The Origin of Life: Models and Data

Abstract

A general framework for conventional models of the origin of life (OOL) is the specification of a 'privileged function.' A privileged function is an extant biological function that is excised from its biological context, elevated in importance over other functions, and transported back in time to a primitive chemical or geological environment. In RNA or Clay Worlds, the privileged function is replication. In Metabolism-First Worlds, the privileged function is metabolism. In Thermal Vent Worlds, the privileged function is energy harvesting from chemical gradients. In Membrane Worlds, the privileged function is compartmentalization. In evaluating these models, we consider the contents and properties of the Universal Gene Set of life, which is the set of orthologous genes conserved throughout the tree of life and found in every living system. We also consider the components and properties of the Molecular Toolbox of Life, which contains twenty amino acids, eight nucleotides, glucose, polypeptide, polynucleotide, and several other components. OOL models based on privileged functions necessarily depend on "takeovers" to transition from previous genetic and catalytic systems to the extant DNA/RNA/protein system, requiring replacement of one Molecular Toolbox with another and of one Universal Gene Set with another. The observed robustness and contents of the Toolbox of Life and the Universal Gene Set over the last 3.7 billion years are thought to be post hoc phenomena. Once the takeover processes are acknowledged and are reasonably considered, the privileged function models are seen to be extremely complex with low predictive power. These models require indeterminacy and plasticity of biological and chemical processes.

Keywords: Clay world; Membrane world; Metabolism world; Molecular toolbox of Life; Origins of life; RNA world; Thermal vent world; Translation.

Fig. 1

Schematic of the universal tree of life illustrating privileged functions in various OOL models. Each model leads to the last universal common ancestor (LUCA)

Fig. 2

The central dogma of molecular biology, emphasizing the contents of Universal Gene Set of life, which includes genes for ribosomal RNAs, ribosomal proteins, aminoacyl tRNA synthetases and translation factors

Fig. 3

Schematic of the molecular toolbox of life, which contains the small molecules and macromolecular backbones and motifs that are universal to all living systems. This image was inspired by Jacob (1977)

Fig. 4

The oxidation of guanine to form 8-oxoguanine. Guanine spontaneously degrades in the oxidative environment of the post-GOE earth