Why life is hot

TL;DR

This paper explains that biological systems optimize various fitness functions through coupling chemical networks to out-of-equilibrium reservoirs, which requires significant heat dissipation, explaining why life is energetically costly.

Contribution

It introduces a universal mechanism for optimizing multiple fitness functions in cellular networks via out-of-equilibrium reservoirs, supported by theory and numerical analysis.

Findings

Heat dissipation is essential for optimization in cellular networks.

E. coli's heat flux from kinetic proofreading is a significant part of total heat flux.

Organisms operate near the saturation of optimality despite high energetic costs.

Abstract

The process of evolution by natural selection leads to phenotypes of increasing fitness. For cellular chemical reaction networks, this means optimising a variety of fitness functions such as robustness, precision, or sensitivity to external stimuli. We argue that these diverse goals can be achieved by a versatile, generic mechanism: coupling chemical reaction networks to reservoirs that are strongly out of equilibrium. Using theory and numerics we show that this mechanism of optimization comes at the price of significant heat dissipation. We compute the heat flux caused by kinetic proofreading in {\it Escherichia coli} and show that it constitutes a significant fraction of the total heat flux experimentally measured in this model organism. We then demonstrate that the degree of optimality achievable saturates, and that Nature appears to operate near saturation despite high energetic costs. We conclude that `life is hot' largely because of the need for a versatile mechanism to optimise a variety of fitness functions.