THEORY-492: Life was forced into existence by geochemistry: core metabolism, rooted in the reductive citric-acid cycle, formed as a channel relieving the free-energy stresses abiotic processes keep building, as lightning relieves a charge separation, so its early steps would recur on any similar planet and selection on metabolism came before replication

Source

Morowitz & Smith, Complexity 13(1):51–59 (2007), LIT-528, read in full in NOTE-425 from Santa Fe Institute Working Paper 2006-08-029 (7 August 2006). The journal version was not seen and may differ. The formal results the paper leans on (Smith 1998, 1999, 2005; Corbet & Morowitz 1972) are not in the record and were taken as the paper describes them.

NOTE-425 concludes that “no new THEORY is indicated”. This document files the paper’s thesis as Proposed, because it is a definite account of the origin of life that the record’s other dissipation papers do not state.

What was actually shown

The thesis. “The continuous generation of sources of free energy by abiotic processes may have forced life into existence as a means to alleviate the buildup of free energy stresses.” If so, life “had to emerge on the earth” (C1, a conjecture, stated as one).

The analogy. Lightning and hurricanes are channels that carry charge or heat between reservoirs far faster than diffusion. Metabolism is such a channel “in the chemical domain”, carrying redox electrons from H₂ to CO₂ and phosphate from polymer to orthophosphate.

The evidence from metabolism (§II). The anabolic core of autotrophs is fewer than 500 molecules under 400 Da, rooted in the eleven carboxylic acids of the citric-acid cycle. Run in reverse, the cycle “can duplicate its own members from abiotic CO₂ and electrons”, which the paper calls network autocatalysis. The cascade built on it “leaves no energetic waste products”. The cycle is said to capture “about one third” of the redox energy from CO₂ to acetate, fatty-acid synthesis another third and methanogenesis the rest; these figures are stated, not computed (C2, moderate as a description).

The framework (§III). Statistical mechanics as inference: maximum entropy, with entropies allowed to depend on currents, predicts that currents form, with Ohm’s and Fourier’s laws as the linear cases. With positive feedback, thresholds appear that are phase transitions “equivalent in all statistical respects to equilibrium phase transitions”, and the ordered state is a better channel. The principle is “not equivalent to maximization of the inter-reservoir current”. Entropy-production principles “ultimately fail as general principles” (C4, a summary of prior work, with no argument given here).

The collapse (§IV). The abiotic earth was metastable, and the emergence of life was its “collapse” to greater stability, like phase separation in an alloy. Later chemical transitions should be further, irreversible collapses (C6, an analogy).

Metabolism first. Selective advantage came from interaction with metabolites before replication was coordinated, which the authors note is “directly opposite” to the RNA-world premise (C7, a hypothesis).

What could have come out otherwise. Nothing in the paper could have. It reports no test. What could fail is the programme’s open question: a network supplied with geochemical free energy could relax without forming the reductive cycle.

What this does not say

• That it has been shown. The authors say the thesis “has not been quantitatively demonstrated”, and that the framework has “few instances that usefully reach beyond equilibrium”.
• That present metabolism records its origin. The case reads the structure of today’s metabolism back into biogenesis, which it assumes (“modern metabolism recapitulates the process of biogenesis”). The authors also say that “universality due to descent from common ancestors becomes indistinguishable from universality due to evolutionary convergence”, which takes away the observation that would tell the thesis from its rival.
• That both energy sources were there. The phosphate half is flagged as uncertain: polyphosphates are not reported at hydrothermal vents (fn. 5). The placement of methanogenesis is disputed (fn. 6).
• That biomass is a thermodynamic state. The “collapse” is an analogy; the authors say biomass is “probably” not such a state.
• That living and non-living channels differ in kind. The one asymmetry allowed is the “informational richness” of life’s chemical substrate. Individuality is “a by-product of cellular form”.
• That entropy production is maximized. The paper rejects that.

Connections

• Gradient dissipation (THEORY-532). Schneider and Kay read the biosphere as a channel too, and also reject entropy-production principles, but put a restated second law in their place.
• Maximum entropy production (THEORY-671). The paper’s Jaynesian framework is the same inference Dewar applies to paths (LIT-521), used here to predict currents rather than to derive MEP, and the paper rejects MEP. No rivals edge is declared, because the paper gives no argument against MEP of its own.
• England’s replication bound (THEORY-679) argues that a fast RNA replicator is thermodynamically possible where a DNA one is not. It concerns which replicator, not whether replication came first.
• Self-organized cycles. The reductive cycle’s network autocatalysis is the chemical counterpart of the spatially self-organized catalytic cycles of LIT-036. Neither paper connects them.
• The demarcation question. On life’s continuity with lightning, see LIT-192 and NOTE-094, and THEORY-072 for the record’s account of where the line falls.