Conventional wisdom on the origin and early evolution of life attributes the emergence of all essential features of life to rare, random, accidental events within a large and chaotic field of chemical and genetic possibilities. The theory of a chemo-autotrophic origin of life by transition metal-catalyzed, autocatalytic carbon fixation in a volcanic flow setting gives a different picture. The paucity of possibilities of a synthesis of low-molecular weight organic compounds by carbon fixation cycles provides us with the perspective of a chemically predetermined sequence of events. It begins with an origin of autocatalytic carbon fixation cycles on transition metal minerals giving rise to lipids. It proceeds through the chemically predetermined lipophilization of mineral surfaces to an inevitable formation of mineral-supported, semi-cellular structures.
The membranes of these semi-cellular structures became self-supporting by the chemically predetermined emergence of wedge-shaped phosphoglycerol lipids. At that stage the emergence of the genetic machinery set in to supplement the primary, direct, chemically deterministic track of evolution by a secondary, indirect stochastic track of evolution by genetic chance events. This marks the beginning of Darwinian selection with an indirect adaptation of the emerging polymer sequences to the chemically predetermined possibilities of pathway evolution. It is proposed that the primary, track of direct evolution continued at least until the stage of the emergence of the domains Bacteria and Archaea.
More specifically, it is proposed that the organisms, which are ancestral to the Bacteria and Archaea had a membrane of a racemate of chiral phospho-glycerol lipids. Note that racemic membranes are known to segregate into a patchwork of homochiral membrane domains. In the absence of cell walls the population of ancestral organisms must have undergone frequent fusions and fissions leading to a partitioning into two subpopulations with a predominance of one lipid enantiomer or the other.
These two subpopulations served then as the placeholders for the later emergence of the domains of the Archaea and Bacteria. This simply required the emergence of enantioselective enzymes of lipid biosynthesis by genetic adaptation.
