Abstract
Heritable gene expression arises readily in a simple non-genetic system employing known small-RNA biochemistry. Pooled cross-templating ribonucleotides show varied chemical competence on which selection acts, even calculating only minimal effects. Evolution can be quick—computed progress toward encoded gene expression can require only days or weeks for two millimolar, partly activated complementary 5′ ribonucleotides. After only one product selection cycle, early templating can become prevailing pool behavior. Subsequently, a selected templated product is efficiently amplified as a pool ages, frequently accumulated in the same order of concentration as incoming nucleotides. Pools spontaneously favor templating because sporadic nucleotide accumulations increase it—and selection increases templating in pools of all ages. Nonetheless, templated chemical competence appears most easily in young pools. Pool history is critical—pools can perish from periodic hazards (like tides), or alternatively, from hazards roughly constant in time (like rainfall). Selection is greatly enhanced in constant hazard pools—more effective if pools have varied ages. Stronger selection is disproportionately more effective. Selected evolutionary change has an uncomplicated molecular basis—progress from chemical product synthesis to templated, proto-genetic inheritance exploits identity between templating and entropic catalysis. Though discovered by computation, selection of an elevated product of template catalysis is plausible, independent of any chemical or mathematical assumption. Selected chemical variation before genetics (chance utility) therefore inaugurates inheritance, even when hindered by unstable, dilute nucleotides, erratically supplied in undependable quantities. Remarkably, such uncontrolled conditions are not necessarily hostile, but can instead accelerate appearance of primordial gene-like behavior.
Highlights
The Origin of LifeThe origin of life on Earth is more appropriately a succession of molecular innovations, rather than a single event
For the G–C system, the above implies that dimer synthesis in templated stacks is equal in rate to that in nucleotide stacks free in solution at a particular template concentration ðtemplateÞ 1⁄4 kchem 1⁄4 2 1⁄4 1:22 Â 10À3 M: ð3Þ
Temp/chem is plotted in Fig. 5b, which plots the change in templating (D temp/chem) under selection—determining the index for the selected pool, normalizing to temp/chem for the prior, unselected pool. This calculation is shown for pools under selection at times from 10 to 150, reasoning that these times cover a complete transition from early small, idealized pools (Fig. 1b) to later synthesis-with-significant-decay and nucleotide consumption (Fig. 1c) and slower later increase in temp/chem (Fig. 1b)
Summary
The origin of life on Earth is more appropriately a succession of molecular innovations, rather than a single event. Each innovation (reproduction, metabolism, cellularization...) has modern partisans whose disagreements about priority can stem from the fact that every such innovation was a logically indispensable, important, step toward a complete biological repertoire. There is recent progress at the early and late ends of a credible origin chain. Simple biomolecules of different classes, including nucleotides, can be obtained from reactions involving HCN and H2S—plausibly primordial and plausibly co-existent in one landscape (Sutherland 2016). Protocells might have encapsulated RNA-like replicators that did not require catalysis (Prywes et al 2016).
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