Origin and evolution of the genetic code: the universal enigma
The genetic code is nearly universal, and the arrangement of the codons in the standard codon table is highly non-random. The three main concepts on the origin and evolution of the code are the stereochemical theory, according to which codon assignments are dictated by physico-chemical affinity between amino acids and the cognate codons (anticodons); the coevolution theory, which posits that the code structure coevolved with amino acid biosynthesis pathways; and the error minimization theory under which selection to minimize the adverse effect of point mutations and translation errors was the principal factor of the code’s evolution.
However, such scenarios for the code evolution are based on formal schemes whose relevance to the actual primordial evolution is uncertain. A real understanding of the code origin and evolution is likely to be attainable only in conjunction with a credible scenario for the evolution of the coding principle itself and the translation system.
How did the code evolve (and will we ever know)?
In our opinion, despite extensive and, in many cases, elaborate attempts to model code optimization, ingenious theorizing along the lines of the coevolution theory, and considerable experimentation, very little definitive progress has been made.
…the code is not based on a straightforward stereochemical correspondence between amino acids and their cognate codons (or anticodons).
Whether or not other recognized and/or still unknown factors also contributed remains a matter to be addressed in further theoretical, modeling and experimental research.
…do the analyses described here, focused on the properties and evolution of the code per se, have the potential to actually solve the enigma of the code’s origin?
…this proposal, even if quite plausible, is only one facet of a much more general and difficult problem, perhaps, the most formidable problem of all evolutionary biology.
Indeed, it stands to reason that any scenario of the code origin and evolution will remain vacuous if not combined with understanding of the origin of the coding principle itself and the translation system that embodies it. At the heart of this problem is a dreary vicious circle: what would be the selective force behind the evolution of the extremely complex translation system before there were functional proteins? And, of course, there could be no proteins without a sufficiently effective translation system.
Nevertheless, these and other theoretical approaches lack the ability to take the reconstruction of the evolutionary past beyond the complexity threshold that is required to yield functional proteins, and we must admit that concrete ways to cross that horizon are not currently known.
Summarizing the state of the art in the study of the code evolution, we cannot escape considerable skepticism. It seems that the two-pronged fundamental question: “why is the genetic code the way it is and how did it come to be?”, that was asked over 50 years ago, at the dawn of molecular biology, might remain pertinent even in another 50 years. Our consolation is that we cannot think of a more fundamental problem in biology.
Mucho ruido y pocas nueces (Much Ado About Nothing)
Fairy tale of a boring kind. Simply pathetic.
Complex functional specified information can only be the product of conscious design.
Common Design 