Virus - the replicating molecules

Metabolism, net energy, cell and mass: With mass specific metabolism generating net energy for self-replication (Witting, 2017a), the evolution of a self-replicator is dependent on the natural selection of metabolism. And with initial metabolism being dependent on the mass of the metabolic molecules, the selection of metabolism is dependent on the mass of the self-replicating molecules.

This dependence [ β ∝ w_β^β_β• ] of mass specific metabolism on mass is the likely cause for the evolution of a cell. Although extremely low levels of metabolism are not dependent on a compartment like a cell, the evolution of an advanced intrinsic metabolism is dependent on the development of a cell where the molecules of the metabolic pathways can concentrate (e.g., Oparin, 1957; Miller and Orgel, 1974; Maynard:Smith and Szathmary, 1995; Michod, 1999; Wachtershauser, 2000; Koch and Silver, 2005). The increase in net energy for self-replication with increased metabolism may then be the primary selection that drives the evolution of a cell and all its associated mass; let it be the mass of the metabolic molecules, the mass of the cell membrane, and the mass of the underlying heritable code.

For the self-replication rate to increase with mass, the net energy that is generated from an increase in mass specific metabolism with mass will have to outbalance the quality-quantity trade-off, that generates a proportional decline in replication with mass. A self-replicating cell with heredity and an internal metabolism can then be selected only from the sub-sets of the potential biochemistry that have an initial pre-mass exponent for the dependence of mass specific metabolism on mass that is larger than unity [ β_β,0^• = max(β_β^•) > 1; Witting, 2017b].

A biochemical replicator with a β_β,0^• exponent below unity is thus unable to evolve an intrinsic metabolism by natural selection. Unlike selected self-replicators, these replicators cannot increase replication by an increase in mass specific metabolism. This is because the energetic demands of the offspring mass is increasing stronger than the increase in net energy that is generated by the increase in mass. The replicators may instead increase their rate of replication by a mass that evolves towards zero, with the side effect that they are shutting down their metabolic processes.

Life history: With β_β,0^• < 1, the selected life history is that of virus-like replicating molecules; i.e., no internal metabolism, no cell, practically no mass, and a replication rate that is dependent on an extrinsic source of metabolism; let it be from the metabolism of a host, or from the random encounter of molecules in abiotic environments.

Allometries: Having no internal metabolism, and a biotic time-scale that is defined by the extrinsic metabolism, viruses are selected beyond the usual concept of allometries.

Download publication

References

• Koch, A.L., and S.Silver 2005. The first cell. Advances in Microbial Physiology 50:227--259.
• MaynardSmith, J., and E.Szathmary 1995. The major transitions in evolution. W.H. Freeman Spektrum, Oxford.
• Michod, R.E. 1999. Darwinian dynamics. Evolutionary transitions in fitness and individuality. Princeton University Press, Princeton.
• Miller, S.L., and L.E. Orgel 1974. The origins of life on the Earth. Prentice-Hall, Englewood Cliffs, NJ.
• Oparin, A.I. 1957. The origin of life on Earth. Academic Press, New York.
• chtershauser, 2000Wachtershauser:2000Wachtershauser, G. 2000. Origin of life: life as we don't know it. Science 289:1307--1308.
• Witting, L. 2017a. The natural selection of metabolism and mass selects allometric transitions from prokaryotes to mammals. Theoretical Population Biology 117:23--42, https://dx.doi.org/10.1016/j.tpb.2017.08.005.
• Witting, L. 2017b. The natural selection of metabolism and mass selects lifeforms from viruses to multicellular animals. Ecology and Evolution 7:9098--9118, https://dx.doi.org/10.1002/ece3.3432.