2005) is getting wider. Is there anything that will force evolutionary OOL researchers out of the naturalistic pool? Robinson’s “two new discoveries” are pathetically inadequate. Adding a little more hydrogen to revive the Miller myth is like tossing iron filings into the Grand Canyon, hoping a bridge will emerge. Describing how some amino acids might catalyze some sugars is like the self-replicating robot story (09/30/2005); it was pathetically simple compared to a real person, and even then, only worked with a lot of intelligent assistance. This is all too little, too late. The OOL pool of scientifically verifiable facts belongs to intelligent design. Notice that there is no PNA in it. Let’s keep it that way. We won’t swim in their toilet of speculation if they won’t PNA in our pool.