In BIO-Complexity, Meyer and Nelson Debunk DRT
Origin-of-life research has a big problem, and the DRT model purports to solve part of it. In a peer-reviewed paper published this week in BIO-Complexity, Stephen C. Meyer and Paul Nelson take on DRT. What is DRT, exactly, you ask? Some background will help in explaining.
While DNA carries information necessary to build cells, it performs no chemistry and builds no cellular structures by itself. Rather, the information in DNA must be translated into proteins, which then can carry out the various chemical and structural functions of life. But there is no direct way to convert a given DNA sequence into a protein sequence -- no direct chemical association between DNA nucleotides and amino acids. Some sort of decoding mechanism is needed to translate the information encoded in DNA into protein.
That decoding mechanism involves a whole host of enzymes, RNAs and regulatory molecules, all functioning as an elegant, efficient, accurate and complicated system for copying and translating the information in DNA into a usable form. (For a comprehensive and engaging description of how information is processed in the cell, and how the details of this process have been discovered, see Stephen C. Meyer's Signature in the Cell.)
The problem is, this decoding system is self-referential and causally circular. Explaining its origin becomes a chicken and egg problem. As it stands now, you need the machinery that translates DNA into protein in order to make the very same machinery that translates DNA into protein. This should give us pause, because causal circularity cannot be explained in purely naturalistic terms. In order to avoid this trap, neo-Darwinian evolution would require the prior existence of another way to specify and carry out protein-like functions in a heritable fashion, but apart from the usual machinery -- DNA, RNA and protein, all three working together.
So when it was discovered that some RNAs could carry out (very limited!) chemical reactions, scientists seeking a purely materialistic explanation for life's origin were thrilled. Perhaps here was the solution to the conundrum. Perhaps RNAs could be both catalysts and heritable information carriers. Perhaps the first living world was RNA-based.
Fast forward to now. Researchers continue to try to design RNAs that can copy themselves, and try to expand the range of chemistries they can carry out. The RNA world, if it ever existed, though, would be a very impoverished place, based on what human designers have been able to produce so far. And the problem of how an RNA world could become a DNA/RNA/protein world would still remain.
Enter the Direct RNA Templating (DRT) model of Michael Yarus et al. His hypothesis was originally based on the discovery that the activity of one RNA catalyst could be blocked by the presence of the amino acid arginine. From this result Yarus hypothesized that perhaps other RNAs would show an affinity for particular amino acids. In a series of papers he and his coworkers identified other such RNAs. Then, based on statistical analysis, they argued that these RNAs contained a higher than expected frequency of triplets corresponding to the particular codons or anticodons now used in the modern genetic code to specify the particular amino acid they bound.
But is their analysis correct? Meyer and Nelson carefully examine the claims of Yarus et al. and find them wanting. Inadequate null hypotheses, arbitrary selection of data for analysis, and unrealistic assumptions about prebiotic chemistry are just a few of the problems. Rather than go through their arguments here, I encourage you to read their paper yourself.
Why does it matter? Critics of intelligent design have advanced the DRT model as the answer to the sequencing problem -- how genetic information in RNA (in the hypothetical RNA world) eventually could have been translated into more stable and versatile proteins. Based on the analysis in this paper, however, the sequencing problem has not been solved, even partially. There is no natural affinity between RNAs, amino acids, and codes. And the origin of life remains inexplicable in materialistic terms.