Because everything has the same genetic code, it is obvious that all life evolved from the same ultimate ancestry as evolution states. So none of the man-made gods invented by us enter into this picture, as they always tell a silly and primitive set of stories that are obviously tribal tales extracted from ignorance. It only remains for us to speculate on whether or not the "complexity" of genetic coding can be reasonably accounted for through natural selection.
The Mechanism of Adaptive Code Evolution
This leads to the question of the evolutionary mechanisms responsible for an adaptive canonical code. The many models of precanonical code evolution, reviewed extensively elsewhere (Knight, Freeland, and Landweber 1999<$REFLINK> ), permit two major possibilities: that an adaptive code was selected from a large pool of variants, or that an adaptive code arose de novo by code expansion (or simplification) within adaptive, error-minimizing constraints. Individual codon reassignments, necessary for adaptive code shuffling, are certainly possible, but the question remains unresolved, and two lines of evidence increasingly favor the latter explanation.
First, the notion of code expansion from a simpler primordial form, although still lacking in detail, is now associated with a diverse body of empirical and phylogenetic evidence (Knight, Freeland, and Landweber 1999<$REFLINK> ). It seems unlikely that clear patterns of biosynthetic relatedness would be found in a code which had undergone extensive codon assignment shuffling. Additionally, while adaptive code structure is unlikely to be an artifact of a stereochemically determined code, empirical evidence suggests that stereochemistry is not without a role. For example, RNA molecules artificially selected to bind Arginine contain disproportionately many CGN/AGR codons (Knight and Landweber 1998<$REFLINK> ). If all or most amino acids show stereochemical affinities for their corresponding codons, this would suggest that natural selection worked in concert with stereochemical interactions and biosynthetic expansion to produce the canonical code de novo, “choosing” the current 20 amino acids as those that satisfied criteria for both stereochemical affinity and error minimization. This interpretation would thus offer a novel insight into the selection of the proteinaceous amino acids from the near-infinite possibilities of both prebiotic syntheses and biosynthetic modification.
Previous SectionNext Section
Conclusions
We have presented comprehensive evidence that the standard genetic code is a product of natural selection to minimize the phenotypic impact of genetic error; the arrangement of codon assignments meets, to an extraordinary degree, the predictions of the adaptive hypothesis and cannot be explained as an artifact of stereochemistry, biosynthetically mediated code expansion, or analytical methodology. However, the process by which an adaptive code evolved at present remains unclear, and yet its resolution may be of key importance to our understanding of the amino acid components universal to life."
mbe.oxfordjournals.org |
