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No Blind Watchmaker Created the RNA World


In his 1986 book The Blind Watchmaker, Richard Dawkins proposed that “life began when both DNA and its protein-based replication machinery spontaneously chanced to come into existence” (p. 146). Dawkins felt his proposal was reasonable because, as he put it, “Given infinite time, or infinite opportunities, anything is possible” (p. 139). Of course, Dawkins was off by an infinitely large order of magnitude, because “infinite time” or “infinite opportunities” were not available. Thus scientists felt his sort of model was too unlikely to take seriously, as Frank Salisbury had already explained 15 years earlier:

It’s nice to talk about replicating DNA molecules arising in a soupy sea, but in modern cells this replication requires the presence of suitable enzymes. … [T]he link between DNA and the enzyme is a highly complex one, involving RNA and an enzyme for its synthesis on a DNA template; ribosomes; enzymes to activate the amino acids; and transfer-RNA molecules. … How, in the absence of the final enzyme, could selection act upon DNA and all the mechanisms for replicating it? It’s as though everything must happen at once: the entire system must come into being as one unit, or it is worthless. There may well be ways out of this dilemma, but I don’t see them at the moment.

(Frank B. Salisbury, “Doubts about the Modern Synthetic Theory of Evolution,” American Biology Teacher, 33: 335-338 (September, 1971).)

Of course, some origin-of-life theorists thought they had found a way out of this dilemma with the RNA-world hypothesis. They hoped RNA might perform the roles of both DNA (by carrying information) and proteins (by catalyzing reactions). All you need to do is somehow explain how a self-replicating RNA molecule popped into existence. Now, a new article in The Scientist, “ RNA World 2.0,” admits this too is unlikely:

The odds of suddenly having a self-replicating RNA pop out of a prebiotic soup are vanishingly low,” says evolutionary biochemist Niles Lehman of Portland State University in Oregon.

Aside from serious problems in generating by chance the right sequence of nucleotides capable of self-replicating, the RNA-world hypothesis faces other problems:

[A] long-standing weakness of the RNA-world hypothesis has been the inability to spontaneously generate the molecule’s component nucleotides from the basic ingredients presumed to be available on the prebiotic Earth. Still today, “nobody has made all four of the nucleotides from one pot of simple starting materials,” says Georgia Tech biochemist Nicholas Hud.

In particular, ribose, the five-carbon sugar that constitutes RNA’s backbone, is difficult to form under prebiotic conditions, and purine and pyrimidine nucleobases, the variable parts of nucleotides, do not efficiently form covalent bonds with ribose.

The article mentions the experiments of John Sutherland and Matthew Powner — work that has generated some (though not all) of the components of RNA, but has been criticized by Stephen Meyer and other ID theorists because the experiments carefully manipulated the parameters such that the they did not mimic natural, earthlike conditions. In addition to ribose, The Scientist article explains that “Scientists have yet to produce the purine nucleotides adenosine (A) and guanosine (G) under similar prebiotic conditions.”

Some scientists are confident that someday they may eventually produce RNA (or at least, its constituents) under prebiotic conditions, but that still would not overcome the information-sequencing problem: How would the nucleotides be properly ordered to create a self-replicating RNA? That’s probably the biggest problem facing origin-of-life research. Judging from this article, nobody’s even thinking about it.

Understandably, some scientists are skeptical that that problems involved in assembling RNA under natural conditions will ever be solved:

But the notion that RNA, on its own, spontaneously assembled and evolved on early Earth has fallen out of favor. More likely, whatever conditions spawned compounds as complex as nucleotides also generated other organics, perhaps early forms of modern amino acids and fatty acids, the constituent parts of proteins and membranes. “I’m not sure how many people anymore believe in a pure RNA world. I certainly don’t,” says [Nick] Lane. “I think the field has drifted away from that, and there’s now an acknowledgment it had to be ‘dirty.'”

Because of these sorts of problems, scientists are falling back to pre-RNA worlds that don’t form the basis of life in the real world of biology, and are thereby much harder to define, involving “threose nucleic acid” (TNA) or “phosphoramidate DNA.” These have not been demonstrated to form under prebiotic conditions, either, and the article says very little about them, suggesting they’re pretty speculative ideas at this stage. Instead, it reminisces about a self-replicating ribozyme that Gerald Joyce created at the turn of this century:

Joyce and Scripps colleague Natasha Paul hit the jackpot. In a 2002 PNAS paper, they described an RNA molecule that could, for all intents and purposes, make copies of itself. It wasn’t complicated: a ribozyme that the researchers dubbed “E” joined together two component RNA pieces, “A” and “B;” when ligated, “A” and “B” made “E.”

It didn’t do much other than self-replicate, Joyce admits, but it suggested the possibility that RNA could, without experimenter intervention, evolve. “We don’t have the smoking gun of some RNA-based life form out there . . . [and] we don’t have direct fossils of the RNA world,” he says. “So then you fall back on: What can we make in the laboratory to teach us about what RNA can do?” (emphasis added)

“We don’t have the smoking gun of some RNA-based life form out there” and “we don’t have direct fossils of the RNA world”? That’s certainly contradicts the optimistic story we often hear about the RNA world.
The article goes on to explain that eventually Joyce’s lab engineered a system where “two different small RNA molecules made copies of the other” and “with a bit more directed evolution, Joyce’s PhD student Tracey Lincoln was able to improve the system’s kinetic properties such that it began replicating exponentially.” Then, there’s this key admission:

Of course, these artificial systems are unlikely to resemble the first RNAs to appear on the young planet, Joyce notes. “There was no Tracey [directing evolution] on the primitive Earth. This is not that kind of game.” (emphasis added)

Clear enough? Remember, this is a mainstream scientific article on the origin of life.

Yes, directed evolution can accomplish impressive feats in the lab. However, there is no reason to think that the enormous probabilistic resources available in such experiments were at the disposal of the early Earth. Origin-of-life scientists are not blind watchmakers. They are intelligent, far-sighted watchmakers. Their work intentionally guarantees far more “opportunities” (as Dawkins put it) for the desired prebiotic molecules to arise than could ever have been available on our planet. Ribozyme experiments suggest that for life to originate, what was needed was a goal in mind, an agent in charge, with the means to implement a preconceived plan, drawing it to completion. We have a name for that. It’s called intelligent design.

Photo credit: mustardgreen/Flickr.

Casey Luskin

Associate Director and Senior Fellow, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



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