Modelling Evolution : From non-life, to life, to a variety of life

Abstract: Life is able to replicate itself, e.g., a microorganism is able to divide into two identical ones, and a single plant is able to forest a whole island. But life is the only example of self-replication (note that a computer virus seems able to replicate itself, but it needs the assistance of a processor such as a CPU, and thus not a truly self-replicating entity). So before the appearance of life, nothing can self-replicate. How does life, a truly self-replicating entity, evolve from substances which is not able to self-replicate? Why can it ever happen? Is there a general underlying mechanism that governs how self-replicating entities can develop de novo on Earth, or even other plants?As long as the first life appears, it has the potential to cover the whole plant. But one single life form cannot do the job. Life has branched into a huge number of biological classes and species. Different species interact with each other, and with their environment, which, as a whole, is defined as an ecosystem. Distinct ecosystems are found at different scales and different places, e.g., microbes cross-feed and compete for resources within natural communities; and different types of cells interact by exchanging metabolite within an organism body. But, why sometimes we consider an ecosystem as an individual (such as the human body which is, in fact, an ecosystem inhabited by a huge number of microorganisms without which we cannot survive) while sometimes not? What really distinguishes an individual-level life from a system-level life? Are there general properties only a system-level life has, emerged from the interactions among its compositional individual-level life?This thesis is to investigate these two questions by mathematical models. For the evolution from non-life to life, namely the origin of life, we build an artificial chemistry model to investigate why an independent self-replicating entity can develop spontaneously from some chemical reaction system in which no reaction is self-replicating. For the evolution from life to a variety of life, we build an artificial ecosystem model to investigate general properties of ecosystems.