Coffee cools down because nothing is heating it up, but England’s calculations suggested that groups of atoms that are driven by external energy sources can behave differently: They tend to start tapping into those energy sources, aligning and rearranging so as to better absorb the energy and dissipate it as heat.  He further showed that this statistical tendency to dissipate energy might foster self-replication. ( As he explained it in 2014, “A great way of dissipating more is to make more copies of yourself.”)  England sees life, and its extraordinary confluence of form and function, as the ultimate outcome of dissipation-driven adaptation and self-replication.  However, even with the fluctuation theorems in hand, the conditions on early Earth or inside a cell are far too complex to predict from first principles.  That’s why the ideas have to be tested in simplified, computer-simulated environments that aim to capture the flavor of reality. 

In the Physical Review Letters paper, England and his coauthors Tal Kachman and Jeremy Owen of MIT simulated a system of interacting particles.  They found that the system increases its energy absorption over time by forming and breaking bonds in order to better resonate with a driving frequency. “ This is in some sense a little bit more basic as a result” than the PNAS findings involving the chemical reaction network, England said. 

We need chemical reaction networks that can get up and walk away from the environment where they originated. 

Crucially, in the latter work, he and Horowitz created a challenging environment where special configurations would be required to tap into the available energy sources, just as the special atomic arrangement of a bacterium enables it to metabolize energy.  In the simulated environment, external energy sources boosted (or “forced”) certain chemical reactions in the reaction network.  The extent of this forcing depended on the concentrations of the different chemical species.  As the reactions progressed and the concentrations evolved, the amount of forcing would change abruptly.  Such a rugged forcing landscape made it difficult for the system “to find combinations of reactions which are capable of extracting free energy optimally,” explained Jeremy Gunawardena, a mathematician and systems biologist at Harvard Medical School. 

Yet when the researchers let the chemical reaction networks play out in such an environment, the networks seemed to become fine-tuned to the landscape.  A randomized set of starting points went on to achieve rare states of vigorous chemical activity and extreme forcing four times more often than would be expected.  And when these outcomes happened, they happened dramatically: These chemical networks ended up in the 99th percentile in terms of how much forcing they experienced compared with all possible outcomes.  As these systems churned through reaction cycles and dissipated energy in the process, the basic form-function relationship that England sees as essential to life set in. 

Information Processors

Experts said an important next step for England and his collaborators would be to scale up their chemical reaction network and to see if it still dynamically evolves to rare fixed points of extreme forcing.  They might also try to make the simulation less abstract by basing the chemical concentrations, reaction rates and forcing landscapes on conditions that might have existed in tidal pools or near volcanic vents in early Earth’s primordial soup (but replicating the conditions that actually gave rise to life is guesswork).  Rahul Sarpeshkar, a professor of engineering, physics and microbiology at Dartmouth College, said, “It would be nice to have some concrete physical instantiation of these abstract constructs.”  He hopes to see the simulations re-created in real experiments, perhaps using biologically relevant chemicals and energy sources such as glucose.  But even if the fine-tuned fixed points can be observed in settings that are increasingly evocative of life and its putative beginnings, some researchers see England’s overarching thesis as “necessary but not sufficient” to explain life, as Walker put it, because it cannot account for what many see as the true hallmark of biological systems: their information-processing capacity.  From simple chemotaxis (the ability of bacteria to move toward nutrient concentrations or away from poisons) to human communication, life-forms take in and respond to information about their environment. 

To Walker’s mind, this distinguishes us from other systems that fall under the umbrella of England’s dissipation-driven adaptation theory, such as Jupiter’s Great Red Spot. “ That’s a highly non-equilibrium dissipative structure that’s existed for at least 300 years, and it’s quite different from the non-equilibrium dissipative structures that are existing on Earth right now that have been evolving for billions of years,” she said.  Understanding what distinguishes life, she added, “requires some explicit notion of information that takes it beyond the non-equilibrium dissipative structures-type process.”  In her view, the ability to respond to information is key: “We need chemical reaction networks that can get up and walk away from the environment where they originated.”