Sunday, January 16, 2011

Origin of life: Simple cells inevitable?

A friend flags Nick Lane's "Chance or Necessity?: Bioenergetics and the Probability of Life" (Journal of Cosmology, August 2010, Vol 10, 3286-3304, suggesting that it represents a significant step in the history of origin of life research. Lane thinks bacteria would "naturally" emerge on wet, rocky planets, but that more complex life forms are a matter of chance.

Lane pin his hopes on "white smokers", that is, alkaline hydrothermal vent systems, of which he writes,
... alkaline hydrothermal vent systems should be seen as not merely the most promising setting for the origin of life, but as the only model that makes the emergence of life look like a probable and deterministic outcome of geology, geochemistry and thermodynamics (Table 1). Alkaline vents are electrochemical reactors that provide integrity, concentration, catalysis, replication and a suitable environment for selection. It is hard to imagine life not emerging in such a system, especially if one pictures the oceanic crust as host to practically contiguous vent systems, as might indeed have been the case (Russell and Arndt, 2005). One could even imagine a natural selection of vents, in which life emerges from the system with the best balance of H2, flow and catalysis, perhaps going on to infect nearby systems.
The abstract reads,
Abstract: The emergence of life is probable on any wet, rocky planet. Serpentinization gives rise to alkaline hydrothermal vents that form: (i) simple organics; (ii) catalysts that direct primordial metabolism (iii) micropores with cell-like properties; and (iv) proton gradients equivalent to the proton-motive force. Thermodynamic constraints dictate that all anaerobic chemolithotrophic cells must depend on chemiosmotic coupling, explaining the near-universal use of proton gradients today. But proton gradients also limit the evolutionary potential of prokaryotes. Only a rare and stochastic event, an endosymbiosis between prokaryotes, permitted the evolution of morphologically complex life on Earth, as only such an endosymbiosis made it possible for chemiosmotic coupling to be controlled by multiple small genome outposts across a wide area of internal membranes. This leap in bioenergetic capacity in turn enabled the expansion in cell volume and genome size characteristic of eukaryotes. The origin of life and evolution of prokaryotes is therefore deterministic and probable (necessity), while the evolution of more complex eukaryotic life is stochastic and improbable (chance). These bioenergetic principles are likely to apply throughout the universe.
I'm not sure why my friend thinks this is so significant. Didn't it used to be black smokers? But the good thing about this particular theory is that Lane spells it out clearly enough that we can know if it is not demonstrable. None of the usual mights and maybes for him.