The Good Symbiont

Abstract

A self-reproducing cycle has the fundamental organization, $A+X \longrightarrow 2A$, and is autocatalytic, i.e. the products catalyze the formation of the products. The rate of increase of A is proportional to A, i.e. exponential. Asexual living entities often grow exponentially when resources are abundant, and decay exponentially when resources are scarce, according to autocatalytic kinetics. If two previously independently replicating autocatalytic entities can form a physical union that is still capable of autocatalysis but with a reduced decay rate, then the symbiosis can be viable in an environment in which resources have been depleted, even if the symbiont has a lower growth rate than either of its component particles. A good symbiont possesses the following features: i. low steric hindrance between components, ii. policing of defection or cheating by symbiont components. iii. low decay rate back to components. iv. absence of emergence of active sites susceptible to decay reactions. v. high rate of the final reproductive step. Failure to form stable symbiosis can result from deficits in any of these features, and is a problem central to the origin of both metabolism and template replication.