RNA World Is Sterile — And the Mystery of Life’s Origin Remains
Charles Thaxton, Walter Bradley, and Roger Olsen have just released The Mystery of Life’s Origin: The Continuing Controversy, a greatly expanded and updated edition of the 1984 book whose first edition had a profound influence on the intelligent design movement. The new book includes a historical introduction by David Klinghoffer and new chapters contributed by James Tour, Guillermo Gonzalez, Stephen Meyer, Brian Miller, and Jonathan Wells.
The book has proved a fertile source of ideas, influencing Meyer, William Dembski, Michael Behe, Paul Nelson, and other leading ID proponents. Meanwhile, materialist hypotheses about the origin of life remain sterile. A case in point is the mythical RNA world.
A world of lifeless molecules, interacting at random, going nowhere — that’s the RNA world. It’s an uninhabited, inhospitable place where hopes die for life by chance. One can furnish its warm little ponds with copious quantities of RNA molecules. Nothing will happen.
Two Meanings of “Sterile”
The word sterile means “free from living germs or microorganisms.” It can also mean “incapable of producing offspring” or “not producing offspring.” But is the boundary between fertile and sterile fuzzy? Some clarification is needed. Certain hybrids, like the mule, are sterile, but they enjoy all the lively benefits of metabolism and motility. Origin-of-life research is down to basics. It has to get from lifeless chemistry to the first “living germs or microorganisms.”
Imagine a world where viruses were the only complex molecular entities. It would be sterile, because without a host to infect, viruses are incapable of producing offspring. And yet no hospital would risk having certain ones around. Origin-of-life theorists do not consider viruses as transitional forms to living cells, so no progress would occur on a virus world toward free-living, metabolizing, faithfully reproducing cells. Design theorists might consider the complex specified information in the virus particles evidence of an intelligent origin. The potential exists for an explosion of replication were an unlucky animal to parachute to the surface. Left to itself, though, a virus world would be sterile.
“How to Build a Cell”
How about the imagined “RNA world” long envisioned by many in the origin-of-life community? Given liquid water, sufficient temperature, and organic molecules, interesting things could happen. But the RNA world lacks even the head-start of the virus world. Its molecules would have no complex specified information from an intelligent source. Indeed, no intelligence would even exist yet in the RNA world’s cosmos, billions of years before humans evolved. The imaginary RNA world would have chemistry without biology. Crossing the boundary from sterile to fertile requires explaining the origin of metabolism and faithful replication of genetic information within a boundary, as shown in the animation “How to Build a Cell” from Illustra Media’s film, Origin. That’s one giant leap for RNA kind.
Hope and Hopelessness
Hope that an RNA world could make that leap has diminished considerably since it was proposed by Wally Gilbert in 1986. It was built on the idea that RNA could combine the roles of genetic information and metabolism. Some RNA molecules called “ribozymes” can do simple things like cut off parts of themselves. Because RNA, like DNA, stores genetic information in living cells, and could conceivably perform catalytic functions, like proteins, RNA became the hoped-for bridge between two requirements essential for a living cell. But if hopelessness represents the ground level of hope, Philip Ball started digging downward in an article this month in Chemistry World. From “Flaws in the RNA World”:
It’s an alluring picture — catalytic RNAs appear by chance on the early Earth as molecular replicators that gradually evolve into complex molecules capable of encoding proteins, metabolic systems and ultimately DNA. But it’s almost certainly wrong. For even an RNA-based replication process needs energy: it can’t shelve metabolism until later. And although relatively simple self-copying ribozymes have been made, they typically work only if provided with just the right oligonucleotide components to work on. What’s more, sustained cycles of replication and proliferation require special conditions to ensure that RNA templates can be separated from copies made on them. [Emphasis added.]
This is a telling admission, coming from a popular science writer who believes in evolution and the origin of life by unguided material processes. Here are the main problems with the RNA world that Ball describes:
1. Probability: ribozymes are “highly complex molecules that seem very unlikely to have randomly polymerised in a prebiotic soup.”
2. Chaos: researchers must acknowledge “what a complex mess of chemicals any plausible prebiotic soup would have been.” One cannot ignore damaging cross-reactions.
3. Concentration: without “mechanisms for both concentrating and segregating prebiotic molecules,” RNA molecules would not be likely to meet up and interact.
4. Sequence: without a functional sequence, it’s hard to imagine ribozymes having “any hope of copying themselves rather than just churning out junk.”
Ball tells how a leading RNA-world advocate, Gerald Joyce at Scripps, has acknowledged the need for a replicator prior to RNA: perhaps a “peptide-nucleic acid hybrid” without as high a threshold for functional complexity. That idea “may simply defer some of the problems rather than solving them,” Ball says.
An Application of Intelligent Design
Applying a great deal of intelligent design, the Scripps lab took a ribozyme through “14 rounds of evolution” (artificial selection, that is) to achieve “he most complex functional RNA that has been synthesized by a ribozyme,” according to Joyce. They hope that “with further in vitro evolution, they might obtain a ribozyme of similar complexity that is genuinely able to make itself.” Is Ball impressed by this attempt to make the RNA world hypothesis credible by using intelligent design to create a highly improbable molecule? No. Because the error rate is so high in the copying tests, “it points to another problem” —
5. Fidelity: chemical evolution could not proceed without faithful replication, because errors accumulate. This is the phenomenon of error catastrophe.
These errors would be critical to the prospects of molecular evolution, since there is a threshold error rate above which a replicating molecule loses any Darwinian advantage over the rest of the population — in other words, evolution depends on good enough replication. Fidelity of copying could thus be a problem, hitherto insufficiently recognised, for the appearance of a self-sustaining, evolving RNA-based system: that is, for an RNA world.
The rest of Ball’s article pretty much demolishes the RNA world hypothesis. Looking out of his hole, he sees blue sky overhead.
Maybe this obstacle could have been overcome in time. But my hunch is that any prebiotic molecule will have been too inefficient, inaccurate, dilute and noise-ridden to have cleared the hurdle. Rather, we’ll need to look for ways in which noisy, heterogeneous and perhaps compartmentalised molecular collectives could have bootstrapped their way to life. And that, after all, makes complete sense when you recognise that this is precisely what cells still are.
In short: cells exist; therefore they evolved. The best candidate for the origin of life is dead. Long live the origin of life!
The Real Issue
In Biology Direct in 2012, Harold S. Bernhardt described the RNA world hypothesis as “the worst theory of the early evolution of life (except for all the others).” For a survey of all the other theories, read Susan Mazur’s 2016 book, The Origin of Life Circus, and watch the world’s experts undermine the RNA world on various grounds without offering anything better. One calls the RNA world a “baseless fantasy.” Another one says it has had its “last hurrah.”
Philip Ball could have read The Mystery of Life’s Origin in 1984 to understand that the real issue is not just getting the right molecules, but arranging them in the right order. Ball understands the thermodynamic hurdle of joining nucleotides without the required energy, but there’s another, bigger hurdle stressed by Thaxton, Bradley, and Olsen in their book, affectionately abbreviated MOLO: overcoming the “configurational entropy” required to have molecules perform functions such as metabolism and replication. The focus is always on getting the “building blocks of life” to form and link up without making them spell anything.
MOLO’s 1997 update contained a new Appendix specifically mentioning the RNA world hypothesis, which had become popular after the original edition. They mentioned all the problems Ball talked about, and more: interfering cross-reactions, the improbability of ribose and adenine forming naturally, and the most important problem of all:
The central problem in nearly all origin-of-life discussions published to date is that no provision has been taken into account for abiotically supplying the configurational entropy work, which is quite substantial in the synthesis of macromolecules. As a result, ALL models and scenarios of the origin of life that have been reviewed in this book and update chapter are, as we said in Chapter 11, “woefully inadequate,” carrying with them a fundamental incompleteness.
That was in 1997. In the intervening 23 years, Chemistry World has not been able to fix the RNA world.