Figure 1.

An evolving view of life's origins: from discontinuity to continuity. (a) Pioneering, mid-twentieth-century science that founded the molecular biology revolution [13] perceived a universal biochemical basis for life that implied a sharp discontinuity between abiotic chemistry and biological chemistry: life's origin was clearly the transition between these two, though further evolution of metabolism might refine the system of replication and evolution (e.g. protein enzymes that identify and correct genetic errors during replication). (b) By the start of the twenty-first century, it was clear that early evolution played a more significant role in establishing the central dogma than had been thought previously: DNA arrived in a world of RNA genes that encoded protein enzymes; RNA can and does take on functionality usually associated with protein enzymes; and both RNA and the standard genetic code appeared optimized relative to plausible chemical alternatives. (c) A current view adds the standard amino acid alphabet to the list of central dogma components, which appear optimized relative to plausible alternatives, along with strengthened evidence for RNA and the genetic code as outcomes of natural selection. Emerging insights about adaptive, evolutionary behaviour from collections of molecules far removed from nucleic acid sequences suggest that biological evolution by natural selection is a narrowed (refined) subset of broader processes by which matter (chemicals) change over time. Philosophically, this view aligns with calls to re-think life's emergence as a continuous process rather than any specific point in time or biochemistry. More practically, these same findings dissolve any clear distinction between the evolution of genetic versus metabolic aspects of life's biochemistry.