Historical and conceptual background of self-organization by reactive processes.

Order, form, pattern and organization are properties central to much living matter. The physicochemical processes by which an initially homogeneous solution of reacting chemicals or biochemicals might self-organize is hence a question of fundamental biological importance. In most cases, solutions of reacting chemicals in a test-tube do not self-organize. Because of this, for many years, it was not thought possible that reactive processes could result in self-organization. However, progressively over the last hundred years, it has been shown that this is not always the case, and under certain conditions, the combination of reaction with molecular diffusion can lead to macroscopic self-organization. In 'complex' systems comprised of populations of strongly coupled elements, new 'emergent' properties, such as self-organization, arise by way of the dynamics of the system. Self-organizing reaction-diffusion systems form a specific type of complex system. Here, I will give a personal overview of the conceptual and historical background to this approach with an emphasis on biological self-organization.