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comment by Torbjorn_Larsson
Torbjorn_Larsson  ·  4200 days ago  ·  link  ·    ·  parent  ·  post: From Non-Life to Life

"a study by chemists Addy Pross and Robert Pascal"

I thought for a moment I had missed something. But no, it is the same sweeping ideas that are so often promoted in this area.

I can understand that they are alluring. But they are based on some fundamental misunderstandings of biology. From my viewpoint of studying astrobiology, here they are:

- The idea that we need new mechanisms for chemical evolution.

First, we observe that chemical evolution works throughout time and space in the universe.

Second, the speed with which life was established on Earth speaks for an easy and/or often enough attempted process transitioning to biological evolution.

- The idea that evolution isn't falsifiable.

Evolution gives phylogenies, which by construction are enormously constrained combinatorial networks, a handful of potential pathways (species lineages) in a truly vast space of networks. We don't need,nor ask for, the exact pathways as local resolution can be too low, yet the precision of the entire network staggering. (Many orders of magnitude certainty.)

They are tested by adding species. Famously "a precambrian rabbit" falsifies the standard phylogeny. Here it would be "pre-Earth genes", say. Eminently testable, all gene or protein fold phylogenies converge on ~ 4 billion years as the earliest "rabbit".

- The idea that biology is an equilibrium and/or stability regime.

The thermodynamics of the planet (biosphere driven by the Sun, radiating to space) rejects that. The evolutionary biological process is as such very little coupled to thermodynamics and there is no inherent ecological (population) stability.

Instead, where is astrobiology today?

- Lane & Martin has shown that classical bottleneck constraints (chicken-or-egg problems) makes alkaline hydrothermal vent chemistry preceding earliest autotroph metabolism. As expected, these mechanisms were as they note in the paper homologous chemical networks.

- Thermodynamics shows that a) RNA is the only pre-protein nucleotide that fulfill the thermodynamic bound for replicators, b) a random strand 'gas' population of RNA _will_ crystallize to a replicator within ~ 30 000 years in the phosphate activating environment of alkaline hydrothermal vents.

The pathways from replicator strands to genomes are legion, but the simplest goes through a simplest possible brwonian ratchet making RNA strand replication one way and unchained from vent thermal environment. Coincidentally, the minimum ratchet is a 3 basepair codon polypeptide, the initially random sequencing (no function except ratcheting) consistent with early fold properties (random peptides outside of fold function).

These two bottleneck systems marry well, the first genomes would support local organics producing metabolic cellular compartments and vice versa.





randominality  ·  4198 days ago  ·  link  ·  

    Thermodynamics shows that a) RNA is the only pre-protein nucleotide that fulfill the thermodynamic bound for replicators, b) a random strand 'gas' population of RNA _will_ crystallize to a replicator within ~ 30 000 years in the phosphate activating environment of alkaline hydrothermal vents.

Could you link to any papers or discussions about this point? The work to establish this seems like it would be really interesting.

Torbjorn_Larsson  ·  3898 days ago  ·  link  ·  

Seems the links were cut. It's England Lab publications. Main one Statistical physics of self-replication Jeremy L. England Citation: J. Chem. Phys. 139, 121923 (2013); doi: 10.1063/1.4818538

but also his seminar.

Torbjorn_Larsson  ·  3898 days ago  ·  link  ·  

Found mail in old archive. Maybe your interest remains.

a) also

b) Thermodynamic Basis for the Emergence of Genomes during Prebiotic Evolution Hyung-June Woo, Ravi Vijaya Satya, Jaques Reifman mail

Published: May 31, 2012DOI: 10.1371/journal.pcbi.1002534