Structural and functional growth in self-reproducing cellular automata

In this article, we analyze the dynamics of change in two-dimensional self-reproducers, identifying the processes that drive their evolution. We show that changes in self- reproducers structure and behavior depend on their genetic memory. This consists of distinct yet interlinked components determining their form and function. In some cases these components degrade gracefully, changing only slightly, in others the changes destroy the original structure and function of the self- reproducer. We sketch these processes at the genotype and the phenotype level-showing that they follow distinct trajectories within mutation space and quantifying the degree of change produced by different trajectories. We show that changes in structure and behavior depend on the interplay between the genotype and the phenotype. This determines universal structures, from which it is possible to construct a great number of self- reproducing systems, as we observe in biology. Creative processes of change produce divergent and/or convergent methods for the generation of self- reproducers. Divergence involves the creation of completely new information convergence involves local change and specialization of the structures concerned. (c) 2006 Wiley Periodicals, Inc.