Selection in Evolving Chemical Mixtures

The emergence of chemical selectivity presents one of the greatest challenges in the origins-of-life research. Complex or even relatively simple chemical mixtures undergoing chemical transformations tend to combinatorically explode. Large numbers of different chemical products arise because of the large number of ways by which mixtures of reactants can combine. Recent empirical work has shown that, under kinetic control conditions, combinatorial compression, i.e., a reduced numbers of species compared to those expected by combinatorics, can be observed. The mechanisms underlying combinatorial compression are yet to be elucidated. In this paper, we combine transition state theory with computer simulations to track the evolution of chemical species (i.e., changes in concentrations) under a wide range of parameter scenarios. Our study reveals that the experimentally observed combinatorial compression requires (i) chemical connectivity, (ii) kinetic dominance by an especially reactive ‘compressor’, and (iii) appropriate temperatures and reaction times. Our results shed new light on mechanisms of chemical evolution and can guide future experiments.