A mechanism of abiogenesis based on complex reaction networks organized by seed-dependent autocatalytic systems

Abstract

Life is the canonical example of a complex system, consisting of diverse chemical components that are organized in a specific way that allows perpetuation of the living state. In contrast, the abiotic environment, which life feeds on and originated from, is much simpler and less organized. The complexity gap between the biotic and abiotic worlds, and the lack of direct observation of abiogenesis, has made explaining the origin of life one of the hardest scientific questions. A promising strategy for addressing this problem is to identify features shared by abiotic and biotic chemical systems that permit the stepwise accretion of complexity. We used such a rationale to compare abiotic and biotic reaction networks in order to evaluate the presence of autocatalysis, the underlying basis of biological self-propagation, to see if it is structured in such a way as to permit stepwise complexification. We develop the concept of, and provide an algorithm to detect, seed-dependent autocatalytic systems (SDASs), namely subnetworks that can use food chemicals to self-propagate but cannot emerge without being first seeded by some non-food chemicals. We show that serial activation of SDASs can result in incremental complexification. Furthermore, we identify life-like features that emerge during the accretion of SDASs that open up new ecological opportunities and improve the efficiency of food utilization. SDAS theory, thus, provides a conceptual roadmap from a simple abiotic environment to primitive forms of life, without the need for linear genetic polymers at the outset (though these may be added later). This framework also suggests new experiments that have the potential to detect the spontaneous emergence of life-like features, such as self-propagation and adaptability.