Heritable, mutable, and selectable spatial patterns from bistable chemical reaction networks in weakly-coupled reactor arrays

The origins of genetic information processing remain a mystery in prebiotic chemistry research. Genetic systems encode information as digital sequences of nucleotide residues and require multiple interdependent and complex machineries that were likely to have been established late in the prebiotic evolutionary process. Candidate predecessor systems are potentially insightful for examining how genetic systems could have been scaffolded by alternatives that were simpler, yet capable of performing comparable functions. Some researchers have proposed that relative concentrations of simple chemical species (i.e., chemical compositions) could encode heritable information in an analog manner. While conceptually plausible, it is also difficult to explain how most forms of analog inheritance (which can be highly sensitive to interference) could underpin emergent characteristics that are necessary for adaptive evolution afforded by high-fidelity, polymer-based digital inheritance. Here, by simulating bistable reaction systems with two simple autocatalytic cycles in two-dimensional lattices of connected flow reactors, we show that without linear polymers, it is still possible to encode spatial configurations of discrete states of chemical compositions that are heritable and mutable. Different configurations can have differing likelihoods of propagating to new reactors or recovering from perturbations, which means that they can respond to at least some types of selective environments or conditions. Taken together, these spatial configurations are heritable, mutable, and selectable (HMS). They are similar to analog inheritance because they depend on chemical compositions, and they are similar to digital inheritance because they consist of spatially distributed, discretized units. Although such discrete HMS spatial configurations are far less heritable, more mutable, and less selectable than nucleotide-sequence-based digital inheritance, they represent a possible bridge between analog and digital inheritance in complex chemical systems.