Three-stage Origin of Life as a Result of Directional Darwinian Evolution

The original hypothesis about Three-stage origin of life (TOL) on the Earth is developed and discussed. The role of the temperature factor in life origin is considered. It is supposed, that three stages of abiogenesis (DNA world, RNA world and the Protein world) consistently followed each other during Darwinian evolution. At the same time, the natural directional selection of the most stable macromolecules and effective catalytic reactions took place. The direction of this selection is related to action of the principle of {\guillemotleft}Increasing Independence from the Environment{\guillemotright} (IIE) and is caused by temperature evolution of the atmosphere of the Earth. The direction of Anagenesis and inevitability of occurrence of genetic mechanisms is discussed.

💡 Research Summary

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The paper presents a novel three‑stage model for the origin of life (TOL) that integrates the long‑term cooling of Earth’s atmosphere and oceans as the primary driver of biochemical evolution. The authors argue that the decreasing temperature created a sequential selection landscape in which three distinct macromolecular worlds—DNA, RNA, and protein—successively dominated. Each stage is characterized by a specific set of physicochemical advantages that confer increasing independence from environmental constraints, a principle they label “Increasing Independence from the Environment” (IIE).

Stage 1: DNA World (≈90 °C and above).
In the earliest hot Earth, the authors contend that DNA would have been more thermally stable than RNA because phosphodiester bonds and base‑pair hydrogen bonds retain integrity at high temperatures. They cite experimental data showing that double‑stranded DNA resists thermal denaturation better than RNA oligomers under comparable conditions. Consequently, a primitive self‑replicating system could have been based on DNA, providing a robust information storage medium even before the emergence of catalytic RNAs. The selection pressure at this stage was primarily thermal stability; molecules that could persist in a high‑temperature aqueous environment were favored, leading to an early “environment‑independent” genetic system.

Stage 2: RNA World (≈70 °C to 30 °C).
As the planetary surface cooled, the authors argue that RNA’s catalytic potential became advantageous. In the intermediate temperature range, RNA can fold into complex secondary and tertiary structures, forming ribozymes that accelerate a variety of reactions while still being capable of templated replication. The reduction in temperature also lowers water activity and changes ion concentrations, which stabilizes RNA’s 2‑mer and higher‑order folds. This stage thus combines information storage with catalysis, acting as a bridge between the purely informational DNA world and the later metabolic protein world. The IIE principle manifests here as a shift from pure thermal resilience to functional versatility: RNA molecules that could both store genetic code and catalyze reactions gained a selective edge.

Stage 3: Protein World (≈30 °C and below).
When temperatures fell into the range conducive to stable protein folding, amino acids polymerized into polypeptides that could adopt diverse three‑dimensional conformations. Proteins, with their superior catalytic efficiency and structural diversity, enabled the emergence of complex metabolic pathways, cellular compartmentalization, and eventually the first protocells. The authors emphasize that proteins outperform nucleic acids in catalytic turnover and can couple exergonic and endergonic reactions, thereby expanding the energetic landscape of early life. At this final stage, IIE is realized as maximal environmental independence: metabolic networks become largely self‑sufficient, and the reliance on external temperature cues diminishes dramatically.

The IIE Principle and Directional Anagenesis.
The central theoretical contribution is the formulation of IIE, which posits that natural selection not only optimizes fitness but also systematically reduces dependence on fluctuating environmental parameters. In the TOL framework, each successive macromolecular world represents a step toward greater autonomy: DNA provides thermal stability, RNA adds functional flexibility, and proteins deliver metabolic self‑sufficiency. The authors argue that this directional trend is driven by the monotonic cooling of Earth’s atmosphere—a “temperature gradient” that imposes a predictable sequence of selective pressures. Consequently, the evolution of replication, transcription, and translation mechanisms is portrayed as inevitable rather than contingent, because each mechanism becomes a necessary adaptation to the prevailing thermal regime.

Critical Evaluation.
While the model is conceptually appealing, several limitations are evident. First, the hypothesis that DNA preceded RNA contradicts the prevailing view that RNA’s dual role as information carrier and catalyst makes it the most plausible primordial polymer. Empirical data on DNA stability at >90 °C are sparse, and the synthesis pathways for deoxyribonucleotides under prebiotic conditions remain poorly constrained. Second, the model focuses almost exclusively on temperature, neglecting other crucial variables such as pH, redox potential, metal ion availability, and UV radiation, all of which likely co‑evolved with temperature and could have altered the selection landscape. Third, the mechanistic details of the transitions—how a DNA‑based replication system would give rise to an RNA‑based ribozyme network, and subsequently to a protein‑driven metabolism—are not fully elaborated, leaving a gap between the conceptual stages and plausible chemical pathways.

Nevertheless, the paper’s integration of a geophysical driver (planetary cooling) with evolutionary theory offers a fresh quantitative framework. By framing evolution as a process that systematically reduces environmental dependence, the authors extend classic Darwinian concepts and provide testable predictions: for example, experimental simulations of high‑temperature DNA replication, intermediate‑temperature ribozyme activity, and low‑temperature protein catalysis could be arranged in a sequential manner to assess whether the proposed directional trend emerges spontaneously.

Conclusion.
The “Three‑stage Origin of Life” model posits that Earth’s cooling created a deterministic sequence—DNA → RNA → protein—each stage selected for molecules that were increasingly independent of external temperature. The IIE principle encapsulates this trend, suggesting that natural selection can be viewed as a drive toward environmental autonomy. While the hypothesis challenges established ideas and requires further empirical validation, it contributes a valuable perspective that links planetary physics with molecular evolution, opening new avenues for interdisciplinary research into the origin of life.