Tracing a Pathway to DNA
Yesterday's post on supercoiling identified a constraint inherent to the topological structure of DNA which supports a front loading perspective. It also makes a gradual evolutionary approach to DNA dubious based on properties of DNA. Imagination is a wonderful thing but unconstrained imagination, applied to the solution of scientific dilemnas, is not.
A selection perspective of pathways to DNA should be guided by considerations that go beyond supercoiling. Enzymes enabling deoxyribose metabolism have obvious selection value. But that does not explain their origin. Enzymes are needed prior to the biosynthesis of deoxyribose. Yet what selection value would they confer prior to the point in time when DNA was a repository for genomic information?
Which brings me to a more substantial point. DNA enables cellular functions because it comes loaded with genetic information, mechanisms that enable gene expression and a genetic code already in place. These would have to be accounted for by any viable origins theory. Fitting theory within a selection framework is confounded by the very nature of genes and mechanisms needed to allow for their expression. Step by step approaches are not suggested by the biological systems discussed.
A designer faced with the task of incorporating DNA within a cellular environment would front load genetic information and the means of accessing and expressing it. It would be good design. Yet we are to expect unidentified forces on nature to have accomplished the same. But of what biological use is a gradual encoding process when minimally functional genomes number in the dozens of genes? How do transcription and translation functions gradually evolve? If the structures discussed were anything but biological, a front loaded origin would seem obvious based on the nature of the structures themselves.
Fear of designer implications ought not guide rational considerations of origin matters. That includes irreducibly complex DNA.